main: version 0.7.1

This release contains a small fix for some atsamd21-based boards to make them usable on macOS: it now allows to specify the serial port using the -port flag.
ci: fix Go image on the Debian Stretch images
2026-07-26 14:48:40 +00:00 · 2019-07-27 10:02:10 -07:00 · 2019-07-27 09:51:38 -07:00 · 2019-07-25 10:17:16 -07:00 · 2019-07-17 15:36:38 +02:00 · 2019-07-17 06:30:58 -07:00
126 changed files with 3846 additions and 997 deletions
@@ -44,20 +44,14 @@ commands:
    steps:
      - restore_cache:
          keys:
-            - llvm-source-8-v3
+            - llvm-source-8-v5
      - run:
          name: "Fetch LLVM source"
          command: make llvm-source
      - save_cache:
-          key: llvm-source-8-v3
+          key: llvm-source-8-v5
          paths:
-            - llvm
-  smoketest:
-    steps:
-      - run: make smoketest
-  smoketest-no-avr:
-    steps:
-      - run: make smoketest-no-avr
+            - llvm-project
  test-linux:
    steps:
      - checkout
@@ -73,7 +67,7 @@ commands:
      - run: go install .
      - run: go test -v
      - run: make gen-device -j4
-      - smoketest
+      - run: make smoketest RISCV=0
      - save_cache:
          key: go-cache-{{ checksum "Gopkg.lock" }}-{{ .Environment.CIRCLE_BUILD_NUM }}
          paths:
@@ -106,7 +100,7 @@ commands:
      - llvm-source-linux
      - restore_cache:
          keys:
-            - llvm-build-8-linux-v5
+            - llvm-build-8-linux-v7
      - run:
          name: "Build LLVM"
          command: |
@@ -124,7 +118,7 @@ commands:
              make llvm-build
            fi
      - save_cache:
-          key: llvm-build-8-linux-v5
+          key: llvm-build-8-linux-v7
          paths:
            llvm-build
      - run:
@@ -155,7 +149,12 @@ commands:
            tar -C ~/lib -xf /tmp/tinygo.linux-amd64.tar.gz
            ln -s ~/lib/tinygo/bin/tinygo /go/bin/tinygo
            tinygo version
-      - smoketest
+      - run:
+          name: "Download SiFive GNU toolchain"
+          command: |
+            curl -O https://static.dev.sifive.com/dev-tools/riscv64-unknown-elf-gcc-8.2.0-2019.05.3-x86_64-linux-ubuntu14.tar.gz
+            sudo tar -C /usr/local --strip-components=1 -xf riscv64-unknown-elf-gcc-8.2.0-2019.05.3-x86_64-linux-ubuntu14.tar.gz
+      - run: make smoketest
  build-macos:
    steps:
      - checkout
@@ -169,17 +168,17 @@ commands:
            HOMEBREW_NO_AUTO_UPDATE=1 brew install qemu
      - restore_cache:
          keys:
-            - llvm-source-8-macos-v3
+            - llvm-source-8-macos-v5
      - run:
          name: "Fetch LLVM source"
          command: make llvm-source
      - save_cache:
-          key: llvm-source-8-macos-v3
+          key: llvm-source-8-macos-v5
          paths:
-            - llvm
+            - llvm-project
      - restore_cache:
          keys:
-            - llvm-build-8-macos-v4
+            - llvm-build-8-macos-v6
      - run:
          name: "Build LLVM"
          command: |
@@ -191,7 +190,7 @@ commands:
              make llvm-build
            fi
      - save_cache:
-          key: llvm-build-8-macos-v4
+          key: llvm-build-8-macos-v6
          paths:
            llvm-build
      - run:
@@ -215,23 +214,28 @@ commands:
            tar -C /usr/local/opt -xf /tmp/tinygo.darwin-amd64.tar.gz
            ln -s /usr/local/opt/tinygo/bin/tinygo /usr/local/bin/tinygo
            tinygo version
-      - smoketest-no-avr
+      - run:
+          name: "Download SiFive GNU toolchain"
+          command: |
+            curl -O https://static.dev.sifive.com/dev-tools/riscv64-unknown-elf-gcc-8.2.0-2019.05.3-x86_64-apple-darwin.tar.gz
+            sudo tar -C /usr/local --strip-components=1 -xf riscv64-unknown-elf-gcc-8.2.0-2019.05.3-x86_64-apple-darwin.tar.gz
+      - run: make smoketest AVR=0


 jobs:
  test-llvm8-go111:
    docker:
-      - image: circleci/golang:1.11
+      - image: circleci/golang:1.11-stretch
    steps:
      - test-linux
  test-llvm8-go112:
    docker:
-      - image: circleci/golang:1.12
+      - image: circleci/golang:1.12-stretch
    steps:
      - test-linux
  build-linux:
    docker:
-      - image: circleci/golang:1.12
+      - image: circleci/golang:1.12-stretch
    steps:
      - build-linux
  build-macos:
@@ -5,10 +5,12 @@ src/device/avr/*.ld
 src/device/avr/*.s
 src/device/nrf/*.go
 src/device/nrf/*.s
-src/device/stm32/*.go
-src/device/stm32/*.s
 src/device/sam/*.go
 src/device/sam/*.s
+src/device/sifive/*.go
+src/device/sifive/*.s
+src/device/stm32/*.go
+src/device/stm32/*.s
 vendor
 llvm
 llvm-build
@@ -9,7 +9,7 @@
 	url = https://github.com/avr-rust/avr-mcu.git
 [submodule "lib/cmsis-svd"]
 	path = lib/cmsis-svd
-	url = https://github.com/posborne/cmsis-svd
+	url = https://github.com/tinygo-org/cmsis-svd
 [submodule "lib/compiler-rt"]
 	path = lib/compiler-rt
 	url = https://github.com/llvm-mirror/compiler-rt.git
@@ -27,8 +27,8 @@ on a different system like Mac.

 ## Download the source

-The first step is to download the TinyGo sources. Then, inside the directory,
-perform these steps:
+The first step is to download the TinyGo sources (use `--recursive` if you clone
+the git repository). Then, inside the directory, perform these steps:

    dep ensure -vendor-only # download Go dependencies
    make llvm-source        # download LLVM
@@ -1,3 +1,50 @@
+0.7.1
+---
+* **targets**
+  - `atsamd21`: add support for the `-port` flag in the flash subcommand
+
+0.7.0
+---
+* **command line**
+  - try more locations to find Clang built-in headers
+  - add support for `tinygo test`
+  - build current directory if no package is specified
+  - support custom .json target spec with `-target` flag
+  - use zversion.go to detect version of GOROOT version
+  - make initial heap size configurable for some targets (currently WebAssembly
+    only)
+* **cgo**
+  - add support for bitfields using generated getters and setters
+  - add support for anonymous structs
+* **compiler**
+  - show an error instead of panicking on duplicate function definitions
+  - allow packages like github.com/tinygo-org/tinygo/src/\* by aliasing it
+  - remove `//go:volatile` support  
+    It has been replaced with the runtime/volatile package.
+  - allow poiners in map keys
+  - support non-constant syscall numbers
+  - implement non-blocking selects
+  - add support for the `-tags` flag
+  - add support for `string` to `[]rune` conversion
+  - implement a portable conservative garbage collector (with support for wasm)
+  - add the `//go:noinline` pragma
+* **standard library**
+  - `os`: add `os.Exit` and `syscall.Exit`
+  - `os`: add several stubs
+  - `runtime`: fix heap corruption in conservative GC
+  - `runtime`: add support for math intrinsics where supported, massively
+    speeding up some benchmarks
+  - `testing`: add basic support for testing
+* **targets**
+  - add support for a generic target that calls `__tinygo_*` functions for
+    peripheral access
+  - `arduino-nano33`: add support for this board
+  - `hifive1`: add support for this RISC-V board
+  - `reelboard`: add e-paper pins
+  - `reelboard`: add `PowerSupplyActive` to enable voltage for on-board devices
+  - `wasm`: put the stack at the start of linear memory, to detect stack
+    overflows
+
 0.6.0
 ---
 * **command line**
@@ -16,12 +16,16 @@ Please open a Github issue with your problem, and we will be happy to assist.

 We probably have not implemented it yet. Please take a look at our [Roadmap](https://github.com/tinygo-org/tinygo/wiki/Roadmap). Your pull request adding the functionality to TinyGo would be greatly appreciated.

+Please open a Github issue. We want to help, and also make sure that there is no duplications of efforts. Sometimes what you need is already being worked on by someone else.
+
 A long tail of small (and large) language features haven't been implemented yet. In almost all cases, the compiler will show a `todo:` error from `compiler/compiler.go` when you try to use it. You can try implementing it, or open a bug report with a small code sample that fails to compile.

 ### Some specific hardware you want to use does not appear to be in TinyGo

 As above, we probably have not implemented it yet. Your contribution adding the hardware support to TinyGo would be greatly appreciated.

+Please start by opening a Github issue. We want to help you to help us to help you.
+
 Lots of targets/boards are still unsupported. Adding an architecture often requires a few compiler changes, but if the architecture is supported you can try implementing support for a new chip or board in `src/runtime`. For details, see [this wiki entry on adding archs/chips/boards](https://github.com/tinygo-org/tinygo/wiki/Adding-a-new-board).

 Microcontrollers have lots of peripherals (I2C, SPI, ADC, etc.) and many don't have an implementation yet in the `machine` package. Adding support for new peripherals is very useful.
@@ -3,12 +3,12 @@
 all: tinygo
 tinygo: build/tinygo

-.PHONY: all tinygo build/tinygo test llvm-build llvm-source clean fmt gen-device gen-device-nrf gen-device-avr
-
 # Default build and source directories, as created by `make llvm-build`.
 LLVM_BUILDDIR ?= llvm-build
-CLANG_SRC ?= llvm/tools/clang
-LLD_SRC ?= llvm/tools/lld
+CLANG_SRC ?= llvm-project/clang
+LLD_SRC ?= llvm-project/lld
+
+.PHONY: all tinygo build/tinygo test $(LLVM_BUILDDIR) llvm-source clean fmt gen-device gen-device-nrf gen-device-avr

 LLVM_COMPONENTS = all-targets analysis asmparser asmprinter bitreader bitwriter codegen core coroutines debuginfodwarf executionengine instrumentation interpreter ipo irreader linker lto mc mcjit objcarcopts option profiledata scalaropts support target

@@ -18,15 +18,17 @@ ifeq ($(UNAME_S),Linux)
    END_GROUP = -Wl,--end-group
 endif

-CLANG_LIBS = $(START_GROUP) $(abspath $(LLVM_BUILDDIR))/lib/libclang.a -lclangAnalysis -lclangARCMigrate -lclangAST -lclangASTMatchers -lclangBasic -lclangCodeGen -lclangCrossTU -lclangDriver -lclangDynamicASTMatchers -lclangEdit -lclangFormat -lclangFrontend -lclangFrontendTool -lclangHandleCXX -lclangHandleLLVM -lclangIndex -lclangLex -lclangParse -lclangRewrite -lclangRewriteFrontend -lclangSema -lclangSerialization -lclangStaticAnalyzerCheckers -lclangStaticAnalyzerCore -lclangStaticAnalyzerFrontend -lclangTooling -lclangToolingASTDiff -lclangToolingCore -lclangToolingInclusions -lclangToolingRefactor $(END_GROUP) -lstdc++
+CLANG_LIBS = $(START_GROUP) $(abspath $(LLVM_BUILDDIR))/lib/libclang.a -lclangAnalysis -lclangARCMigrate -lclangAST -lclangASTMatchers -lclangBasic -lclangCodeGen -lclangCrossTU -lclangDriver -lclangDynamicASTMatchers -lclangEdit -lclangFormat -lclangFrontend -lclangFrontendTool -lclangHandleCXX -lclangHandleLLVM -lclangIndex -lclangLex -lclangParse -lclangRewrite -lclangRewriteFrontend -lclangSema -lclangSerialization -lclangStaticAnalyzerCheckers -lclangStaticAnalyzerCore -lclangStaticAnalyzerFrontend -lclangTooling -lclangToolingASTDiff -lclangToolingCore -lclangToolingInclusions $(END_GROUP) -lstdc++

 LLD_LIBS = $(START_GROUP) -llldCOFF -llldCommon -llldCore -llldDriver -llldELF -llldMachO -llldMinGW -llldReaderWriter -llldWasm -llldYAML $(END_GROUP)


 # For static linking.
-CGO_CPPFLAGS=$(shell $(LLVM_BUILDDIR)/bin/llvm-config --cppflags) -I$(abspath $(CLANG_SRC))/include -I$(abspath $(LLD_SRC))/include
-CGO_CXXFLAGS=-std=c++11
-CGO_LDFLAGS=-L$(LLVM_BUILDDIR)/lib $(CLANG_LIBS) $(LLD_LIBS) $(shell $(LLVM_BUILDDIR)/bin/llvm-config --ldflags --libs --system-libs $(LLVM_COMPONENTS))
+ifneq ("$(wildcard $(LLVM_BUILDDIR)/bin/llvm-config)","")
+    CGO_CPPFLAGS=$(shell $(LLVM_BUILDDIR)/bin/llvm-config --cppflags) -I$(abspath $(CLANG_SRC))/include -I$(abspath $(LLD_SRC))/include
+    CGO_CXXFLAGS=-std=c++11
+    CGO_LDFLAGS=-L$(LLVM_BUILDDIR)/lib $(CLANG_LIBS) $(LLD_LIBS) $(shell $(LLVM_BUILDDIR)/bin/llvm-config --ldflags --libs --system-libs $(LLVM_COMPONENTS))
+endif


 clean:
@@ -38,7 +40,8 @@ fmt:
 fmt-check:
 	@unformatted=$$(gofmt -l $(FMT_PATHS)); [ -z "$$unformatted" ] && exit 0; echo "Unformatted:"; for fn in $$unformatted; do echo "  $$fn"; done; exit 1

-gen-device: gen-device-avr gen-device-nrf gen-device-sam gen-device-stm32
+
+gen-device: gen-device-avr gen-device-nrf gen-device-sam gen-device-sifive gen-device-stm32

 gen-device-avr:
 	./tools/gen-device-avr.py lib/avr/packs/atmega src/device/avr/
@@ -53,42 +56,43 @@ gen-device-sam:
 	./tools/gen-device-svd.py lib/cmsis-svd/data/Atmel/ src/device/sam/ --source=https://github.com/posborne/cmsis-svd/tree/master/data/Atmel
 	go fmt ./src/device/sam

+gen-device-sifive:
+	./tools/gen-device-svd.py lib/cmsis-svd/data/SiFive-Community/ src/device/sifive/ --source=https://github.com/AdaCore/svd2ada/tree/master/CMSIS-SVD/SiFive-Community
+	go fmt ./src/device/sifive
+
 gen-device-stm32:
 	./tools/gen-device-svd.py lib/cmsis-svd/data/STMicro/ src/device/stm32/ --source=https://github.com/posborne/cmsis-svd/tree/master/data/STMicro
 	go fmt ./src/device/stm32


 # Get LLVM sources.
-llvm/README.txt:
-	git clone -b release_80 https://github.com/llvm-mirror/llvm.git llvm
-llvm/tools/clang/README.txt:
-	git clone -b release_80 https://github.com/llvm-mirror/clang.git llvm/tools/clang
-llvm/tools/lld/README.md:
-	git clone -b release_80 https://github.com/llvm-mirror/lld.git llvm/tools/lld
-llvm-source: llvm/README.txt llvm/tools/clang/README.txt llvm/tools/lld/README.md
+llvm-project/README.md:
+	git clone -b release/8.x https://github.com/llvm/llvm-project
+llvm-source: llvm-project/README.md

 # Configure LLVM.
-llvm-build/build.ninja: llvm-source
-	mkdir -p llvm-build; cd llvm-build; cmake -G Ninja ../llvm "-DLLVM_TARGETS_TO_BUILD=X86;ARM;AArch64;WebAssembly" "-DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=AVR" -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_ASSERTIONS=OFF -DLIBCLANG_BUILD_STATIC=ON -DLLVM_ENABLE_TERMINFO=OFF -DLLVM_ENABLE_ZLIB=OFF
+TINYGO_SOURCE_DIR=$(shell pwd)
+$(LLVM_BUILDDIR)/build.ninja: llvm-source
+	mkdir -p $(LLVM_BUILDDIR); cd $(LLVM_BUILDDIR); cmake -G Ninja $(TINYGO_SOURCE_DIR)/llvm-project/llvm "-DLLVM_TARGETS_TO_BUILD=X86;ARM;AArch64;WebAssembly" "-DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=AVR;RISCV" -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_ASSERTIONS=OFF -DLIBCLANG_BUILD_STATIC=ON -DLLVM_ENABLE_TERMINFO=OFF -DLLVM_ENABLE_ZLIB=OFF -DLLVM_ENABLE_PROJECTS="clang;lld" -DLLVM_TOOL_CLANG_TOOLS_EXTRA_BUILD=OFF

 # Build LLVM.
-llvm-build: llvm-build/build.ninja
-	cd llvm-build; ninja
+$(LLVM_BUILDDIR): $(LLVM_BUILDDIR)/build.ninja
+	cd $(LLVM_BUILDDIR); ninja


 # Build the Go compiler.
 build/tinygo:
-	@if [ ! -f llvm-build/bin/llvm-config ]; then echo "Fetch and build LLVM first by running:\n  make llvm-source\n  make llvm-build"; exit 1; fi
+	@if [ ! -f "$(LLVM_BUILDDIR)/bin/llvm-config" ]; then echo "Fetch and build LLVM first by running:"; echo "  make llvm-source"; echo "  make $(LLVM_BUILDDIR)"; exit 1; fi
 	CGO_CPPFLAGS="$(CGO_CPPFLAGS)" CGO_CXXFLAGS="$(CGO_CXXFLAGS)" CGO_LDFLAGS="$(CGO_LDFLAGS)" go build -o build/tinygo -tags byollvm .

 test:
 	CGO_CPPFLAGS="$(CGO_CPPFLAGS)" CGO_CXXFLAGS="$(CGO_CXXFLAGS)" CGO_LDFLAGS="$(CGO_LDFLAGS)" go test -v -tags byollvm .

-.PHONY: smoketest smoketest-no-avr
-smoketest: smoketest-no-avr
-	tinygo build -size short -o test.elf -target=arduino             examples/blinky1
-	tinygo build -size short -o test.elf -target=digispark           examples/blinky1
-smoketest-no-avr:
+tinygo-test:
+	cd tests/tinygotest && tinygo test
+
+.PHONY: smoketest
+smoketest:
 	# test all examples
 	tinygo build -size short -o test.elf -target=pca10040            examples/blinky1
 	tinygo build -size short -o test.elf -target=pca10040            examples/adc
@@ -104,7 +108,7 @@ smoketest-no-avr:
 	tinygo build -size short -o test.elf -target=pca10040            examples/serial
 	tinygo build -size short -o test.elf -target=pca10040            examples/test
 	# test all targets/boards
-	tinygo build             -o test.elf                             examples/blinky2 # TODO: re-enable -size flag with MachO support
+	tinygo build             -o test.wasm -tags=pca10040             examples/blinky2
 	tinygo build -size short -o test.elf -target=microbit            examples/echo
 	tinygo build -size short -o test.elf -target=nrf52840-mdk        examples/blinky1
 	tinygo build -size short -o test.elf -target=pca10031            examples/blinky1
@@ -120,6 +124,13 @@ smoketest-no-avr:
 	tinygo build -size short -o test.elf -target=stm32f4disco        examples/blinky1
 	tinygo build -size short -o test.elf -target=stm32f4disco        examples/blinky2
 	tinygo build -size short -o test.elf -target=circuitplay-express examples/i2s
+ifneq ($(AVR), 0)
+	tinygo build -size short -o test.elf -target=arduino             examples/blinky1
+	tinygo build -size short -o test.elf -target=digispark           examples/blinky1
+endif
+ifneq ($(RISCV), 0)
+	tinygo build -size short -o test.elf -target=hifive1b            examples/blinky1
+endif
 	tinygo build             -o wasm.wasm -target=wasm               examples/wasm/export
 	tinygo build             -o wasm.wasm -target=wasm               examples/wasm/main

@@ -43,12 +43,13 @@ See the [getting started instructions](https://tinygo.org/getting-started/) for

 You can compile TinyGo programs for microcontrollers, WebAssembly and Linux.

-The following 14 microcontroller boards are currently supported:
+The following 15 microcontroller boards are currently supported:

 * [Adafruit Circuit Playground Express](https://www.adafruit.com/product/3333)
 * [Adafruit Feather M0](https://www.adafruit.com/product/2772)
 * [Adafruit ItsyBitsy M0](https://www.adafruit.com/product/3727)
 * [Adafruit Trinket M0](https://www.adafruit.com/product/3500)
+* [Arduino Nano33 IoT](https://store.arduino.cc/nano-33-iot)
 * [Arduino Uno](https://store.arduino.cc/arduino-uno-rev3)
 * [BBC micro:bit](https://microbit.org/)
 * [ST Micro STM32F103XX "Bluepill"](http://wiki.stm32duino.com/index.php?title=Blue_Pill)
@@ -36,6 +36,7 @@ type cgoPackage struct {
 	typedefs        map[string]*typedefInfo
 	elaboratedTypes map[string]*elaboratedTypeInfo
 	enums           map[string]enumInfo
+	anonStructNum   int
 }

 // constantInfo stores some information about a CGo constant found by libclang
@@ -68,8 +69,20 @@ type typedefInfo struct {
 // elaboratedTypeInfo contains some information about an elaborated type
 // (struct, union) found in the C AST.
 type elaboratedTypeInfo struct {
-	typeExpr ast.Expr
+	typeExpr  *ast.StructType
+	pos       token.Pos
+	bitfields []bitfieldInfo
+}
+
+// bitfieldInfo contains information about a single bitfield in a struct. It
+// keeps information about the start, end, and the special (renamed) base field
+// of this bitfield.
+type bitfieldInfo struct {
+	field    *ast.Field
+	name     string
 	pos      token.Pos
+	startBit int64
+	endBit   int64 // may be 0 meaning "until the end of the field"
 }

 // enumInfo contains information about an enum in the C.
@@ -581,10 +594,299 @@ func (p *cgoPackage) addElaboratedTypes() {
 		}
 		obj.Decl = typeSpec
 		gen.Specs = append(gen.Specs, typeSpec)
+		// If this struct has bitfields, create getters for them.
+		for _, bitfield := range typ.bitfields {
+			p.createBitfieldGetter(bitfield, typeName)
+			p.createBitfieldSetter(bitfield, typeName)
+		}
 	}
 	p.generated.Decls = append(p.generated.Decls, gen)
 }

+// createBitfieldGetter creates a bitfield getter function like the following:
+//
+//     func (s *C.struct_foo) bitfield_b() byte {
+//         return (s.__bitfield_1 >> 5) & 0x1
+//     }
+func (p *cgoPackage) createBitfieldGetter(bitfield bitfieldInfo, typeName string) {
+	// The value to return from the getter.
+	// Not complete: this is just an expression to get the complete field.
+	var result ast.Expr = &ast.SelectorExpr{
+		X: &ast.Ident{
+			NamePos: bitfield.pos,
+			Name:    "s",
+			Obj:     nil,
+		},
+		Sel: &ast.Ident{
+			NamePos: bitfield.pos,
+			Name:    bitfield.field.Names[0].Name,
+		},
+	}
+	if bitfield.startBit != 0 {
+		// Shift to the right by .startBit so that fields that come before are
+		// shifted off.
+		result = &ast.BinaryExpr{
+			X:     result,
+			OpPos: bitfield.pos,
+			Op:    token.SHR,
+			Y: &ast.BasicLit{
+				ValuePos: bitfield.pos,
+				Kind:     token.INT,
+				Value:    strconv.FormatInt(bitfield.startBit, 10),
+			},
+		}
+	}
+	if bitfield.endBit != 0 {
+		// Mask off the high bits so that fields that come after this field are
+		// masked off.
+		and := (uint64(1) << uint64(bitfield.endBit-bitfield.startBit)) - 1
+		result = &ast.BinaryExpr{
+			X:     result,
+			OpPos: bitfield.pos,
+			Op:    token.AND,
+			Y: &ast.BasicLit{
+				ValuePos: bitfield.pos,
+				Kind:     token.INT,
+				Value:    "0x" + strconv.FormatUint(and, 16),
+			},
+		}
+	}
+
+	// Create the getter function.
+	getter := &ast.FuncDecl{
+		Recv: &ast.FieldList{
+			Opening: bitfield.pos,
+			List: []*ast.Field{
+				&ast.Field{
+					Names: []*ast.Ident{
+						&ast.Ident{
+							NamePos: bitfield.pos,
+							Name:    "s",
+							Obj: &ast.Object{
+								Kind: ast.Var,
+								Name: "s",
+								Decl: nil,
+							},
+						},
+					},
+					Type: &ast.StarExpr{
+						Star: bitfield.pos,
+						X: &ast.Ident{
+							NamePos: bitfield.pos,
+							Name:    typeName,
+							Obj:     nil,
+						},
+					},
+				},
+			},
+			Closing: bitfield.pos,
+		},
+		Name: &ast.Ident{
+			NamePos: bitfield.pos,
+			Name:    "bitfield_" + bitfield.name,
+		},
+		Type: &ast.FuncType{
+			Func: bitfield.pos,
+			Params: &ast.FieldList{
+				Opening: bitfield.pos,
+				Closing: bitfield.pos,
+			},
+			Results: &ast.FieldList{
+				List: []*ast.Field{
+					&ast.Field{
+						Type: bitfield.field.Type,
+					},
+				},
+			},
+		},
+		Body: &ast.BlockStmt{
+			Lbrace: bitfield.pos,
+			List: []ast.Stmt{
+				&ast.ReturnStmt{
+					Return: bitfield.pos,
+					Results: []ast.Expr{
+						result,
+					},
+				},
+			},
+			Rbrace: bitfield.pos,
+		},
+	}
+	p.generated.Decls = append(p.generated.Decls, getter)
+}
+
+// createBitfieldSetter creates a bitfield setter function like the following:
+//
+//     func (s *C.struct_foo) set_bitfield_b(value byte) {
+//         s.__bitfield_1 = s.__bitfield_1 ^ 0x60 | ((value & 1) << 5)
+//     }
+//
+// Or the following:
+//
+//     func (s *C.struct_foo) set_bitfield_c(value byte) {
+//         s.__bitfield_1 = s.__bitfield_1 & 0x3f | (value << 6)
+//     }
+func (p *cgoPackage) createBitfieldSetter(bitfield bitfieldInfo, typeName string) {
+	// The full field with all bitfields.
+	var field ast.Expr = &ast.SelectorExpr{
+		X: &ast.Ident{
+			NamePos: bitfield.pos,
+			Name:    "s",
+			Obj:     nil,
+		},
+		Sel: &ast.Ident{
+			NamePos: bitfield.pos,
+			Name:    bitfield.field.Names[0].Name,
+		},
+	}
+	// The value to insert into the field.
+	var valueToInsert ast.Expr = &ast.Ident{
+		NamePos: bitfield.pos,
+		Name:    "value",
+	}
+
+	if bitfield.endBit != 0 {
+		// Make sure the value is in range with a mask.
+		valueToInsert = &ast.BinaryExpr{
+			X:     valueToInsert,
+			OpPos: bitfield.pos,
+			Op:    token.AND,
+			Y: &ast.BasicLit{
+				ValuePos: bitfield.pos,
+				Kind:     token.INT,
+				Value:    "0x" + strconv.FormatUint((uint64(1)<<uint64(bitfield.endBit-bitfield.startBit))-1, 16),
+			},
+		}
+		// Create a mask for the AND NOT operation.
+		mask := ((uint64(1) << uint64(bitfield.endBit-bitfield.startBit)) - 1) << uint64(bitfield.startBit)
+		// Zero the bits in the field that will soon be inserted.
+		field = &ast.BinaryExpr{
+			X:     field,
+			OpPos: bitfield.pos,
+			Op:    token.AND_NOT,
+			Y: &ast.BasicLit{
+				ValuePos: bitfield.pos,
+				Kind:     token.INT,
+				Value:    "0x" + strconv.FormatUint(mask, 16),
+			},
+		}
+	} else { // bitfield.endBit == 0
+		// We don't know exactly how many high bits should be zeroed. So we do
+		// something different: keep the low bits with a mask and OR the new
+		// value with it.
+		mask := (uint64(1) << uint64(bitfield.startBit)) - 1
+		// Extract the lower bits.
+		field = &ast.BinaryExpr{
+			X:     field,
+			OpPos: bitfield.pos,
+			Op:    token.AND,
+			Y: &ast.BasicLit{
+				ValuePos: bitfield.pos,
+				Kind:     token.INT,
+				Value:    "0x" + strconv.FormatUint(mask, 16),
+			},
+		}
+	}
+
+	// Bitwise OR with the new value (after the new value has been shifted).
+	field = &ast.BinaryExpr{
+		X:     field,
+		OpPos: bitfield.pos,
+		Op:    token.OR,
+		Y: &ast.BinaryExpr{
+			X:     valueToInsert,
+			OpPos: bitfield.pos,
+			Op:    token.SHL,
+			Y: &ast.BasicLit{
+				ValuePos: bitfield.pos,
+				Kind:     token.INT,
+				Value:    strconv.FormatInt(bitfield.startBit, 10),
+			},
+		},
+	}
+
+	// Create the setter function.
+	setter := &ast.FuncDecl{
+		Recv: &ast.FieldList{
+			Opening: bitfield.pos,
+			List: []*ast.Field{
+				&ast.Field{
+					Names: []*ast.Ident{
+						&ast.Ident{
+							NamePos: bitfield.pos,
+							Name:    "s",
+							Obj: &ast.Object{
+								Kind: ast.Var,
+								Name: "s",
+								Decl: nil,
+							},
+						},
+					},
+					Type: &ast.StarExpr{
+						Star: bitfield.pos,
+						X: &ast.Ident{
+							NamePos: bitfield.pos,
+							Name:    typeName,
+							Obj:     nil,
+						},
+					},
+				},
+			},
+			Closing: bitfield.pos,
+		},
+		Name: &ast.Ident{
+			NamePos: bitfield.pos,
+			Name:    "set_bitfield_" + bitfield.name,
+		},
+		Type: &ast.FuncType{
+			Func: bitfield.pos,
+			Params: &ast.FieldList{
+				Opening: bitfield.pos,
+				List: []*ast.Field{
+					&ast.Field{
+						Names: []*ast.Ident{
+							&ast.Ident{
+								NamePos: bitfield.pos,
+								Name:    "value",
+								Obj:     nil,
+							},
+						},
+						Type: bitfield.field.Type,
+					},
+				},
+				Closing: bitfield.pos,
+			},
+		},
+		Body: &ast.BlockStmt{
+			Lbrace: bitfield.pos,
+			List: []ast.Stmt{
+				&ast.AssignStmt{
+					Lhs: []ast.Expr{
+						&ast.SelectorExpr{
+							X: &ast.Ident{
+								NamePos: bitfield.pos,
+								Name:    "s",
+								Obj:     nil,
+							},
+							Sel: &ast.Ident{
+								NamePos: bitfield.pos,
+								Name:    bitfield.field.Names[0].Name,
+							},
+						},
+					},
+					TokPos: bitfield.pos,
+					Tok:    token.ASSIGN,
+					Rhs: []ast.Expr{
+						field,
+					},
+				},
+			},
+			Rbrace: bitfield.pos,
+		},
+	}
+	p.generated.Decls = append(p.generated.Decls, setter)
+}
+
 // addEnumTypes adds C enums to the AST. For example, the following C code:
 //
 //     enum option {
@@ -51,6 +51,7 @@ CXSourceRange tinygo_clang_getCursorExtent(GoCXCursor c);
 CXTranslationUnit tinygo_clang_Cursor_getTranslationUnit(GoCXCursor c);
 long long tinygo_clang_getEnumConstantDeclValue(GoCXCursor c);
 CXType tinygo_clang_getEnumDeclIntegerType(GoCXCursor c);
+unsigned tinygo_clang_Cursor_isBitField(GoCXCursor c);

 int tinygo_clang_globals_visitor(GoCXCursor c, GoCXCursor parent, CXClientData client_data);
 int tinygo_clang_struct_visitor(GoCXCursor c, GoCXCursor parent, CXClientData client_data);
@@ -512,78 +513,48 @@ func (p *cgoPackage) makeASTType(typ C.CXType, pos token.Pos) ast.Expr {
 	case C.CXType_Record:
 		cursor := C.tinygo_clang_getTypeDeclaration(typ)
 		name := getString(C.tinygo_clang_getCursorSpelling(cursor))
-		var cgoName string
-		switch C.tinygo_clang_getCursorKind(cursor) {
-		case C.CXCursor_StructDecl:
-			cgoName = "struct_" + name
-		case C.CXCursor_UnionDecl:
-			cgoName = "union_" + name
-		default:
-			panic("unknown record declaration")
-		}
-		if _, ok := p.elaboratedTypes[cgoName]; !ok {
-			p.elaboratedTypes[cgoName] = nil // predeclare (to avoid endless recursion)
-			fieldList := &ast.FieldList{
-				Opening: pos,
-				Closing: pos,
+		if name == "" {
+			// Anonymous record, probably inside a typedef.
+			typeExpr, bitfieldList := p.makeASTRecordType(cursor, pos)
+			if bitfieldList != nil {
+				// This struct has bitfields, so we have to declare it as a
+				// named type (for bitfield getters/setters to work).
+				p.anonStructNum++
+				cgoName := "struct_" + strconv.Itoa(p.anonStructNum)
+				p.elaboratedTypes[cgoName] = &elaboratedTypeInfo{
+					typeExpr:  typeExpr,
+					pos:       pos,
+					bitfields: bitfieldList,
+				}
+				return &ast.Ident{
+					NamePos: pos,
+					Name:    "C." + cgoName,
+				}
 			}
-			ref := storedRefs.Put(struct {
-				fieldList *ast.FieldList
-				pkg       *cgoPackage
-			}{fieldList, p})
-			defer storedRefs.Remove(ref)
-			C.tinygo_clang_visitChildren(cursor, C.CXCursorVisitor(C.tinygo_clang_struct_visitor), C.CXClientData(ref))
+			return typeExpr
+		} else {
+			var cgoName string
 			switch C.tinygo_clang_getCursorKind(cursor) {
 			case C.CXCursor_StructDecl:
-				p.elaboratedTypes[cgoName] = &elaboratedTypeInfo{
-					typeExpr: &ast.StructType{
-						Struct: pos,
-						Fields: fieldList,
-					},
-					pos: pos,
-				}
+				cgoName = "struct_" + name
 			case C.CXCursor_UnionDecl:
-				if len(fieldList.List) > 1 {
-					// Insert a special field at the front (of zero width) as a
-					// marker that this is struct is actually a union. This is done
-					// by giving the field a name that cannot be expressed directly
-					// in Go.
-					// Other parts of the compiler look at the first element in a
-					// struct (of size > 2) to know whether this is a union.
-					// Note that we don't have to insert it for single-element
-					// unions as they're basically equivalent to a struct.
-					unionMarker := &ast.Field{
-						Type: &ast.StructType{
-							Struct: pos,
-						},
-					}
-					unionMarker.Names = []*ast.Ident{
-						&ast.Ident{
-							NamePos: pos,
-							Name:    "C union",
-							Obj: &ast.Object{
-								Kind: ast.Var,
-								Name: "C union",
-								Decl: unionMarker,
-							},
-						},
-					}
-					fieldList.List = append([]*ast.Field{unionMarker}, fieldList.List...)
-				}
-				p.elaboratedTypes[cgoName] = &elaboratedTypeInfo{
-					typeExpr: &ast.StructType{
-						Struct: pos,
-						Fields: fieldList,
-					},
-					pos: pos,
-				}
+				cgoName = "union_" + name
 			default:
-				panic("unreachable")
+				panic("unknown record declaration")
+			}
+			if _, ok := p.elaboratedTypes[cgoName]; !ok {
+				p.elaboratedTypes[cgoName] = nil // predeclare (to avoid endless recursion)
+				typeExpr, bitfieldList := p.makeASTRecordType(cursor, pos)
+				p.elaboratedTypes[cgoName] = &elaboratedTypeInfo{
+					typeExpr:  typeExpr,
+					pos:       pos,
+					bitfields: bitfieldList,
+				}
+			}
+			return &ast.Ident{
+				NamePos: pos,
+				Name:    "C." + cgoName,
 			}
-		}
-		return &ast.Ident{
-			NamePos: pos,
-			Name:    "C." + cgoName,
 		}
 	case C.CXType_Enum:
 		cursor := C.tinygo_clang_getTypeDeclaration(typ)
@@ -629,25 +600,143 @@ func (p *cgoPackage) makeASTType(typ C.CXType, pos token.Pos) ast.Expr {
 	}
 }

+// makeASTRecordType parses a C record (struct or union) and translates it into
+// a Go struct type. Unions are implemented by setting the first field to a
+// zero-lengt "C union" field, which cannot be written in Go directly.
+func (p *cgoPackage) makeASTRecordType(cursor C.GoCXCursor, pos token.Pos) (*ast.StructType, []bitfieldInfo) {
+	fieldList := &ast.FieldList{
+		Opening: pos,
+		Closing: pos,
+	}
+	var bitfieldList []bitfieldInfo
+	inBitfield := false
+	bitfieldNum := 0
+	ref := storedRefs.Put(struct {
+		fieldList    *ast.FieldList
+		pkg          *cgoPackage
+		inBitfield   *bool
+		bitfieldNum  *int
+		bitfieldList *[]bitfieldInfo
+	}{fieldList, p, &inBitfield, &bitfieldNum, &bitfieldList})
+	defer storedRefs.Remove(ref)
+	C.tinygo_clang_visitChildren(cursor, C.CXCursorVisitor(C.tinygo_clang_struct_visitor), C.CXClientData(ref))
+	switch C.tinygo_clang_getCursorKind(cursor) {
+	case C.CXCursor_StructDecl:
+		return &ast.StructType{
+			Struct: pos,
+			Fields: fieldList,
+		}, bitfieldList
+	case C.CXCursor_UnionDecl:
+		if bitfieldList != nil {
+			// This is valid C... but please don't do this.
+			p.errors = append(p.errors, scanner.Error{
+				Pos: p.fset.PositionFor(pos, true),
+				Msg: fmt.Sprintf("bitfield in a union is not supported"),
+			})
+		}
+		if len(fieldList.List) > 1 {
+			// Insert a special field at the front (of zero width) as a
+			// marker that this is struct is actually a union. This is done
+			// by giving the field a name that cannot be expressed directly
+			// in Go.
+			// Other parts of the compiler look at the first element in a
+			// struct (of size > 2) to know whether this is a union.
+			// Note that we don't have to insert it for single-element
+			// unions as they're basically equivalent to a struct.
+			unionMarker := &ast.Field{
+				Type: &ast.StructType{
+					Struct: pos,
+				},
+			}
+			unionMarker.Names = []*ast.Ident{
+				&ast.Ident{
+					NamePos: pos,
+					Name:    "C union",
+					Obj: &ast.Object{
+						Kind: ast.Var,
+						Name: "C union",
+						Decl: unionMarker,
+					},
+				},
+			}
+			fieldList.List = append([]*ast.Field{unionMarker}, fieldList.List...)
+		}
+		return &ast.StructType{
+			Struct: pos,
+			Fields: fieldList,
+		}, bitfieldList
+	default:
+		panic("unknown record declaration")
+	}
+}
+
 //export tinygo_clang_struct_visitor
 func tinygo_clang_struct_visitor(c, parent C.GoCXCursor, client_data C.CXClientData) C.int {
 	passed := storedRefs.Get(unsafe.Pointer(client_data)).(struct {
-		fieldList *ast.FieldList
-		pkg       *cgoPackage
+		fieldList    *ast.FieldList
+		pkg          *cgoPackage
+		inBitfield   *bool
+		bitfieldNum  *int
+		bitfieldList *[]bitfieldInfo
 	})
 	fieldList := passed.fieldList
 	p := passed.pkg
+	inBitfield := passed.inBitfield
+	bitfieldNum := passed.bitfieldNum
+	bitfieldList := passed.bitfieldList
 	if C.tinygo_clang_getCursorKind(c) != C.CXCursor_FieldDecl {
 		panic("expected field inside cursor")
 	}
 	name := getString(C.tinygo_clang_getCursorSpelling(c))
+	if name == "" {
+		// Assume this is a bitfield of 0 bits.
+		// Warning: this is not necessarily true!
+		return C.CXChildVisit_Continue
+	}
 	typ := C.tinygo_clang_getCursorType(c)
+	pos := p.getCursorPosition(c)
 	field := &ast.Field{
 		Type: p.makeASTType(typ, p.getCursorPosition(c)),
 	}
+	offsetof := int64(C.clang_Type_getOffsetOf(C.tinygo_clang_getCursorType(parent), C.CString(name)))
+	alignOf := int64(C.clang_Type_getAlignOf(typ) * 8)
+	bitfieldOffset := offsetof % alignOf
+	if bitfieldOffset != 0 {
+		if C.tinygo_clang_Cursor_isBitField(c) != 1 {
+			panic("expected a bitfield")
+		}
+		if !*inBitfield {
+			*bitfieldNum++
+		}
+		bitfieldName := "__bitfield_" + strconv.Itoa(*bitfieldNum)
+		prevField := fieldList.List[len(fieldList.List)-1]
+		if !*inBitfield {
+			// The previous element also was a bitfield, but wasn't noticed
+			// then. Add it now.
+			*inBitfield = true
+			*bitfieldList = append(*bitfieldList, bitfieldInfo{
+				field:    prevField,
+				name:     prevField.Names[0].Name,
+				startBit: 0,
+				pos:      prevField.Names[0].NamePos,
+			})
+			prevField.Names[0].Name = bitfieldName
+			prevField.Names[0].Obj.Name = bitfieldName
+		}
+		prevBitfield := &(*bitfieldList)[len(*bitfieldList)-1]
+		prevBitfield.endBit = bitfieldOffset
+		*bitfieldList = append(*bitfieldList, bitfieldInfo{
+			field:    prevField,
+			name:     name,
+			startBit: bitfieldOffset,
+			pos:      pos,
+		})
+		return C.CXChildVisit_Continue
+	}
+	*inBitfield = false
 	field.Names = []*ast.Ident{
 		&ast.Ident{
-			NamePos: p.getCursorPosition(c),
+			NamePos: pos,
 			Name:    name,
 			Obj: &ast.Object{
 				Kind: ast.Var,
@@ -64,3 +64,7 @@ long long tinygo_clang_getEnumConstantDeclValue(CXCursor c) {
 CXType tinygo_clang_getEnumDeclIntegerType(CXCursor c) {
 	return clang_getEnumDeclIntegerType(c);
 }
+
+unsigned tinygo_clang_Cursor_isBitField(CXCursor c) {
+	return clang_Cursor_isBitField(c);
+}
@@ -37,6 +37,7 @@ func execCommand(cmdNames []string, args ...string) error {
 				// this command was not found, try the next
 				continue
 			}
+			return err
 		}
 		return nil
 	}
@@ -38,7 +38,7 @@ func (c *Compiler) createCall(fn llvm.Value, args []llvm.Value, name string) llv
 }

 // Expand an argument type to a list that can be used in a function call
-// paramter list.
+// parameter list.
 func (c *Compiler) expandFormalParamType(t llvm.Type) []llvm.Type {
 	switch t.TypeKind() {
 	case llvm.StructTypeKind:
@@ -4,6 +4,7 @@ package compiler
 // or pseudo-operations that are lowered during goroutine lowering.

 import (
+	"fmt"
 	"go/types"

 	"golang.org/x/tools/go/ssa"
@@ -12,11 +13,22 @@ import (

 // emitMakeChan returns a new channel value for the given channel type.
 func (c *Compiler) emitMakeChan(expr *ssa.MakeChan) (llvm.Value, error) {
-	chanType := c.mod.GetTypeByName("runtime.channel")
-	size := c.targetData.TypeAllocSize(chanType)
+	chanType := c.getLLVMType(expr.Type())
+	size := c.targetData.TypeAllocSize(chanType.ElementType())
 	sizeValue := llvm.ConstInt(c.uintptrType, size, false)
 	ptr := c.createRuntimeCall("alloc", []llvm.Value{sizeValue}, "chan.alloc")
-	ptr = c.builder.CreateBitCast(ptr, llvm.PointerType(chanType, 0), "chan")
+	ptr = c.builder.CreateBitCast(ptr, chanType, "chan")
+	// Set the elementSize field
+	elementSizePtr := c.builder.CreateGEP(ptr, []llvm.Value{
+		llvm.ConstInt(c.ctx.Int32Type(), 0, false),
+		llvm.ConstInt(c.ctx.Int32Type(), 0, false),
+	}, "")
+	elementSize := c.targetData.TypeAllocSize(c.getLLVMType(expr.Type().(*types.Chan).Elem()))
+	if elementSize > 0xffff {
+		return ptr, c.makeError(expr.Pos(), fmt.Sprintf("element size is %d bytes, which is bigger than the maximum of %d bytes", elementSize, 0xffff))
+	}
+	elementSizeValue := llvm.ConstInt(c.ctx.Int16Type(), elementSize, false)
+	c.builder.CreateStore(elementSizeValue, elementSizePtr)
 	return ptr, nil
 }

@@ -33,8 +45,7 @@ func (c *Compiler) emitChanSend(frame *Frame, instr *ssa.Send) {

 	// Do the send.
 	coroutine := c.createRuntimeCall("getCoroutine", nil, "")
-	valueSize := llvm.ConstInt(c.uintptrType, c.targetData.TypeAllocSize(chanValue.Type()), false)
-	c.createRuntimeCall("chanSend", []llvm.Value{coroutine, ch, valueAllocaCast, valueSize}, "")
+	c.createRuntimeCall("chanSend", []llvm.Value{coroutine, ch, valueAllocaCast}, "")

 	// End the lifetime of the alloca.
 	// This also works around a bug in CoroSplit, at least in LLVM 8:
@@ -53,8 +64,7 @@ func (c *Compiler) emitChanRecv(frame *Frame, unop *ssa.UnOp) llvm.Value {

 	// Do the receive.
 	coroutine := c.createRuntimeCall("getCoroutine", nil, "")
-	valueSize := llvm.ConstInt(c.uintptrType, c.targetData.TypeAllocSize(valueType), false)
-	c.createRuntimeCall("chanRecv", []llvm.Value{coroutine, ch, valueAllocaCast, valueSize}, "")
+	c.createRuntimeCall("chanRecv", []llvm.Value{coroutine, ch, valueAllocaCast}, "")
 	received := c.builder.CreateLoad(valueAlloca, "chan.received")
 	c.emitLifetimeEnd(valueAllocaCast, valueAllocaSize)

@@ -72,8 +82,157 @@ func (c *Compiler) emitChanRecv(frame *Frame, unop *ssa.UnOp) llvm.Value {

 // emitChanClose closes the given channel.
 func (c *Compiler) emitChanClose(frame *Frame, param ssa.Value) {
-	valueType := c.getLLVMType(param.Type().(*types.Chan).Elem())
-	valueSize := llvm.ConstInt(c.uintptrType, c.targetData.TypeAllocSize(valueType), false)
 	ch := c.getValue(frame, param)
-	c.createRuntimeCall("chanClose", []llvm.Value{ch, valueSize}, "")
+	c.createRuntimeCall("chanClose", []llvm.Value{ch}, "")
+}
+
+// emitSelect emits all IR necessary for a select statements. That's a
+// non-trivial amount of code because select is very complex to implement.
+func (c *Compiler) emitSelect(frame *Frame, expr *ssa.Select) llvm.Value {
+	if len(expr.States) == 0 {
+		// Shortcuts for some simple selects.
+		llvmType := c.getLLVMType(expr.Type())
+		if expr.Blocking {
+			// Blocks forever:
+			//     select {}
+			c.createRuntimeCall("deadlockStub", nil, "")
+			return llvm.Undef(llvmType)
+		} else {
+			// No-op:
+			//     select {
+			//     default:
+			//     }
+			retval := llvm.Undef(llvmType)
+			retval = c.builder.CreateInsertValue(retval, llvm.ConstInt(c.intType, 0xffffffffffffffff, true), 0, "")
+			return retval // {-1, false}
+		}
+	}
+
+	// This code create a (stack-allocated) slice containing all the select
+	// cases and then calls runtime.chanSelect to perform the actual select
+	// statement.
+	// Simple selects (blocking and with just one case) are already transformed
+	// into regular chan operations during SSA construction so we don't have to
+	// optimize such small selects.
+
+	// Go through all the cases. Create the selectStates slice and and
+	// determine the receive buffer size and alignment.
+	recvbufSize := uint64(0)
+	recvbufAlign := 0
+	hasReceives := false
+	var selectStates []llvm.Value
+	chanSelectStateType := c.getLLVMRuntimeType("chanSelectState")
+	for _, state := range expr.States {
+		ch := c.getValue(frame, state.Chan)
+		selectState := c.getZeroValue(chanSelectStateType)
+		selectState = c.builder.CreateInsertValue(selectState, ch, 0, "")
+		switch state.Dir {
+		case types.RecvOnly:
+			// Make sure the receive buffer is big enough and has the correct alignment.
+			llvmType := c.getLLVMType(state.Chan.Type().(*types.Chan).Elem())
+			if size := c.targetData.TypeAllocSize(llvmType); size > recvbufSize {
+				recvbufSize = size
+			}
+			if align := c.targetData.ABITypeAlignment(llvmType); align > recvbufAlign {
+				recvbufAlign = align
+			}
+			hasReceives = true
+		case types.SendOnly:
+			// Store this value in an alloca and put a pointer to this alloca
+			// in the send state.
+			sendValue := c.getValue(frame, state.Send)
+			alloca := c.createEntryBlockAlloca(sendValue.Type(), "select.send.value")
+			c.builder.CreateStore(sendValue, alloca)
+			ptr := c.builder.CreateBitCast(alloca, c.i8ptrType, "")
+			selectState = c.builder.CreateInsertValue(selectState, ptr, 1, "")
+		default:
+			panic("unreachable")
+		}
+		selectStates = append(selectStates, selectState)
+	}
+
+	// Create a receive buffer, where the received value will be stored.
+	recvbuf := llvm.Undef(c.i8ptrType)
+	if hasReceives {
+		allocaType := llvm.ArrayType(c.ctx.Int8Type(), int(recvbufSize))
+		recvbufAlloca := c.builder.CreateAlloca(allocaType, "select.recvbuf.alloca")
+		recvbufAlloca.SetAlignment(recvbufAlign)
+		recvbuf = c.builder.CreateGEP(recvbufAlloca, []llvm.Value{
+			llvm.ConstInt(c.ctx.Int32Type(), 0, false),
+			llvm.ConstInt(c.ctx.Int32Type(), 0, false),
+		}, "select.recvbuf")
+	}
+
+	// Create the states slice (allocated on the stack).
+	statesAllocaType := llvm.ArrayType(chanSelectStateType, len(selectStates))
+	statesAlloca := c.builder.CreateAlloca(statesAllocaType, "select.states.alloca")
+	for i, state := range selectStates {
+		// Set each slice element to the appropriate channel.
+		gep := c.builder.CreateGEP(statesAlloca, []llvm.Value{
+			llvm.ConstInt(c.ctx.Int32Type(), 0, false),
+			llvm.ConstInt(c.ctx.Int32Type(), uint64(i), false),
+		}, "")
+		c.builder.CreateStore(state, gep)
+	}
+	statesPtr := c.builder.CreateGEP(statesAlloca, []llvm.Value{
+		llvm.ConstInt(c.ctx.Int32Type(), 0, false),
+		llvm.ConstInt(c.ctx.Int32Type(), 0, false),
+	}, "select.states")
+	statesLen := llvm.ConstInt(c.uintptrType, uint64(len(selectStates)), false)
+
+	// Convert the 'blocking' flag on this select into a LLVM value.
+	blockingInt := uint64(0)
+	if expr.Blocking {
+		blockingInt = 1
+	}
+	blockingValue := llvm.ConstInt(c.ctx.Int1Type(), blockingInt, false)
+
+	// Do the select in the runtime.
+	results := c.createRuntimeCall("chanSelect", []llvm.Value{
+		recvbuf,
+		statesPtr, statesLen, statesLen, // []chanSelectState
+		blockingValue,
+	}, "")
+
+	// The result value does not include all the possible received values,
+	// because we can't load them in advance. Instead, the *ssa.Extract
+	// instruction will treat a *ssa.Select specially and load it there inline.
+	// Store the receive alloca in a sidetable until we hit this extract
+	// instruction.
+	if frame.selectRecvBuf == nil {
+		frame.selectRecvBuf = make(map[*ssa.Select]llvm.Value)
+	}
+	frame.selectRecvBuf[expr] = recvbuf
+
+	return results
+}
+
+// getChanSelectResult returns the special values from a *ssa.Extract expression
+// when extracting a value from a select statement (*ssa.Select). Because
+// *ssa.Select cannot load all values in advance, it does this later in the
+// *ssa.Extract expression.
+func (c *Compiler) getChanSelectResult(frame *Frame, expr *ssa.Extract) llvm.Value {
+	if expr.Index == 0 {
+		// index
+		value := c.getValue(frame, expr.Tuple)
+		index := c.builder.CreateExtractValue(value, expr.Index, "")
+		if index.Type().IntTypeWidth() < c.intType.IntTypeWidth() {
+			index = c.builder.CreateSExt(index, c.intType, "")
+		}
+		return index
+	} else if expr.Index == 1 {
+		// comma-ok
+		value := c.getValue(frame, expr.Tuple)
+		return c.builder.CreateExtractValue(value, expr.Index, "")
+	} else {
+		// Select statements are (index, ok, ...) where ... is a number of
+		// received values, depending on how many receive statements there
+		// are. They are all combined into one alloca (because only one
+		// receive can proceed at a time) so we'll get that alloca, bitcast
+		// it to the correct type, and dereference it.
+		recvbuf := frame.selectRecvBuf[expr.Tuple.(*ssa.Select)]
+		typ := llvm.PointerType(c.getLLVMType(expr.Type()), 0)
+		ptr := c.builder.CreateBitCast(recvbuf, typ, "")
+		return c.builder.CreateLoad(ptr, "")
+	}
 }
@@ -3,6 +3,7 @@ package compiler
 import (
 	"errors"
 	"fmt"
+	"go/ast"
 	"go/build"
 	"go/constant"
 	"go/token"
@@ -26,6 +27,9 @@ func init() {
 	llvm.InitializeAllAsmPrinters()
 }

+// The TinyGo import path.
+const tinygoPath = "github.com/tinygo-org/tinygo"
+
 // Configure the compiler.
 type Config struct {
 	Triple        string   // LLVM target triple, e.g. x86_64-unknown-linux-gnu (empty string means default)
@@ -37,12 +41,19 @@ type Config struct {
 	PanicStrategy string   // panic strategy ("abort" or "trap")
 	CFlags        []string // cflags to pass to cgo
 	LDFlags       []string // ldflags to pass to cgo
+	ClangHeaders  string   // Clang built-in header include path
 	DumpSSA       bool     // dump Go SSA, for compiler debugging
 	Debug         bool     // add debug symbols for gdb
 	GOROOT        string   // GOROOT
 	TINYGOROOT    string   // GOROOT for TinyGo
 	GOPATH        string   // GOPATH, like `go env GOPATH`
 	BuildTags     []string // build tags for TinyGo (empty means {Config.GOOS/Config.GOARCH})
+	TestConfig    TestConfig
+}
+
+type TestConfig struct {
+	CompileTestBinary bool
+	// TODO: Filter the test functions to run, include verbose flag, etc
 }

 type Compiler struct {
@@ -63,6 +74,7 @@ type Compiler struct {
 	interfaceInvokeWrappers []interfaceInvokeWrapper
 	ir                      *ir.Program
 	diagnostics             []error
+	astComments             map[string]*ast.CommentGroup
 }

 type Frame struct {
@@ -79,6 +91,7 @@ type Frame struct {
 	deferFuncs        map[*ir.Function]int
 	deferInvokeFuncs  map[string]int
 	deferClosureFuncs map[*ir.Function]int
+	selectRecvBuf     map[*ssa.Select]llvm.Value
 }

 type Phi struct {
@@ -154,11 +167,10 @@ func (c *Compiler) TargetData() llvm.TargetData {

 // selectGC picks an appropriate GC strategy if none was provided.
 func (c *Compiler) selectGC() string {
-	gc := c.GC
-	if gc == "" {
-		gc = "dumb"
+	if c.GC != "" {
+		return c.GC
 	}
-	return gc
+	return "conservative"
 }

 // Compile the given package path or .go file path. Return an error when this
@@ -198,22 +210,29 @@ func (c *Compiler) Compile(mainPath string) []error {
 			Compiler:    "gc", // must be one of the recognized compilers
 			BuildTags:   append([]string{"tinygo", "gc." + c.selectGC()}, c.BuildTags...),
 		},
-		ShouldOverlay: func(path string) bool {
+		OverlayPath: func(path string) string {
+			// Return the (overlay) import path when it should be overlaid, and
+			// "" if it should not.
+			if strings.HasPrefix(path, tinygoPath+"/src/") {
+				// Avoid issues with packages that are imported twice, one from
+				// GOPATH and one from TINYGOPATH.
+				path = path[len(tinygoPath+"/src/"):]
+			}
 			switch path {
-			case "machine", "os", "reflect", "runtime", "runtime/volatile", "sync":
-				return true
+			case "machine", "os", "reflect", "runtime", "runtime/volatile", "sync", "testing":
+				return path
 			default:
 				if strings.HasPrefix(path, "device/") || strings.HasPrefix(path, "examples/") {
-					return true
+					return path
 				} else if path == "syscall" {
 					for _, tag := range c.BuildTags {
-						if tag == "avr" || tag == "cortexm" || tag == "darwin" {
-							return true
+						if tag == "avr" || tag == "cortexm" || tag == "darwin" || tag == "riscv" {
+							return path
 						}
 					}
 				}
 			}
-			return false
+			return ""
 		},
 		TypeChecker: types.Config{
 			Sizes: &StdSizes{
@@ -222,10 +241,12 @@ func (c *Compiler) Compile(mainPath string) []error {
 				MaxAlign: int64(c.targetData.PrefTypeAlignment(c.i8ptrType)),
 			},
 		},
-		Dir:        wd,
-		TINYGOROOT: c.TINYGOROOT,
-		CFlags:     c.CFlags,
+		Dir:          wd,
+		TINYGOROOT:   c.TINYGOROOT,
+		CFlags:       c.CFlags,
+		ClangHeaders: c.ClangHeaders,
 	}
+
 	if strings.HasSuffix(mainPath, ".go") {
 		_, err = lprogram.ImportFile(mainPath)
 		if err != nil {
@@ -237,12 +258,13 @@ func (c *Compiler) Compile(mainPath string) []error {
 			return []error{err}
 		}
 	}
+
 	_, err = lprogram.Import("runtime", "")
 	if err != nil {
 		return []error{err}
 	}

-	err = lprogram.Parse()
+	err = lprogram.Parse(c.TestConfig.CompileTestBinary)
 	if err != nil {
 		return []error{err}
 	}
@@ -265,39 +287,7 @@ func (c *Compiler) Compile(mainPath string) []error {

 	var frames []*Frame

-	// Declare all named struct types.
-	for _, t := range c.ir.NamedTypes {
-		if named, ok := t.Type.Type().(*types.Named); ok {
-			if _, ok := named.Underlying().(*types.Struct); ok {
-				t.LLVMType = c.ctx.StructCreateNamed(named.Obj().Pkg().Path() + "." + named.Obj().Name())
-			}
-		}
-	}
-
-	// Define all named struct types.
-	for _, t := range c.ir.NamedTypes {
-		if named, ok := t.Type.Type().(*types.Named); ok {
-			if st, ok := named.Underlying().(*types.Struct); ok {
-				llvmType := c.getLLVMType(st)
-				t.LLVMType.StructSetBody(llvmType.StructElementTypes(), false)
-			}
-		}
-	}
-
-	// Declare all globals.
-	for _, g := range c.ir.Globals {
-		typ := g.Type().(*types.Pointer).Elem()
-		llvmType := c.getLLVMType(typ)
-		global := c.mod.NamedGlobal(g.LinkName())
-		if global.IsNil() {
-			global = llvm.AddGlobal(c.mod, llvmType, g.LinkName())
-		}
-		g.LLVMGlobal = global
-		if !g.IsExtern() {
-			global.SetLinkage(llvm.InternalLinkage)
-			global.SetInitializer(c.getZeroValue(llvmType))
-		}
-	}
+	c.loadASTComments(lprogram)

 	// Declare all functions.
 	for _, f := range c.ir.Functions {
@@ -371,6 +361,15 @@ func (c *Compiler) Compile(mainPath string) []error {
 	// See emitNilCheck in asserts.go.
 	c.mod.NamedFunction("runtime.isnil").AddAttributeAtIndex(1, nocapture)

+	// This function is necessary for tracking pointers on the stack in a
+	// portable way (see gc.go). Indicate to the optimizer that the only thing
+	// we'll do is read the pointer.
+	trackPointer := c.mod.NamedFunction("runtime.trackPointer")
+	if !trackPointer.IsNil() {
+		trackPointer.AddAttributeAtIndex(1, nocapture)
+		trackPointer.AddAttributeAtIndex(1, readonly)
+	}
+
 	// Memory copy operations do not capture pointers, even though some weird
 	// pointer arithmetic is happening in the Go implementation.
 	for _, fnName := range []string{"runtime.memcpy", "runtime.memmove"} {
@@ -403,6 +402,22 @@ func (c *Compiler) Compile(mainPath string) []error {
 	return c.diagnostics
 }

+// getRuntimeType obtains a named type from the runtime package and returns it
+// as a Go type.
+func (c *Compiler) getRuntimeType(name string) types.Type {
+	return c.ir.Program.ImportedPackage("runtime").Type(name).Type()
+}
+
+// getLLVMRuntimeType obtains a named type from the runtime package and returns
+// it as a LLVM type, creating it if necessary. It is a shorthand for
+// getLLVMType(getRuntimeType(name)).
+func (c *Compiler) getLLVMRuntimeType(name string) llvm.Type {
+	return c.getLLVMType(c.getRuntimeType(name))
+}
+
+// getLLVMType creates and returns a LLVM type for a Go type. In the case of
+// named struct types (or Go types implemented as named LLVM structs such as
+// strings) it also creates it first if necessary.
 func (c *Compiler) getLLVMType(goType types.Type) llvm.Type {
 	switch typ := goType.(type) {
 	case *types.Array:
@@ -431,7 +446,7 @@ func (c *Compiler) getLLVMType(goType types.Type) llvm.Type {
 		case types.Complex128:
 			return c.ctx.StructType([]llvm.Type{c.ctx.DoubleType(), c.ctx.DoubleType()}, false)
 		case types.String, types.UntypedString:
-			return c.mod.GetTypeByName("runtime._string")
+			return c.getLLVMRuntimeType("_string")
 		case types.Uintptr:
 			return c.uintptrType
 		case types.UnsafePointer:
@@ -440,16 +455,23 @@ func (c *Compiler) getLLVMType(goType types.Type) llvm.Type {
 			panic("unknown basic type: " + typ.String())
 		}
 	case *types.Chan:
-		return llvm.PointerType(c.mod.GetTypeByName("runtime.channel"), 0)
+		return llvm.PointerType(c.getLLVMRuntimeType("channel"), 0)
 	case *types.Interface:
-		return c.mod.GetTypeByName("runtime._interface")
+		return c.getLLVMRuntimeType("_interface")
 	case *types.Map:
-		return llvm.PointerType(c.mod.GetTypeByName("runtime.hashmap"), 0)
+		return llvm.PointerType(c.getLLVMRuntimeType("hashmap"), 0)
 	case *types.Named:
-		if _, ok := typ.Underlying().(*types.Struct); ok {
-			llvmType := c.mod.GetTypeByName(typ.Obj().Pkg().Path() + "." + typ.Obj().Name())
+		if st, ok := typ.Underlying().(*types.Struct); ok {
+			// Structs are a special case. While other named types are ignored
+			// in LLVM IR, named structs are implemented as named structs in
+			// LLVM. This is because it is otherwise impossible to create
+			// self-referencing types such as linked lists.
+			llvmName := typ.Obj().Pkg().Path() + "." + typ.Obj().Name()
+			llvmType := c.mod.GetTypeByName(llvmName)
 			if llvmType.IsNil() {
-				panic("underlying type not found: " + typ.Obj().Pkg().Path() + "." + typ.Obj().Name())
+				llvmType = c.ctx.StructCreateNamed(llvmName)
+				underlying := c.getLLVMType(st)
+				llvmType.StructSetBody(underlying.StructElementTypes(), false)
 			}
 			return llvmType
 		}
@@ -826,7 +848,8 @@ func (c *Compiler) parseFunc(frame *Frame) {
 		fmt.Printf("\nfunc %s:\n", frame.fn.Function)
 	}
 	if !frame.fn.LLVMFn.IsDeclaration() {
-		panic("function is already defined: " + frame.fn.LLVMFn.Name())
+		c.addError(frame.fn.Pos(), "function is already defined:"+frame.fn.LLVMFn.Name())
+		return
 	}
 	if !frame.fn.IsExported() {
 		frame.fn.LLVMFn.SetLinkage(llvm.InternalLinkage)
@@ -842,6 +865,10 @@ func (c *Compiler) parseFunc(frame *Frame) {
 		// Add LLVM inline hint to functions with //go:inline pragma.
 		inline := c.ctx.CreateEnumAttribute(llvm.AttributeKindID("inlinehint"), 0)
 		frame.fn.LLVMFn.AddFunctionAttr(inline)
+	case ir.InlineNone:
+		// Add LLVM attribute to always avoid inlining this function.
+		noinline := c.ctx.CreateEnumAttribute(llvm.AttributeKindID("noinline"), 0)
+		frame.fn.LLVMFn.AddFunctionAttr(noinline)
 	}

 	// Add debug info, if needed.
@@ -994,6 +1021,9 @@ func (c *Compiler) parseInstr(frame *Frame, instr ssa.Instruction) {
 			frame.locals[instr] = llvm.Undef(c.getLLVMType(instr.Type()))
 		} else {
 			frame.locals[instr] = value
+			if len(*instr.Referrers()) != 0 && c.needsStackObjects() {
+				c.trackExpr(frame, instr, value)
+			}
 		}
 	case *ssa.DebugRef:
 		// ignore
@@ -1075,12 +1105,7 @@ func (c *Compiler) parseInstr(frame *Frame, instr ssa.Instruction) {
 			// nothing to store
 			return
 		}
-		store := c.builder.CreateStore(llvmVal, llvmAddr)
-		valType := instr.Addr.Type().Underlying().(*types.Pointer).Elem()
-		if c.ir.IsVolatile(valType) {
-			// Volatile store, for memory-mapped registers.
-			store.SetVolatile(true)
-		}
+		c.builder.CreateStore(llvmVal, llvmAddr)
 	default:
 		c.addError(instr.Pos(), "unknown instruction: "+instr.String())
 	}
@@ -1283,11 +1308,11 @@ func (c *Compiler) parseCall(frame *Frame, instr *ssa.CallCommon) (llvm.Value, e
 	if fn := instr.StaticCallee(); fn != nil {
 		name := fn.RelString(nil)
 		switch {
-		case name == "device/arm.ReadRegister":
-			return c.emitReadRegister(instr.Args)
-		case name == "device/arm.Asm" || name == "device/avr.Asm":
+		case name == "device/arm.ReadRegister" || name == "device/riscv.ReadRegister":
+			return c.emitReadRegister(name, instr.Args)
+		case name == "device/arm.Asm" || name == "device/avr.Asm" || name == "device/riscv.Asm":
 			return c.emitAsm(instr.Args)
-		case name == "device/arm.AsmFull" || name == "device/avr.AsmFull":
+		case name == "device/arm.AsmFull" || name == "device/avr.AsmFull" || name == "device/riscv.AsmFull":
 			return c.emitAsmFull(frame, instr)
 		case strings.HasPrefix(name, "device/arm.SVCall"):
 			return c.emitSVCall(frame, instr.Args)
@@ -1327,10 +1352,7 @@ func (c *Compiler) parseCall(frame *Frame, instr *ssa.CallCommon) (llvm.Value, e
 		value := c.getValue(frame, instr.Value)
 		// This is a func value, which cannot be called directly. We have to
 		// extract the function pointer and context first from the func value.
-		funcPtr, context, err := c.decodeFuncValue(value, instr.Value.Type().Underlying().(*types.Signature))
-		if err != nil {
-			return llvm.Value{}, err
-		}
+		funcPtr, context := c.decodeFuncValue(value, instr.Value.Type().Underlying().(*types.Signature))
 		c.emitNilCheck(frame, funcPtr, "fpcall")
 		return c.parseFunctionCall(frame, instr.Args, funcPtr, context, false), nil
 	}
@@ -1350,9 +1372,9 @@ func (c *Compiler) getValue(frame *Frame, expr ssa.Value) llvm.Value {
 		}
 		return c.createFuncValue(fn.LLVMFn, llvm.Undef(c.i8ptrType), fn.Signature)
 	case *ssa.Global:
-		value := c.ir.GetGlobal(expr).LLVMGlobal
+		value := c.getGlobal(expr)
 		if value.IsNil() {
-			c.addError(expr.Pos(), "global not found: "+c.ir.GetGlobal(expr).LinkName())
+			c.addError(expr.Pos(), "global not found: "+expr.RelString(nil))
 			return llvm.Undef(c.getLLVMType(expr.Type()))
 		}
 		return value
@@ -1385,7 +1407,6 @@ func (c *Compiler) parseExpr(frame *Frame, expr ssa.Value) (llvm.Value, error) {
 				// Size would be truncated if truncated to uintptr.
 				return llvm.Value{}, c.makeError(expr.Pos(), fmt.Sprintf("value is too big (%v bytes)", size))
 			}
-			// TODO: escape analysis
 			sizeValue := llvm.ConstInt(c.uintptrType, size, false)
 			buf := c.createRuntimeCall("alloc", []llvm.Value{sizeValue}, expr.Comment)
 			buf = c.builder.CreateBitCast(buf, llvm.PointerType(typ, 0), "")
@@ -1449,9 +1470,11 @@ func (c *Compiler) parseExpr(frame *Frame, expr ssa.Value) (llvm.Value, error) {
 		x := c.getValue(frame, expr.X)
 		return c.parseConvert(expr.X.Type(), expr.Type(), x, expr.Pos())
 	case *ssa.Extract:
+		if _, ok := expr.Tuple.(*ssa.Select); ok {
+			return c.getChanSelectResult(frame, expr), nil
+		}
 		value := c.getValue(frame, expr.Tuple)
-		result := c.builder.CreateExtractValue(value, expr.Index, "")
-		return result, nil
+		return c.builder.CreateExtractValue(value, expr.Index, ""), nil
 	case *ssa.Field:
 		value := c.getValue(frame, expr.X)
 		if s := expr.X.Type().Underlying().(*types.Struct); s.NumFields() > 2 && s.Field(0).Name() == "C union" {
@@ -1630,7 +1653,6 @@ func (c *Compiler) parseExpr(frame *Frame, expr ssa.Value) (llvm.Value, error) {
 		c.emitSliceBoundsCheck(frame, maxSize, sliceLen, sliceCap, expr.Len.Type().(*types.Basic), expr.Cap.Type().(*types.Basic))

 		// Allocate the backing array.
-		// TODO: escape analysis
 		sliceCapCast, err := c.parseConvert(expr.Cap.Type(), types.Typ[types.Uintptr], sliceCap, expr.Pos())
 		if err != nil {
 			return llvm.Value{}, err
@@ -1690,9 +1712,9 @@ func (c *Compiler) parseExpr(frame *Frame, expr ssa.Value) (llvm.Value, error) {
 		var iteratorType llvm.Type
 		switch typ := expr.X.Type().Underlying().(type) {
 		case *types.Basic: // string
-			iteratorType = c.mod.GetTypeByName("runtime.stringIterator")
+			iteratorType = c.getLLVMRuntimeType("stringIterator")
 		case *types.Map:
-			iteratorType = c.mod.GetTypeByName("runtime.hashmapIterator")
+			iteratorType = c.getLLVMRuntimeType("hashmapIterator")
 		default:
 			panic("unknown type in range: " + typ.String())
 		}
@@ -1700,25 +1722,7 @@ func (c *Compiler) parseExpr(frame *Frame, expr ssa.Value) (llvm.Value, error) {
 		c.builder.CreateStore(c.getZeroValue(iteratorType), it)
 		return it, nil
 	case *ssa.Select:
-		if len(expr.States) == 0 {
-			// Shortcuts for some simple selects.
-			llvmType := c.getLLVMType(expr.Type())
-			if expr.Blocking {
-				// Blocks forever:
-				//     select {}
-				c.createRuntimeCall("deadlockStub", nil, "")
-				return llvm.Undef(llvmType), nil
-			} else {
-				// No-op:
-				//     select {
-				//     default:
-				//     }
-				retval := llvm.Undef(llvmType)
-				retval = c.builder.CreateInsertValue(retval, llvm.ConstInt(c.intType, 0xffffffffffffffff, true), 0, "")
-				return retval, nil // {-1, false}
-			}
-		}
-		return llvm.Value{}, c.makeError(expr.Pos(), "unimplemented: "+expr.String())
+		return c.emitSelect(frame, expr), nil
 	case *ssa.Slice:
 		if expr.Max != nil {
 			return llvm.Value{}, c.makeError(expr.Pos(), "todo: full slice expressions (with max): "+expr.Type().String())
@@ -1852,7 +1856,7 @@ func (c *Compiler) parseExpr(frame *Frame, expr ssa.Value) (llvm.Value, error) {

 			newPtr := c.builder.CreateInBoundsGEP(oldPtr, []llvm.Value{low}, "")
 			newLen := c.builder.CreateSub(high, low, "")
-			str := llvm.Undef(c.mod.GetTypeByName("runtime._string"))
+			str := llvm.Undef(c.getLLVMRuntimeType("_string"))
 			str = c.builder.CreateInsertValue(str, newPtr, 0, "")
 			str = c.builder.CreateInsertValue(str, newLen, 1, "")
 			return str, nil
@@ -2231,7 +2235,7 @@ func (c *Compiler) parseConst(prefix string, expr *ssa.Const) llvm.Value {
 			global.SetUnnamedAddr(true)
 			zero := llvm.ConstInt(c.ctx.Int32Type(), 0, false)
 			strPtr := c.builder.CreateInBoundsGEP(global, []llvm.Value{zero, zero}, "")
-			strObj := llvm.ConstNamedStruct(c.mod.GetTypeByName("runtime._string"), []llvm.Value{strPtr, strLen})
+			strObj := llvm.ConstNamedStruct(c.getLLVMRuntimeType("_string"), []llvm.Value{strPtr, strLen})
 			return strObj
 		} else if typ.Kind() == types.UnsafePointer {
 			if !expr.IsNil() {
@@ -2284,7 +2288,7 @@ func (c *Compiler) parseConst(prefix string, expr *ssa.Const) llvm.Value {
 			llvm.ConstInt(c.uintptrType, 0, false),
 			llvm.ConstPointerNull(c.i8ptrType),
 		}
-		return llvm.ConstNamedStruct(c.mod.GetTypeByName("runtime._interface"), fields)
+		return llvm.ConstNamedStruct(c.getLLVMRuntimeType("_interface"), fields)
 	case *types.Pointer:
 		if expr.Value != nil {
 			panic("expected nil pointer constant")
@@ -2467,8 +2471,10 @@ func (c *Compiler) parseConvert(typeFrom, typeTo types.Type, value llvm.Value, p
 		switch elemType.Kind() {
 		case types.Byte:
 			return c.createRuntimeCall("stringToBytes", []llvm.Value{value}, ""), nil
+		case types.Rune:
+			return c.createRuntimeCall("stringToRunes", []llvm.Value{value}, ""), nil
 		default:
-			return llvm.Value{}, c.makeError(pos, "todo: convert from string: "+elemType.String())
+			panic("unexpected type in string to slice conversion")
 		}

 	default:
@@ -2494,7 +2500,7 @@ func (c *Compiler) parseUnOp(frame *Frame, unop *ssa.UnOp) (llvm.Value, error) {
 			return llvm.Value{}, c.makeError(unop.Pos(), "todo: unknown type for negate: "+unop.X.Type().Underlying().String())
 		}
 	case token.MUL: // *x, dereference pointer
-		valType := unop.X.Type().Underlying().(*types.Pointer).Elem()
+		unop.X.Type().Underlying().(*types.Pointer).Elem()
 		if c.targetData.TypeAllocSize(x.Type().ElementType()) == 0 {
 			// zero-length data
 			return c.getZeroValue(x.Type().ElementType()), nil
@@ -2504,8 +2510,8 @@ func (c *Compiler) parseUnOp(frame *Frame, unop *ssa.UnOp) (llvm.Value, error) {
 			//     var C.add unsafe.Pointer
 			// Instead of a load from the global, create a bitcast of the
 			// function pointer itself.
-			global := c.ir.GetGlobal(unop.X.(*ssa.Global))
-			name := global.LinkName()[:len(global.LinkName())-len("$funcaddr")]
+			globalName := c.getGlobalInfo(unop.X.(*ssa.Global)).linkName
+			name := globalName[:len(globalName)-len("$funcaddr")]
 			fn := c.mod.NamedFunction(name)
 			if fn.IsNil() {
 				return llvm.Value{}, c.makeError(unop.Pos(), "cgo function not found: "+name)
@@ -2514,10 +2520,6 @@ func (c *Compiler) parseUnOp(frame *Frame, unop *ssa.UnOp) (llvm.Value, error) {
 		} else {
 			c.emitNilCheck(frame, x, "deref")
 			load := c.builder.CreateLoad(x, "")
-			if c.ir.IsVolatile(valType) {
-				// Volatile load, for memory-mapped registers.
-				load.SetVolatile(true)
-			}
 			return load, nil
 		}
 	case token.XOR: // ^x, toggle all bits in integer
@@ -29,7 +29,7 @@ func (c *Compiler) deferInitFunc(frame *Frame) {
 	frame.deferClosureFuncs = make(map[*ir.Function]int)

 	// Create defer list pointer.
-	deferType := llvm.PointerType(c.mod.GetTypeByName("runtime._defer"), 0)
+	deferType := llvm.PointerType(c.getLLVMRuntimeType("_defer"), 0)
 	frame.deferPtr = c.builder.CreateAlloca(deferType, "deferPtr")
 	c.builder.CreateStore(llvm.ConstPointerNull(deferType), frame.deferPtr)
 }
@@ -130,6 +130,9 @@ func (c *Compiler) emitDefer(frame *Frame, instr *ssa.Defer) {
 	// Put this struct in an alloca.
 	alloca := c.builder.CreateAlloca(deferFrameType, "defer.alloca")
 	c.builder.CreateStore(deferFrame, alloca)
+	if c.needsStackObjects() {
+		c.trackPointer(alloca)
+	}

 	// Push it on top of the linked list by replacing deferPtr.
 	allocaCast := c.builder.CreateBitCast(alloca, next.Type(), "defer.alloca.cast")
@@ -200,7 +203,7 @@ func (c *Compiler) emitRunDefers(frame *Frame) {
 			}

 			// Get the real defer struct type and cast to it.
-			valueTypes := []llvm.Type{c.uintptrType, llvm.PointerType(c.mod.GetTypeByName("runtime._defer"), 0), c.i8ptrType}
+			valueTypes := []llvm.Type{c.uintptrType, llvm.PointerType(c.getLLVMRuntimeType("_defer"), 0), c.i8ptrType}
 			for _, arg := range callback.Args {
 				valueTypes = append(valueTypes, c.getLLVMType(arg.Type()))
 			}
@@ -231,7 +234,7 @@ func (c *Compiler) emitRunDefers(frame *Frame) {
 			// Direct call.

 			// Get the real defer struct type and cast to it.
-			valueTypes := []llvm.Type{c.uintptrType, llvm.PointerType(c.mod.GetTypeByName("runtime._defer"), 0)}
+			valueTypes := []llvm.Type{c.uintptrType, llvm.PointerType(c.getLLVMRuntimeType("_defer"), 0)}
 			for _, param := range callback.Params {
 				valueTypes = append(valueTypes, c.getLLVMType(param.Type()))
 			}
@@ -260,7 +263,7 @@ func (c *Compiler) emitRunDefers(frame *Frame) {
 		case *ssa.MakeClosure:
 			// Get the real defer struct type and cast to it.
 			fn := c.ir.GetFunction(callback.Fn.(*ssa.Function))
-			valueTypes := []llvm.Type{c.uintptrType, llvm.PointerType(c.mod.GetTypeByName("runtime._defer"), 0)}
+			valueTypes := []llvm.Type{c.uintptrType, llvm.PointerType(c.getLLVMRuntimeType("_defer"), 0)}
 			params := fn.Signature.Params()
 			for i := 0; i < params.Len(); i++ {
 				valueTypes = append(valueTypes, c.getLLVMType(params.At(i).Type()))
@@ -51,7 +51,7 @@ func (c *Compiler) LowerFuncValues() {
 	}

 	// Find all func values used in the program with their signatures.
-	funcValueWithSignaturePtr := llvm.PointerType(c.mod.GetTypeByName("runtime.funcValueWithSignature"), 0)
+	funcValueWithSignaturePtr := llvm.PointerType(c.getLLVMRuntimeType("funcValueWithSignature"), 0)
 	signatures := map[string]*funcSignatureInfo{}
 	for global := c.mod.FirstGlobal(); !global.IsNil(); global = llvm.NextGlobal(global) {
 		if global.Type() != funcValueWithSignaturePtr {
@@ -52,7 +52,7 @@ func (c *Compiler) createFuncValue(funcPtr, context llvm.Value, sig *types.Signa
 		funcValueWithSignatureGlobalName := funcPtr.Name() + "$withSignature"
 		funcValueWithSignatureGlobal := c.mod.NamedGlobal(funcValueWithSignatureGlobalName)
 		if funcValueWithSignatureGlobal.IsNil() {
-			funcValueWithSignatureType := c.mod.GetTypeByName("runtime.funcValueWithSignature")
+			funcValueWithSignatureType := c.getLLVMRuntimeType("funcValueWithSignature")
 			funcValueWithSignature := llvm.ConstNamedStruct(funcValueWithSignatureType, []llvm.Value{
 				llvm.ConstPtrToInt(funcPtr, c.uintptrType),
 				sigGlobal,
@@ -103,7 +103,7 @@ func (c *Compiler) extractFuncContext(funcValue llvm.Value) llvm.Value {

 // decodeFuncValue extracts the context and the function pointer from this func
 // value. This may be an expensive operation.
-func (c *Compiler) decodeFuncValue(funcValue llvm.Value, sig *types.Signature) (funcPtr, context llvm.Value, err error) {
+func (c *Compiler) decodeFuncValue(funcValue llvm.Value, sig *types.Signature) (funcPtr, context llvm.Value) {
 	context = c.builder.CreateExtractValue(funcValue, 0, "")
 	switch c.funcImplementation() {
 	case funcValueDoubleword:
@@ -126,7 +126,7 @@ func (c *Compiler) getFuncType(typ *types.Signature) llvm.Type {
 		rawPtr := c.getRawFuncType(typ)
 		return c.ctx.StructType([]llvm.Type{c.i8ptrType, rawPtr}, false)
 	case funcValueSwitch:
-		return c.mod.GetTypeByName("runtime.funcValue")
+		return c.getLLVMRuntimeType("funcValue")
 	default:
 		panic("unimplemented func value variant")
 	}
@@ -0,0 +1,471 @@
+package compiler
+
+// This file provides IR transformations necessary for precise and portable
+// garbage collectors.
+
+import (
+	"go/token"
+	"math/big"
+
+	"golang.org/x/tools/go/ssa"
+	"tinygo.org/x/go-llvm"
+)
+
+// needsStackObjects returns true if the compiler should insert stack objects
+// that can be traced by the garbage collector.
+func (c *Compiler) needsStackObjects() bool {
+	if c.selectGC() != "conservative" {
+		return false
+	}
+	for _, tag := range c.BuildTags {
+		if tag == "cortexm" || tag == "tinygo.riscv" {
+			return false
+		}
+	}
+
+	return true
+}
+
+// trackExpr inserts pointer tracking intrinsics for the GC if the expression is
+// one of the expressions that need this.
+func (c *Compiler) trackExpr(frame *Frame, expr ssa.Value, value llvm.Value) {
+	// There are uses of this expression, Make sure the pointers
+	// are tracked during GC.
+	switch expr := expr.(type) {
+	case *ssa.Alloc, *ssa.MakeChan, *ssa.MakeMap:
+		// These values are always of pointer type in IR.
+		c.trackPointer(value)
+	case *ssa.Call, *ssa.Convert, *ssa.MakeClosure, *ssa.MakeInterface, *ssa.MakeSlice, *ssa.Next:
+		if !value.IsNil() {
+			c.trackValue(value)
+		}
+	case *ssa.Select:
+		if alloca, ok := frame.selectRecvBuf[expr]; ok {
+			if alloca.IsAUndefValue().IsNil() {
+				c.trackPointer(alloca)
+			}
+		}
+	case *ssa.UnOp:
+		switch expr.Op {
+		case token.MUL:
+			// Pointer dereference.
+			c.trackValue(value)
+		case token.ARROW:
+			// Channel receive operator.
+			// It's not necessary to look at commaOk here, because in that
+			// case it's just an aggregate and trackValue will extract the
+			// pointer in there (if there is one).
+			c.trackValue(value)
+		}
+	}
+}
+
+// trackValue locates pointers in a value (possibly an aggregate) and tracks the
+// individual pointers
+func (c *Compiler) trackValue(value llvm.Value) {
+	typ := value.Type()
+	switch typ.TypeKind() {
+	case llvm.PointerTypeKind:
+		c.trackPointer(value)
+	case llvm.StructTypeKind:
+		if !typeHasPointers(typ) {
+			return
+		}
+		numElements := typ.StructElementTypesCount()
+		for i := 0; i < numElements; i++ {
+			subValue := c.builder.CreateExtractValue(value, i, "")
+			c.trackValue(subValue)
+		}
+	case llvm.ArrayTypeKind:
+		if !typeHasPointers(typ) {
+			return
+		}
+		numElements := typ.ArrayLength()
+		for i := 0; i < numElements; i++ {
+			subValue := c.builder.CreateExtractValue(value, i, "")
+			c.trackValue(subValue)
+		}
+	}
+}
+
+// trackPointer creates a call to runtime.trackPointer, bitcasting the poitner
+// first if needed. The input value must be of LLVM pointer type.
+func (c *Compiler) trackPointer(value llvm.Value) {
+	if value.Type() != c.i8ptrType {
+		value = c.builder.CreateBitCast(value, c.i8ptrType, "")
+	}
+	c.createRuntimeCall("trackPointer", []llvm.Value{value}, "")
+}
+
+// typeHasPointers returns whether this type is a pointer or contains pointers.
+// If the type is an aggregate type, it will check whether there is a pointer
+// inside.
+func typeHasPointers(t llvm.Type) bool {
+	switch t.TypeKind() {
+	case llvm.PointerTypeKind:
+		return true
+	case llvm.StructTypeKind:
+		for _, subType := range t.StructElementTypes() {
+			if typeHasPointers(subType) {
+				return true
+			}
+		}
+		return false
+	case llvm.ArrayTypeKind:
+		if typeHasPointers(t.ElementType()) {
+			return true
+		}
+		return false
+	default:
+		return false
+	}
+}
+
+// makeGCStackSlots converts all calls to runtime.trackPointer to explicit
+// stores to stack slots that are scannable by the GC.
+func (c *Compiler) makeGCStackSlots() bool {
+	// Check whether there are allocations at all.
+	alloc := c.mod.NamedFunction("runtime.alloc")
+	if alloc.IsNil() {
+		// Nothing to. Make sure all remaining bits and pieces for stack
+		// chains are neutralized.
+		for _, call := range getUses(c.mod.NamedFunction("runtime.trackPointer")) {
+			call.EraseFromParentAsInstruction()
+		}
+		stackChainStart := c.mod.NamedGlobal("runtime.stackChainStart")
+		if !stackChainStart.IsNil() {
+			stackChainStart.SetInitializer(c.getZeroValue(stackChainStart.Type().ElementType()))
+			stackChainStart.SetGlobalConstant(true)
+		}
+	}
+
+	trackPointer := c.mod.NamedFunction("runtime.trackPointer")
+	if trackPointer.IsNil() || trackPointer.FirstUse().IsNil() {
+		return false // nothing to do
+	}
+
+	// Look at *all* functions to see whether they are free of function pointer
+	// calls.
+	// This takes less than 5ms for ~100kB of WebAssembly but would perhaps be
+	// faster when written in C++ (to avoid the CGo overhead).
+	funcsWithFPCall := map[llvm.Value]struct{}{}
+	n := 0
+	for fn := c.mod.FirstFunction(); !fn.IsNil(); fn = llvm.NextFunction(fn) {
+		n++
+		if _, ok := funcsWithFPCall[fn]; ok {
+			continue // already found
+		}
+		done := false
+		for bb := fn.FirstBasicBlock(); !bb.IsNil() && !done; bb = llvm.NextBasicBlock(bb) {
+			for call := bb.FirstInstruction(); !call.IsNil() && !done; call = llvm.NextInstruction(call) {
+				if call.IsACallInst().IsNil() {
+					continue // only looking at calls
+				}
+				called := call.CalledValue()
+				if !called.IsAFunction().IsNil() {
+					continue // only looking for function pointers
+				}
+				funcsWithFPCall[fn] = struct{}{}
+				markParentFunctions(funcsWithFPCall, fn)
+				done = true
+			}
+		}
+	}
+
+	// Determine which functions need stack objects. Many leaf functions don't
+	// need it: it only causes overhead for them.
+	// Actually, in one test it was only able to eliminate stack object from 12%
+	// of functions that had a call to runtime.trackPointer (8 out of 68
+	// functions), so this optimization is not as big as it may seem.
+	allocatingFunctions := map[llvm.Value]struct{}{} // set of allocating functions
+
+	// Work from runtime.alloc and trace all parents to check which functions do
+	// a heap allocation (and thus which functions do not).
+	markParentFunctions(allocatingFunctions, alloc)
+
+	// Also trace all functions that call a function pointer.
+	for fn := range funcsWithFPCall {
+		// Assume that functions that call a function pointer do a heap
+		// allocation as a conservative guess because the called function might
+		// do a heap allocation.
+		allocatingFunctions[fn] = struct{}{}
+		markParentFunctions(allocatingFunctions, fn)
+	}
+
+	// Collect some variables used below in the loop.
+	stackChainStart := c.mod.NamedGlobal("runtime.stackChainStart")
+	if stackChainStart.IsNil() {
+		panic("stack chain start not found!")
+	}
+	stackChainStartType := stackChainStart.Type().ElementType()
+	stackChainStart.SetInitializer(c.getZeroValue(stackChainStartType))
+
+	// Iterate until runtime.trackPointer has no uses left.
+	for use := trackPointer.FirstUse(); !use.IsNil(); use = trackPointer.FirstUse() {
+		// Pick the first use of runtime.trackPointer.
+		call := use.User()
+		if call.IsACallInst().IsNil() {
+			panic("expected runtime.trackPointer use to be a call")
+		}
+
+		// Pick the parent function.
+		fn := call.InstructionParent().Parent()
+
+		if _, ok := allocatingFunctions[fn]; !ok {
+			// This function nor any of the functions it calls (recursively)
+			// allocate anything from the heap, so it will not trigger a garbage
+			// collection cycle. Thus, it does not need to track local pointer
+			// values.
+			// This is a useful optimization but not as big as you might guess,
+			// as described above (it avoids stack objects for ~12% of
+			// functions).
+			call.EraseFromParentAsInstruction()
+			continue
+		}
+
+		// Find all calls to runtime.trackPointer in this function.
+		var calls []llvm.Value
+		var returns []llvm.Value
+		for bb := fn.FirstBasicBlock(); !bb.IsNil(); bb = llvm.NextBasicBlock(bb) {
+			for inst := bb.FirstInstruction(); !inst.IsNil(); inst = llvm.NextInstruction(inst) {
+				switch inst.InstructionOpcode() {
+				case llvm.Call:
+					if inst.CalledValue() == trackPointer {
+						calls = append(calls, inst)
+					}
+				case llvm.Ret:
+					returns = append(returns, inst)
+				}
+			}
+		}
+
+		// Determine what to do with each call.
+		var allocas, pointers []llvm.Value
+		for _, call := range calls {
+			ptr := call.Operand(0)
+			call.EraseFromParentAsInstruction()
+			if ptr.IsAInstruction().IsNil() {
+				continue
+			}
+
+			// Some trivial optimizations.
+			if ptr.IsAInstruction().IsNil() {
+				continue
+			}
+			switch ptr.InstructionOpcode() {
+			case llvm.PHI, llvm.GetElementPtr:
+				// These values do not create new values: the values already
+				// existed locally in this function so must have been tracked
+				// already.
+				continue
+			case llvm.ExtractValue, llvm.BitCast:
+				// These instructions do not create new values, but their
+				// original value may not be tracked. So keep tracking them for
+				// now.
+				// With more analysis, it should be possible to optimize a
+				// significant chunk of these away.
+			case llvm.Call, llvm.Load, llvm.IntToPtr:
+				// These create new values so must be stored locally. But
+				// perhaps some of these can be fused when they actually refer
+				// to the same value.
+			default:
+				// Ambiguous. These instructions are uncommon, but perhaps could
+				// be optimized if needed.
+			}
+
+			if !ptr.IsAAllocaInst().IsNil() {
+				if typeHasPointers(ptr.Type().ElementType()) {
+					allocas = append(allocas, ptr)
+				}
+			} else {
+				pointers = append(pointers, ptr)
+			}
+		}
+
+		if len(allocas) == 0 && len(pointers) == 0 {
+			// This function does not need to keep track of stack pointers.
+			continue
+		}
+
+		// Determine the type of the required stack slot.
+		fields := []llvm.Type{
+			stackChainStartType, // Pointer to parent frame.
+			c.uintptrType,       // Number of elements in this frame.
+		}
+		for _, alloca := range allocas {
+			fields = append(fields, alloca.Type().ElementType())
+		}
+		for _, ptr := range pointers {
+			fields = append(fields, ptr.Type())
+		}
+		stackObjectType := c.ctx.StructType(fields, false)
+
+		// Create the stack object at the function entry.
+		c.builder.SetInsertPointBefore(fn.EntryBasicBlock().FirstInstruction())
+		stackObject := c.builder.CreateAlloca(stackObjectType, "gc.stackobject")
+		initialStackObject := c.getZeroValue(stackObjectType)
+		numSlots := (c.targetData.TypeAllocSize(stackObjectType) - c.targetData.TypeAllocSize(c.i8ptrType)*2) / uint64(c.targetData.ABITypeAlignment(c.uintptrType))
+		numSlotsValue := llvm.ConstInt(c.uintptrType, numSlots, false)
+		initialStackObject = llvm.ConstInsertValue(initialStackObject, numSlotsValue, []uint32{1})
+		c.builder.CreateStore(initialStackObject, stackObject)
+
+		// Update stack start.
+		parent := c.builder.CreateLoad(stackChainStart, "")
+		gep := c.builder.CreateGEP(stackObject, []llvm.Value{
+			llvm.ConstInt(c.ctx.Int32Type(), 0, false),
+			llvm.ConstInt(c.ctx.Int32Type(), 0, false),
+		}, "")
+		c.builder.CreateStore(parent, gep)
+		stackObjectCast := c.builder.CreateBitCast(stackObject, stackChainStartType, "")
+		c.builder.CreateStore(stackObjectCast, stackChainStart)
+
+		// Replace all independent allocas with GEPs in the stack object.
+		for i, alloca := range allocas {
+			gep := c.builder.CreateGEP(stackObject, []llvm.Value{
+				llvm.ConstInt(c.ctx.Int32Type(), 0, false),
+				llvm.ConstInt(c.ctx.Int32Type(), uint64(2+i), false),
+			}, "")
+			alloca.ReplaceAllUsesWith(gep)
+			alloca.EraseFromParentAsInstruction()
+		}
+
+		// Do a store to the stack object after each new pointer that is created.
+		for i, ptr := range pointers {
+			c.builder.SetInsertPointBefore(llvm.NextInstruction(ptr))
+			gep := c.builder.CreateGEP(stackObject, []llvm.Value{
+				llvm.ConstInt(c.ctx.Int32Type(), 0, false),
+				llvm.ConstInt(c.ctx.Int32Type(), uint64(2+len(allocas)+i), false),
+			}, "")
+			c.builder.CreateStore(ptr, gep)
+		}
+
+		// Make sure this stack object is popped from the linked list of stack
+		// objects at return.
+		for _, ret := range returns {
+			c.builder.SetInsertPointBefore(ret)
+			c.builder.CreateStore(parent, stackChainStart)
+		}
+	}
+
+	return true
+}
+
+func (c *Compiler) addGlobalsBitmap() bool {
+	if c.mod.NamedGlobal("runtime.trackedGlobalsStart").IsNil() {
+		return false // nothing to do: no GC in use
+	}
+
+	var trackedGlobals []llvm.Value
+	var trackedGlobalTypes []llvm.Type
+	for global := c.mod.FirstGlobal(); !global.IsNil(); global = llvm.NextGlobal(global) {
+		if global.IsDeclaration() {
+			continue
+		}
+		typ := global.Type().ElementType()
+		ptrs := c.getPointerBitmap(typ, global.Name())
+		if ptrs.BitLen() == 0 {
+			continue
+		}
+		trackedGlobals = append(trackedGlobals, global)
+		trackedGlobalTypes = append(trackedGlobalTypes, typ)
+	}
+
+	globalsBundleType := c.ctx.StructType(trackedGlobalTypes, false)
+	globalsBundle := llvm.AddGlobal(c.mod, globalsBundleType, "tinygo.trackedGlobals")
+	globalsBundle.SetLinkage(llvm.InternalLinkage)
+	globalsBundle.SetUnnamedAddr(true)
+	initializer := llvm.Undef(globalsBundleType)
+	for i, global := range trackedGlobals {
+		initializer = llvm.ConstInsertValue(initializer, global.Initializer(), []uint32{uint32(i)})
+		gep := llvm.ConstGEP(globalsBundle, []llvm.Value{
+			llvm.ConstInt(c.ctx.Int32Type(), 0, false),
+			llvm.ConstInt(c.ctx.Int32Type(), uint64(i), false),
+		})
+		global.ReplaceAllUsesWith(gep)
+		global.EraseFromParentAsGlobal()
+	}
+	globalsBundle.SetInitializer(initializer)
+
+	trackedGlobalsStart := llvm.ConstPtrToInt(globalsBundle, c.uintptrType)
+	c.mod.NamedGlobal("runtime.trackedGlobalsStart").SetInitializer(trackedGlobalsStart)
+
+	alignment := c.targetData.PrefTypeAlignment(c.i8ptrType)
+	trackedGlobalsLength := llvm.ConstInt(c.uintptrType, c.targetData.TypeAllocSize(globalsBundleType)/uint64(alignment), false)
+	c.mod.NamedGlobal("runtime.trackedGlobalsLength").SetInitializer(trackedGlobalsLength)
+
+	bitmapBytes := c.getPointerBitmap(globalsBundleType, "globals bundle").Bytes()
+	bitmapValues := make([]llvm.Value, len(bitmapBytes))
+	for i, b := range bitmapBytes {
+		bitmapValues[len(bitmapBytes)-i-1] = llvm.ConstInt(c.ctx.Int8Type(), uint64(b), false)
+	}
+	bitmapArray := llvm.ConstArray(llvm.ArrayType(c.ctx.Int8Type(), len(bitmapBytes)), bitmapValues)
+	bitmapNew := llvm.AddGlobal(c.mod, bitmapArray.Type(), "runtime.trackedGlobalsBitmap.tmp")
+	bitmapOld := c.mod.NamedGlobal("runtime.trackedGlobalsBitmap")
+	bitmapOld.ReplaceAllUsesWith(bitmapNew)
+	bitmapNew.SetInitializer(bitmapArray)
+	bitmapNew.SetName("runtime.trackedGlobalsBitmap")
+
+	return true // the IR was changed
+}
+
+func (c *Compiler) getPointerBitmap(typ llvm.Type, name string) *big.Int {
+	alignment := c.targetData.PrefTypeAlignment(c.i8ptrType)
+	switch typ.TypeKind() {
+	case llvm.IntegerTypeKind, llvm.FloatTypeKind, llvm.DoubleTypeKind:
+		return big.NewInt(0)
+	case llvm.PointerTypeKind:
+		return big.NewInt(1)
+	case llvm.StructTypeKind:
+		ptrs := big.NewInt(0)
+		for i, subtyp := range typ.StructElementTypes() {
+			subptrs := c.getPointerBitmap(subtyp, name)
+			if subptrs.BitLen() == 0 {
+				continue
+			}
+			offset := c.targetData.ElementOffset(typ, i)
+			if offset%uint64(alignment) != 0 {
+				panic("precise GC: global contains unaligned pointer: " + name)
+			}
+			subptrs.Lsh(subptrs, uint(offset)/uint(alignment))
+			ptrs.Or(ptrs, subptrs)
+		}
+		return ptrs
+	case llvm.ArrayTypeKind:
+		subtyp := typ.ElementType()
+		subptrs := c.getPointerBitmap(subtyp, name)
+		ptrs := big.NewInt(0)
+		if subptrs.BitLen() == 0 {
+			return ptrs
+		}
+		elementSize := c.targetData.TypeAllocSize(subtyp)
+		for i := 0; i < typ.ArrayLength(); i++ {
+			ptrs.Lsh(ptrs, uint(elementSize)/uint(alignment))
+			ptrs.Or(ptrs, subptrs)
+		}
+		return ptrs
+	default:
+		panic("unknown type kind of global: " + name)
+	}
+}
+
+// markParentFunctions traverses all parent function calls (recursively) and
+// adds them to the set of marked functions. It only considers function calls:
+// any other uses of such a function is ignored.
+func markParentFunctions(marked map[llvm.Value]struct{}, fn llvm.Value) {
+	worklist := []llvm.Value{fn}
+	for len(worklist) != 0 {
+		fn := worklist[len(worklist)-1]
+		worklist = worklist[:len(worklist)-1]
+		for _, use := range getUses(fn) {
+			if use.IsACallInst().IsNil() || use.CalledValue() != fn {
+				// Not the parent function.
+				continue
+			}
+			parent := use.InstructionParent().Parent()
+			if _, ok := marked[parent]; !ok {
+				marked[parent] = struct{}{}
+				worklist = append(worklist, parent)
+			}
+		}
+	}
+}
@@ -321,7 +321,7 @@ func (c *Compiler) markAsyncFunctions() (needsScheduler bool, err error) {

 		// Coroutine setup.
 		c.builder.SetInsertPointBefore(f.EntryBasicBlock().FirstInstruction())
-		taskState := c.builder.CreateAlloca(c.mod.GetTypeByName("runtime.taskState"), "task.state")
+		taskState := c.builder.CreateAlloca(c.getLLVMRuntimeType("taskState"), "task.state")
 		stateI8 := c.builder.CreateBitCast(taskState, c.i8ptrType, "task.state.i8")
 		id := c.builder.CreateCall(coroIdFunc, []llvm.Value{
 			llvm.ConstInt(c.ctx.Int32Type(), 0, false),
@@ -336,6 +336,9 @@ func (c *Compiler) markAsyncFunctions() (needsScheduler bool, err error) {
 			size = c.builder.CreateZExt(size, c.uintptrType, "task.size.uintptr")
 		}
 		data := c.createRuntimeCall("alloc", []llvm.Value{size}, "task.data")
+		if c.needsStackObjects() {
+			c.trackPointer(data)
+		}
 		frame.taskHandle = c.builder.CreateCall(coroBeginFunc, []llvm.Value{id, data}, "task.handle")

 		// Modify async calls so this function suspends right after the child
@@ -18,10 +18,19 @@ import (
 //     func ReadRegister(name string) uintptr
 //
 // The register name must be a constant, for example "sp".
-func (c *Compiler) emitReadRegister(args []ssa.Value) (llvm.Value, error) {
+func (c *Compiler) emitReadRegister(name string, args []ssa.Value) (llvm.Value, error) {
 	fnType := llvm.FunctionType(c.uintptrType, []llvm.Type{}, false)
 	regname := constant.StringVal(args[0].(*ssa.Const).Value)
-	target := llvm.InlineAsm(fnType, "mov $0, "+regname, "=r", false, false, 0)
+	var asm string
+	switch name {
+	case "device/arm.ReadRegister":
+		asm = "mov $0, " + regname
+	case "device/riscv.ReadRegister":
+		asm = "mv $0, " + regname
+	default:
+		panic("unknown architecture")
+	}
+	target := llvm.InlineAsm(fnType, asm, "=r", false, false, 0)
 	return c.builder.CreateCall(target, nil, ""), nil
 }

@@ -163,8 +163,8 @@ func (c *Compiler) LowerInterfaces() {
 // run runs the pass itself.
 func (p *lowerInterfacesPass) run() {
 	// Collect all type codes.
-	typecodeIDPtr := llvm.PointerType(p.mod.GetTypeByName("runtime.typecodeID"), 0)
-	typeInInterfacePtr := llvm.PointerType(p.mod.GetTypeByName("runtime.typeInInterface"), 0)
+	typecodeIDPtr := llvm.PointerType(p.getLLVMRuntimeType("typecodeID"), 0)
+	typeInInterfacePtr := llvm.PointerType(p.getLLVMRuntimeType("typeInInterface"), 0)
 	var typesInInterfaces []llvm.Value
 	for global := p.mod.FirstGlobal(); !global.IsNil(); global = llvm.NextGlobal(global) {
 		switch global.Type() {
@@ -28,14 +28,14 @@ func (c *Compiler) parseMakeInterface(val llvm.Value, typ types.Type, pos token.
 	itfMethodSetGlobal := c.getTypeMethodSet(typ)
 	itfConcreteTypeGlobal := c.mod.NamedGlobal("typeInInterface:" + itfTypeCodeGlobal.Name())
 	if itfConcreteTypeGlobal.IsNil() {
-		typeInInterface := c.mod.GetTypeByName("runtime.typeInInterface")
+		typeInInterface := c.getLLVMRuntimeType("typeInInterface")
 		itfConcreteTypeGlobal = llvm.AddGlobal(c.mod, typeInInterface, "typeInInterface:"+itfTypeCodeGlobal.Name())
 		itfConcreteTypeGlobal.SetInitializer(llvm.ConstNamedStruct(typeInInterface, []llvm.Value{itfTypeCodeGlobal, itfMethodSetGlobal}))
 		itfConcreteTypeGlobal.SetGlobalConstant(true)
 		itfConcreteTypeGlobal.SetLinkage(llvm.PrivateLinkage)
 	}
 	itfTypeCode := c.builder.CreatePtrToInt(itfConcreteTypeGlobal, c.uintptrType, "")
-	itf := llvm.Undef(c.mod.GetTypeByName("runtime._interface"))
+	itf := llvm.Undef(c.getLLVMRuntimeType("_interface"))
 	itf = c.builder.CreateInsertValue(itf, itfTypeCode, 0, "")
 	itf = c.builder.CreateInsertValue(itf, itfValue, 1, "")
 	return itf
@@ -48,7 +48,7 @@ func (c *Compiler) getTypeCode(typ types.Type) llvm.Value {
 	globalName := "type:" + getTypeCodeName(typ)
 	global := c.mod.NamedGlobal(globalName)
 	if global.IsNil() {
-		global = llvm.AddGlobal(c.mod, c.mod.GetTypeByName("runtime.typecodeID"), globalName)
+		global = llvm.AddGlobal(c.mod, c.getLLVMRuntimeType("typecodeID"), globalName)
 		global.SetGlobalConstant(true)
 	}
 	return global
@@ -163,11 +163,11 @@ func (c *Compiler) getTypeMethodSet(typ types.Type) llvm.Value {
 	ms := c.ir.Program.MethodSets.MethodSet(typ)
 	if ms.Len() == 0 {
 		// no methods, so can leave that one out
-		return llvm.ConstPointerNull(llvm.PointerType(c.mod.GetTypeByName("runtime.interfaceMethodInfo"), 0))
+		return llvm.ConstPointerNull(llvm.PointerType(c.getLLVMRuntimeType("interfaceMethodInfo"), 0))
 	}

 	methods := make([]llvm.Value, ms.Len())
-	interfaceMethodInfoType := c.mod.GetTypeByName("runtime.interfaceMethodInfo")
+	interfaceMethodInfoType := c.getLLVMRuntimeType("interfaceMethodInfo")
 	for i := 0; i < ms.Len(); i++ {
 		method := ms.At(i)
 		signatureGlobal := c.getMethodSignature(method.Obj().(*types.Func))
@@ -35,7 +35,7 @@ func (c *Compiler) emitMapLookup(keyType, valueType types.Type, m, key llvm.Valu
 		c.emitLifetimeEnd(mapKeyPtr, mapKeySize)
 	} else {
 		// Not trivially comparable using memcmp.
-		return llvm.Value{}, c.makeError(pos, "only strings, bools, ints or structs of bools/ints are supported as map keys, but got: "+keyType.String())
+		return llvm.Value{}, c.makeError(pos, "only strings, bools, ints, pointers or structs of bools/ints are supported as map keys, but got: "+keyType.String())
 	}

 	// Load the resulting value from the hashmap. The value is set to the zero
@@ -69,7 +69,7 @@ func (c *Compiler) emitMapUpdate(keyType types.Type, m, key, value llvm.Value, p
 		c.createRuntimeCall("hashmapBinarySet", params, "")
 		c.emitLifetimeEnd(keyPtr, keySize)
 	} else {
-		c.addError(pos, "only strings, bools, ints or structs of bools/ints are supported as map keys, but got: "+keyType.String())
+		c.addError(pos, "only strings, bools, ints, pointers or structs of bools/ints are supported as map keys, but got: "+keyType.String())
 	}
 	c.emitLifetimeEnd(valuePtr, valueSize)
 }
@@ -89,7 +89,7 @@ func (c *Compiler) emitMapDelete(keyType types.Type, m, key llvm.Value, pos toke
 		c.emitLifetimeEnd(keyPtr, keySize)
 		return nil
 	} else {
-		return c.makeError(pos, "only strings, bools, ints or structs of bools/ints are supported as map keys, but got: "+keyType.String())
+		return c.makeError(pos, "only strings, bools, ints, pointers or structs of bools/ints are supported as map keys, but got: "+keyType.String())
 	}
 }

@@ -121,6 +121,8 @@ func hashmapIsBinaryKey(keyType types.Type) bool {
 	switch keyType := keyType.(type) {
 	case *types.Basic:
 		return keyType.Info()&(types.IsBoolean|types.IsInteger) != 0
+	case *types.Pointer:
+		return true
 	case *types.Struct:
 		for i := 0; i < keyType.NumFields(); i++ {
 			fieldType := keyType.Field(i).Type().Underlying()
@@ -114,6 +114,14 @@ func (c *Compiler) Optimize(optLevel, sizeLevel int, inlinerThreshold uint) erro
 	builder.Populate(modPasses)
 	modPasses.Run(c.mod)

+	hasGCPass := c.addGlobalsBitmap()
+	hasGCPass = c.makeGCStackSlots() || hasGCPass
+	if hasGCPass {
+		if err := c.Verify(); err != nil {
+			return errors.New("GC pass caused a verification failure")
+		}
+	}
+
 	return nil
 }

@@ -0,0 +1,107 @@
+package compiler
+
+// This file manages symbols, that is, functions and globals. It reads their
+// pragmas, determines the link name, etc.
+
+import (
+	"go/ast"
+	"go/token"
+	"go/types"
+	"strings"
+
+	"github.com/tinygo-org/tinygo/loader"
+	"golang.org/x/tools/go/ssa"
+	"tinygo.org/x/go-llvm"
+)
+
+// globalInfo contains some information about a specific global. By default,
+// linkName is equal to .RelString(nil) on a global and extern is false, but for
+// some symbols this is different (due to //go:extern for example).
+type globalInfo struct {
+	linkName string // go:extern
+	extern   bool   // go:extern
+}
+
+// loadASTComments loads comments on globals from the AST, for use later in the
+// program. In particular, they are required for //go:extern pragmas on globals.
+func (c *Compiler) loadASTComments(lprogram *loader.Program) {
+	c.astComments = map[string]*ast.CommentGroup{}
+	for _, pkgInfo := range lprogram.Sorted() {
+		for _, file := range pkgInfo.Files {
+			for _, decl := range file.Decls {
+				switch decl := decl.(type) {
+				case *ast.GenDecl:
+					switch decl.Tok {
+					case token.VAR:
+						if len(decl.Specs) != 1 {
+							continue
+						}
+						for _, spec := range decl.Specs {
+							switch spec := spec.(type) {
+							case *ast.ValueSpec: // decl.Tok == token.VAR
+								for _, name := range spec.Names {
+									id := pkgInfo.Pkg.Path() + "." + name.Name
+									c.astComments[id] = decl.Doc
+								}
+							}
+						}
+					}
+				}
+			}
+		}
+	}
+}
+
+// getGlobal returns a LLVM IR global value for a Go SSA global. It is added to
+// the LLVM IR if it has not been added already.
+func (c *Compiler) getGlobal(g *ssa.Global) llvm.Value {
+	info := c.getGlobalInfo(g)
+	llvmGlobal := c.mod.NamedGlobal(info.linkName)
+	if llvmGlobal.IsNil() {
+		llvmType := c.getLLVMType(g.Type().(*types.Pointer).Elem())
+		llvmGlobal = llvm.AddGlobal(c.mod, llvmType, info.linkName)
+		if !info.extern {
+			llvmGlobal.SetInitializer(c.getZeroValue(llvmType))
+			llvmGlobal.SetLinkage(llvm.InternalLinkage)
+		}
+	}
+	return llvmGlobal
+}
+
+// getGlobalInfo returns some information about a specific global.
+func (c *Compiler) getGlobalInfo(g *ssa.Global) globalInfo {
+	info := globalInfo{}
+	if strings.HasPrefix(g.Name(), "C.") {
+		// Created by CGo: such a name cannot be created by regular C code.
+		info.linkName = g.Name()[2:]
+		info.extern = true
+	} else {
+		// Pick the default linkName.
+		info.linkName = g.RelString(nil)
+		// Check for //go: pragmas, which may change the link name (among
+		// others).
+		doc := c.astComments[info.linkName]
+		if doc != nil {
+			info.parsePragmas(doc)
+		}
+	}
+	return info
+}
+
+// Parse //go: pragma comments from the source. In particular, it parses the
+// //go:extern pragma on globals.
+func (info *globalInfo) parsePragmas(doc *ast.CommentGroup) {
+	for _, comment := range doc.List {
+		if !strings.HasPrefix(comment.Text, "//go:") {
+			continue
+		}
+		parts := strings.Fields(comment.Text)
+		switch parts[0] {
+		case "//go:extern":
+			info.extern = true
+			if len(parts) == 2 {
+				info.linkName = parts[1]
+			}
+		}
+	}
+}
@@ -4,7 +4,6 @@ package compiler
 // compiler builtins.

 import (
-	"go/constant"
 	"strconv"

 	"golang.org/x/tools/go/ssa"
@@ -14,7 +13,7 @@ import (
 // emitSyscall emits an inline system call instruction, depending on the target
 // OS/arch.
 func (c *Compiler) emitSyscall(frame *Frame, call *ssa.CallCommon) (llvm.Value, error) {
-	num, _ := constant.Uint64Val(call.Args[0].(*ssa.Const).Value)
+	num := c.getValue(frame, call.Args[0])
 	var syscallResult llvm.Value
 	switch {
 	case c.GOARCH == "amd64":
@@ -29,12 +28,12 @@ func (c *Compiler) emitSyscall(frame *Frame, call *ssa.CallCommon) (llvm.Value,
 			// > All system classes enter the kernel via the syscall instruction.
 			//
 			// Source: https://opensource.apple.com/source/xnu/xnu-792.13.8/osfmk/mach/i386/syscall_sw.h
-			num += 0x2000000
+			num = c.builder.CreateOr(num, llvm.ConstInt(c.uintptrType, 0x2000000, false), "")
 		}
 		// Sources:
 		//   https://stackoverflow.com/a/2538212
 		//   https://en.wikibooks.org/wiki/X86_Assembly/Interfacing_with_Linux#syscall
-		args := []llvm.Value{llvm.ConstInt(c.uintptrType, num, false)}
+		args := []llvm.Value{num}
 		argTypes := []llvm.Type{c.uintptrType}
 		// Constraints will look something like:
 		//   "={rax},0,{rdi},{rsi},{rdx},{r10},{r8},{r9},~{rcx},~{r11}"
@@ -81,7 +80,7 @@ func (c *Compiler) emitSyscall(frame *Frame, call *ssa.CallCommon) (llvm.Value,
 			args = append(args, llvmValue)
 			argTypes = append(argTypes, llvmValue.Type())
 		}
-		args = append(args, llvm.ConstInt(c.uintptrType, num, false))
+		args = append(args, num)
 		argTypes = append(argTypes, c.uintptrType)
 		constraints += ",{r7}" // syscall number
 		for i := len(call.Args) - 1; i < 4; i++ {
@@ -111,7 +110,7 @@ func (c *Compiler) emitSyscall(frame *Frame, call *ssa.CallCommon) (llvm.Value,
 			args = append(args, llvmValue)
 			argTypes = append(argTypes, llvmValue.Type())
 		}
-		args = append(args, llvm.ConstInt(c.uintptrType, num, false))
+		args = append(args, num)
 		argTypes = append(argTypes, c.uintptrType)
 		constraints += ",{x8}" // syscall number
 		for i := len(call.Args) - 1; i < 8; i++ {
@@ -39,6 +39,9 @@ func (c *Compiler) emitPointerPack(values []llvm.Value) llvm.Value {
 		// Packed data is bigger than a pointer, so allocate it on the heap.
 		sizeValue := llvm.ConstInt(c.uintptrType, size, false)
 		packedHeapAlloc = c.createRuntimeCall("alloc", []llvm.Value{sizeValue}, "")
+		if c.needsStackObjects() {
+			c.trackPointer(packedHeapAlloc)
+		}
 		packedAlloc = c.builder.CreateBitCast(packedHeapAlloc, llvm.PointerType(packedType, 0), "")
 	}
 	// Store all values in the alloca or heap pointer.
@@ -176,6 +176,20 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 					continue // special case: bitcast of alloc
 				}
 			}
+			if _, ok := fr.getLocal(operand).(*MapValue); ok {
+				// Special case for runtime.trackPointer calls.
+				// Note: this might not be entirely sound in some rare cases
+				// where the map is stored in a dirty global.
+				uses := getUses(inst)
+				if len(uses) == 1 {
+					use := uses[0]
+					if !use.IsACallInst().IsNil() && !use.CalledValue().IsAFunction().IsNil() && use.CalledValue().Name() == "runtime.trackPointer" {
+						continue
+					}
+				}
+				// It is not possible in Go to bitcast a map value to a pointer.
+				panic("unimplemented: bitcast of map")
+			}
 			value := fr.getLocal(operand).(*LocalValue)
 			fr.locals[inst] = &LocalValue{fr.Eval, fr.builder.CreateBitCast(value.Value(), inst.Type(), "")}

@@ -368,6 +382,8 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 				fr.locals[inst] = &LocalValue{fr.Eval, llvm.ConstInt(fr.Mod.Context().Int64Type(), 0, false)}
 			case callee.Name() == "llvm.dbg.value":
 				// do nothing
+			case callee.Name() == "runtime.trackPointer":
+				// do nothing
 			case strings.HasPrefix(callee.Name(), "runtime.print") || callee.Name() == "runtime._panic":
 				// This are all print instructions, which necessarily have side
 				// effects but no results.
@@ -35,6 +35,8 @@ func (e *Eval) hasSideEffects(fn llvm.Value) *sideEffectResult {
 		return &sideEffectResult{severity: sideEffectLimited}
 	case "runtime.interfaceImplements":
 		return &sideEffectResult{severity: sideEffectNone}
+	case "runtime.trackPointer":
+		return &sideEffectResult{severity: sideEffectNone}
 	case "llvm.dbg.value":
 		return &sideEffectResult{severity: sideEffectNone}
 	}
@@ -2,7 +2,6 @@ package ir

 import (
 	"go/ast"
-	"go/token"
 	"go/types"
 	"sort"
 	"strings"
@@ -23,10 +22,6 @@ type Program struct {
 	mainPkg       *ssa.Package
 	Functions     []*Function
 	functionMap   map[*ssa.Function]*Function
-	Globals       []*Global
-	globalMap     map[*ssa.Global]*Global
-	comments      map[string]*ast.CommentGroup
-	NamedTypes    []*NamedType
 }

 // Function or method.
@@ -41,28 +36,6 @@ type Function struct {
 	inline    InlineType // go:inline
 }

-// Global variable, possibly constant.
-type Global struct {
-	*ssa.Global
-	program    *Program
-	LLVMGlobal llvm.Value
-	linkName   string // go:extern
-	extern     bool   // go:extern
-}
-
-// Type with a name and possibly methods.
-type NamedType struct {
-	*ssa.Type
-	LLVMType llvm.Type
-}
-
-// Type that is at some point put in an interface.
-type TypeWithMethods struct {
-	t       types.Type
-	Num     int
-	Methods map[string]*types.Selection
-}
-
 // Interface type that is at some point used in a type assert (to check whether
 // it implements another interface).
 type Interface struct {
@@ -83,39 +56,14 @@ const (
 	// //go:inline). The compiler will be more likely to inline this function,
 	// but it is not a guarantee.
 	InlineHint
+
+	// Don't inline, just like the GCC noinline attribute. Signalled using
+	// //go:noinline.
+	InlineNone
 )

 // Create and initialize a new *Program from a *ssa.Program.
 func NewProgram(lprogram *loader.Program, mainPath string) *Program {
-	comments := map[string]*ast.CommentGroup{}
-	for _, pkgInfo := range lprogram.Sorted() {
-		for _, file := range pkgInfo.Files {
-			for _, decl := range file.Decls {
-				switch decl := decl.(type) {
-				case *ast.GenDecl:
-					switch decl.Tok {
-					case token.TYPE, token.VAR:
-						if len(decl.Specs) != 1 {
-							continue
-						}
-						for _, spec := range decl.Specs {
-							switch spec := spec.(type) {
-							case *ast.TypeSpec: // decl.Tok == token.TYPE
-								id := pkgInfo.Pkg.Path() + "." + spec.Name.Name
-								comments[id] = decl.Doc
-							case *ast.ValueSpec: // decl.Tok == token.VAR
-								for _, name := range spec.Names {
-									id := pkgInfo.Pkg.Path() + "." + name.Name
-									comments[id] = decl.Doc
-								}
-							}
-						}
-					}
-				}
-			}
-		}
-	}
-
 	program := lprogram.LoadSSA()
 	program.Build()

@@ -187,8 +135,6 @@ func NewProgram(lprogram *loader.Program, mainPath string) *Program {
 		LoaderProgram: lprogram,
 		mainPkg:       mainPkg,
 		functionMap:   make(map[*ssa.Function]*Function),
-		globalMap:     make(map[*ssa.Global]*Global),
-		comments:      comments,
 	}

 	for _, pkg := range packageList {
@@ -213,8 +159,6 @@ func (p *Program) AddPackage(pkg *ssa.Package) {
 		case *ssa.Function:
 			p.addFunction(member)
 		case *ssa.Type:
-			t := &NamedType{Type: member}
-			p.NamedTypes = append(p.NamedTypes, t)
 			methods := getAllMethods(pkg.Prog, member.Type())
 			if !types.IsInterface(member.Type()) {
 				// named type
@@ -223,13 +167,7 @@ func (p *Program) AddPackage(pkg *ssa.Package) {
 				}
 			}
 		case *ssa.Global:
-			g := &Global{program: p, Global: member}
-			doc := p.comments[g.RelString(nil)]
-			if doc != nil {
-				g.parsePragmas(doc)
-			}
-			p.Globals = append(p.Globals, g)
-			p.globalMap[member] = g
+			// Ignore. Globals are not handled here.
 		case *ssa.NamedConst:
 			// Ignore: these are already resolved.
 		default:
@@ -263,10 +201,6 @@ func (p *Program) GetFunction(ssaFn *ssa.Function) *Function {
 	return p.functionMap[ssaFn]
 }

-func (p *Program) GetGlobal(ssaGlobal *ssa.Global) *Global {
-	return p.globalMap[ssaGlobal]
-}
-
 func (p *Program) MainPkg() *ssa.Package {
 	return p.mainPkg
 }
@@ -297,6 +231,8 @@ func (f *Function) parsePragmas() {
 				f.exported = true
 			case "//go:inline":
 				f.inline = InlineHint
+			case "//go:noinline":
+				f.inline = InlineNone
 			case "//go:interrupt":
 				if len(parts) != 2 {
 					continue
@@ -389,72 +325,6 @@ func (f *Function) CName() string {
 	return ""
 }

-// Parse //go: pragma comments from the source.
-func (g *Global) parsePragmas(doc *ast.CommentGroup) {
-	for _, comment := range doc.List {
-		if !strings.HasPrefix(comment.Text, "//go:") {
-			continue
-		}
-		parts := strings.Fields(comment.Text)
-		switch parts[0] {
-		case "//go:extern":
-			g.extern = true
-			if len(parts) == 2 {
-				g.linkName = parts[1]
-			}
-		}
-	}
-}
-
-// Return the link name for this global.
-func (g *Global) LinkName() string {
-	if g.linkName != "" {
-		return g.linkName
-	}
-	if name := g.CName(); name != "" {
-		return name
-	}
-	return g.RelString(nil)
-}
-
-func (g *Global) IsExtern() bool {
-	return g.extern || g.CName() != ""
-}
-
-// Return the name of the C global if this is a CGo wrapper. Otherwise, return a
-// zero-length string.
-func (g *Global) CName() string {
-	name := g.Name()
-	if strings.HasPrefix(name, "C.") {
-		// created by ../loader/cgo.go
-		return name[2:]
-	}
-	return ""
-}
-
-// Return true if this named type is annotated with the //go:volatile pragma,
-// for volatile loads and stores.
-func (p *Program) IsVolatile(t types.Type) bool {
-	if t, ok := t.(*types.Named); !ok {
-		return false
-	} else {
-		if t.Obj().Pkg() == nil {
-			return false
-		}
-		id := t.Obj().Pkg().Path() + "." + t.Obj().Name()
-		doc := p.comments[id]
-		if doc == nil {
-			return false
-		}
-		for _, line := range doc.List {
-			if strings.TrimSpace(line.Text) == "//go:volatile" {
-				return true
-			}
-		}
-		return false
-	}
-}
-
 // Get all methods of a type.
 func getAllMethods(prog *ssa.Program, typ types.Type) []*types.Selection {
 	ms := prog.MethodSets.MethodSet(typ)
@@ -63,6 +63,7 @@ func Link(linker string, flags ...string) error {
 		cmd := exec.Command(linker, flags...)
 		cmd.Stdout = os.Stdout
 		cmd.Stderr = os.Stderr
+		cmd.Dir = sourceDir()
 		return cmd.Run()
 	}
 }
@@ -20,5 +20,6 @@ func Link(linker string, flags ...string) error {
 	cmd := exec.Command(linker, flags...)
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr
+	cmd.Dir = sourceDir()
 	return cmd.Run()
 }
@@ -1,6 +1,7 @@
 package loader

 import (
+	"bytes"
 	"errors"
 	"go/ast"
 	"go/build"
@@ -10,22 +11,26 @@ import (
 	"os"
 	"path/filepath"
 	"sort"
+	"strings"
+	"text/template"

 	"github.com/tinygo-org/tinygo/cgo"
 )

 // Program holds all packages and some metadata about the program as a whole.
 type Program struct {
-	Build         *build.Context
-	OverlayBuild  *build.Context
-	ShouldOverlay func(path string) bool
-	Packages      map[string]*Package
-	sorted        []*Package
-	fset          *token.FileSet
-	TypeChecker   types.Config
-	Dir           string // current working directory (for error reporting)
-	TINYGOROOT    string // root of the TinyGo installation or root of the source code
-	CFlags        []string
+	mainPkg      string
+	Build        *build.Context
+	OverlayBuild *build.Context
+	OverlayPath  func(path string) string
+	Packages     map[string]*Package
+	sorted       []*Package
+	fset         *token.FileSet
+	TypeChecker  types.Config
+	Dir          string // current working directory (for error reporting)
+	TINYGOROOT   string // root of the TinyGo installation or root of the source code
+	CFlags       []string
+	ClangHeaders string
 }

 // Package holds a loaded package, its imports, and its parsed files.
@@ -48,8 +53,9 @@ func (p *Program) Import(path, srcDir string) (*Package, error) {

 	// Load this package.
 	ctx := p.Build
-	if p.ShouldOverlay(path) {
+	if newPath := p.OverlayPath(path); newPath != "" {
 		ctx = p.OverlayBuild
+		path = newPath
 	}
 	buildPkg, err := ctx.Import(path, srcDir, build.ImportComment)
 	if err != nil {
@@ -62,6 +68,11 @@ func (p *Program) Import(path, srcDir string) (*Package, error) {
 	p.sorted = nil // invalidate the sorted order of packages
 	pkg := p.newPackage(buildPkg)
 	p.Packages[buildPkg.ImportPath] = pkg
+
+	if p.mainPkg == "" {
+		p.mainPkg = buildPkg.ImportPath
+	}
+
 	return pkg, nil
 }

@@ -91,6 +102,11 @@ func (p *Program) ImportFile(path string) (*Package, error) {
 	p.sorted = nil // invalidate the sorted order of packages
 	pkg := p.newPackage(buildPkg)
 	p.Packages[buildPkg.ImportPath] = pkg
+
+	if p.mainPkg == "" {
+		p.mainPkg = buildPkg.ImportPath
+	}
+
 	return pkg, nil
 }

@@ -169,10 +185,12 @@ func (p *Program) sort() {
 // The returned error may be an Errors error, which contains a list of errors.
 //
 // Idempotent.
-func (p *Program) Parse() error {
+func (p *Program) Parse(compileTestBinary bool) error {
+	includeTests := compileTestBinary
+
 	// Load all imports
 	for _, pkg := range p.Sorted() {
-		err := pkg.importRecursively()
+		err := pkg.importRecursively(includeTests)
 		if err != nil {
 			if err, ok := err.(*ImportCycleError); ok {
 				if pkg.ImportPath != err.Packages[0] {
@@ -185,7 +203,14 @@ func (p *Program) Parse() error {

 	// Parse all packages.
 	for _, pkg := range p.Sorted() {
-		err := pkg.Parse()
+		err := pkg.Parse(includeTests)
+		if err != nil {
+			return err
+		}
+	}
+
+	if compileTestBinary {
+		err := p.SwapTestMain()
 		if err != nil {
 			return err
 		}
@@ -202,6 +227,83 @@ func (p *Program) Parse() error {
 	return nil
 }

+func (p *Program) SwapTestMain() error {
+	var tests []string
+
+	isTestFunc := func(f *ast.FuncDecl) bool {
+		// TODO: improve signature check
+		if strings.HasPrefix(f.Name.Name, "Test") && f.Name.Name != "TestMain" {
+			return true
+		}
+		return false
+	}
+	mainPkg := p.Packages[p.mainPkg]
+	for _, f := range mainPkg.Files {
+		for i, d := range f.Decls {
+			switch v := d.(type) {
+			case *ast.FuncDecl:
+				if isTestFunc(v) {
+					tests = append(tests, v.Name.Name)
+				}
+				if v.Name.Name == "main" {
+					// Remove main
+					if len(f.Decls) == 1 {
+						f.Decls = make([]ast.Decl, 0)
+					} else {
+						f.Decls[i] = f.Decls[len(f.Decls)-1]
+						f.Decls = f.Decls[:len(f.Decls)-1]
+					}
+				}
+			}
+		}
+	}
+
+	// TODO: Check if they defined a TestMain and call it instead of testing.TestMain
+	const mainBody = `package main
+
+import (
+	"testing"
+)
+
+func main () {
+	m := &testing.M{
+		Tests: []testing.TestToCall{
+{{range .TestFunctions}}
+			{Name: "{{.}}", Func: {{.}}},
+{{end}}
+		},
+	}
+
+	testing.TestMain(m)
+}
+`
+	tmpl := template.Must(template.New("testmain").Parse(mainBody))
+	b := bytes.Buffer{}
+	tmplData := struct {
+		TestFunctions []string
+	}{
+		TestFunctions: tests,
+	}
+
+	err := tmpl.Execute(&b, tmplData)
+	if err != nil {
+		return err
+	}
+	path := filepath.Join(p.mainPkg, "$testmain.go")
+
+	if p.fset == nil {
+		p.fset = token.NewFileSet()
+	}
+
+	newMain, err := parser.ParseFile(p.fset, path, b.Bytes(), parser.AllErrors)
+	if err != nil {
+		return err
+	}
+	mainPkg.Files = append(mainPkg.Files, newMain)
+
+	return nil
+}
+
 // parseFile is a wrapper around parser.ParseFile.
 func (p *Program) parseFile(path string, mode parser.Mode) (*ast.File, error) {
 	if p.fset == nil {
@@ -226,7 +328,7 @@ func (p *Program) parseFile(path string, mode parser.Mode) (*ast.File, error) {
 // Parse parses and typechecks this package.
 //
 // Idempotent.
-func (p *Package) Parse() error {
+func (p *Package) Parse(includeTests bool) error {
 	if len(p.Files) != 0 {
 		return nil
 	}
@@ -240,7 +342,7 @@ func (p *Package) Parse() error {
 		return nil
 	}

-	files, err := p.parseFiles()
+	files, err := p.parseFiles(includeTests)
 	if err != nil {
 		return err
 	}
@@ -279,11 +381,21 @@ func (p *Package) Check() error {
 }

 // parseFiles parses the loaded list of files and returns this list.
-func (p *Package) parseFiles() ([]*ast.File, error) {
+func (p *Package) parseFiles(includeTests bool) ([]*ast.File, error) {
 	// TODO: do this concurrently.
 	var files []*ast.File
 	var fileErrs []error
-	for _, file := range p.GoFiles {
+
+	var gofiles []string
+	if includeTests {
+		gofiles = make([]string, 0, len(p.GoFiles)+len(p.TestGoFiles))
+		gofiles = append(gofiles, p.GoFiles...)
+		gofiles = append(gofiles, p.TestGoFiles...)
+	} else {
+		gofiles = p.GoFiles
+	}
+
+	for _, file := range gofiles {
 		f, err := p.parseFile(filepath.Join(p.Package.Dir, file), parser.ParseComments)
 		if err != nil {
 			fileErrs = append(fileErrs, err)
@@ -305,15 +417,11 @@ func (p *Package) parseFiles() ([]*ast.File, error) {
 		files = append(files, f)
 	}
 	if len(p.CgoFiles) != 0 {
-		clangIncludes := ""
-		if _, err := os.Stat(filepath.Join(p.TINYGOROOT, "llvm", "tools", "clang", "lib", "Headers")); !os.IsNotExist(err) {
-			// Running from the source directory.
-			clangIncludes = filepath.Join(p.TINYGOROOT, "llvm", "tools", "clang", "lib", "Headers")
-		} else {
-			// Running from the installation directory.
-			clangIncludes = filepath.Join(p.TINYGOROOT, "lib", "clang", "include")
+		cflags := append(p.CFlags, "-I"+p.Package.Dir)
+		if p.ClangHeaders != "" {
+			cflags = append(cflags, "-I"+p.ClangHeaders)
 		}
-		generated, errs := cgo.Process(files, p.Program.Dir, p.fset, append(p.CFlags, "-I"+p.Package.Dir, "-I"+clangIncludes))
+		generated, errs := cgo.Process(files, p.Program.Dir, p.fset, cflags)
 		if errs != nil {
 			fileErrs = append(fileErrs, errs...)
 		}
@@ -322,6 +430,7 @@ func (p *Package) parseFiles() ([]*ast.File, error) {
 	if len(fileErrs) != 0 {
 		return nil, Errors{p, fileErrs}
 	}
+
 	return files, nil
 }

@@ -342,9 +451,15 @@ func (p *Package) Import(to string) (*types.Package, error) {
 // importRecursively() on the imported packages as well.
 //
 // Idempotent.
-func (p *Package) importRecursively() error {
+func (p *Package) importRecursively(includeTests bool) error {
 	p.Importing = true
-	for _, to := range p.Package.Imports {
+
+	imports := p.Package.Imports
+	if includeTests {
+		imports = append(imports, p.Package.TestImports...)
+	}
+
+	for _, to := range imports {
 		if to == "C" {
 			// Do CGo processing in a later stage.
 			continue
@@ -362,7 +477,7 @@ func (p *Package) importRecursively() error {
 		if importedPkg.Importing {
 			return &ImportCycleError{[]string{p.ImportPath, importedPkg.ImportPath}, p.ImportPos[to]}
 		}
-		err = importedPkg.importRecursively()
+		err = importedPkg.importRecursively(false)
 		if err != nil {
 			if err, ok := err.(*ImportCycleError); ok {
 				err.Packages = append([]string{p.ImportPath}, err.Packages...)
@@ -53,7 +53,10 @@ type BuildConfig struct {
 	printSizes    string
 	cFlags        []string
 	ldFlags       []string
+	tags          string
 	wasmAbi       string
+	heapSize      int64
+	testConfig    compiler.TestConfig
 }

 // Helper function for Compiler object.
@@ -81,16 +84,19 @@ func Compile(pkgName, outpath string, spec *TargetSpec, config *BuildConfig, act
 		return errors.New("cannot locate $GOROOT, please set it manually")
 	}
 	tags := spec.BuildTags
-	major, minor := getGorootVersion(goroot)
+	major, minor, err := getGorootVersion(goroot)
+	if err != nil {
+		return fmt.Errorf("could not read version from GOROOT (%v): %v", goroot, err)
+	}
 	if major != 1 {
-		if major == 0 {
-			return errors.New("could not read version from GOROOT: " + goroot)
-		}
 		return fmt.Errorf("expected major version 1, got go%d.%d", major, minor)
 	}
 	for i := 1; i <= minor; i++ {
 		tags = append(tags, fmt.Sprintf("go1.%d", i))
 	}
+	if extraTags := strings.Fields(config.tags); len(extraTags) != 0 {
+		tags = append(tags, extraTags...)
+	}
 	compilerConfig := compiler.Config{
 		Triple:        spec.Triple,
 		CPU:           spec.CPU,
@@ -101,12 +107,14 @@ func Compile(pkgName, outpath string, spec *TargetSpec, config *BuildConfig, act
 		PanicStrategy: config.panicStrategy,
 		CFlags:        cflags,
 		LDFlags:       ldflags,
+		ClangHeaders:  getClangHeaderPath(root),
 		Debug:         config.debug,
 		DumpSSA:       config.dumpSSA,
 		TINYGOROOT:    root,
 		GOROOT:        goroot,
 		GOPATH:        getGopath(),
 		BuildTags:     tags,
+		TestConfig:    config.testConfig,
 	}
 	c, err := compiler.NewCompiler(pkgName, compilerConfig)
 	if err != nil {
@@ -233,10 +241,16 @@ func Compile(pkgName, outpath string, spec *TargetSpec, config *BuildConfig, act
 		// Prepare link command.
 		executable := filepath.Join(dir, "main")
 		tmppath := executable // final file
-		ldflags := append(ldflags, "-o", executable, objfile, "-L", root)
+		ldflags = append(ldflags, "-o", executable, objfile, "-L", root)
 		if spec.RTLib == "compiler-rt" {
 			ldflags = append(ldflags, librt)
 		}
+		if spec.GOARCH == "wasm" {
+			// Round heap size to next multiple of 65536 (the WebAssembly page
+			// size).
+			heapSize := (config.heapSize + (65536 - 1)) &^ (65536 - 1)
+			ldflags = append(ldflags, "--initial-memory="+strconv.FormatInt(heapSize, 10))
+		}

 		// Compile extra files.
 		for i, path := range spec.ExtraFiles {
@@ -348,6 +362,33 @@ func Build(pkgName, outpath, target string, config *BuildConfig) error {
 	})
 }

+func Test(pkgName, target string, config *BuildConfig) error {
+	spec, err := LoadTarget(target)
+	if err != nil {
+		return err
+	}
+
+	spec.BuildTags = append(spec.BuildTags, "test")
+	config.testConfig.CompileTestBinary = true
+	return Compile(pkgName, ".elf", spec, config, func(tmppath string) error {
+		cmd := exec.Command(tmppath)
+		cmd.Stdout = os.Stdout
+		cmd.Stderr = os.Stderr
+		err := cmd.Run()
+		if err != nil {
+			// Propagate the exit code
+			if err, ok := err.(*exec.ExitError); ok {
+				if status, ok := err.Sys().(syscall.WaitStatus); ok {
+					os.Exit(status.ExitStatus())
+				}
+				os.Exit(1)
+			}
+			return &commandError{"failed to run compiled binary", tmppath, err}
+		}
+		return nil
+	})
+}
+
 func Flash(pkgName, target, port string, config *BuildConfig) error {
 	spec, err := LoadTarget(target)
 	if err != nil {
@@ -506,6 +547,30 @@ func Run(pkgName, target string, config *BuildConfig) error {
 	})
 }

+// parseSize converts a human-readable size (with k/m/g suffix) into a plain
+// number.
+func parseSize(s string) (int64, error) {
+	s = strings.ToLower(strings.TrimSpace(s))
+	if len(s) == 0 {
+		return 0, errors.New("no size provided")
+	}
+	multiply := int64(1)
+	switch s[len(s)-1] {
+	case 'k':
+		multiply = 1 << 10
+	case 'm':
+		multiply = 1 << 20
+	case 'g':
+		multiply = 1 << 30
+	}
+	if multiply != 1 {
+		s = s[:len(s)-1]
+	}
+	n, err := strconv.ParseInt(s, 0, 64)
+	n *= multiply
+	return n, err
+}
+
 func usage() {
 	fmt.Fprintln(os.Stderr, "TinyGo is a Go compiler for small places.")
 	fmt.Fprintln(os.Stderr, "version:", version)
@@ -513,6 +578,7 @@ func usage() {
 	fmt.Fprintln(os.Stderr, "\ncommands:")
 	fmt.Fprintln(os.Stderr, "  build: compile packages and dependencies")
 	fmt.Fprintln(os.Stderr, "  run:   compile and run immediately")
+	fmt.Fprintln(os.Stderr, "  test:  test packages")
 	fmt.Fprintln(os.Stderr, "  flash: compile and flash to the device")
 	fmt.Fprintln(os.Stderr, "  gdb:   run/flash and immediately enter GDB")
 	fmt.Fprintln(os.Stderr, "  clean: empty cache directory ("+cacheDir()+")")
@@ -523,23 +589,24 @@ func usage() {

 func handleCompilerError(err error) {
 	if err != nil {
-		if errUnsupported, ok := err.(*interp.Unsupported); ok {
+		switch err := err.(type) {
+		case *interp.Unsupported:
 			// hit an unknown/unsupported instruction
 			fmt.Fprintln(os.Stderr, "unsupported instruction during init evaluation:")
-			errUnsupported.Inst.Dump()
+			err.Inst.Dump()
 			fmt.Fprintln(os.Stderr)
-		} else if errCompiler, ok := err.(types.Error); ok {
-			fmt.Fprintln(os.Stderr, errCompiler)
-		} else if errLoader, ok := err.(loader.Errors); ok {
-			fmt.Fprintln(os.Stderr, "#", errLoader.Pkg.ImportPath)
-			for _, err := range errLoader.Errs {
+		case types.Error:
+			fmt.Fprintln(os.Stderr, err)
+		case loader.Errors:
+			fmt.Fprintln(os.Stderr, "#", err.Pkg.ImportPath)
+			for _, err := range err.Errs {
 				fmt.Fprintln(os.Stderr, err)
 			}
-		} else if errMulti, ok := err.(*multiError); ok {
-			for _, err := range errMulti.Errs {
+		case *multiError:
+			for _, err := range err.Errs {
 				fmt.Fprintln(os.Stderr, err)
 			}
-		} else {
+		default:
 			fmt.Fprintln(os.Stderr, "error:", err)
 		}
 		os.Exit(1)
@@ -549,11 +616,12 @@ func handleCompilerError(err error) {
 func main() {
 	outpath := flag.String("o", "", "output filename")
 	opt := flag.String("opt", "z", "optimization level: 0, 1, 2, s, z")
-	gc := flag.String("gc", "", "garbage collector to use (none, dumb, marksweep)")
+	gc := flag.String("gc", "", "garbage collector to use (none, leaking, conservative)")
 	panicStrategy := flag.String("panic", "print", "panic strategy (abort, trap)")
 	printIR := flag.Bool("printir", false, "print LLVM IR")
 	dumpSSA := flag.Bool("dumpssa", false, "dump internal Go SSA")
-	target := flag.String("target", "", "LLVM target")
+	tags := flag.String("tags", "", "a space-separated list of extra build tags")
+	target := flag.String("target", "", "LLVM target | .json file with TargetSpec")
 	printSize := flag.String("size", "", "print sizes (none, short, full)")
 	nodebug := flag.Bool("no-debug", false, "disable DWARF debug symbol generation")
 	ocdOutput := flag.Bool("ocd-output", false, "print OCD daemon output during debug")
@@ -561,6 +629,7 @@ func main() {
 	cFlags := flag.String("cflags", "", "additional cflags for compiler")
 	ldFlags := flag.String("ldflags", "", "additional ldflags for linker")
 	wasmAbi := flag.String("wasm-abi", "js", "WebAssembly ABI conventions: js (no i64 params) or generic")
+	heapSize := flag.String("heap-size", "1M", "default heap size in bytes (only supported by WebAssembly)")

 	if len(os.Args) < 2 {
 		fmt.Fprintln(os.Stderr, "No command-line arguments supplied.")
@@ -578,6 +647,7 @@ func main() {
 		dumpSSA:       *dumpSSA,
 		debug:         !*nodebug,
 		printSizes:    *printSize,
+		tags:          *tags,
 		wasmAbi:       *wasmAbi,
 	}

@@ -595,6 +665,13 @@ func main() {
 		os.Exit(1)
 	}

+	var err error
+	if config.heapSize, err = parseSize(*heapSize); err != nil {
+		fmt.Fprintln(os.Stderr, "Could not read heap size:", *heapSize)
+		usage()
+		os.Exit(1)
+	}
+
 	os.Setenv("CC", "clang -target="+*target)

 	switch command {
@@ -604,8 +681,11 @@ func main() {
 			usage()
 			os.Exit(1)
 		}
-		if flag.NArg() != 1 {
-			fmt.Fprintln(os.Stderr, "No package specified.")
+		pkgName := "."
+		if flag.NArg() == 1 {
+			pkgName = flag.Arg(0)
+		} else if flag.NArg() > 1 {
+			fmt.Fprintln(os.Stderr, "build only accepts a single positional argument: package name, but multiple were specified")
 			usage()
 			os.Exit(1)
 		}
@@ -613,7 +693,7 @@ func main() {
 		if target == "" && filepath.Ext(*outpath) == ".wasm" {
 			target = "wasm"
 		}
-		err := Build(flag.Arg(0), *outpath, target, config)
+		err := Build(pkgName, *outpath, target, config)
 		handleCompilerError(err)
 	case "build-builtins":
 		// Note: this command is only meant to be used while making a release!
@@ -655,6 +735,17 @@ func main() {
 		}
 		err := Run(flag.Arg(0), *target, config)
 		handleCompilerError(err)
+	case "test":
+		pkgName := "."
+		if flag.NArg() == 1 {
+			pkgName = flag.Arg(0)
+		} else if flag.NArg() > 1 {
+			fmt.Fprintln(os.Stderr, "test only accepts a single positional argument: package name, but multiple were specified")
+			usage()
+			os.Exit(1)
+		}
+		err := Test(pkgName, *target, config)
+		handleCompilerError(err)
 	case "clean":
 		// remove cache directory
 		dir := cacheDir()
@@ -30,6 +30,7 @@
 package arm

 import (
+	"runtime/volatile"
 	"unsafe"
 )

@@ -69,9 +70,6 @@ func SVCall3(num uintptr, a1, a2, a3 interface{}) uintptr
 // Run the following system call (SVCall) with 4 arguments.
 func SVCall4(num uintptr, a1, a2, a3, a4 interface{}) uintptr

-//go:volatile
-type RegValue uint32
-
 const (
 	SCS_BASE  = 0xE000E000
 	NVIC_BASE = SCS_BASE + 0x0100
@@ -82,24 +80,24 @@ const (
 // Source:
 // http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0553a/CIHIGCIF.html
 type NVIC_Type struct {
-	ISER [8]RegValue // Interrupt Set-enable Registers
+	ISER [8]volatile.Register32 // Interrupt Set-enable Registers
 	_    [24]uint32
-	ICER [8]RegValue // Interrupt Clear-enable Registers
+	ICER [8]volatile.Register32 // Interrupt Clear-enable Registers
 	_    [24]uint32
-	ISPR [8]RegValue // Interrupt Set-pending Registers
+	ISPR [8]volatile.Register32 // Interrupt Set-pending Registers
 	_    [24]uint32
-	ICPR [8]RegValue // Interrupt Clear-pending Registers
+	ICPR [8]volatile.Register32 // Interrupt Clear-pending Registers
 	_    [24]uint32
-	IABR [8]RegValue // Interrupt Active Bit Registers
+	IABR [8]volatile.Register32 // Interrupt Active Bit Registers
 	_    [56]uint32
-	IPR  [60]RegValue // Interrupt Priority Registers
+	IPR  [60]volatile.Register32 // Interrupt Priority Registers
 }

 var NVIC = (*NVIC_Type)(unsafe.Pointer(uintptr(NVIC_BASE)))

 // Enable the given interrupt number.
 func EnableIRQ(irq uint32) {
-	NVIC.ISER[irq>>5] = 1 << (irq & 0x1F)
+	NVIC.ISER[irq>>5].Set(1 << (irq & 0x1F))
 }

 // Set the priority of the given interrupt number.
@@ -116,7 +114,7 @@ func SetPriority(irq uint32, priority uint32) {
 	regpos := irq % 4
 	mask := uint32(0xff) << (regpos * 8) // bits to clear
 	priority = priority << (regpos * 8)  // bits to set
-	NVIC.IPR[regnum] = RegValue((uint32(NVIC.IPR[regnum]) &^ mask) | priority)
+	NVIC.IPR[regnum].Set((uint32(NVIC.IPR[regnum].Get()) &^ mask) | priority)
 }

 // DisableInterrupts disables all interrupts, and returns the old state.
@@ -0,0 +1,10 @@
+package riscv
+
+// Run the given assembly code. The code will be marked as having side effects,
+// as it doesn't produce output and thus would normally be eliminated by the
+// optimizer.
+func Asm(asm string)
+
+// ReadRegister returns the contents of the specified register. The register
+// must be a processor register, reachable with the "mov" instruction.
+func ReadRegister(name string) uintptr
@@ -0,0 +1,13 @@
+.section .init
+.global _start
+.type _start,@function
+
+_start:
+    // Workaround for missing support of the la pseudo-instruction in Clang 8:
+    // https://reviews.llvm.org/D55325
+    lui sp,      %hi(_stack_top)
+    addi sp, sp, %lo(_stack_top)
+    // see https://gnu-mcu-eclipse.github.io/arch/riscv/programmer/#the-gp-global-pointer-register
+    lui gp,      %hi(__global_pointer$)
+    addi gp, gp, %lo(__global_pointer$)
+    call main
@@ -1,4 +1,4 @@
-// +build avr,arduino
+// +build arduino

 package machine

@@ -0,0 +1,138 @@
+// +build sam,atsamd21,arduino_nano33
+
+// This contains the pin mappings for the Arduino Nano33 IoT board.
+//
+// For more information, see: https://store.arduino.cc/nano-33-iot
+//
+package machine
+
+import "device/sam"
+
+// GPIO Pins
+const (
+	RX0 Pin = PB23 // UART2 RX
+	TX1 Pin = PB22 // UART2 TX
+
+	D2 Pin = PB10 // PWM available
+	D3 Pin = PB11 // PWM available
+	D4 Pin = PA07
+	D5 Pin = PA05 // PWM available
+	D6 Pin = PA04 // PWM available
+	D7 Pin = PA06
+
+	D8  Pin = PA18
+	D9  Pin = PA20 // PWM available
+	D10 Pin = PA21 // PWM available
+	D11 Pin = PA16 // PWM available
+	D12 Pin = PA19 // PWM available
+
+	D13 Pin = PA17
+)
+
+// Analog pins
+const (
+	A0 Pin = PA02 // ADC/AIN[0]
+	A1 Pin = PB02 // ADC/AIN[10]
+	A2 Pin = PA11 // ADC/AIN[19]
+	A3 Pin = PA10 // ADC/AIN[18]
+	A4 Pin = PB08 // ADC/AIN[2], SCL:  SERCOM2/PAD[1]
+	A5 Pin = PB09 // ADC/AIN[3], SDA:  SERCOM2/PAD[1]
+	A6 Pin = PA09 // ADC/AIN[17]
+	A7 Pin = PB03 // ADC/AIN[11]
+)
+
+const (
+	LED = D13
+)
+
+// NINA-W102 Pins
+
+const (
+	NINA_MOSI   Pin = PA12
+	NINA_MISO   Pin = PA13
+	NINA_CS     Pin = PA14
+	NINA_SCK    Pin = PA15
+	NINA_GPIO0  Pin = PA27
+	NINA_RESETN Pin = PA08
+	NINA_ACK    Pin = PA28
+)
+
+// UART0 aka USBCDC pins
+const (
+	USBCDC_DM_PIN Pin = PA24
+	USBCDC_DP_PIN Pin = PA25
+)
+
+// UART1 on the Arduino Nano 33 connects to the onboard NINA-W102 WiFi chip.
+var (
+	UART1 = UART{Bus: sam.SERCOM5_USART,
+		Buffer: NewRingBuffer(),
+		Mode:   PinSERCOMAlt,
+		IRQVal: sam.IRQ_SERCOM5,
+	}
+)
+
+// UART1 pins
+const (
+	UART_TX_PIN Pin = PA22
+	UART_RX_PIN Pin = PA23
+)
+
+//go:export SERCOM5_IRQHandler
+func handleUART1() {
+	defaultUART1Handler()
+}
+
+// UART2 on the Arduino Nano 33 connects to the normal TX/RX pins.
+var (
+	UART2 = UART{Bus: sam.SERCOM3_USART,
+		Buffer: NewRingBuffer(),
+		Mode:   PinSERCOMAlt,
+		IRQVal: sam.IRQ_SERCOM3,
+	}
+)
+
+//go:export SERCOM3_IRQHandler
+func handleUART2() {
+	// should reset IRQ
+	UART2.Receive(byte((UART2.Bus.DATA.Get() & 0xFF)))
+	UART2.Bus.INTFLAG.SetBits(sam.SERCOM_USART_INTFLAG_RXC)
+}
+
+// I2C pins
+const (
+	SDA_PIN Pin = A4 // SDA: SERCOM4/PAD[1]
+	SCL_PIN Pin = A5 // SCL: SERCOM4/PAD[1]
+)
+
+// I2C on the Arduino Nano 33.
+var (
+	I2C0 = I2C{Bus: sam.SERCOM4_I2CM,
+		SDA:     SDA_PIN,
+		SCL:     SCL_PIN,
+		PinMode: PinSERCOMAlt}
+)
+
+// SPI pins
+const (
+	SPI0_SCK_PIN  Pin = PB11 // SCK: SERCOM4/PAD[3]
+	SPI0_MOSI_PIN Pin = PB10 // MOSI: SERCOM4/PAD[2]
+	SPI0_MISO_PIN Pin = PA12 // MISO: SERCOM4/PAD[0]
+)
+
+// SPI on the Arduino Nano 33.
+var (
+	SPI0 = SPI{Bus: sam.SERCOM1_SPI}
+)
+
+// I2S pins
+const (
+	I2S_SCK_PIN Pin = PA10
+	I2S_SD_PIN  Pin = PA08
+	I2S_WS_PIN      = NoPin // TODO: figure out what this is on Arduino Nano 33.
+)
+
+// I2S on the Arduino Nano 33.
+var (
+	I2S0 = I2S{Bus: sam.I2S}
+)
@@ -1,4 +1,4 @@
-// +build stm32,bluepill
+// +build bluepill

 package machine

@@ -65,6 +65,20 @@ const (
 	UART_RX_PIN = PB09 // PORTB
 )

+// UART1 on the Circuit Playground Express.
+var (
+	UART1 = UART{Bus: sam.SERCOM1_USART,
+		Buffer: NewRingBuffer(),
+		Mode:   PinSERCOM,
+		IRQVal: sam.IRQ_SERCOM1,
+	}
+)
+
+//go:export SERCOM1_IRQHandler
+func handleUART1() {
+	defaultUART1Handler()
+}
+
 // I2C pins
 const (
 	SDA_PIN = PB02 // I2C0 external
@@ -1,4 +1,4 @@
-// +build attiny85,digispark
+// +build digispark

 package machine

@@ -0,0 +1,38 @@
+// +build hifive1b
+
+package machine
+
+const (
+	P00 Pin = 0
+	P01 Pin = 1
+	P02 Pin = 2
+	P03 Pin = 3
+	P04 Pin = 4
+	P05 Pin = 5
+	P06 Pin = 6
+	P07 Pin = 7
+	P08 Pin = 8
+	P09 Pin = 9
+	P10 Pin = 10
+	P11 Pin = 11
+	P12 Pin = 12
+	P13 Pin = 13
+	P14 Pin = 14
+	P15 Pin = 15
+	P16 Pin = 16
+	P17 Pin = 17
+	P18 Pin = 18
+	P19 Pin = 19
+	P20 Pin = 20
+	P21 Pin = 21
+	P22 Pin = 22
+	P23 Pin = 23
+	P24 Pin = 24
+	P25 Pin = 25
+	P26 Pin = 26
+	P27 Pin = 27
+	P28 Pin = 28
+	P29 Pin = 29
+	P30 Pin = 30
+	P31 Pin = 31
+)
@@ -48,6 +48,20 @@ const (
 	UART_RX_PIN = D11
 )

+// UART1 on the Feather M0.
+var (
+	UART1 = UART{Bus: sam.SERCOM1_USART,
+		Buffer: NewRingBuffer(),
+		Mode:   PinSERCOM,
+		IRQVal: sam.IRQ_SERCOM1,
+	}
+)
+
+//go:export SERCOM1_IRQHandler
+func handleUART1() {
+	defaultUART1Handler()
+}
+
 // I2C pins
 const (
 	SDA_PIN = PA22 // SDA: SERCOM3/PAD[0]
@@ -0,0 +1,19 @@
+// +build hifive1b
+
+package machine
+
+const (
+	LED       = LED1
+	LED1      = LED_RED
+	LED2      = LED_GREEN
+	LED3      = LED_BLUE
+	LED_RED   = P22
+	LED_GREEN = P19
+	LED_BLUE  = P21
+)
+
+const (
+	// TODO: figure out the pin numbers for these.
+	UART_TX_PIN = NoPin
+	UART_RX_PIN = NoPin
+)
@@ -48,6 +48,20 @@ const (
 	UART_RX_PIN = D11
 )

+// UART1 on the ItsyBitsy M0.
+var (
+	UART1 = UART{Bus: sam.SERCOM1_USART,
+		Buffer: NewRingBuffer(),
+		Mode:   PinSERCOM,
+		IRQVal: sam.IRQ_SERCOM1,
+	}
+)
+
+//go:export SERCOM1_IRQHandler
+func handleUART1() {
+	defaultUART1Handler()
+}
+
 // I2C pins
 const (
 	SDA_PIN = PA22 // SDA: SERCOM3/PAD[0]
@@ -1,4 +1,4 @@
-// +build nrf51,microbit
+// +build microbit

 package machine

@@ -1,4 +1,4 @@
-// +build nrf51,pca10031
+// +build pca10031

 // pca10031 is a nrf51 based dongle, intended for use in wireless applications.
 //
@@ -1,4 +1,4 @@
-// +build nrf,pca10040
+// +build pca10040

 package machine

@@ -4,17 +4,24 @@ package machine

 const HasLowFrequencyCrystal = true

-// LEDs on the reel board
+// Pins on the reel board
 const (
-	LED        Pin = LED1
-	LED1       Pin = LED_YELLOW
-	LED2       Pin = LED_RED
-	LED3       Pin = LED_GREEN
-	LED4       Pin = LED_BLUE
-	LED_RED    Pin = 11
-	LED_GREEN  Pin = 12
-	LED_BLUE   Pin = 41
-	LED_YELLOW Pin = 13
+	LED              Pin = LED1
+	LED1             Pin = LED_YELLOW
+	LED2             Pin = LED_RED
+	LED3             Pin = LED_GREEN
+	LED4             Pin = LED_BLUE
+	LED_RED          Pin = 11
+	LED_GREEN        Pin = 12
+	LED_BLUE         Pin = 41
+	LED_YELLOW       Pin = 13
+	EPD_BUSY_PIN     Pin = 14
+	EPD_RESET_PIN    Pin = 15
+	EPD_DC_PIN       Pin = 16
+	EPD_CS_PIN       Pin = 17
+	EPD_SCK_PIN      Pin = 19
+	EPD_MOSI_PIN     Pin = 20
+	POWER_SUPPLY_PIN Pin = 32
 )

 // User "a" button on the reel board
@@ -40,3 +47,15 @@ const (
 	SPI0_MOSI_PIN Pin = 45
 	SPI0_MISO_PIN Pin = 46
 )
+
+// PowerSupplyActive enables the supply voltages for nRF52840 and peripherals (true) or only for nRF52840 (false)
+// This controls the TPS610981 boost converter. You must turn the power supply active in order to use the EPD and
+// other onboard peripherals.
+func PowerSupplyActive(active bool) {
+	POWER_SUPPLY_PIN.Configure(PinConfig{Mode: PinOutput})
+	if active {
+		POWER_SUPPLY_PIN.High()
+	} else {
+		POWER_SUPPLY_PIN.Low()
+	}
+}
@@ -0,0 +1,16 @@
+// +build bluepill stm32f4disco
+
+package machine
+
+// Peripheral abstraction layer for the stm32.
+
+const (
+	portA Pin = iota * 16
+	portB
+	portC
+	portD
+	portE
+	portF
+	portG
+	portH
+)
@@ -1,4 +1,4 @@
-// +build stm32,stm32f4disco
+// +build stm32f4disco

 package machine

@@ -39,6 +39,20 @@ const (
 	UART_RX_PIN = D3
 )

+// UART1 on the Trinket M0.
+var (
+	UART1 = UART{Bus: sam.SERCOM1_USART,
+		Buffer: NewRingBuffer(),
+		Mode:   PinSERCOM,
+		IRQVal: sam.IRQ_SERCOM1,
+	}
+)
+
+//go:export SERCOM1_IRQHandler
+func handleUART1() {
+	defaultUART1Handler()
+}
+
 // SPI pins
 const (
 	SPI0_SCK_PIN  = D3
@@ -1,9 +1,10 @@
 package machine

-const bufferSize = 128
+import (
+	"runtime/volatile"
+)

-//go:volatile
-type volatileByte byte
+const bufferSize = 128

 // RingBuffer is ring buffer implementation inspired by post at
 // https://www.embeddedrelated.com/showthread/comp.arch.embedded/77084-1.php
@@ -12,9 +13,9 @@ type volatileByte byte
 // members of a struct are not compiled correctly by TinyGo.
 // See https://github.com/tinygo-org/tinygo/issues/151 for details.
 type RingBuffer struct {
-	rxbuffer [bufferSize]volatileByte
-	head     volatileByte
-	tail     volatileByte
+	rxbuffer [bufferSize]volatile.Register8
+	head     volatile.Register8
+	tail     volatile.Register8
 }

 // NewRingBuffer returns a new ring buffer.
@@ -24,15 +25,15 @@ func NewRingBuffer() *RingBuffer {

 // Used returns how many bytes in buffer have been used.
 func (rb *RingBuffer) Used() uint8 {
-	return uint8(rb.head - rb.tail)
+	return uint8(rb.head.Get() - rb.tail.Get())
 }

 // Put stores a byte in the buffer. If the buffer is already
 // full, the method will return false.
 func (rb *RingBuffer) Put(val byte) bool {
 	if rb.Used() != bufferSize {
-		rb.head++
-		rb.rxbuffer[rb.head%bufferSize] = volatileByte(val)
+		rb.head.Set(rb.head.Get() + 1)
+		rb.rxbuffer[rb.head.Get()%bufferSize].Set(val)
 		return true
 	}
 	return false
@@ -42,8 +43,8 @@ func (rb *RingBuffer) Put(val byte) bool {
 // the method will return a false as the second value.
 func (rb *RingBuffer) Get() (byte, bool) {
 	if rb.Used() != 0 {
-		rb.tail++
-		return byte(rb.rxbuffer[rb.tail%bufferSize]), true
+		rb.tail.Set(rb.tail.Get() + 1)
+		return rb.rxbuffer[rb.tail.Get()%bufferSize].Get(), true
 	}
 	return 0, false
 }
@@ -1,4 +1,4 @@
-// +build avr nrf sam stm32f103xx
+// +build !stm32f4disco,!hifive1b

 package machine

@@ -4,6 +4,7 @@ package machine

 import (
 	"device/avr"
+	"runtime/volatile"
 )

 // Configure sets the pin to input or output.
@@ -34,7 +35,7 @@ func (p Pin) Get() bool {
 	}
 }

-func (p Pin) getPortMask() (*avr.Register8, uint8) {
+func (p Pin) getPortMask() (*volatile.Register8, uint8) {
 	if p < 8 {
 		return avr.PORTD, 1 << uint8(p)
 	} else {
@@ -250,14 +250,13 @@ func waitADCSync() {
 type UART struct {
 	Buffer *RingBuffer
 	Bus    *sam.SERCOM_USART_Type
+	Mode   PinMode
+	IRQVal uint32
 }

 var (
 	// UART0 is actually a USB CDC interface.
 	UART0 = USBCDC{Buffer: NewRingBuffer()}
-
-	// The first hardware serial port on the SAMD21. Uses the SERCOM0 interface.
-	UART1 = UART{Bus: sam.SERCOM1_USART, Buffer: NewRingBuffer()}
 )

 const (
@@ -300,6 +299,8 @@ func (uart UART) Configure(config UARTConfig) {
 		txpad = sercomTXPad2
 	case PA16:
 		txpad = sercomTXPad0
+	case PA22:
+		txpad = sercomTXPad0
 	default:
 		panic("Invalid TX pin for UART")
 	}
@@ -315,13 +316,15 @@ func (uart UART) Configure(config UARTConfig) {
 		rxpad = sercomRXPad3
 	case PA17:
 		rxpad = sercomRXPad1
+	case PA23:
+		rxpad = sercomRXPad1
 	default:
 		panic("Invalid RX pin for UART")
 	}

 	// configure pins
-	config.TX.Configure(PinConfig{Mode: PinSERCOM})
-	config.RX.Configure(PinConfig{Mode: PinSERCOM})
+	config.TX.Configure(PinConfig{Mode: uart.Mode})
+	config.RX.Configure(PinConfig{Mode: uart.Mode})

 	// reset SERCOM0
 	uart.Bus.CTRLA.SetBits(sam.SERCOM_USART_CTRLA_SWRST)
@@ -372,13 +375,7 @@ func (uart UART) Configure(config UARTConfig) {
 	uart.Bus.INTENSET.Set(sam.SERCOM_USART_INTENSET_RXC)

 	// Enable RX IRQ.
-	if config.TX == PA10 {
-		// UART0
-		arm.EnableIRQ(sam.IRQ_SERCOM0)
-	} else {
-		// UART1 which is the normal default, since UART0 is used for USBCDC.
-		arm.EnableIRQ(sam.IRQ_SERCOM1)
-	}
+	arm.EnableIRQ(uart.IRQVal)
 }

 // SetBaudRate sets the communication speed for the UART.
@@ -404,8 +401,8 @@ func (uart UART) WriteByte(c byte) error {
 	return nil
 }

-//go:export SERCOM1_IRQHandler
-func handleUART1() {
+// defaultUART1Handler handles the UART1 IRQ.
+func defaultUART1Handler() {
 	// should reset IRQ
 	UART1.Receive(byte((UART1.Bus.DATA.Get() & 0xFF)))
 	UART1.Bus.INTFLAG.SetBits(sam.SERCOM_USART_INTFLAG_RXC)
@@ -1182,23 +1179,35 @@ func (usbcdc USBCDC) WriteByte(c byte) error {
 		usbEndpointDescriptors[usb_CDC_ENDPOINT_IN].DeviceDescBank[1].PCKSIZE.ClearBits(usb_DEVICE_PCKSIZE_MULTI_PACKET_SIZE_Mask << usb_DEVICE_PCKSIZE_MULTI_PACKET_SIZE_Pos)

 		// set count of bytes to be sent
-		usbEndpointDescriptors[usb_CDC_ENDPOINT_IN].DeviceDescBank[1].PCKSIZE.SetBits((1&usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask)<<usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos |
-			(epPacketSize(64) << usb_DEVICE_PCKSIZE_SIZE_Pos))
+		usbEndpointDescriptors[usb_CDC_ENDPOINT_IN].DeviceDescBank[1].PCKSIZE.SetBits((1 & usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask) << usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos)

-		// ack transfer complete flag
+		// clear transfer complete flag
 		setEPINTFLAG(usb_CDC_ENDPOINT_IN, sam.USB_DEVICE_EPINTFLAG_TRCPT1)

 		// send data by setting bank ready
 		setEPSTATUSSET(usb_CDC_ENDPOINT_IN, sam.USB_DEVICE_EPSTATUSSET_BK1RDY)

 		// wait for transfer to complete
+		timeout := 3000
 		for (getEPINTFLAG(usb_CDC_ENDPOINT_IN) & sam.USB_DEVICE_EPINTFLAG_TRCPT1) == 0 {
+			timeout--
+			if timeout == 0 {
+				return errors.New("USBCDC write byte timeout")
+			}
 		}
 	}

 	return nil
 }

+func (usbcdc USBCDC) DTR() bool {
+	return (usbLineInfo.lineState & usb_CDC_LINESTATE_DTR) > 0
+}
+
+func (usbcdc USBCDC) RTS() bool {
+	return (usbLineInfo.lineState & usb_CDC_LINESTATE_RTS) > 0
+}
+
 const (
 	// these are SAMD21 specific.
 	usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos  = 0
@@ -1346,6 +1355,7 @@ func handleUSB() {

 		// Clear the Bank 0 ready flag on Control OUT
 		setEPSTATUSCLR(0, sam.USB_DEVICE_EPSTATUSCLR_BK0RDY)
+		usbEndpointDescriptors[0].DeviceDescBank[0].PCKSIZE.ClearBits(usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask << usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos)

 		ok := false
 		if (setup.bmRequestType & usb_REQUEST_TYPE) == usb_REQUEST_STANDARD {
@@ -1375,19 +1385,24 @@ func handleUSB() {
 		}
 	}

-	// Now the actual transfer handlers
-	eptInts := sam.USB_DEVICE.EPINTSMRY.Get() & 0xFE // Remove endpoint number 0 (setup)
+	// Now the actual transfer handlers, ignore endpoint number 0 (setup)
 	var i uint32
 	for i = 1; i < uint32(len(endPoints)); i++ {
 		// Check if endpoint has a pending interrupt
-		if eptInts&(1<<i) > 0 {
-			// yes, so handle flags
-			epFlags := getEPINTFLAG(i)
-			setEPINTFLAG(i, epFlags)
+		epFlags := getEPINTFLAG(i)
+		if epFlags > 0 {
+			switch i {
+			case usb_CDC_ENDPOINT_OUT:
+				if (epFlags & sam.USB_DEVICE_EPINTFLAG_TRCPT0) > 0 {
+					handleEndpoint(i)
+				}
+				setEPINTFLAG(i, epFlags)
+			case usb_CDC_ENDPOINT_IN, usb_CDC_ENDPOINT_ACM:
+				// set bank ready
+				setEPSTATUSCLR(i, sam.USB_DEVICE_EPSTATUSCLR_BK1RDY)

-			// Endpoint Transfer Complete Interrupt
-			if (epFlags & sam.USB_DEVICE_EPINTFLAG_TRCPT0) > 0 {
-				handleEndpoint(i)
+				// ack transfer complete
+				setEPINTFLAG(i, sam.USB_DEVICE_EPINTFLAG_TRCPT1)
 			}
 		}
 	}
@@ -1403,7 +1418,7 @@ func initEndpoint(ep, config uint32) {
 		usbEndpointDescriptors[ep].DeviceDescBank[1].ADDR.Set(uint32(uintptr(unsafe.Pointer(&udd_ep_in_cache_buffer[ep]))))

 		// set endpoint type
-		setEPCFG(ep, getEPCFG(ep)|((usb_ENDPOINT_TYPE_INTERRUPT+1)<<sam.USB_DEVICE_EPCFG_EPTYPE1_Pos))
+		setEPCFG(ep, ((usb_ENDPOINT_TYPE_INTERRUPT + 1) << sam.USB_DEVICE_EPCFG_EPTYPE1_Pos))

 	case usb_ENDPOINT_TYPE_BULK | usbEndpointOut:
 		// set packet size
@@ -1413,11 +1428,14 @@ func initEndpoint(ep, config uint32) {
 		usbEndpointDescriptors[ep].DeviceDescBank[0].ADDR.Set(uint32(uintptr(unsafe.Pointer(&udd_ep_out_cache_buffer[ep]))))

 		// set endpoint type
-		setEPCFG(ep, getEPCFG(ep)|((usb_ENDPOINT_TYPE_BULK+1)<<sam.USB_DEVICE_EPCFG_EPTYPE0_Pos))
+		setEPCFG(ep, ((usb_ENDPOINT_TYPE_BULK + 1) << sam.USB_DEVICE_EPCFG_EPTYPE0_Pos))

-		// ack the current transfer
+		// receive interrupts when current transfer complete
 		setEPINTENSET(ep, sam.USB_DEVICE_EPINTENSET_TRCPT0)

+		// set byte count to zero, we have not received anything yet
+		usbEndpointDescriptors[ep].DeviceDescBank[0].PCKSIZE.ClearBits(usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask << usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos)
+
 		// ready for next transfer
 		setEPSTATUSCLR(ep, sam.USB_DEVICE_EPSTATUSCLR_BK0RDY)

@@ -1432,7 +1450,7 @@ func initEndpoint(ep, config uint32) {
 		usbEndpointDescriptors[ep].DeviceDescBank[1].ADDR.Set(uint32(uintptr(unsafe.Pointer(&udd_ep_in_cache_buffer[ep]))))

 		// set endpoint type
-		setEPCFG(ep, getEPCFG(ep)|((usb_ENDPOINT_TYPE_BULK+1)<<sam.USB_DEVICE_EPCFG_EPTYPE1_Pos))
+		setEPCFG(ep, ((usb_ENDPOINT_TYPE_BULK + 1) << sam.USB_DEVICE_EPCFG_EPTYPE1_Pos))

 		// NAK on endpoint IN, the bank is not yet filled in.
 		setEPSTATUSCLR(ep, sam.USB_DEVICE_EPSTATUSCLR_BK1RDY)
@@ -1515,7 +1533,12 @@ func handleStandardSetup(setup usbSetup) bool {
 		setEPSTATUSSET(0, sam.USB_DEVICE_EPSTATUSSET_BK1RDY)

 		// wait for transfer to complete
+		timeout := 3000
 		for (getEPINTFLAG(0) & sam.USB_DEVICE_EPINTFLAG_TRCPT1) == 0 {
+			timeout--
+			if timeout == 0 {
+				return true
+			}
 		}

 		// last, set the device address to that requested by host
@@ -1659,11 +1682,21 @@ func armRecvCtrlOUT(ep uint32) uint32 {
 	setEPSTATUSCLR(ep, sam.USB_DEVICE_EPSTATUSCLR_BK0RDY)

 	// Wait until OUT transfer is ready.
+	timeout := 3000
 	for (getEPSTATUS(ep) & sam.USB_DEVICE_EPSTATUS_BK0RDY) == 0 {
+		timeout--
+		if timeout == 0 {
+			return 0
+		}
 	}

 	// Wait until OUT transfer is completed.
+	timeout = 3000
 	for (getEPINTFLAG(ep) & sam.USB_DEVICE_EPINTFLAG_TRCPT0) == 0 {
+		timeout--
+		if timeout == 0 {
+			return 0
+		}
 	}

 	// return number of bytes received
@@ -1800,9 +1833,14 @@ func handleEndpoint(ep uint32) {
 		UART0.Receive(byte((udd_ep_out_cache_buffer[ep][i] & 0xFF)))
 	}

+	// set byte count to zero
+	usbEndpointDescriptors[ep].DeviceDescBank[0].PCKSIZE.ClearBits(usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask << usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos)
+
+	// set multi packet size to 64
+	usbEndpointDescriptors[ep].DeviceDescBank[0].PCKSIZE.SetBits(64 << usb_DEVICE_PCKSIZE_MULTI_PACKET_SIZE_Pos)
+
 	// set ready for next data
 	setEPSTATUSCLR(ep, sam.USB_DEVICE_EPSTATUSCLR_BK0RDY)
-
 }

 func sendZlp(ep uint32) {
@@ -4,6 +4,7 @@ package machine

 import (
 	"device/avr"
+	"runtime/volatile"
 )

 // Configure sets the pin to input or output.
@@ -15,7 +16,7 @@ func (p Pin) Configure(config PinConfig) {
 	}
 }

-func (p Pin) getPortMask() (*avr.Register8, uint8) {
+func (p Pin) getPortMask() (*volatile.Register8, uint8) {
 	return avr.PORTB, 1 << uint8(p)
 }

@@ -4,6 +4,7 @@ package machine

 import (
 	"device/avr"
+	"runtime/volatile"
 )

 type PinMode uint8
@@ -30,7 +31,7 @@ func (p Pin) Set(value bool) {
 // Warning: there are no separate pin set/clear registers on the AVR. The
 // returned mask is only valid as long as no other pin in the same port has been
 // changed.
-func (p Pin) PortMaskSet() (*avr.Register8, uint8) {
+func (p Pin) PortMaskSet() (*volatile.Register8, uint8) {
 	port, mask := p.getPortMask()
 	return port, port.Get() | mask
 }
@@ -41,7 +42,7 @@ func (p Pin) PortMaskSet() (*avr.Register8, uint8) {
 // Warning: there are no separate pin set/clear registers on the AVR. The
 // returned mask is only valid as long as no other pin in the same port has been
 // changed.
-func (p Pin) PortMaskClear() (*avr.Register8, uint8) {
+func (p Pin) PortMaskClear() (*volatile.Register8, uint8) {
 	port, mask := p.getPortMask()
 	return port, port.Get() &^ mask
 }
@@ -1,40 +0,0 @@
-// +build !avr,!nrf,!sam,!stm32
-
-package machine
-
-// Dummy machine package, filled with no-ops.
-
-type PinMode uint8
-
-const (
-	PinInput PinMode = iota
-	PinOutput
-)
-
-// Fake LED numbers, for testing.
-const (
-	LED  Pin = LED1
-	LED1 Pin = 0
-	LED2 Pin = 0
-	LED3 Pin = 0
-	LED4 Pin = 0
-)
-
-// Fake button numbers, for testing.
-const (
-	BUTTON  Pin = BUTTON1
-	BUTTON1 Pin = 0
-	BUTTON2 Pin = 0
-	BUTTON3 Pin = 0
-	BUTTON4 Pin = 0
-)
-
-func (p Pin) Configure(config PinConfig) {
-}
-
-func (p Pin) Set(value bool) {
-}
-
-func (p Pin) Get() bool {
-	return false
-}
@@ -0,0 +1,54 @@
+// +build fe310
+
+package machine
+
+import (
+	"device/sifive"
+)
+
+type PinMode uint8
+
+const (
+	PinInput PinMode = iota
+	PinOutput
+)
+
+// Configure this pin with the given configuration.
+func (p Pin) Configure(config PinConfig) {
+	sifive.GPIO0.INPUT_EN.SetBits(1 << uint8(p))
+	if config.Mode == PinOutput {
+		sifive.GPIO0.OUTPUT_EN.SetBits(1 << uint8(p))
+	}
+}
+
+// Set the pin to high or low.
+func (p Pin) Set(high bool) {
+	if high {
+		sifive.GPIO0.PORT.SetBits(1 << uint8(p))
+	} else {
+		sifive.GPIO0.PORT.ClearBits(1 << uint8(p))
+	}
+}
+
+type UART struct {
+	Bus    *sifive.UART_Type
+	Buffer *RingBuffer
+}
+
+var (
+	UART0 = UART{Bus: sifive.UART0, Buffer: NewRingBuffer()}
+)
+
+func (uart UART) Configure(config UARTConfig) {
+	// Assuming a 16Mhz Crystal (which is Y1 on the HiFive1), the divisor for a
+	// 115200 baud rate is 138.
+	sifive.UART0.DIV.Set(138)
+	sifive.UART0.TXCTRL.Set(sifive.UART_TXCTRL_ENABLE)
+}
+
+func (uart UART) WriteByte(c byte) {
+	for sifive.UART0.TXDATA.Get()&sifive.UART_TXDATA_FULL != 0 {
+	}
+
+	sifive.UART0.TXDATA.Set(uint32(c))
+}
@@ -0,0 +1,184 @@
+// +build !avr,!nrf,!sam,!sifive,!stm32
+
+package machine
+
+// Dummy machine package that calls out to external functions.
+
+var (
+	SPI0  = SPI{0}
+	I2C0  = I2C{0}
+	UART0 = UART{0}
+)
+
+type PinMode uint8
+
+const (
+	PinInput PinMode = iota
+	PinOutput
+	PinInputPullup
+	PinInputPulldown
+)
+
+func (p Pin) Configure(config PinConfig) {
+	gpioConfigure(p, config)
+}
+
+func (p Pin) Set(value bool) {
+	gpioSet(p, value)
+}
+
+func (p Pin) Get() bool {
+	return gpioGet(p)
+}
+
+//go:export __tinygo_gpio_configure
+func gpioConfigure(pin Pin, config PinConfig)
+
+//go:export __tinygo_gpio_set
+func gpioSet(pin Pin, value bool)
+
+//go:export __tinygo_gpio_get
+func gpioGet(pin Pin) bool
+
+type SPI struct {
+	Bus uint8
+}
+
+type SPIConfig struct {
+	Frequency uint32
+	SCK       Pin
+	MOSI      Pin
+	MISO      Pin
+	Mode      uint8
+}
+
+func (spi SPI) Configure(config SPIConfig) {
+	spiConfigure(spi.Bus, config.SCK, config.MOSI, config.MISO)
+}
+
+// Transfer writes/reads a single byte using the SPI interface.
+func (spi SPI) Transfer(w byte) (byte, error) {
+	return spiTransfer(spi.Bus, w), nil
+}
+
+//go:export __tinygo_spi_configure
+func spiConfigure(bus uint8, sck Pin, mosi Pin, miso Pin)
+
+//go:export __tinygo_spi_transfer
+func spiTransfer(bus uint8, w uint8) uint8
+
+// InitADC enables support for ADC peripherals.
+func InitADC() {
+	// Nothing to do here.
+}
+
+// Configure configures an ADC pin to be able to be used to read data.
+func (adc ADC) Configure() {
+}
+
+// Get reads the current analog value from this ADC peripheral.
+func (adc ADC) Get() uint16 {
+	return adcRead(adc.Pin)
+}
+
+//go:export __tinygo_adc_read
+func adcRead(pin Pin) uint16
+
+// InitPWM enables support for PWM peripherals.
+func InitPWM() {
+	// Nothing to do here.
+}
+
+// Configure configures a PWM pin for output.
+func (pwm PWM) Configure() {
+}
+
+// Set turns on the duty cycle for a PWM pin using the provided value.
+func (pwm PWM) Set(value uint16) {
+	pwmSet(pwm.Pin, value)
+}
+
+//go:export __tinygo_pwm_set
+func pwmSet(pin Pin, value uint16)
+
+// I2C is a generic implementation of the Inter-IC communication protocol.
+type I2C struct {
+	Bus uint8
+}
+
+// I2CConfig is used to store config info for I2C.
+type I2CConfig struct {
+	Frequency uint32
+	SCL       Pin
+	SDA       Pin
+}
+
+// Configure is intended to setup the I2C interface.
+func (i2c I2C) Configure(config I2CConfig) {
+	i2cConfigure(i2c.Bus, config.SCL, config.SDA)
+}
+
+// Tx does a single I2C transaction at the specified address.
+func (i2c I2C) Tx(addr uint16, w, r []byte) error {
+	i2cTransfer(i2c.Bus, &w[0], len(w), &r[0], len(r))
+	// TODO: do something with the returned error code.
+	return nil
+}
+
+//go:export __tinygo_i2c_configure
+func i2cConfigure(bus uint8, scl Pin, sda Pin)
+
+//go:export __tinygo_i2c_transfer
+func i2cTransfer(bus uint8, w *byte, wlen int, r *byte, rlen int) int
+
+type UART struct {
+	Bus uint8
+}
+
+type UARTConfig struct {
+	BaudRate uint32
+	TX       Pin
+	RX       Pin
+}
+
+// Configure the UART.
+func (uart UART) Configure(config UARTConfig) {
+	uartConfigure(uart.Bus, config.TX, config.RX)
+}
+
+// Read from the UART.
+func (uart UART) Read(data []byte) (n int, err error) {
+	return uartRead(uart.Bus, &data[0], len(data)), nil
+}
+
+// Write to the UART.
+func (uart UART) Write(data []byte) (n int, err error) {
+	return uartWrite(uart.Bus, &data[0], len(data)), nil
+}
+
+// Buffered returns the number of bytes currently stored in the RX buffer.
+func (uart UART) Buffered() int {
+	return 0
+}
+
+// ReadByte reads a single byte from the UART.
+func (uart UART) ReadByte() (byte, error) {
+	var b byte
+	uartRead(uart.Bus, &b, 1)
+	return b, nil
+}
+
+// WriteByte writes a single byte to the UART.
+func (uart UART) WriteByte(b byte) error {
+	uartWrite(uart.Bus, &b, 1)
+	return nil
+}
+
+//go:export __tinygo_uart_configure
+func uartConfigure(bus uint8, tx Pin, rx Pin)
+
+//go:export __tinygo_uart_read
+func uartRead(bus uint8, buf *byte, bufLen int) int
+
+//go:export __tinygo_uart_write
+func uartWrite(bus uint8, buf *byte, bufLen int) int
@@ -5,14 +5,3 @@ package machine
 // Peripheral abstraction layer for the stm32.

 type PinMode uint8
-
-const (
-	portA Pin = iota * 16
-	portB
-	portC
-	portD
-	portE
-	portF
-	portG
-	portH
-)
@@ -1,4 +1,4 @@
-// +build nrf stm32f103xx atsamd21g18a
+// +build !stm32f407,!avr,!hifive1b

 package machine

@@ -1,4 +1,4 @@
-// +build avr nrf sam stm32
+// +build avr nrf sam sifive stm32

 package machine

@@ -4,9 +4,9 @@ package machine

 import (
 	"bytes"
-	"device/sam"
 	"encoding/binary"
 	"errors"
+	"runtime/volatile"
 )

 const deviceDescriptorSize = 18
@@ -473,6 +473,9 @@ const (
 	usb_CDC_CS_INTERFACE                = 0x24
 	usb_CDC_CS_ENDPOINT                 = 0x25
 	usb_CDC_DATA_INTERFACE_CLASS        = 0x0A
+
+	usb_CDC_LINESTATE_DTR = 0x01
+	usb_CDC_LINESTATE_RTS = 0x02
 )

 // usbDeviceDescBank is the USB device endpoint descriptor.
@@ -484,11 +487,11 @@ const (
 // 		 RoReg8                    Reserved1[0x5];
 //   } UsbDeviceDescBank;
 type usbDeviceDescBank struct {
-	ADDR      sam.Register32
-	PCKSIZE   sam.Register32
-	EXTREG    sam.Register16
-	STATUS_BK sam.Register8
-	_reserved [5]sam.Register8
+	ADDR      volatile.Register32
+	PCKSIZE   volatile.Register32
+	EXTREG    volatile.Register16
+	STATUS_BK volatile.Register8
+	_reserved [5]volatile.Register8
 }

 type usbDeviceDescriptor struct {
@@ -11,7 +11,8 @@ import (

 // Portable analogs of some common system call errors.
 var (
-	ErrUnsupported = errors.New("operation not supported")
+	errUnsupported = errors.New("operation not supported")
+	notImplemented = errors.New("os: not implemented")
 )

 // Stdin, Stdout, and Stderr are open Files pointing to the standard input,
@@ -28,6 +29,21 @@ type File struct {
 	name string
 }

+// Readdir is a stub, not yet implemented
+func (f *File) Readdir(n int) ([]FileInfo, error) {
+	return nil, notImplemented
+}
+
+// Readdirnames is a stub, not yet implemented
+func (f *File) Readdirnames(n int) (names []string, err error) {
+	return nil, notImplemented
+}
+
+// Stat is a stub, not yet implemented
+func (f *File) Stat() (FileInfo, error) {
+	return nil, notImplemented
+}
+
 // NewFile returns a new File with the given file descriptor and name.
 func NewFile(fd uintptr, name string) *File {
 	return &File{fd, name}
@@ -38,3 +54,146 @@ func NewFile(fd uintptr, name string) *File {
 func (f *File) Fd() uintptr {
 	return f.fd
 }
+
+const (
+	PathSeparator     = '/' // OS-specific path separator
+	PathListSeparator = ':' // OS-specific path list separator
+)
+
+// IsPathSeparator reports whether c is a directory separator character.
+func IsPathSeparator(c uint8) bool {
+	return PathSeparator == c
+}
+
+// PathError records an error and the operation and file path that caused it.
+type PathError struct {
+	Op   string
+	Path string
+	Err  error
+}
+
+func (e *PathError) Error() string { return e.Op + " " + e.Path + ": " + e.Err.Error() }
+
+// Open is a super simple stub function (for now), only capable of opening stdin, stdout, and stderr
+func Open(name string) (*File, error) {
+	fd := uintptr(999)
+	switch name {
+	case "/dev/stdin":
+		fd = 0
+	case "/dev/stdout":
+		fd = 1
+	case "/dev/stderr":
+		fd = 2
+	default:
+		return nil, &PathError{"open", name, notImplemented}
+	}
+	return &File{fd, name}, nil
+}
+
+// OpenFile is a stub, passing through to the stub Open() call
+func OpenFile(name string, flag int, perm FileMode) (*File, error) {
+	return Open(name)
+}
+
+// Create is a stub, passing through to the stub Open() call
+func Create(name string) (*File, error) {
+	return Open(name)
+}
+
+type FileMode uint32
+
+// Mode constants, copied from the mainline Go source
+// https://github.com/golang/go/blob/4ce6a8e89668b87dce67e2f55802903d6eb9110a/src/os/types.go#L35-L63
+const (
+	// The single letters are the abbreviations used by the String method's formatting.
+	ModeDir        FileMode = 1 << (32 - 1 - iota) // d: is a directory
+	ModeAppend                                     // a: append-only
+	ModeExclusive                                  // l: exclusive use
+	ModeTemporary                                  // T: temporary file; Plan 9 only
+	ModeSymlink                                    // L: symbolic link
+	ModeDevice                                     // D: device file
+	ModeNamedPipe                                  // p: named pipe (FIFO)
+	ModeSocket                                     // S: Unix domain socket
+	ModeSetuid                                     // u: setuid
+	ModeSetgid                                     // g: setgid
+	ModeCharDevice                                 // c: Unix character device, when ModeDevice is set
+	ModeSticky                                     // t: sticky
+	ModeIrregular                                  // ?: non-regular file; nothing else is known about this file
+
+	// Mask for the type bits. For regular files, none will be set.
+	ModeType = ModeDir | ModeSymlink | ModeNamedPipe | ModeSocket | ModeDevice | ModeCharDevice | ModeIrregular
+
+	ModePerm FileMode = 0777 // Unix permission bits
+)
+
+// IsDir is a stub, always returning false
+func (m FileMode) IsDir() bool {
+	return false
+}
+
+// Stub constants
+const (
+	O_RDONLY int = 1
+	O_WRONLY int = 2
+	O_RDWR   int = 4
+	O_APPEND int = 8
+	O_CREATE int = 16
+	O_EXCL   int = 32
+	O_SYNC   int = 64
+	O_TRUNC  int = 128
+)
+
+// A FileInfo describes a file and is returned by Stat and Lstat.
+type FileInfo interface {
+	Name() string   // base name of the file
+	Size() int64    // length in bytes for regular files; system-dependent for others
+	Mode() FileMode // file mode bits
+	// ModTime() time.Time // modification time
+	IsDir() bool      // abbreviation for Mode().IsDir()
+	Sys() interface{} // underlying data source (can return nil)
+}
+
+// Stat is a stub, not yet implemented
+func Stat(name string) (FileInfo, error) {
+	return nil, notImplemented
+}
+
+// Lstat is a stub, not yet implemented
+func Lstat(name string) (FileInfo, error) {
+	return nil, notImplemented
+}
+
+// Getwd is a stub (for now), always returning an empty string
+func Getwd() (string, error) {
+	return "", nil
+}
+
+// Readlink is a stub (for now), always returning the string it was given
+func Readlink(name string) (string, error) {
+	return name, nil
+}
+
+// TempDir is a stub (for now), always returning the string "/tmp"
+func TempDir() string {
+	return "/tmp"
+}
+
+// Mkdir is a stub, not yet implemented
+func Mkdir(name string, perm FileMode) error {
+	return notImplemented
+}
+
+// IsExist is a stub (for now), always returning false
+func IsExist(err error) bool {
+	return false
+}
+
+// IsNotExist is a stub (for now), always returning false
+func IsNotExist(err error) bool {
+	return false
+}
+
+// Getpid is a stub (for now), always returning 1
+func Getpid() int {
+	return 1
+}
@@ -1,4 +1,4 @@
-// +build avr cortexm wasm
+// +build avr cortexm tinygo.riscv wasm

 package os

@@ -8,7 +8,7 @@ import (

 // Read is unsupported on this system.
 func (f *File) Read(b []byte) (n int, err error) {
-	return 0, ErrUnsupported
+	return 0, errUnsupported
 }

 // Write writes len(b) bytes to the output. It returns the number of bytes
@@ -21,13 +21,13 @@ func (f *File) Write(b []byte) (n int, err error) {
 		}
 		return len(b), nil
 	default:
-		return 0, ErrUnsupported
+		return 0, errUnsupported
 	}
 }

 // Close is unsupported on this system.
 func (f *File) Close() error {
-	return ErrUnsupported
+	return errUnsupported
 }

 //go:linkname putchar runtime.putchar
@@ -1,4 +1,4 @@
-// +build darwin linux,!avr,!cortexm
+// +build darwin linux,!avr,!cortexm,!tinygo.riscv

 package os

@@ -0,0 +1,17 @@
+// Package os implements a subset of the Go "os" package. See
+// https://godoc.org/os for details.
+//
+// Note that the current implementation is blocking. This limitation should be
+// removed in a future version.
+package os
+
+import (
+	"syscall"
+)
+
+// Exit causes the current program to exit with the given status code.
+// Conventionally, code zero indicates success, non-zero an error.
+// The program terminates immediately; deferred functions are not run.
+func Exit(code int) {
+	syscall.Exit(code)
+}
@@ -92,7 +92,7 @@ func (v Value) Pointer() uintptr {
 }

 func (v Value) IsValid() bool {
-	panic("unimplemented: (reflect.Value).IsValid()")
+	return v.typecode != 0
 }

 func (v Value) CanInterface() bool {
@@ -502,6 +502,14 @@ func MakeSlice(typ Type, len, cap int) Value {
 	panic("unimplemented: reflect.MakeSlice()")
 }

+func Zero(typ Type) Value {
+	panic("unimplemented: reflect.Zero()")
+}
+
+func New(typ Type) Value {
+	panic("unimplemented: reflect.New()")
+}
+
 type funcHeader struct {
 	Context unsafe.Pointer
 	Code    unsafe.Pointer
@@ -1,4 +1,4 @@
-// +build arm,!avr,!cortexm
+// +build arm,!avr,!cortexm,!tinygo.riscv

 package runtime

@@ -2,26 +2,11 @@

 package runtime

-import (
-	"unsafe"
-)
-
-const GOARCH = "avr"
+const GOARCH = "arm" // avr pretends to be arm

 // The bitness of the CPU (e.g. 8, 32, 64).
 const TargetBits = 8

-//go:extern _heap_start
-var heapStartSymbol unsafe.Pointer
-
-//go:extern _heap_end
-var heapEndSymbol unsafe.Pointer
-
-var (
-	heapStart = uintptr(unsafe.Pointer(&heapStartSymbol))
-	heapEnd   = uintptr(unsafe.Pointer(&heapEndSymbol))
-)
-
 // Align on a word boundary.
 func align(ptr uintptr) uintptr {
 	// No alignment necessary on the AVR.
@@ -3,8 +3,6 @@
 package runtime

 import (
-	"unsafe"
-
 	"device/arm"
 )

@@ -13,29 +11,6 @@ const GOARCH = "arm"
 // The bitness of the CPU (e.g. 8, 32, 64).
 const TargetBits = 32

-//go:extern _heap_start
-var heapStartSymbol unsafe.Pointer
-
-//go:extern _heap_end
-var heapEndSymbol unsafe.Pointer
-
-//go:extern _globals_start
-var globalsStartSymbol unsafe.Pointer
-
-//go:extern _globals_end
-var globalsEndSymbol unsafe.Pointer
-
-//go:extern _stack_top
-var stackTopSymbol unsafe.Pointer
-
-var (
-	heapStart    = uintptr(unsafe.Pointer(&heapStartSymbol))
-	heapEnd      = uintptr(unsafe.Pointer(&heapEndSymbol))
-	globalsStart = uintptr(unsafe.Pointer(&globalsStartSymbol))
-	globalsEnd   = uintptr(unsafe.Pointer(&globalsEndSymbol))
-	stackTop     = uintptr(unsafe.Pointer(&stackTopSymbol))
-)
-
 // Align on word boundary.
 func align(ptr uintptr) uintptr {
 	return (ptr + 3) &^ 3
@@ -0,0 +1,19 @@
+// +build tinygo.riscv
+
+package runtime
+
+import "device/riscv"
+
+const GOARCH = "arm" // riscv pretends to be arm
+
+// The bitness of the CPU (e.g. 8, 32, 64).
+const TargetBits = 32
+
+// Align on word boundary.
+func align(ptr uintptr) uintptr {
+	return (ptr + 3) &^ 3
+}
+
+func getCurrentStackPointer() uintptr {
+	return riscv.ReadRegister("sp")
+}
@@ -14,9 +14,12 @@ const TargetBits = 32
 //go:extern __heap_base
 var heapStartSymbol unsafe.Pointer

+//go:export llvm.wasm.memory.size.i32
+func wasm_memory_size(index int32) int32
+
 var (
 	heapStart = uintptr(unsafe.Pointer(&heapStartSymbol))
-	heapEnd   = (heapStart + wasmPageSize - 1) &^ (wasmPageSize - 1) // conservative guess: one page of heap memory
+	heapEnd   = uintptr(wasm_memory_size(0) * wasmPageSize)
 )

 const wasmPageSize = 64 * 1024
@@ -0,0 +1,30 @@
+// +build avr cortexm tinygo.riscv
+
+package runtime
+
+import (
+	"unsafe"
+)
+
+//go:extern _heap_start
+var heapStartSymbol unsafe.Pointer
+
+//go:extern _heap_end
+var heapEndSymbol unsafe.Pointer
+
+//go:extern _globals_start
+var globalsStartSymbol unsafe.Pointer
+
+//go:extern _globals_end
+var globalsEndSymbol unsafe.Pointer
+
+//go:extern _stack_top
+var stackTopSymbol unsafe.Pointer
+
+var (
+	heapStart    = uintptr(unsafe.Pointer(&heapStartSymbol))
+	heapEnd      = uintptr(unsafe.Pointer(&heapEndSymbol))
+	globalsStart = uintptr(unsafe.Pointer(&globalsStartSymbol))
+	globalsEnd   = uintptr(unsafe.Pointer(&globalsEndSymbol))
+	stackTop     = uintptr(unsafe.Pointer(&stackTopSymbol))
+)
@@ -28,24 +28,35 @@ import (
 )

 type channel struct {
-	state   uint8
-	blocked *coroutine
+	elementSize uint16 // the size of one value in this channel
+	state       chanState
+	blocked     *coroutine
 }

+type chanState uint8
+
 const (
-	chanStateEmpty = iota
+	chanStateEmpty chanState = iota
 	chanStateRecv
 	chanStateSend
 	chanStateClosed
 )

+// chanSelectState is a single channel operation (send/recv) in a select
+// statement. The value pointer is either nil (for receives) or points to the
+// value to send (for sends).
+type chanSelectState struct {
+	ch    *channel
+	value unsafe.Pointer
+}
+
 func deadlockStub()

 // chanSend sends a single value over the channel. If this operation can
 // complete immediately (there is a goroutine waiting for a value), it sends the
 // value and re-activates both goroutines. If not, it sets itself as waiting on
 // a value.
-func chanSend(sender *coroutine, ch *channel, value unsafe.Pointer, size uintptr) {
+func chanSend(sender *coroutine, ch *channel, value unsafe.Pointer) {
 	if ch == nil {
 		// A nil channel blocks forever. Do not scheduler this goroutine again.
 		return
@@ -58,7 +69,7 @@ func chanSend(sender *coroutine, ch *channel, value unsafe.Pointer, size uintptr
 	case chanStateRecv:
 		receiver := ch.blocked
 		receiverPromise := receiver.promise()
-		memcpy(receiverPromise.ptr, value, size)
+		memcpy(receiverPromise.ptr, value, uintptr(ch.elementSize))
 		receiverPromise.data = 1 // commaOk = true
 		ch.blocked = receiverPromise.next
 		receiverPromise.next = nil
@@ -80,7 +91,7 @@ func chanSend(sender *coroutine, ch *channel, value unsafe.Pointer, size uintptr
 // sender, it receives the value immediately and re-activates both coroutines.
 // If not, it sets itself as available for receiving. If the channel is closed,
 // it immediately activates itself with a zero value as the result.
-func chanRecv(receiver *coroutine, ch *channel, value unsafe.Pointer, size uintptr) {
+func chanRecv(receiver *coroutine, ch *channel, value unsafe.Pointer) {
 	if ch == nil {
 		// A nil channel blocks forever. Do not scheduler this goroutine again.
 		return
@@ -89,7 +100,7 @@ func chanRecv(receiver *coroutine, ch *channel, value unsafe.Pointer, size uintp
 	case chanStateSend:
 		sender := ch.blocked
 		senderPromise := sender.promise()
-		memcpy(value, senderPromise.ptr, size)
+		memcpy(value, senderPromise.ptr, uintptr(ch.elementSize))
 		receiver.promise().data = 1 // commaOk = true
 		ch.blocked = senderPromise.next
 		senderPromise.next = nil
@@ -103,7 +114,7 @@ func chanRecv(receiver *coroutine, ch *channel, value unsafe.Pointer, size uintp
 		ch.state = chanStateRecv
 		ch.blocked = receiver
 	case chanStateClosed:
-		memzero(value, size)
+		memzero(value, uintptr(ch.elementSize))
 		receiver.promise().data = 0 // commaOk = false
 		activateTask(receiver)
 	case chanStateRecv:
@@ -115,7 +126,7 @@ func chanRecv(receiver *coroutine, ch *channel, value unsafe.Pointer, size uintp

 // chanClose closes the given channel. If this channel has a receiver or is
 // empty, it closes the channel. Else, it panics.
-func chanClose(ch *channel, size uintptr) {
+func chanClose(ch *channel) {
 	if ch == nil {
 		// Not allowed by the language spec.
 		runtimePanic("close of nil channel")
@@ -133,7 +144,7 @@ func chanClose(ch *channel, size uintptr) {
 	case chanStateRecv:
 		// The receiver must be re-activated with a zero value.
 		receiverPromise := ch.blocked.promise()
-		memzero(receiverPromise.ptr, size)
+		memzero(receiverPromise.ptr, uintptr(ch.elementSize))
 		receiverPromise.data = 0 // commaOk = false
 		activateTask(ch.blocked)
 		ch.state = chanStateClosed
@@ -143,3 +154,63 @@ func chanClose(ch *channel, size uintptr) {
 		ch.state = chanStateClosed
 	}
 }
+
+// chanSelect is the runtime implementation of the select statement. This is
+// perhaps the most complicated statement in the Go spec. It returns the
+// selected index and the 'comma-ok' value.
+//
+// TODO: do this in a round-robin fashion (as specified in the Go spec) instead
+// of picking the first one that can proceed.
+func chanSelect(recvbuf unsafe.Pointer, states []chanSelectState, blocking bool) (uintptr, bool) {
+	// See whether we can receive from one of the channels.
+	for i, state := range states {
+		if state.ch == nil {
+			// A nil channel blocks forever, so don't consider it here.
+			continue
+		}
+		if state.value == nil {
+			// A receive operation.
+			switch state.ch.state {
+			case chanStateSend:
+				// We can receive immediately.
+				sender := state.ch.blocked
+				senderPromise := sender.promise()
+				memcpy(recvbuf, senderPromise.ptr, uintptr(state.ch.elementSize))
+				state.ch.blocked = senderPromise.next
+				senderPromise.next = nil
+				activateTask(sender)
+				if state.ch.blocked == nil {
+					state.ch.state = chanStateEmpty
+				}
+				return uintptr(i), true // commaOk = true
+			case chanStateClosed:
+				// Receive the zero value.
+				memzero(recvbuf, uintptr(state.ch.elementSize))
+				return uintptr(i), false // commaOk = false
+			}
+		} else {
+			// A send operation: state.value is not nil.
+			switch state.ch.state {
+			case chanStateRecv:
+				receiver := state.ch.blocked
+				receiverPromise := receiver.promise()
+				memcpy(receiverPromise.ptr, state.value, uintptr(state.ch.elementSize))
+				receiverPromise.data = 1 // commaOk = true
+				state.ch.blocked = receiverPromise.next
+				receiverPromise.next = nil
+				activateTask(receiver)
+				if state.ch.blocked == nil {
+					state.ch.state = chanStateEmpty
+				}
+				return uintptr(i), false
+			case chanStateClosed:
+				runtimePanic("send on closed channel")
+			}
+		}
+	}
+
+	if !blocking {
+		return ^uintptr(0), false
+	}
+	panic("unimplemented: blocking select")
+}
@@ -1,4 +1,4 @@
-// +build gc.marksweep
+// +build gc.conservative

 package runtime

@@ -119,7 +119,7 @@ func (b gcBlock) findHead() gcBlock {
 // findNext returns the first block just past the end of the tail. This may or
 // may not be the head of an object.
 func (b gcBlock) findNext() gcBlock {
-	if b.state() == blockStateHead {
+	if b.state() == blockStateHead || b.state() == blockStateMark {
 		b++
 	}
 	for b.state() == blockStateTail {
@@ -203,6 +203,7 @@ func init() {

 // alloc tries to find some free space on the heap, possibly doing a garbage
 // collection cycle if needed. If no space is free, it panics.
+//go:noinline
 func alloc(size uintptr) unsafe.Pointer {
 	if size == 0 {
 		return unsafe.Pointer(&zeroSizedAlloc)
@@ -282,8 +283,8 @@ func GC() {
 	}

 	// Mark phase: mark all reachable objects, recursively.
-	markRoots(globalsStart, globalsEnd)
-	markRoots(getCurrentStackPointer(), stackTop) // assume a descending stack
+	markGlobals()
+	markStack()

 	// Sweep phase: free all non-marked objects and unmark marked objects for
 	// the next collection cycle.
@@ -303,21 +304,30 @@ func markRoots(start, end uintptr) {
 	if gcDebug {
 		println("mark from", start, "to", end, int(end-start))
 	}
+	if gcAsserts {
+		if start >= end {
+			runtimePanic("gc: unexpected range to mark")
+		}
+	}

 	for addr := start; addr != end; addr += unsafe.Sizeof(addr) {
 		root := *(*uintptr)(unsafe.Pointer(addr))
-		if looksLikePointer(root) {
-			block := blockFromAddr(root)
-			head := block.findHead()
-			if head.state() != blockStateMark {
-				if gcDebug {
-					println("found unmarked pointer", root, "at address", addr)
-				}
-				head.setState(blockStateMark)
-				next := block.findNext()
-				// TODO: avoid recursion as much as possible
-				markRoots(head.address(), next.address())
+		markRoot(addr, root)
+	}
+}
+
+func markRoot(addr, root uintptr) {
+	if looksLikePointer(root) {
+		block := blockFromAddr(root)
+		head := block.findHead()
+		if head.state() != blockStateMark {
+			if gcDebug {
+				println("found unmarked pointer", root, "at address", addr)
 			}
+			head.setState(blockStateMark)
+			next := block.findNext()
+			// TODO: avoid recursion as much as possible
+			markRoots(head.address(), next.address())
 		}
 	}
 }
@@ -0,0 +1,12 @@
+// +build gc.conservative
+// +build cortexm tinygo.riscv
+
+package runtime
+
+// markGlobals marks all globals, which are reachable by definition.
+//
+// This implementation marks all globals conservatively and assumes it can use
+// linker-defined symbols for the start and end of the .data section.
+func markGlobals() {
+	markRoots(globalsStart, globalsEnd)
+}
@@ -0,0 +1,35 @@
+// +build gc.conservative
+// +build !cortexm,!tinygo.riscv
+
+package runtime
+
+import (
+	"unsafe"
+)
+
+//go:extern runtime.trackedGlobalsStart
+var trackedGlobalsStart uintptr
+
+//go:extern runtime.trackedGlobalsLength
+var trackedGlobalsLength uintptr
+
+//go:extern runtime.trackedGlobalsBitmap
+var trackedGlobalsBitmap [0]uint8
+
+// markGlobals marks all globals, which are reachable by definition.
+//
+// This implementation relies on a compiler pass that stores all globals in a
+// single global (adjusting all uses of them accordingly) and creates a bit
+// vector with the locations of each pointer. This implementation then walks the
+// bit vector and for each pointer it indicates, it marks the root.
+//
+//go:nobounds
+func markGlobals() {
+	for i := uintptr(0); i < trackedGlobalsLength; i++ {
+		if trackedGlobalsBitmap[i/8]&(1<<(i%8)) != 0 {
+			addr := trackedGlobalsStart + i*unsafe.Alignof(uintptr(0))
+			root := *(*uintptr)(unsafe.Pointer(addr))
+			markRoot(addr, root)
+		}
+	}
+}
@@ -1,4 +1,4 @@
-// +build gc.dumb
+// +build gc.leaking

 package runtime

@@ -0,0 +1,39 @@
+// +build gc.conservative
+// +build !cortexm,!tinygo.riscv
+
+package runtime
+
+import (
+	"unsafe"
+)
+
+//go:extern runtime.stackChainStart
+var stackChainStart *stackChainObject
+
+type stackChainObject struct {
+	parent   *stackChainObject
+	numSlots uintptr
+}
+
+// markStack marks all root pointers found on the stack.
+//
+// This implementation is conservative and relies on the compiler inserting code
+// to manually push/pop stack objects that are stored in a linked list starting
+// with stackChainStart. Manually keeping track of stack values is _much_ more
+// expensive than letting the compiler do it and it inhibits a few important
+// optimizations, but it has the big advantage of being portable to basically
+// any ISA, including WebAssembly.
+func markStack() {
+	stackObject := stackChainStart
+	for stackObject != nil {
+		start := uintptr(unsafe.Pointer(stackObject)) + unsafe.Sizeof(uintptr(0))*2
+		end := start + stackObject.numSlots*unsafe.Alignof(uintptr(0))
+		markRoots(start, end)
+		stackObject = stackObject.parent
+	}
+}
+
+// trackPointer is a stub function call inserted by the compiler during IR
+// construction. Calls to it are later replaced with regular stack bookkeeping
+// code.
+func trackPointer(ptr unsafe.Pointer)
@@ -0,0 +1,13 @@
+// +build gc.conservative
+// +build cortexm tinygo.riscv
+
+package runtime
+
+// markStack marks all root pointers found on the stack.
+//
+// This implementation is conservative and relies on the stack top (provided by
+// the linker) and getting the current stack pointer from a register. Also, it
+// assumes a descending stack. Thus, it is not very portable.
+func markStack() {
+	markRoots(getCurrentStackPointer(), stackTop)
+}
@@ -56,7 +56,15 @@ func math_Cbrt(x float64) float64 { return math_cbrt(x) }
 func math_cbrt(x float64) float64

 //go:linkname math_Ceil math.Ceil
-func math_Ceil(x float64) float64 { return math_ceil(x) }
+func math_Ceil(x float64) float64 {
+	if GOARCH == "arm64" || GOARCH == "wasm" {
+		return llvm_ceil(x)
+	}
+	return math_ceil(x)
+}
+
+//go:export llvm.ceil.f64
+func llvm_ceil(x float64) float64

 //go:linkname math_ceil math.ceil
 func math_ceil(x float64) float64
@@ -104,7 +112,15 @@ func math_Exp2(x float64) float64 { return math_exp2(x) }
 func math_exp2(x float64) float64

 //go:linkname math_Floor math.Floor
-func math_Floor(x float64) float64 { return math_floor(x) }
+func math_Floor(x float64) float64 {
+	if GOARCH == "arm64" || GOARCH == "wasm" {
+		return llvm_floor(x)
+	}
+	return math_floor(x)
+}
+
+//go:export llvm.floor.f64
+func llvm_floor(x float64) float64

 //go:linkname math_floor math.floor
 func math_floor(x float64) float64
@@ -152,13 +168,29 @@ func math_Log2(x float64) float64 { return math_log2(x) }
 func math_log2(x float64) float64

 //go:linkname math_Max math.Max
-func math_Max(x, y float64) float64 { return math_max(x, y) }
+func math_Max(x, y float64) float64 {
+	if GOARCH == "arm64" || GOARCH == "wasm" {
+		return llvm_maximum(x, y)
+	}
+	return math_max(x, y)
+}
+
+//go:export llvm.maximum.f64
+func llvm_maximum(x, y float64) float64

 //go:linkname math_max math.max
 func math_max(x, y float64) float64

 //go:linkname math_Min math.Min
-func math_Min(x, y float64) float64 { return math_min(x, y) }
+func math_Min(x, y float64) float64 {
+	if GOARCH == "arm64" || GOARCH == "wasm" {
+		return llvm_minimum(x, y)
+	}
+	return math_min(x, y)
+}
+
+//go:export llvm.minimum.f64
+func llvm_minimum(x, y float64) float64

 //go:linkname math_min math.min
 func math_min(x, y float64) float64
@@ -200,7 +232,15 @@ func math_Sinh(x float64) float64 { return math_sinh(x) }
 func math_sinh(x float64) float64

 //go:linkname math_Sqrt math.Sqrt
-func math_Sqrt(x float64) float64 { return math_sqrt(x) }
+func math_Sqrt(x float64) float64 {
+	if GOARCH == "x86" || GOARCH == "amd64" || GOARCH == "wasm" {
+		return llvm_sqrt(x)
+	}
+	return math_sqrt(x)
+}
+
+//go:export llvm.sqrt.f64
+func llvm_sqrt(x float64) float64

 //go:linkname math_sqrt math.sqrt
 func math_sqrt(x float64) float64
@@ -218,7 +258,15 @@ func math_Tanh(x float64) float64 { return math_tanh(x) }
 func math_tanh(x float64) float64

 //go:linkname math_Trunc math.Trunc
-func math_Trunc(x float64) float64 { return math_trunc(x) }
+func math_Trunc(x float64) float64 {
+	if GOARCH == "arm64" || GOARCH == "wasm" {
+		return llvm_trunc(x)
+	}
+	return math_trunc(x)
+}
+
+//go:export llvm.trunc.f64
+func llvm_trunc(x float64) float64

 //go:linkname math_trunc math.trunc
 func math_trunc(x float64) float64
@@ -6,6 +6,7 @@ import (
 	"device/arm"
 	"device/sam"
 	"machine"
+	"runtime/volatile"
 	"unsafe"
 )

@@ -230,10 +231,7 @@ var (
 	timerLastCounter uint64
 )

-//go:volatile
-type isrFlag bool
-
-var timerWakeup isrFlag
+var timerWakeup volatile.Register8

 const asyncScheduler = false

@@ -262,7 +260,7 @@ func ticks() timeUnit {

 // ticks are in microseconds
 func timerSleep(ticks uint32) {
-	timerWakeup = false
+	timerWakeup.Set(0)
 	if ticks < 30 {
 		// have to have at least one clock count
 		ticks = 30
@@ -280,7 +278,7 @@ func timerSleep(ticks uint32) {
 	// enable IRQ for CMP0 compare
 	sam.RTC_MODE0.INTENSET.SetBits(sam.RTC_MODE0_INTENSET_CMP0)

-	for !timerWakeup {
+	for timerWakeup.Get() == 0 {
 		arm.Asm("wfi")
 	}
 }
@@ -290,7 +288,7 @@ func handleRTC() {
 	// disable IRQ for CMP0 compare
 	sam.RTC_MODE0.INTFLAG.Set(sam.RTC_MODE0_INTENSET_CMP0)

-	timerWakeup = true
+	timerWakeup.Set(1)
 }

 func initUSBClock() {
@@ -0,0 +1,115 @@
+// +build fe310
+
+// This file implements target-specific things for the FE310 chip as used in the
+// HiFive1.
+
+package runtime
+
+import (
+	"machine"
+	"unsafe"
+
+	"device/riscv"
+	"device/sifive"
+)
+
+type timeUnit int64
+
+const tickMicros = 32768 // RTC runs at 32.768kHz
+
+//go:extern _sbss
+var _sbss unsafe.Pointer
+
+//go:extern _ebss
+var _ebss unsafe.Pointer
+
+//go:extern _sdata
+var _sdata unsafe.Pointer
+
+//go:extern _sidata
+var _sidata unsafe.Pointer
+
+//go:extern _edata
+var _edata unsafe.Pointer
+
+//go:export main
+func main() {
+	preinit()
+	initAll()
+	callMain()
+	abort()
+}
+
+func init() {
+	pric_init()
+	machine.UART0.Configure(machine.UARTConfig{})
+}
+
+func pric_init() {
+	// Make sure the HFROSC is on
+	sifive.PRIC.HFROSCCFG.SetBits(sifive.PRIC_HFROSCCFG_ENABLE)
+
+	// Run off 16 MHz Crystal for accuracy.
+	sifive.PRIC.PLLCFG.SetBits(sifive.PRIC_PLLCFG_REFSEL | sifive.PRIC_PLLCFG_BYPASS)
+	sifive.PRIC.PLLCFG.SetBits(sifive.PRIC_PLLCFG_SEL)
+
+	// Turn off HFROSC to save power
+	sifive.PRIC.HFROSCCFG.ClearBits(sifive.PRIC_HFROSCCFG_ENABLE)
+
+	// Enable the RTC.
+	sifive.RTC.CONFIG.Set(sifive.RTC_CONFIG_ENALWAYS)
+}
+
+func preinit() {
+	// Initialize .bss: zero-initialized global variables.
+	ptr := uintptr(unsafe.Pointer(&_sbss))
+	for ptr != uintptr(unsafe.Pointer(&_ebss)) {
+		*(*uint32)(unsafe.Pointer(ptr)) = 0
+		ptr += 4
+	}
+
+	// Initialize .data: global variables initialized from flash.
+	src := uintptr(unsafe.Pointer(&_sidata))
+	dst := uintptr(unsafe.Pointer(&_sdata))
+	for dst != uintptr(unsafe.Pointer(&_edata)) {
+		*(*uint32)(unsafe.Pointer(dst)) = *(*uint32)(unsafe.Pointer(src))
+		dst += 4
+		src += 4
+	}
+}
+
+func putchar(c byte) {
+	machine.UART0.WriteByte(c)
+}
+
+func ticks() timeUnit {
+	// Combining the low bits and the high bits yields a time span of over 270
+	// years without counter rollover.
+	highBits := sifive.RTC.HI.Get()
+	for {
+		lowBits := sifive.RTC.LO.Get()
+		newHighBits := sifive.RTC.HI.Get()
+		if newHighBits == highBits {
+			// High bits stayed the same.
+			return timeUnit(lowBits) | (timeUnit(highBits) << 32)
+		}
+		// Retry, because there was a rollover in the low bits (happening every
+		// 1.5 days).
+		highBits = newHighBits
+	}
+}
+
+const asyncScheduler = false
+
+func sleepTicks(d timeUnit) {
+	target := ticks() + d
+	for ticks() < target {
+	}
+}
+
+func abort() {
+	// lock up forever
+	for {
+		riscv.Asm("wfi")
+	}
+}
@@ -6,6 +6,7 @@ import (
 	"device/arm"
 	"device/nrf"
 	"machine"
+	"runtime/volatile"
 )

 type timeUnit int64
@@ -79,14 +80,11 @@ func ticks() timeUnit {
 	return timestamp
 }

-//go:volatile
-type isrFlag bool
-
-var rtc_wakeup isrFlag
+var rtc_wakeup volatile.Register8

 func rtc_sleep(ticks uint32) {
 	nrf.RTC1.INTENSET.Set(nrf.RTC_INTENSET_COMPARE0)
-	rtc_wakeup = false
+	rtc_wakeup.Set(0)
 	if ticks == 1 {
 		// Race condition (even in hardware) at ticks == 1.
 		// TODO: fix this in a better way by detecting it, like the manual
@@ -94,7 +92,7 @@ func rtc_sleep(ticks uint32) {
 		ticks = 2
 	}
 	nrf.RTC1.CC[0].Set((nrf.RTC1.COUNTER.Get() + ticks) & 0x00ffffff)
-	for !rtc_wakeup {
+	for rtc_wakeup.Get() == 0 {
 		arm.Asm("wfi")
 	}
 }
@@ -103,5 +101,5 @@ func rtc_sleep(ticks uint32) {
 func handleRTC1() {
 	nrf.RTC1.INTENCLR.Set(nrf.RTC_INTENSET_COMPARE0)
 	nrf.RTC1.EVENTS_COMPARE[0].Set(0)
-	rtc_wakeup = true
+	rtc_wakeup.Set(1)
 }
@@ -7,6 +7,7 @@ package runtime

 import (
 	"device/arm"
+	"runtime/volatile"
 	"unsafe"
 )

@@ -36,12 +37,9 @@ func ticks() timeUnit {
 	return timestamp
 }

-//go:volatile
-type regValue uint32
-
 // UART0 output register.
-var stdoutWrite *regValue = (*regValue)(unsafe.Pointer(uintptr(0x4000c000)))
+var stdoutWrite = (*volatile.Register8)(unsafe.Pointer(uintptr(0x4000c000)))

 func putchar(c byte) {
-	*stdoutWrite = regValue(c)
+	stdoutWrite.Set(uint8(c))
 }
@@ -6,6 +6,7 @@ import (
 	"device/arm"
 	"device/stm32"
 	"machine"
+	"runtime/volatile"
 )

 func init() {
@@ -58,10 +59,7 @@ var (
 	timerLastCounter uint64
 )

-//go:volatile
-type isrFlag bool
-
-var timerWakeup isrFlag
+var timerWakeup volatile.Register8

 func initRTC() {
 	// Enable the PWR and BKP.
@@ -136,7 +134,7 @@ func ticks() timeUnit {

 // ticks are in microseconds
 func timerSleep(ticks uint32) {
-	timerWakeup = false
+	timerWakeup.Set(0)

 	// STM32 timer update event period is calculated as follows:
 	//
@@ -177,7 +175,7 @@ func timerSleep(ticks uint32) {
 	stm32.TIM3.CR1.SetBits(stm32.TIM_CR1_CEN)

 	// wait till timer wakes up
-	for !timerWakeup {
+	for timerWakeup.Get() == 0 {
 		arm.Asm("wfi")
 	}
 }
@@ -192,6 +190,6 @@ func handleTIM3() {
 		stm32.TIM3.SR.ClearBits(stm32.TIM_SR_UIF)

 		// timer was triggered
-		timerWakeup = true
+		timerWakeup.Set(1)
 	}
 }
@@ -6,6 +6,7 @@ import (
 	"device/arm"
 	"device/stm32"
 	"machine"
+	"runtime/volatile"
 )

 func init() {
@@ -114,10 +115,7 @@ var (
 	tickCount timeUnit
 )

-//go:volatile
-type isrFlag bool
-
-var timerWakeup isrFlag
+var timerWakeup volatile.Register8

 // Enable the TIM3 clock.(sleep count)
 func initTIM3() {
@@ -160,7 +158,7 @@ func ticks() timeUnit {

 // ticks are in microseconds
 func timerSleep(ticks uint32) {
-	timerWakeup = false
+	timerWakeup.Set(0)

 	// CK_INT = APB1 x2 = 84mhz
 	// prescale counter down from 84mhz to 10khz aka 0.1 ms frequency.
@@ -180,7 +178,7 @@ func timerSleep(ticks uint32) {
 	stm32.TIM3.CR1.SetBits(stm32.TIM_CR1_CEN)

 	// wait till timer wakes up
-	for !timerWakeup {
+	for timerWakeup.Get() == 0 {
 		arm.Asm("wfi")
 	}
 }
@@ -195,7 +193,7 @@ func handleTIM3() {
 		stm32.TIM3.SR.ClearBits(stm32.TIM_SR_UIF)

 		// timer was triggered
-		timerWakeup = true
+		timerWakeup.Set(1)
 	}
 }

@@ -0,0 +1,19 @@
+// +build tinygo.riscv
+
+package runtime
+
+import "unsafe"
+
+// Implement memset for LLVM.
+//go:export memset
+func libc_memset(ptr unsafe.Pointer, c byte, size uintptr) {
+	for i := uintptr(0); i < size; i++ {
+		*(*byte)(unsafe.Pointer(uintptr(ptr) + i)) = c
+	}
+}
+
+// Implement memmove for LLVM.
+//go:export memmove
+func libc_memmove(dst, src unsafe.Pointer, size uintptr) {
+	memmove(dst, src, size)
+}
@@ -1,4 +1,4 @@
-// +build darwin linux,!avr,!cortexm
+// +build darwin linux,!avr,!cortexm,!tinygo.riscv

 package runtime

@@ -89,6 +89,21 @@ func stringToBytes(x _string) (slice struct {
 	return
 }

+// Convert a string to []rune slice.
+func stringToRunes(s string) []rune {
+	var n = 0
+	for range s {
+		n++
+	}
+	var r = make([]rune, n)
+	n = 0
+	for _, e := range s {
+		r[n] = e
+		n++
+	}
+	return r
+}
+
 // Create a string from a Unicode code point.
 func stringFromUnicode(x rune) _string {
 	array, length := encodeUTF8(x)
@@ -0,0 +1,162 @@
+package volatile
+
+// This file defines Register{8,16,32} types, which are convenience types for
+// volatile register accesses.
+
+// Special types that causes loads/stores to be volatile (necessary for
+// memory-mapped registers).
+type Register8 struct {
+	Reg uint8
+}
+
+// Get returns the value in the register. It is the volatile equivalent of:
+//
+//     *r.Reg
+//
+//go:inline
+func (r *Register8) Get() uint8 {
+	return LoadUint8(&r.Reg)
+}
+
+// Set updates the register value. It is the volatile equivalent of:
+//
+//     *r.Reg = value
+//
+//go:inline
+func (r *Register8) Set(value uint8) {
+	StoreUint8(&r.Reg, value)
+}
+
+// SetBits reads the register, sets the given bits, and writes it back. It is
+// the volatile equivalent of:
+//
+//     r.Reg |= value
+//
+//go:inline
+func (r *Register8) SetBits(value uint8) {
+	StoreUint8(&r.Reg, LoadUint8(&r.Reg)|value)
+}
+
+// ClearBits reads the register, clears the given bits, and writes it back. It
+// is the volatile equivalent of:
+//
+//     r.Reg &^= value
+//
+//go:inline
+func (r *Register8) ClearBits(value uint8) {
+	StoreUint8(&r.Reg, LoadUint8(&r.Reg)&^value)
+}
+
+// HasBits reads the register and then checks to see if the passed bits are set. It
+// is the volatile equivalent of:
+//
+//     (*r.Reg & value) > 0
+//
+//go:inline
+func (r *Register8) HasBits(value uint8) bool {
+	return (r.Get() & value) > 0
+}
+
+type Register16 struct {
+	Reg uint16
+}
+
+// Get returns the value in the register. It is the volatile equivalent of:
+//
+//     *r.Reg
+//
+//go:inline
+func (r *Register16) Get() uint16 {
+	return LoadUint16(&r.Reg)
+}
+
+// Set updates the register value. It is the volatile equivalent of:
+//
+//     *r.Reg = value
+//
+//go:inline
+func (r *Register16) Set(value uint16) {
+	StoreUint16(&r.Reg, value)
+}
+
+// SetBits reads the register, sets the given bits, and writes it back. It is
+// the volatile equivalent of:
+//
+//     r.Reg |= value
+//
+//go:inline
+func (r *Register16) SetBits(value uint16) {
+	StoreUint16(&r.Reg, LoadUint16(&r.Reg)|value)
+}
+
+// ClearBits reads the register, clears the given bits, and writes it back. It
+// is the volatile equivalent of:
+//
+//     r.Reg &^= value
+//
+//go:inline
+func (r *Register16) ClearBits(value uint16) {
+	StoreUint16(&r.Reg, LoadUint16(&r.Reg)&^value)
+}
+
+// HasBits reads the register and then checks to see if the passed bits are set. It
+// is the volatile equivalent of:
+//
+//     (*r.Reg & value) > 0
+//
+//go:inline
+func (r *Register16) HasBits(value uint16) bool {
+	return (r.Get() & value) > 0
+}
+
+type Register32 struct {
+	Reg uint32
+}
+
+// Get returns the value in the register. It is the volatile equivalent of:
+//
+//     *r.Reg
+//
+//go:inline
+func (r *Register32) Get() uint32 {
+	return LoadUint32(&r.Reg)
+}
+
+// Set updates the register value. It is the volatile equivalent of:
+//
+//     *r.Reg = value
+//
+//go:inline
+func (r *Register32) Set(value uint32) {
+	StoreUint32(&r.Reg, value)
+}
+
+// SetBits reads the register, sets the given bits, and writes it back. It is
+// the volatile equivalent of:
+//
+//     r.Reg |= value
+//
+//go:inline
+func (r *Register32) SetBits(value uint32) {
+	StoreUint32(&r.Reg, LoadUint32(&r.Reg)|value)
+}
+
+// ClearBits reads the register, clears the given bits, and writes it back. It
+// is the volatile equivalent of:
+//
+//     r.Reg &^= value
+//
+//go:inline
+func (r *Register32) ClearBits(value uint32) {
+	StoreUint32(&r.Reg, LoadUint32(&r.Reg)&^value)
+}
+
+// HasBits reads the register and then checks to see if the passed bits are set. It
+// is the volatile equivalent of:
+//
+//     (*r.Reg & value) > 0
+//
+//go:inline
+func (r *Register32) HasBits(value uint32) bool {
+	return (r.Get() & value) > 0
+}
@@ -0,0 +1,3 @@
+package syscall
+
+func Exit(code int)
@@ -0,0 +1,6 @@
+package testing
+
+/*
+ This is a sad stub of the upstream testing package because it doesn't compile
+ with tinygo right now.
+*/
@@ -0,0 +1,77 @@
+package testing
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+)
+
+// T is a test helper.
+type T struct {
+	name   string
+	output io.Writer
+
+	// flags the test as having failed when non-zero
+	failed int
+}
+
+// TestToCall is a reference to a test that should be called during a test suite run.
+type TestToCall struct {
+	// Name of the test to call.
+	Name string
+	// Function reference to the test.
+	Func func(*T)
+}
+
+// M is a test suite.
+type M struct {
+	// tests is a list of the test names to execute
+	Tests []TestToCall
+}
+
+// Run the test suite.
+func (m *M) Run() int {
+	failures := 0
+	for _, test := range m.Tests {
+		t := &T{
+			name:   test.Name,
+			output: &bytes.Buffer{},
+		}
+
+		fmt.Printf("=== RUN   %s\n", test.Name)
+		test.Func(t)
+
+		if t.failed == 0 {
+			fmt.Printf("--- PASS: %s\n", test.Name)
+		} else {
+			fmt.Printf("--- FAIL: %s\n", test.Name)
+		}
+		fmt.Println(t.output)
+
+		failures += t.failed
+	}
+
+	if failures > 0 {
+		fmt.Printf("exit status %d\n", failures)
+		fmt.Println("FAIL")
+	}
+	return failures
+}
+
+func TestMain(m *M) {
+	os.Exit(m.Run())
+}
+
+// Error is equivalent to Log followed by Fail
+func (t *T) Error(args ...interface{}) {
+	// This doesn't print the same as in upstream go, but works good enough
+	// TODO: buffer test output like go does
+	fmt.Fprintf(t.output, "\t")
+	fmt.Fprintln(t.output, args...)
+	t.Fail()
+}
+
+func (t *T) Fail() {
+	t.failed = 1
+}
--- a/Show More
+++ b/Show More
Author	SHA1	Message	Date
Ayke van Laethem	7d5542dda7	main: version 0.7.1 This release contains a small fix for some atsamd21-based boards to make them usable on macOS: it now allows to specify the serial port using the -port flag.	2019-07-27 10:02:10 -07:00
Ayke van Laethem	8eb6039052	ci: fix Go image on the Debian Stretch images The build broke because the images got upgraded from stretch to buster. Specify the stretch images (for now) so that it works again. We can upgrade to buster for go1.12 at a later time.	2019-07-27 09:51:38 -07:00
Trevor Rosen	64597de344	Device path at flash time for several boards	2019-07-25 10:17:16 -07:00
Ayke van Laethem	515daa7d3c	main: version 0.7.0	2019-07-17 15:36:38 +02:00
Ron Evans	ced964f039	docs: add Arduino Nano33 IoT to README Signed-off-by: Ron Evans <ron@hybridgroup.com>	2019-07-17 06:30:58 -07:00
Ayke van Laethem	8a704e43fc	os: gofmt	2019-07-15 17:53:01 +02:00
Justin Clift	847681457f	runtime: add several os package stubs	2019-07-15 01:18:37 +02:00
Ayke van Laethem	66d8899aa7	main: set the current working directory when calling an external linker In particular, while LLVM lld supports -L for linker scripts imported with the `INCLUDE` command, GNU ld does not seem to support this. This is a prerequisite for supporting the HiFive1 board in the TinyGo Playground.	2019-07-08 00:37:53 +02:00
Ayke van Laethem	b0cad7ed63	runtime: add support for math intrinsics where supported In particular, add support for a few math intrinsics for WebAssembly, but add a few intrinsics to other systems as well at the same time. Some may be missing still but will be easy to add if needed. This increases the performance of one example by 50% to 100% depending on the browser: the bottleneck was the inefficient sqrt implementation.	2019-07-08 00:32:42 +02:00
Ayke van Laethem	00cc486619	wasm: set the stack at the start of linear memory This makes sure that a stack overflow will cause a "memory access out of bounds" error instead of a corruption of a global variable. Here is more background on a very similar stack overflow protection: https://blog.japaric.io/stack-overflow-protection/	2019-07-08 00:09:59 +02:00
Ayke van Laethem	d627208c48	all: make WebAssembly initial linear memory size configurable When the target supports it, allow the (initial) heap size to be configured. Currently only supported in WebAssembly. This also changes the default heap size of WebAssembly from 64kB to 1MB.	2019-07-08 00:09:59 +02:00
Ayke van Laethem	152caa3b0a	compiler: do not create stack objects for functions that don't allocate This is a useful optimization for targets with the portable garbage collector. It isn't as big as you might guess but it does optimize functions inside the garbage collector itself (which obviously should not allocate). WebAssembly output in one test is about 1% smaller.	2019-07-08 00:02:28 +02:00
Ayke van Laethem	7ed6b45149	compiler: add the //go:noinline pragma This is directly useful to avoid some unsafety around runtime.alloc and should be useful in general. This pragma has the same form as in the main Go compiler: https://github.com/golang/go/issues/12312	2019-07-08 00:02:28 +02:00
Ayke van Laethem	c66d979ba3	compiler: avoid some stack frames when this is unnecessary Some instructions do not create new values, they transform existing values in some way (bitcast, getelementptr, etc.). Do not store them in the stack object. This lowers the size of the repulsion demo from 100kB to 98kB (with a baseline of 72kB for the leaking GC). That's a useful reduction in file size.	2019-07-08 00:02:28 +02:00
Ron Evans	fc9188a298	machine/samd21/arduino-nano33: adds support for Arduino Nano33 IoT along with mapping to NINA-W102 WiFi chip. Also adds DTR and RTS functions along with timeouts to USBCDC functions to prevent lockups. Signed-off-by: Ron Evans <ron@hybridgroup.com>	2019-07-07 18:09:05 +02:00
Ayke van Laethem	ffa38b183b	all: add HiFive1 rev B board with RISC-V architecture This page has been a big help in adding support for this new chip: https://wiki.osdev.org/HiFive-1_Bare_Bones	2019-07-07 14:03:24 +02:00
Ayke van Laethem	f0eb4eef5a	ci: make smoketests more flexible	2019-07-07 14:03:24 +02:00
Ayke van Laethem	fa928e8cd3	tools/gen-device-svd: be a bit more forgiving for stm32 svd files Some newer files have a few mistakes. Allow them to be processed.	2019-07-06 17:16:18 +02:00
Ayke van Laethem	c49d80628c	tools/gen-device-svd: refactor to make the code more declarative	2019-07-06 17:16:18 +02:00
Ayke van Laethem	af523c63d5	ci: fix cache paths for LLVM source This makes the LLVM source code cacheable again.	2019-07-06 14:57:54 +02:00
diamondburned	aabb6ba22b	main: use zversion.go and VERSION files to detect version, fixes #433	2019-07-06 02:31:49 +02:00
Ayke van Laethem	6611578ec8	compiler: remove some TODOs These have long since been implemented.	2019-07-03 21:22:12 +02:00
Ayke van Laethem	d49a363d0d	compiler: track all pointers returned by runtime.alloc In particular, track the pointers to the memory allocated for coroutine frames. Before this change, the following code would show memory corruption: https://github.com/johanbrandhorst/wasm-experiments/blob/master/canvas/main.go	2019-07-03 21:22:12 +02:00
Ayke van Laethem	385d1d0a5d	compiler,runtime: implement a portable conservative GC	2019-07-01 16:30:33 +02:00
Ayke van Laethem	00e91ec569	all: rename garbage collectors dumb -> leaking: make it more clear what this "GC" does: leak everything. marksweep -> conservative: "marksweep" is too generic, use "conservative" to differentiate between future garbage collectors: precise marksweep / mark-compact / refcounting.	2019-07-01 13:03:07 +02:00
Daniel Esteban	1fd0c8d48c	adds PowerSupplyActive to enable supply voltages to nRF52840 and (#430 ) * machine/reelboard: adds PowerSupplyActive to enable supply voltages to nRF52840 and peripherals.	2019-06-30 12:23:44 +02:00
Daniel Esteban	d34bb7e708	add reelboard pins for the epaper display and the reset pin (#429 ) * machine/reelboard: added descriptive pin names for the epaper display and the reset pin	2019-06-30 09:57:07 +02:00
Ayke van Laethem	a328bbdff3	main: small refactor in error printing Use a type switch instead of an if/else chain. This results in much more readable code.	2019-06-29 19:18:46 +02:00
Ayke van Laethem	4ecd478d82	machine: add generic board support on non-baremetal hardware Instead of trying to modify periperhals directly, external functions are called. For example, __tinygo_gpio_set sets a GPIO pin to a specified value (high or low). It is expected that binaries made this way will be linked with some extra libraries that implement support for these functions. One particularly interesting case is this experimental board simulator: https://github.com/aykevl/tinygo-play Compiling code to WebAssembly with the correct build tag for a board will enable this board to be simulated in the browser. Atmel/Microchip based SAMD boards are not currently supported, because their I2C/SPI support is somewhat uncommon and harder to support in the machine API. They may require a modification to the machine API for proper support.	2019-06-28 10:00:14 +02:00
Justin Clift	40b193f1fa	circleci: update source and build cache keys	2019-06-24 16:22:37 +02:00
Justin Clift	7fd5ec8661	Makefile: use the LLVM monorepo The -DLLVM_TOOL_CLANG_TOOLS_EXTRA_BUILD=OFF option turning off the building of the extra clang tools is required, otherwise linking the tinygo binary fails.	2019-06-24 16:22:37 +02:00
m-chichikalov	84618c45eb	Added supporting suctom TargetSpec json file via -target flag.	2019-06-20 19:10:15 +02:00
Carolyn Van Slyck	c0ff4e566d	Include test in helptext	2019-06-20 19:05:06 +02:00
Carolyn Van Slyck	ce9b21a270	Default package name to . when not specified When running tinygo build, and the positional argument for the package is not specified, default it to "."	2019-06-20 19:05:06 +02:00
Ayke van Laethem	ed7c242a09	runtime: fix a heap corruption where some blocks were not marked as reachable This is a rather critical error and I wonder why it hasn't been discovered earlier.	2019-06-20 13:32:45 +02:00
Justin Clift	46872a70b1	Trivial typo fix	2019-06-20 13:30:38 +02:00
scriptonist	e9f6e51fc8	compiler,runtime: implement string to []rune conversion Commit message by aykevl	2019-06-19 01:17:21 +02:00
Ayke van Laethem	fa5855bff5	main: add support for -tags flags	2019-06-18 16:02:20 +02:00
Ron Evans	16201c41dc	test: replace ExitStatus() with go1.11 compatible syntax Signed-off-by: Ron Evans <ron@hybridgroup.com>	2019-06-18 13:45:11 +02:00
Carolyn Van Slyck	208e1719ad	Add test command to tinygo (#243 ) * Add test command to tinygo	2019-06-18 12:23:59 +02:00
Ayke van Laethem	a3d1f1a514	all: try more locations to find Clang built-in headers This commit fixes the case where TinyGo was built with `go build` and LLVM sources were never downloaded into the TinyGo source directory.	2019-06-13 15:21:04 +02:00
Tomer Elmalem	3e1c0d90c5	Add implementation for os.Exit and syscall.Exit	2019-06-12 19:04:34 +02:00
Ayke van Laethem	b7197bcaae	compiler,runtime: implement non-blocking selects Blocking selects are much more complicated, so let's do non-blocking ones first.	2019-06-12 18:26:52 +02:00
Ayke van Laethem	8890a0f3c8	compiler,runtime: store channel size in the channel itself This may have a small effect on code size sometimes, but will simplify the implementation of the select statement.	2019-06-12 18:26:52 +02:00
Justin Clift	5be412dabe	Makefile: using an alternative LLVM build dir now works	2019-06-12 14:05:45 +02:00
Ayke van Laethem	412ec5b789	Makefile: drop the -lclangToolingRefactor library It is not necessary and does not exist in LLVM 9.	2019-06-12 08:43:08 +02:00
Ayke van Laethem	b0e767c4a7	compiler: move global handling from ir to compiler package This is part of a larger rafactor that tries to shrink the ir package and in general tries to shrink the amount of state that is kept around in the compiler. The end goal is being able to compile packages independent of each other, linking them together in a later stage. Along the way, it cleans up lots of old cruft that has accumulated over the months. This refactor also results in globals being loaded lazily. This may be a problem for some specific programs but will probably change back in a commit in the near future.	2019-06-08 22:17:09 +02:00
Ayke van Laethem	6b5b4a681d	compiler: refactor named types to create them lazily This commit refactors named types to be created lazily. Instead of defining all types in advance, do it only when necessary.	2019-06-08 22:17:09 +02:00
Ayke van Laethem	88bb61f287	compiler: return a valid (undef) value from a unsupported select Returning a nil value may lead to problems later on. Just return undef here, so that further compilation will at least be safe (the result will be discarded anyway).	2019-06-08 21:48:05 +02:00
Ayke van Laethem	e169e3b996	compiler: remove superfluous 'err' result in decodeFuncValue	2019-06-08 21:48:05 +02:00
Ayke van Laethem	aa8957dd05	compiler: support non-constant syscall numbers Not all syscalls use constant numbers.	2019-06-08 21:48:05 +02:00
Ayke van Laethem	8e5731aee7	compiler: add support for pointers as map keys	2019-06-08 21:48:05 +02:00
Justin Clift	0cc35b6188	Add a note to use --recursive when cloning the TinyGo repo	2019-06-08 22:50:14 +10:00
Ayke van Laethem	5cf7fba1a4	compiler: remove //go:volatile support	2019-06-06 19:46:49 +02:00
Ayke van Laethem	e67506ee68	arm: update to avoid //go:volatile This change results in changes to all smoketests for Cortex-M based chips: they get a bit smaller (32-48 bytes). I'm not sure why but probably because the inliner made a different inlining decision. There was a similar effect when files generated from SVD files switched to the new volatile types so it's probably harmless.	2019-06-06 19:46:49 +02:00
Ayke van Laethem	f2c205a008	machine: update ringbuffer to use runtime/volatile.Register8 This avoids the //go:volatile pragma, which will be removed soon. There were no changes to the output of the smoke tests.	2019-06-06 19:46:49 +02:00
Ayke van Laethem	c84c625585	runtime: update to avoid //go:volatile There was exactly one change in the output of the smoke tests: examples/test. However, it still runs just fine on a PCA10040.	2019-06-06 19:46:49 +02:00
Ayke van Laethem	9673ad3774	all: move Register{8,16,32} values into runtime/volatile This avoids duplication of code. None of the smoke tests have changed their output.	2019-06-06 19:46:49 +02:00
Ayke van Laethem	66aca428ba	compiler: rename import path if it lies in TINYGOPATH This allows importing (for example) both "github.com/tinygo-org/tinygo/src/machine" and "machine" without issues. The former is renamed to just "machine".	2019-06-06 16:01:25 +02:00
Ayke van Laethem	ec87811420	compiler: do not panic on duplicate functions Instead, show a regular error message. This is much more user-friendly.	2019-06-06 16:01:25 +02:00
Ayke van Laethem	776dc1e0d9	main: show a better error when version detection of GOROOT failed	2019-06-06 13:59:37 +02:00
Ron Evans	beea2f1f30	docs: add note to current/future contributors to please start by opening a GH issue to avoid duplication of effort Signed-off-by: Ron Evans <ron@hybridgroup.com>	2019-06-06 12:09:17 +02:00
Ayke van Laethem	5f9c683abf	main: return an error when running a command failed	2019-06-05 09:08:44 +02:00
Ayke van Laethem	0ce4d90779	cgo: add support for anonymous structs	2019-06-03 20:01:47 +02:00
Tomer Elmalem	1047c9bd05	reflect: stub out reflect.New and reflect.Zero	2019-06-03 19:26:47 +02:00
Ayke van Laethem	1d7cc2c242	cgo: add support for bitfields using generated getters and setters	2019-06-03 16:13:19 +02:00
Ayke van Laethem	23c8d15847	main: add -dev suffix to version	2019-06-03 16:09:29 +02:00