runtime: avoid heap allocs for plain errors

builder/testdata/binary-size.txt

@@ -1,4 +1,4 @@
 target      package               code rodata data  bss
-hifive1b    examples/echo         4533    323    0 2268
-microbit    examples/serial       3002    382    8 2264
-wioterminal examples/pininterrupt 8331   1717  148 7496
+hifive1b    examples/echo         4526    346    0 2268
+microbit    examples/serial       2993    391    8 2264
+wioterminal examples/pininterrupt 8309   1739  148 7496

main_test.go

@@ -168,6 +168,39 @@ func TestBuild(t *testing.T) {
 			runTestWithConfig("print.go", t, opts, nil, nil)
 		})
 
+		t.Run("gc=none-runtime-panic", func(t *testing.T) {
+			t.Parallel()
+			opts := optionsFromTarget("cortex-m-qemu", sema)
+			opts.GC = "none"
+			opts.Scheduler = "none"
+			config, err := builder.NewConfig(&opts)
+			if err != nil {
+				t.Fatal(err)
+			}
+			err = Build("testdata/trivialpanic.go", t.TempDir()+"/trivialpanic", config)
+			if err != nil {
+				w := &bytes.Buffer{}
+				diagnostics.CreateDiagnostics(err).WriteTo(w, "")
+				t.Fatal(w.String())
+			}
+		})
+
+		t.Run("scheduler=none-uefi", func(t *testing.T) {
+			t.Parallel()
+			opts := optionsFromTarget("uefi-amd64", sema)
+			opts.Scheduler = "none"
+			config, err := builder.NewConfig(&opts)
+			if err != nil {
+				t.Fatal(err)
+			}
+			err = Build("testdata/trivialpanic.go", t.TempDir()+"/trivialpanic", config)
+			if err != nil {
+				w := &bytes.Buffer{}
+				diagnostics.CreateDiagnostics(err).WriteTo(w, "")
+				t.Fatal(w.String())
+			}
+		})
+
 		t.Run("ldflags", func(t *testing.T) {
 			t.Parallel()
 			opts := optionsFromTarget("", sema)

src/internal/task/task_none.go

@@ -7,11 +7,11 @@ import "unsafe"
 // There is only one goroutine so the task struct can be a global.
 var mainTask Task
 
-//go:linkname runtimePanic runtime.runtimePanic
-func runtimePanic(str string)
+//go:linkname runtimePanicSchedulerDisabled runtime.runtimePanicSchedulerDisabled
+func runtimePanicSchedulerDisabled()
 
 func Pause() {
-	runtimePanic("scheduler is disabled")
+	runtimePanicSchedulerDisabled()
 }
 
 func Current() *Task {
@@ -22,13 +22,13 @@ func Current() *Task {
 //go:noinline
 func start(fn uintptr, args unsafe.Pointer, stackSize uintptr) {
 	// The compiler will error if this is reachable.
-	runtimePanic("scheduler is disabled")
+	runtimePanicSchedulerDisabled()
 }
 
 type state struct{}
 
 func (t *Task) Resume() {
-	runtimePanic("scheduler is disabled")
+	runtimePanicSchedulerDisabled()
 }
 
 // OnSystemStack returns whether the caller is running on the system stack.
@@ -39,7 +39,7 @@ func OnSystemStack() bool {
 
 func SystemStack() uintptr {
 	// System stack is the current stack, so this shouldn't be called.
-	runtimePanic("scheduler is disabled")
+	runtimePanicSchedulerDisabled()
 	return 0 // unreachable
 }
 

src/internal/task/task_none_uefi.go

@@ -4,5 +4,5 @@ package task
 
 //go:export tinygo_task_exit
 func taskExit() {
-	runtimePanic("scheduler is disabled")
+	runtimePanicSchedulerDisabled()
 }

src/runtime/chan.go

@@ -207,7 +207,7 @@ func (ch *channel) trySend(value unsafe.Pointer) (sent bool, wake *task.Task) {
 		// Note: we cannot currently recover from this panic.
 		// There's some state in the select statement especially that would be
 		// corrupted if we allowed recovering from this panic.
-		runtimePanic("send on closed channel")
+		runtimePanic(errSendOnClosedChannel)
 	}
 
 	// There is no value in the buffer and we have a receiver available. Copy
@@ -266,7 +266,7 @@ func chanSend(ch *channel, value unsafe.Pointer, op *channelOp) {
 	// closed while sending).
 	if t.DataUint32() == chanOperationClosed {
 		// Oops, this channel was closed while sending!
-		runtimePanic("send on closed channel")
+		runtimePanic(errSendOnClosedChannel)
 	}
 }
 
@@ -349,7 +349,7 @@ func chanRecv(ch *channel, value unsafe.Pointer, op *channelOp) bool {
 func chanClose(ch *channel) {
 	if ch == nil {
 		// Not allowed by the language spec.
-		runtimePanic("close of nil channel")
+		runtimePanic(errCloseNilChannel)
 	}
 
 	mask := interrupt.Disable()
@@ -359,7 +359,7 @@ func chanClose(ch *channel) {
 		// Not allowed by the language spec.
 		ch.lock.Unlock()
 		interrupt.Restore(mask)
-		runtimePanic("close of closed channel")
+		runtimePanic(errCloseClosedChannel)
 	}
 
 	// Collect waiters and wake them after unlocking.

src/runtime/error.go

@@ -12,3 +12,30 @@ type plainError string
 
 func (e plainError) Error() string { return string(e) }
 func (e plainError) RuntimeError() {}
+
+const (
+	errNilPointer          = plainError("nil pointer dereference")
+	errNilMap              = plainError("assignment to entry in nil map")
+	errIndexOutOfRange     = plainError("index out of range")
+	errSliceOutOfRange     = plainError("slice out of range")
+	errSliceToArray        = plainError("slice smaller than array")
+	errUnsafeSliceLength   = plainError("unsafe.Slice/String: len out of range")
+	errChannelTooBig       = plainError("new channel is too big")
+	errNegativeShift       = plainError("negative shift")
+	errDivideByZero        = plainError("divide by zero")
+	errBlockingExported    = plainError("trying to do blocking operation in exported function")
+	errTimersUnsupported   = plainError("timers not supported without a scheduler")
+	errIntegerOverflow     = plainError("integer overflow")
+	errUnsupportedSignal   = plainError("unsupported signal number")
+	errUnsupportedExit     = plainError("unsupported: syscall.Exit")
+	errSendOnClosedChannel = plainError("send on closed channel")
+	errCloseNilChannel     = plainError("close of nil channel")
+	errCloseClosedChannel  = plainError("close of closed channel")
+	errWasmBeforeInit      = plainError("//go:wasmexport function called before runtime initialization")
+	errWasmAfterMain       = plainError("//go:wasmexport function called after main.main returned")
+	errWasmDidNotFinish    = plainError("//go:wasmexport function did not finish")
+	errUncomparable        = plainError("comparing un-comparable type")
+	errTypeAssert          = plainError("type assert failed")
+	errSchedulerDisabled   = plainError("scheduler is disabled")
+	errOutOfMemory         = plainError("out of memory")
+)

src/runtime/gc_leaking.go

@@ -49,7 +49,7 @@ func alloc(size uintptr, layout unsafe.Pointer) unsafe.Pointer {
 	heapptr += size
 	if heapptr < addr {
 		// The allocation size overflowed the heap pointer.
-		runtimePanic("out of memory")
+		runtimePanic(errOutOfMemory)
 	}
 	for heapptr > heapEnd {
 		// Try to increase the heap and check again.

src/runtime/hashmap.go

@@ -832,7 +832,7 @@ func hashmapInterfaceHash(itf interface{}, seed uintptr) uint32 {
 		}
 		return hash
 	default:
-		runtimePanic("comparing un-comparable type")
+		runtimePanic(errUncomparable)
 		return 0 // unreachable
 	}
 }

src/runtime/interface.go

@@ -77,7 +77,7 @@ func reflectValueEqual(x, y reflectlite.Value) bool {
 	case reflectlite.Interface:
 		return reflectValueEqual(x.Elem(), y.Elem())
 	default:
-		runtimePanic("comparing un-comparable type")
+		runtimePanic(errUncomparable)
 		return false // unreachable
 	}
 }
@@ -86,7 +86,7 @@ func reflectValueEqual(x, y reflectlite.Value) bool {
 // returns false.
 func interfaceTypeAssert(ok bool) {
 	if !ok {
-		runtimePanic("type assert failed")
+		runtimePanic(errTypeAssert)
 	}
 }
 

src/runtime/panic.go

@@ -84,11 +84,11 @@ func panicOrGoexit(message interface{}, panicking panicState) {
 	abort()
 }
 
-// Cause a runtime panic, which is (currently) always a string.
-func runtimePanic(msg string) {
-	// As long as this function is inined, llvm.returnaddress(0) will return
+// Cause a recoverable runtime panic.
+func runtimePanic(err Error) {
+	// As long as this function is inlined, llvm.returnaddress(0) will return
 	// something sensible.
-	runtimePanicAt(returnAddress(0), msg)
+	runtimePanicAt(returnAddress(0), err)
 }
 
 // runtimeFatal terminates for runtime failures that cannot safely be
@@ -103,7 +103,7 @@ func runtimeFatal(msg string) {
 	abort()
 }
 
-func runtimePanicAt(addr unsafe.Pointer, msg string) {
+func runtimePanicAt(addr unsafe.Pointer, err Error) {
 	if panicStrategy() == tinygo.PanicStrategyTrap {
 		trap()
 	}
@@ -112,7 +112,7 @@ func runtimePanicAt(addr unsafe.Pointer, msg string) {
 		if frame != nil {
 			// Use the normal panic mechanism so that this runtime error
 			// can be recovered with recover().
-			frame.PanicValue = plainError(msg)
+			frame.PanicValue = err
 			frame.Panicking = panicTrue | (frame.Panicking & panicGoexit)
 			tinygo_longjmp(frame)
 			// unreachable
@@ -128,11 +128,15 @@ func runtimePanicAt(addr unsafe.Pointer, msg string) {
 	} else {
 		printstring("panic: runtime error: ")
 	}
-	printstring(msg)
+	printstring(err.Error())
 	printnl()
 	abort()
 }
 
+func runtimePanicSchedulerDisabled() {
+	runtimePanicAt(returnAddress(0), errSchedulerDisabled)
+}
+
 // Called at the start of a function that includes a deferred call.
 // It gets passed in the stack-allocated defer frame and configures it.
 // Note that the frame is not zeroed yet, so we need to initialize all values
@@ -220,54 +224,54 @@ func _recover(useParentFrame bool) interface{} {
 
 // Panic when trying to dereference a nil pointer.
 func nilPanic() {
-	runtimePanicAt(returnAddress(0), "nil pointer dereference")
+	runtimePanicAt(returnAddress(0), errNilPointer)
 }
 
 // Panic when trying to add an entry to a nil map
 func nilMapPanic() {
-	runtimePanicAt(returnAddress(0), "assignment to entry in nil map")
+	runtimePanicAt(returnAddress(0), errNilMap)
 }
 
 // Panic when trying to access an array or slice out of bounds.
 func lookupPanic() {
-	runtimePanicAt(returnAddress(0), "index out of range")
+	runtimePanicAt(returnAddress(0), errIndexOutOfRange)
 }
 
 // Panic when trying to slice a slice out of bounds.
 func slicePanic() {
-	runtimePanicAt(returnAddress(0), "slice out of range")
+	runtimePanicAt(returnAddress(0), errSliceOutOfRange)
 }
 
 // Panic when trying to convert a slice to an array pointer (Go 1.17+) and the
 // slice is shorter than the array.
 func sliceToArrayPointerPanic() {
-	runtimePanicAt(returnAddress(0), "slice smaller than array")
+	runtimePanicAt(returnAddress(0), errSliceToArray)
 }
 
 // Panic when calling unsafe.Slice() (Go 1.17+) or unsafe.String() (Go 1.20+)
 // with a len that's too large (which includes if the ptr is nil and len is
 // nonzero).
 func unsafeSlicePanic() {
-	runtimePanicAt(returnAddress(0), "unsafe.Slice/String: len out of range")
+	runtimePanicAt(returnAddress(0), errUnsafeSliceLength)
 }
 
 // Panic when trying to create a new channel that is too big.
 func chanMakePanic() {
-	runtimePanicAt(returnAddress(0), "new channel is too big")
+	runtimePanicAt(returnAddress(0), errChannelTooBig)
 }
 
 // Panic when a shift value is negative.
 func negativeShiftPanic() {
-	runtimePanicAt(returnAddress(0), "negative shift")
+	runtimePanicAt(returnAddress(0), errNegativeShift)
 }
 
 // Panic when there is a divide by zero.
 func divideByZeroPanic() {
-	runtimePanicAt(returnAddress(0), "divide by zero")
+	runtimePanicAt(returnAddress(0), errDivideByZero)
 }
 
 func blockingPanic() {
-	runtimePanicAt(returnAddress(0), "trying to do blocking operation in exported function")
+	runtimePanicAt(returnAddress(0), errBlockingExported)
 }
 
 //go:linkname fips_fatal crypto/internal/fips140.fatal

src/runtime/runtime_tinygowasm_unknown.go

@@ -34,7 +34,7 @@ func syscall_Exit(code int) {
 	// Because this is the "unknown" target we can't call an exit function.
 	// But we also can't just return since the program will likely expect this
 	// function to never return. So we panic instead.
-	runtimePanic("unsupported: syscall.Exit")
+	runtimePanic(errUnsupportedExit)
 }
 
 // There is not yet any support for any form of parallelism on WebAssembly, so these

src/runtime/runtime_unix.go

@@ -151,9 +151,9 @@ func tinygo_sigpanic() {
 	sig := tinygo_caught_signal
 	switch sig {
 	case sig_SIGSEGV, sig_SIGBUS:
-		runtimePanic("nil pointer dereference")
+		runtimePanic(errNilPointer)
 	case sig_SIGFPE:
-		runtimePanic("divide by zero")
+		runtimePanic(errDivideByZero)
 	default:
 		runtimeFatal("signal")
 	}
@@ -382,7 +382,7 @@ func signal_enable(s uint32) {
 	if s >= 32 {
 		// TODO: to support higher signal numbers, we need to turn
 		// receivedSignals into a uint32 array.
-		runtimePanicAt(returnAddress(0), "unsupported signal number")
+		runtimePanicAt(returnAddress(0), errUnsupportedSignal)
 	}
 
 	// This is intentonally a non-atomic store. This is safe, since hasSignals
@@ -399,7 +399,7 @@ func signal_ignore(s uint32) {
 	if s >= 32 {
 		// TODO: to support higher signal numbers, we need to turn
 		// receivedSignals into a uint32 array.
-		runtimePanicAt(returnAddress(0), "unsupported signal number")
+		runtimePanicAt(returnAddress(0), errUnsupportedSignal)
 	}
 	tinygo_signal_ignore(s)
 }
@@ -409,7 +409,7 @@ func signal_disable(s uint32) {
 	if s >= 32 {
 		// TODO: to support higher signal numbers, we need to turn
 		// receivedSignals into a uint32 array.
-		runtimePanicAt(returnAddress(0), "unsupported signal number")
+		runtimePanicAt(returnAddress(0), errUnsupportedSignal)
 	}
 	tinygo_signal_disable(s)
 }

src/runtime/runtime_wasmentry.go

@@ -66,9 +66,9 @@ var initializeCalled bool
 func wasmExportCheckRun() {
 	switch {
 	case !initializeCalled:
-		runtimePanic("//go:wasmexport function called before runtime initialization")
+		runtimePanic(errWasmBeforeInit)
 	case mainExited:
-		runtimePanic("//go:wasmexport function called after main.main returned")
+		runtimePanic(errWasmAfterMain)
 	}
 }
 
@@ -81,6 +81,6 @@ func wasmExportCheckRun() {
 func wasmExportRun(done *bool) {
 	scheduler(true)
 	if !*done {
-		runtimePanic("//go:wasmexport function did not finish")
+		runtimePanic(errWasmDidNotFinish)
 	}
 }

src/runtime/runtime_windows.go

@@ -315,11 +315,11 @@ func tinygo_init_exception_handler()
 func tinygo_sigpanic_windows(exceptionCode int32) {
 	switch uint32(exceptionCode) {
 	case _EXCEPTION_ACCESS_VIOLATION, _EXCEPTION_IN_PAGE_ERROR:
-		runtimePanic("nil pointer dereference")
+		runtimePanic(errNilPointer)
 	case _EXCEPTION_INT_DIVIDE_BY_ZERO:
-		runtimePanic("divide by zero")
+		runtimePanic(errDivideByZero)
 	case _EXCEPTION_INT_OVERFLOW:
-		runtimePanic("integer overflow")
+		runtimePanic(errIntegerOverflow)
 	default:
 		runtimeFatal("unknown exception")
 	}

src/runtime/scheduler_none.go

@@ -60,15 +60,15 @@ func NumCPU() int {
 }
 
 func addTimer(tim *timerNode) {
-	runtimePanic("timers not supported without a scheduler")
+	runtimePanic(errTimersUnsupported)
 }
 
 func reAddTimer(tn *timerNode) {
-	runtimePanic("timers not supported without a scheduler")
+	runtimePanic(errTimersUnsupported)
 }
 
 func removeTimer(tim *timer) *timerNode {
-	runtimePanic("timers not supported without a scheduler")
+	runtimePanic(errTimersUnsupported)
 	return nil
 }
 

testdata/recover.go

@@ -313,12 +313,29 @@ func recoverMustPanic(name string, f func()) {
 	f()
 }
 
+func recoverRuntimeErrorValue(f func()) {
+	defer func() {
+		r := recover()
+		err, ok := r.(runtime.Error)
+		if ok {
+			println("  recovered runtime error:", err.Error())
+		} else {
+			println("  failed runtime error:", r)
+		}
+	}()
+	f()
+}
+
 // Test recovering from nil map assignment and closed channel send.
 func recoverNilMapAndChan() {
 	recoverMustPanic("nil map", func() {
 		var m map[string]int
 		m["x"] = 1
 	})
+	recoverRuntimeErrorValue(func() {
+		var m map[string]int
+		m["x"] = 1
+	})
 	recoverMustPanic("closed chan", func() {
 		ch := make(chan int)
 		close(ch)

testdata/recover.txt

@@ -52,6 +52,7 @@ outer recovered: repanic value
 
 # recover from nil map and closed channel
   recovered: nil map
+  recovered runtime error: assignment to entry in nil map
   recovered: closed chan
   recovered: close nil chan