wasm: use wasip1 API for parameter/env passing

Instead of hardcoding the command line parameters and the environment
variables in the binary, pass them at runtime to Node.js and use the
WASIp1 API to retrieve them in wasm_exec.js.

The only real benefit right now is that it becomes possible to change
`go.argv` and `go.env` before running a wasm binary.

This also changes the syscall package for GOOS=js: it now becomes more
like a libc (using wasi-libc), which means error values like
`syscall.EEXIST` will actually match the one returned by the relevant
libc function.

Wasm binary size for packages that import the os package will be
increased somewhat.

main.go

@@ -770,12 +770,11 @@ func Run(pkgName string, options *compileopts.Options, cmdArgs []string) error {
 // for the given emulator.
 func buildAndRun(pkgName string, config *compileopts.Config, stdout io.Writer, cmdArgs, environmentVars []string, timeout time.Duration, run func(cmd *exec.Cmd, result builder.BuildResult) error) (builder.BuildResult, error) {
 	// Determine whether we're on a system that supports environment variables
-	// and command line parameters (operating systems, WASI) or not (baremetal,
+	// and command line parameters (operating systems, WASI) or not (baremetal).
-	// WebAssembly in the browser). If we're on a system without an environment,
+	// If we're on a system without an environment, we need to pass command line
-	// we need to pass command line arguments and environment variables through
+	// arguments and environment variables through global variables (built into
-	// global variables (built into the binary directly) instead of the
+	// the binary directly) instead of the conventional way.
-	// conventional way.
+	needsEnvInVars := false
-	needsEnvInVars := config.GOOS() == "js"
 	for _, tag := range config.BuildTags() {
 		if tag == "baremetal" {
 			needsEnvInVars = true

src/runtime/nonhosted.go

@@ -1,4 +1,4 @@
-//go:build baremetal || js || wasm_unknown
+//go:build baremetal || wasm_unknown
 
 package runtime
 

src/runtime/runtime_tinygowasm.go

@@ -29,6 +29,44 @@ func proc_exit(exitcode uint32)
 //export __stdio_exit
 func __stdio_exit()
 
+var args []string
+
+//go:linkname os_runtime_args os.runtime_args
+func os_runtime_args() []string {
+	if args == nil {
+		// Read the number of args (argc) and the buffer size required to store
+		// all these args (argv).
+		var argc, argv_buf_size uint32
+		args_sizes_get(&argc, &argv_buf_size)
+		if argc == 0 {
+			return nil
+		}
+
+		// Obtain the command line arguments
+		argsSlice := make([]unsafe.Pointer, argc)
+		buf := make([]byte, argv_buf_size)
+		args_get(&argsSlice[0], unsafe.Pointer(&buf[0]))
+
+		// Convert the array of C strings to an array of Go strings.
+		args = make([]string, argc)
+		for i, cstr := range argsSlice {
+			length := strlen(cstr)
+			argString := _string{
+				length: length,
+				ptr:    (*byte)(cstr),
+			}
+			args[i] = *(*string)(unsafe.Pointer(&argString))
+		}
+	}
+	return args
+}
+
+//go:wasmimport wasi_snapshot_preview1 args_get
+func args_get(argv *unsafe.Pointer, argv_buf unsafe.Pointer) (errno uint16)
+
+//go:wasmimport wasi_snapshot_preview1 args_sizes_get
+func args_sizes_get(argc *uint32, argv_buf_size *uint32) (errno uint16)
+
 const (
 	putcharBufferSize = 120
 	stdout            = 1

src/runtime/runtime_wasip1.go

@@ -2,10 +2,6 @@
 
 package runtime
 
-import (
-	"unsafe"
-)
-
 type timeUnit int64
 
 // libc constructors
@@ -21,38 +17,6 @@ func init() {
 	__wasm_call_ctors()
 }
 
-var args []string
-
-//go:linkname os_runtime_args os.runtime_args
-func os_runtime_args() []string {
-	if args == nil {
-		// Read the number of args (argc) and the buffer size required to store
-		// all these args (argv).
-		var argc, argv_buf_size uint32
-		args_sizes_get(&argc, &argv_buf_size)
-		if argc == 0 {
-			return nil
-		}
-
-		// Obtain the command line arguments
-		argsSlice := make([]unsafe.Pointer, argc)
-		buf := make([]byte, argv_buf_size)
-		args_get(&argsSlice[0], unsafe.Pointer(&buf[0]))
-
-		// Convert the array of C strings to an array of Go strings.
-		args = make([]string, argc)
-		for i, cstr := range argsSlice {
-			length := strlen(cstr)
-			argString := _string{
-				length: length,
-				ptr:    (*byte)(cstr),
-			}
-			args[i] = *(*string)(unsafe.Pointer(&argString))
-		}
-	}
-	return args
-}
-
 func ticksToNanoseconds(ticks timeUnit) int64 {
 	return int64(ticks)
 }
@@ -97,12 +61,6 @@ func beforeExit() {
 
 // Implementations of WASI APIs
 
-//go:wasmimport wasi_snapshot_preview1 args_get
-func args_get(argv *unsafe.Pointer, argv_buf unsafe.Pointer) (errno uint16)
-
-//go:wasmimport wasi_snapshot_preview1 args_sizes_get
-func args_sizes_get(argc *uint32, argv_buf_size *uint32) (errno uint16)
-
 //go:wasmimport wasi_snapshot_preview1 clock_time_get
 func clock_time_get(clockid uint32, precision uint64, time *uint64) (errno uint16)
 

src/syscall/env_libc.go

@@ -1,4 +1,4 @@
-//go:build nintendoswitch || wasip1
+//go:build js || nintendoswitch || wasip1
 
 package syscall
 

src/syscall/errno_other.go

@@ -1,4 +1,4 @@
-//go:build !wasip1 && !wasip2
+//go:build !js && !wasip1 && !wasip2
 
 package syscall
 

src/syscall/errno_wasmlibc.go

@@ -1,4 +1,4 @@
-//go:build wasip1
+//go:build js || wasip1
 
 package syscall
 

src/syscall/syscall_libc.go

@@ -1,4 +1,4 @@
-//go:build nintendoswitch || wasip1 || wasip2
+//go:build js || nintendoswitch || wasip1 || wasip2
 
 package syscall
 

src/syscall/syscall_libc_wasi.go

@@ -1,4 +1,4 @@
-//go:build wasip1 || wasip2
+//go:build js || wasip1 || wasip2
 
 package syscall
 

src/syscall/syscall_nonhosted.go

@@ -1,4 +1,4 @@
-//go:build baremetal || js || wasm_unknown
+//go:build baremetal || wasm_unknown
 
 package syscall
 

src/syscall/tables_nonhosted.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build baremetal || nintendoswitch || js || wasm_unknown
+//go:build baremetal || nintendoswitch || wasm_unknown
 
 package syscall
 

targets/wasm_exec.js

@@ -135,6 +135,8 @@
 
 	global.Go = class {
 		constructor() {
+			this.argv = ["js"];
+			this.env = {};
 			this._callbackTimeouts = new Map();
 			this._nextCallbackTimeoutID = 1;
 
@@ -235,9 +237,58 @@
 				return decoder.decode(new DataView(this._inst.exports.memory.buffer, ptr, len));
 			}
 
+			const storeStringArraySizes = (array, num_ptr, buf_size_ptr) => {
+				let buf_size = 0;
+				for (let s of array) {
+					buf_size += s.length + 1;
+				}
+				mem().setUint32(num_ptr, array.length, true);
+				mem().setUint32(buf_size_ptr, buf_size, true);
+			}
+
+			const storeStringArray = (array, ptrs_ptr, buf_ptr) => {
+				for (let s of array) {
+					// Put string data in buffer.
+					let data = encoder.encode(s);
+					let dest = new Uint8Array(this._inst.exports.memory.buffer, buf_ptr, data.length);
+					dest.set(data);
+					mem().setUint8(buf_ptr+data.length, 0);
+
+					// Put pointer to buffer in pointers array.
+					mem().setUint32(ptrs_ptr, buf_ptr, true);
+
+					// Advance to the next element in the array.
+					ptrs_ptr += 4;
+					buf_ptr += data.length + 1;
+				}
+			}
+
+			const envArray = () => {
+				let array = [];
+				for (let [key, value] of Object.entries(this.env)) {
+					array.push(`${key}=${value}`);
+				}
+				return array;
+			}
+
 			const timeOrigin = Date.now() - performance.now();
 			this.importObject = {
 				wasi_snapshot_preview1: {
+					args_sizes_get: (argc_ptr, argv_buf_size_ptr) => {
+						storeStringArraySizes(this.argv, argc_ptr, argv_buf_size_ptr);
+						return 0;
+					},
+					args_get: (argv_ptr, argv_buf_ptr) => {
+						storeStringArray(this.argv, argv_ptr, argv_buf_ptr);
+						return 0;
+					},
+					environ_get: (env_ptr, env_buf_ptr) => {
+						storeStringArray(envArray(), env_ptr, env_buf_ptr);
+					},
+					environ_sizes_get: (env_ptr, env_buf_size_ptr) => {
+						storeStringArraySizes(envArray(), env_ptr, env_buf_size_ptr);
+						return 0;
+					},
 					// https://github.com/WebAssembly/WASI/blob/main/phases/snapshot/docs.md#fd_write
 					fd_write: function(fd, iovs_ptr, iovs_len, nwritten_ptr) {
 						let nwritten = 0;
@@ -504,12 +555,14 @@
 		global.process.versions &&
 		!global.process.versions.electron
 	) {
-		if (process.argv.length != 3) {
+		if (process.argv.length < 3) {
 			console.error("usage: go_js_wasm_exec [wasm binary] [arguments]");
 			process.exit(1);
 		}
 
 		const go = new Go();
+		go.argv = process.argv.slice(2);
+		go.env = process.env;
 		WebAssembly.instantiate(fs.readFileSync(process.argv[2]), go.importObject).then((result) => {
 			return go.run(result.instance);
 		}).catch((err) => {