runtime: implement command line arguments in hosted environments

Implement command line arguments for Linux, MacOS and WASI.

src/runtime/runtime.go

@@ -23,7 +23,9 @@ func GOROOT() string {
 	return "/usr/local/go"
 }
 
-// TODO: fill with real args.
+// This is the default set of arguments, if nothing else has been set.
+// This may be overriden by modifying this global at runtime init (for example,
+// on Linux where there are real command line arguments).
 var args = []string{"/proc/self/exe"}
 
 //go:linkname os_runtime_args os.runtime_args
@@ -47,6 +49,9 @@ func memmove(dst, src unsafe.Pointer, size uintptr)
 // llvm.memset.p0i8.i32(ptr, 0, size, false).
 func memzero(ptr unsafe.Pointer, size uintptr)
 
+//export strlen
+func strlen(ptr unsafe.Pointer) uintptr
+
 // Compare two same-size buffers for equality.
 func memequal(x, y unsafe.Pointer, n uintptr) bool {
 	for i := uintptr(0); i < n; i++ {

src/runtime/runtime_unix.go

@@ -43,9 +43,34 @@ func postinit() {}
 
 // Entry point for Go. Initialize all packages and call main.main().
 //export main
-func main() int {
+func main(argc int32, argv *unsafe.Pointer) int {
 	preinit()
 
+	// Make args global big enough so that it can store all command line
+	// arguments. Unfortunately this has to be done with some magic as the heap
+	// is not yet initialized.
+	argsSlice := (*struct {
+		ptr unsafe.Pointer
+		len uintptr
+		cap uintptr
+	})(unsafe.Pointer(&args))
+	argsSlice.ptr = malloc(uintptr(argc) * (unsafe.Sizeof(uintptr(0))) * 3)
+	argsSlice.len = 0
+	argsSlice.cap = uintptr(argc)
+
+	// Initialize command line parameters.
+	for *argv != nil {
+		// Convert the C string to a Go string.
+		length := strlen(*argv)
+		argString := _string{
+			length: length,
+			ptr:    (*byte)(*argv),
+		}
+		args = append(args, *(*string)(unsafe.Pointer(&argString)))
+		// This is the Go equivalent of "argc++" in C.
+		argv = (*unsafe.Pointer)(unsafe.Pointer(uintptr(unsafe.Pointer(argv)) + unsafe.Sizeof(argv)))
+	}
+
 	// Obtain the initial stack pointer right before calling the run() function.
 	// The run function has been moved to a separate (non-inlined) function so
 	// that the correct stack pointer is read.
@@ -65,9 +90,6 @@ func runMain() {
 //go:extern environ
 var environ *unsafe.Pointer
 
-//export strlen
-func strlen(ptr unsafe.Pointer) uintptr
-
 //go:linkname syscall_runtime_envs syscall.runtime_envs
 func syscall_runtime_envs() []string {
 	// Count how many environment variables there are.

src/runtime/runtime_wasm_js.go

@@ -15,6 +15,11 @@ func _start() {
 	run()
 }
 
+//go:linkname syscall_runtime_envs syscall.runtime_envs
+func syscall_runtime_envs() []string {
+	return nil
+}
+
 var handleEvent func()
 
 //go:linkname setEventHandler syscall/js.setEventHandler

src/runtime/runtime_wasm_wasi.go

@@ -21,6 +21,33 @@ func _start() {
 	run()
 }
 
+// Read the command line arguments from WASI.
+// For example, they can be passed to a program with wasmtime like this:
+//
+//     wasmtime ./program.wasm arg1 arg2
+func init() {
+	// 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)
+
+	// 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))
+	}
+}
+
 func ticksToNanoseconds(ticks timeUnit) int64 {
 	return int64(ticks)
 }
@@ -62,7 +89,15 @@ func ticks() timeUnit {
 	return timeUnit(nano)
 }
 
-// Implementations of wasi_unstable APIs
+// Implementations of WASI APIs
+
+//go:wasm-module wasi_snapshot_preview1
+//export args_get
+func args_get(argv *unsafe.Pointer, argv_buf unsafe.Pointer) (errno uint16)
+
+//go:wasm-module wasi_snapshot_preview1
+//export args_sizes_get
+func args_sizes_get(argc *uint32, argv_buf_size *uint32) (errno uint16)
 
 //go:wasm-module wasi_snapshot_preview1
 //export clock_time_get