os,runtime: make sure executable path is fully resolved at process init

Author: dgryski

src/os/executable_darwin.go

@@ -6,14 +6,5 @@ package os
 func runtime_executable_path() string
 
 func Executable() (string, error) {
-	p := runtime_executable_path()
-	if p != "" && p[0] == '/' {
-		// absolute path
-		return p, nil
-	}
-	cwd, err := Getwd()
-	if err != nil {
-		return "", err
-	}
-	return joinPath(cwd, p), nil
+	return runtime_executable_path(), nil
 }

src/runtime/os_darwin.go

@@ -232,10 +232,18 @@ func call_syscall6X(fn, a1, a2, a3, a4, a5, a6 uintptr) uintptr
 
 //go:linkname os_runtime_executable_path os.runtime_executable_path
 func os_runtime_executable_path() string {
-	argv := (*unsafe.Pointer)(unsafe.Pointer(main_argv))
+	return executablePath
+}
+
+var executablePath string
 
+func platform_argv(argc int32, argv *unsafe.Pointer) {
+	executablePath = executable_path(argc, argv)
+}
+
+func executable_path(argc int32, argv *unsafe.Pointer) string {
 	// skip over argv
-	argv = (*unsafe.Pointer)(unsafe.Add(unsafe.Pointer(argv), (uintptr(main_argc)+1)*unsafe.Sizeof(argv)))
+	argv = (*unsafe.Pointer)(unsafe.Add(unsafe.Pointer(argv), (uintptr(argc)+1)*unsafe.Sizeof(argv)))
 
 	// skip over envv
 	for (*argv) != nil {
@@ -251,11 +259,21 @@ func os_runtime_executable_path() string {
 		length: length,
 		ptr:    (*byte)(cstr),
 	}
-	executablePath := *(*string)(unsafe.Pointer(&argString))
+	path := *(*string)(unsafe.Pointer(&argString))
 
 	// strip "executable_path=" prefix if available, it's added after OS X 10.11.
-	executablePath = stringsTrimPrefix(executablePath, "executable_path=")
-	return executablePath
+	path = stringsTrimPrefix(path, "executable_path=")
+
+	if path != "" && path[0] == '/' {
+		// absolute path
+		return path
+	}
+
+	cwd := getcwd()
+	if cwd != "" {
+		path = joinPath(cwd, path)
+	}
+	return path
 }
 
 func stringsTrimPrefix(s, prefix string) string {
@@ -264,3 +282,40 @@ func stringsTrimPrefix(s, prefix string) string {
 	}
 	return s
 }
+
+func joinPath(dir, name string) string {
+	if len(dir) > 0 && dir[len(dir)-1] == '/' {
+		return dir + name
+	}
+	return dir + "/" + name
+}
+
+// from syscall
+func getcwd() string {
+	const pathMax = 1024
+	var buf [4 * pathMax]byte
+	s := libc_getcwd(&buf[0], uint(len(buf)))
+	if s == nil {
+		return ""
+	}
+	n := clen(buf[:])
+	if n < 1 {
+		return ""
+	}
+	return string(buf[:n])
+}
+
+// clen returns the index of the first NULL byte in n or len(n) if n contains no NULL byte.
+func clen(n []byte) int {
+	for i := 0; i < len(n); i++ {
+		if n[i] == 0 {
+			return i
+		}
+	}
+	return len(n)
+}
+
+// char *getcwd(char *buf, size_t size)
+//
+//export getcwd
+func libc_getcwd(buf *byte, size uint) *byte

src/runtime/os_linux.go

@@ -157,3 +157,7 @@ func fcntl(fd int32, cmd int32, arg int32) (ret int32, errno int32) {
 	errno = *libc_errno_location()
 	return
 }
+
+func platform_argv(argc int32, argv *unsafe.Pointer) {
+	// nothing
+}

src/runtime/runtime_unix.go

@@ -95,6 +95,9 @@ func main(argc int32, argv *unsafe.Pointer) int {
 	// The run function has been moved to a separate (non-inlined) function so
 	// that the correct stack pointer is read.
 	stackTop = getCurrentStackPointer()
+
+	platform_argv(main_argc, main_argv)
+
 	runMain()
 
 	// For libc compatibility.