os: implement Getwd

src/os/file.go

@@ -196,9 +196,8 @@ func Lstat(name string) (FileInfo, error) {
 	return nil, &PathError{"lstat", name, ErrNotImplemented}
 }
 
-// Getwd is a stub (for now), always returning an empty string
 func Getwd() (string, error) {
-	return "", nil
+	return syscall.Getwd()
 }
 
 // Readlink is a stub (for now), always returning the string it was given

src/syscall/file_emulated.go

@@ -0,0 +1,10 @@
+// +build baremetal wasi wasm
+
+// This file emulates some file-related functions that are only available
+// under a real operating system.
+
+package syscall
+
+func Getwd() (string, error) {
+	return "", nil
+}

src/syscall/file_hosted.go

@@ -0,0 +1,25 @@
+// +build !baremetal,!wasi,!wasm
+
+// This file assumes there is a libc available that runs on a real operating
+// system.
+
+package syscall
+
+const pathMax = 1024
+
+func Getwd() (string, error) {
+	var buf [pathMax]byte
+	s := libc_getcwd(&buf[0], uint(len(buf)))
+	if s == nil {
+		return "", getErrno()
+	}
+	n := clen(buf[:])
+	if n < 1 {
+		return "", EINVAL
+	}
+	return string(buf[:n]), nil
+}
+
+// char *getcwd(char *buf, size_t size)
+//export getcwd
+func libc_getcwd(buf *byte, size uint) *byte

src/syscall/str.go

@@ -22,3 +22,13 @@ func uitoa(val uint) string {
 	buf[i] = byte(val + '0')
 	return string(buf[i:])
 }
+
+// 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)
+}

src/syscall/syscall_libc_darwin.go

@@ -43,6 +43,7 @@ const (
 	EEXIST      Errno = 0x11
 	EINTR       Errno = 0x4
 	ENOTDIR     Errno = 0x14
+	EINVAL      Errno = 0x16
 	EMFILE      Errno = 0x18
 	EAGAIN      Errno = 0x23
 	ETIMEDOUT   Errno = 0x3c