os: add Executable() (string, error)

// Executable returns the path name for the executable that started
// the current process. There is no guarantee that the path is still
// pointing to the correct executable. If a symlink was used to start
// the process, depending on the operating system, the result might
// be the symlink or the path it pointed to. If a stable result is
// needed, path/filepath.EvalSymlinks might help.
//
// Executable returns an absolute path unless an error occurred.
//
// The main use case is finding resources located relative to an
// executable.
//
// Executable is not supported on nacl or OpenBSD (unless procfs is
// mounted.)
func Executable() (string, error) {
	return executable()
}

Fixes #12773.

Change-Id: I469738d905b12f0b633ea4d88954f8859227a88c
Reviewed-on: https://go-review.googlesource.com/16551
Run-TryBot: Minux Ma <minux@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 33 insertions, 0 deletions

diff --git a/src/os/executable_freebsd.go b/src/os/executable_freebsd.go
new file mode 100644
index 0000000000..ccaf8e6dd4
--- /dev/null
+++ b/src/os/executable_freebsd.go
@@ -0,0 +1,33 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+func executable() (string, error) {
+	mib := [4]int32{1 /* CTL_KERN */, 14 /* KERN_PROC */, 12 /* KERN_PROC_PATHNAME */, -1}
+
+	n := uintptr(0)
+	// get length
+	_, _, err := syscall.Syscall6(syscall.SYS___SYSCTL, uintptr(unsafe.Pointer(&mib[0])), 4, 0, uintptr(unsafe.Pointer(&n)), 0, 0)
+	if err != 0 {
+		return "", err
+	}
+	if n == 0 { // shouldn't happen
+		return "", nil
+	}
+	buf := make([]byte, n)
+	_, _, err = syscall.Syscall6(syscall.SYS___SYSCTL, uintptr(unsafe.Pointer(&mib[0])), 4, uintptr(unsafe.Pointer(&buf[0])), uintptr(unsafe.Pointer(&n)), 0, 0)
+	if err != 0 {
+		return "", err
+	}
+	if n == 0 { // shouldn't happen
+		return "", nil
+	}
+	return string(buf[:n-1]), nil
+}