From 083120a43b3158bb45d7e1a66fa32e3335a2d407 Mon Sep 17 00:00:00 2001
From: Antonio Huete Jimenez <tuxillo@quantumachine.net>
Date: Tue, 28 Jan 2020 11:14:17 +0100
Subject: [PATCH] os: do not use procfs for os.Executable in dragonfly

  procfs(5) is not always mounted in DragonFly BSD, for example during
  the binary package build with synth. os.Executable() consumers
  will then fail, we've spotted this when trying to build tinygo:

    [...]

    copying source files
    ./build/tinygo build-builtins -target=armv6m-none-eabi [...]
    panic: could not get executable path: readlink /proc/curproc/file:
    no such file or directory

    [...]

  Use KERN_PROC_PATHNAME as FreeBSD does.
---
 src/os/executable_dragonfly.go | 12 ++++++++++++
 src/os/executable_freebsd.go   | 33 ++++++--------------------------
 src/os/executable_procfs.go    |  4 +---
 src/os/executable_sysctl.go    | 35 ++++++++++++++++++++++++++++++++++
 4 files changed, 54 insertions(+), 30 deletions(-)
 create mode 100644 src/os/executable_dragonfly.go
 create mode 100644 src/os/executable_sysctl.go

diff --git a/src/os/executable_dragonfly.go b/src/os/executable_dragonfly.go
new file mode 100644
index 0000000000..b0deb7bbe5
--- /dev/null
+++ b/src/os/executable_dragonfly.go
@@ -0,0 +1,12 @@
+// Copyright 2020 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
+
+// From DragonFly's <sys/sysctl.h>
+const (
+        _CTL_KERN           = 1
+        _KERN_PROC          = 14
+        _KERN_PROC_PATHNAME = 9
+)
diff --git a/src/os/executable_freebsd.go b/src/os/executable_freebsd.go
index ccaf8e6dd4..57930b1b16 100644
--- a/src/os/executable_freebsd.go
+++ b/src/os/executable_freebsd.go
@@ -1,33 +1,12 @@
-// Copyright 2016 The Go Authors. All rights reserved.
+// Copyright 2020 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"
+// From FreeBSD's <sys/sysctl.h>
+const (
+        _CTL_KERN           = 1
+        _KERN_PROC          = 14
+        _KERN_PROC_PATHNAME = 12
 )
-
-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
-}
diff --git a/src/os/executable_procfs.go b/src/os/executable_procfs.go
index 2628223b8d..5ee41a4b2e 100644
--- a/src/os/executable_procfs.go
+++ b/src/os/executable_procfs.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.
 
-// +build linux netbsd dragonfly js,wasm
+// +build linux netbsd js,wasm
 
 package os
 
@@ -23,8 +23,6 @@ var executablePath, executablePathErr = func() (string, error) {
 		procfn = "/proc/self/exe"
 	case "netbsd":
 		procfn = "/proc/curproc/exe"
-	case "dragonfly":
-		procfn = "/proc/curproc/file"
 	}
 	return Readlink(procfn)
 }()
diff --git a/src/os/executable_sysctl.go b/src/os/executable_sysctl.go
new file mode 100644
index 0000000000..f9a4b18f60
--- /dev/null
+++ b/src/os/executable_sysctl.go
@@ -0,0 +1,35 @@
+// 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.
+
+// +build freebsd dragonfly
+
+package os
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+func executable() (string, error) {
+	mib := [4]int32{_CTL_KERN, _KERN_PROC, _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
+}