internal/syscall/unix: use fcntl64 on 32-bit GNU/Linux systems

Patch up runtime testing to use the libc fcntl function on Darwin,
which is what we should be doing anyhow. This is similar to how
we handle fcntl on AIX and Solaris.

Fixes #36211

Change-Id: I47ad87e11df043ce21496a0d59523dad28960f76
Reviewed-on: https://go-review.googlesource.com/c/go/+/212299
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

src/internal/syscall/unix/fcntl_linux_32bit.go

+// Copyright 2019 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.
+
+// On 32-bit Linux systems, use SYS_FCNTL64.
+// If you change the build tags here, see syscall/flock_linux_32bit.go.
+
+// +build linux,386 linux,arm linux,mips linux,mipsle
+
+package unix
+
+import "syscall"
+
+func init() {
+	FcntlSyscall = syscall.SYS_FCNTL64
+}

src/internal/syscall/unix/nonblocking.go

@@ -8,8 +8,12 @@ package unix
 
 import "syscall"
 
+// FcntlSyscall is the number for the fcntl system call. This is
+// usually SYS_FCNTL, but can be overridden to SYS_FCNTL64.
+var FcntlSyscall uintptr = syscall.SYS_FCNTL
+
 func IsNonblock(fd int) (nonblocking bool, err error) {
-	flag, _, e1 := syscall.Syscall(syscall.SYS_FCNTL, uintptr(fd), uintptr(syscall.F_GETFL), 0)
+	flag, _, e1 := syscall.Syscall(FcntlSyscall, uintptr(fd), uintptr(syscall.F_GETFL), 0)
 	if e1 != 0 {
 		return false, e1
 	}

src/runtime/export_darwin_test.go

+// Copyright 2019 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 runtime
+
+func Fcntl(fd, cmd, arg uintptr) (uintptr, uintptr) {
+	r := fcntl(int32(fd), int32(cmd), int32(arg))
+	if r < 0 {
+		return ^uintptr(0), uintptr(-r)
+	}
+	return uintptr(r), 0
+}

src/runtime/nbpipe_fcntl_libc_test.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 aix solaris
+// +build aix darwin solaris
 
 package runtime_test
 

src/runtime/nbpipe_fcntl_unix_test.go

@@ -2,13 +2,16 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux netbsd openbsd
+// +build dragonfly freebsd linux netbsd openbsd
 
 package runtime_test
 
-import "syscall"
+import (
+	"internal/syscall/unix"
+	"syscall"
+)
 
 func fcntl(fd uintptr, cmd int, arg uintptr) (uintptr, syscall.Errno) {
-	res, _, err := syscall.Syscall(syscall.SYS_FCNTL, fd, uintptr(cmd), arg)
+	res, _, err := syscall.Syscall(unix.FcntlSyscall, fd, uintptr(cmd), arg)
 	return res, err
 }

src/syscall/flock_linux_32bit.go

-// +build linux,386 linux,arm linux,mips linux,mipsle
-
 // Copyright 2014 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.
 
+// If you change the build tags here, see
+// internal/syscall/unix/fcntl_linux_32bit.go.
+
+// +build linux,386 linux,arm linux,mips linux,mipsle
+
 package syscall
 
 func init() {