internal/syscall/unix: unify GetRandom implementation

The implementation of GetRandom for Linux, FreeBSD and DragonflyBSD can
be shared.

Also remove GRND_INSECURE on DragonflyBSD as pointed out by Ian in the
review of CL 269999.

Change-Id: I5bf4c1bd51ddb2ad600652a57e0bc1bafa1cf40d
Reviewed-on: https://go-review.googlesource.com/c/go/+/299133
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

4 files changed, 42 insertions, 102 deletions

diff --git a/src/internal/syscall/unix/getrandom.go b/src/internal/syscall/unix/getrandom.go
new file mode 100644
index 0000000000..d2c58c0f6f
--- /dev/null
+++ b/src/internal/syscall/unix/getrandom.go
@@ -0,0 +1,40 @@
+// Copyright 2021 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.
+
+//go:build dragonfly || freebsd || linux
+// +build dragonfly freebsd linux
+
+package unix
+
+import (
+	"sync/atomic"
+	"syscall"
+	"unsafe"
+)
+
+var getrandomUnsupported int32 // atomic
+
+// GetRandomFlag is a flag supported by the getrandom system call.
+type GetRandomFlag uintptr
+
+// GetRandom calls the getrandom system call.
+func GetRandom(p []byte, flags GetRandomFlag) (n int, err error) {
+	if len(p) == 0 {
+		return 0, nil
+	}
+	if atomic.LoadInt32(&getrandomUnsupported) != 0 {
+		return 0, syscall.ENOSYS
+	}
+	r1, _, errno := syscall.Syscall(getrandomTrap,
+		uintptr(unsafe.Pointer(&p[0])),
+		uintptr(len(p)),
+		uintptr(flags))
+	if errno != 0 {
+		if errno == syscall.ENOSYS {
+			atomic.StoreInt32(&getrandomUnsupported, 1)
+		}
+		return 0, errno
+	}
+	return int(r1), nil
+}
diff --git a/src/internal/syscall/unix/getrandom_dragonfly.go b/src/internal/syscall/unix/getrandom_dragonfly.go
index b345b4c00c..fbf78f9de8 100644
--- a/src/internal/syscall/unix/getrandom_dragonfly.go
+++ b/src/internal/syscall/unix/getrandom_dragonfly.go
@@ -4,19 +4,8 @@
 
 package unix
 
-import (
-	"sync/atomic"
-	"syscall"
-	"unsafe"
-)
-
-var randomUnsupported int32 // atomic
-
 // DragonFlyBSD getrandom system call number.
-const randomTrap uintptr = 550
-
-// GetRandomFlag is a flag supported by the getrandom system call.
-type GetRandomFlag uintptr
+const getrandomTrap uintptr = 550
 
 const (
 	// GRND_RANDOM is only set for portability purpose, no-op on DragonFlyBSD.
@@ -24,28 +13,4 @@ const (
 
 	// GRND_NONBLOCK means return EAGAIN rather than blocking.
 	GRND_NONBLOCK GetRandomFlag = 0x0002
-
-	// GRND_INSECURE is an GRND_NONBLOCK alias
-	GRND_INSECURE GetRandomFlag = 0x0004
 )
-
-// GetRandom calls the DragonFlyBSD getrandom system call.
-func GetRandom(p []byte, flags GetRandomFlag) (n int, err error) {
-	if len(p) == 0 {
-		return 0, nil
-	}
-	if atomic.LoadInt32(&randomUnsupported) != 0 {
-		return 0, syscall.ENOSYS
-	}
-	r1, _, errno := syscall.Syscall(randomTrap,
-		uintptr(unsafe.Pointer(&p[0])),
-		uintptr(len(p)),
-		uintptr(flags))
-	if errno != 0 {
-		if errno == syscall.ENOSYS {
-			atomic.StoreInt32(&randomUnsupported, 1)
-		}
-		return 0, errno
-	}
-	return int(r1), nil
-}
diff --git a/src/internal/syscall/unix/getrandom_freebsd.go b/src/internal/syscall/unix/getrandom_freebsd.go
index f1ba5730c9..8c4f3dff82 100644
--- a/src/internal/syscall/unix/getrandom_freebsd.go
+++ b/src/internal/syscall/unix/getrandom_freebsd.go
@@ -4,19 +4,8 @@
 
 package unix
 
-import (
-	"sync/atomic"
-	"syscall"
-	"unsafe"
-)
-
-var randomUnsupported int32 // atomic
-
 // FreeBSD getrandom system call number.
-const randomTrap uintptr = 563
-
-// GetRandomFlag is a flag supported by the getrandom system call.
-type GetRandomFlag uintptr
+const getrandomTrap uintptr = 563
 
 const (
 	// GRND_NONBLOCK means return EAGAIN rather than blocking.
@@ -25,24 +14,3 @@ const (
 	// GRND_RANDOM is only set for portability purpose, no-op on FreeBSD.
 	GRND_RANDOM GetRandomFlag = 0x0002
 )
-
-// GetRandom calls the FreeBSD getrandom system call.
-func GetRandom(p []byte, flags GetRandomFlag) (n int, err error) {
-	if len(p) == 0 {
-		return 0, nil
-	}
-	if atomic.LoadInt32(&randomUnsupported) != 0 {
-		return 0, syscall.ENOSYS
-	}
-	r1, _, errno := syscall.Syscall(randomTrap,
-		uintptr(unsafe.Pointer(&p[0])),
-		uintptr(len(p)),
-		uintptr(flags))
-	if errno != 0 {
-		if errno == syscall.ENOSYS {
-			atomic.StoreInt32(&randomUnsupported, 1)
-		}
-		return 0, errno
-	}
-	return int(r1), nil
-}
diff --git a/src/internal/syscall/unix/getrandom_linux.go b/src/internal/syscall/unix/getrandom_linux.go
index 490d516978..8ccd8d328a 100644
--- a/src/internal/syscall/unix/getrandom_linux.go
+++ b/src/internal/syscall/unix/getrandom_linux.go
@@ -4,17 +4,6 @@
 
 package unix
 
-import (
-	"sync/atomic"
-	"syscall"
-	"unsafe"
-)
-
-var randomUnsupported int32 // atomic
-
-// GetRandomFlag is a flag supported by the getrandom system call.
-type GetRandomFlag uintptr
-
 const (
 	// GRND_NONBLOCK means return EAGAIN rather than blocking.
 	GRND_NONBLOCK GetRandomFlag = 0x0001
@@ -22,25 +11,3 @@ const (
 	// GRND_RANDOM means use the /dev/random pool instead of /dev/urandom.
 	GRND_RANDOM GetRandomFlag = 0x0002
 )
-
-// GetRandom calls the Linux getrandom system call.
-// See https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c6e9d6f38894798696f23c8084ca7edbf16ee895
-func GetRandom(p []byte, flags GetRandomFlag) (n int, err error) {
-	if len(p) == 0 {
-		return 0, nil
-	}
-	if atomic.LoadInt32(&randomUnsupported) != 0 {
-		return 0, syscall.ENOSYS
-	}
-	r1, _, errno := syscall.Syscall(getrandomTrap,
-		uintptr(unsafe.Pointer(&p[0])),
-		uintptr(len(p)),
-		uintptr(flags))
-	if errno != 0 {
-		if errno == syscall.ENOSYS {
-			atomic.StoreInt32(&randomUnsupported, 1)
-		}
-		return 0, errno
-	}
-	return int(r1), nil
-}