crypto/rand: use the new getrandom syscall on FreeBSD

Since the 12.x branch, the getrandom syscall had been introduced
with similar interface as Linux's and consistent syscall id
across architectures.

Change-Id: I63d6b45dbe9e29f07f1b5b6c2ec8be4fa624b9ee
GitHub-Last-Rev: 6fb76e6522ef5ccb96d02445ffa39796dae89016
GitHub-Pull-Request: golang/go#25976
Reviewed-on: https://go-review.googlesource.com/120055
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

2 files changed, 52 insertions, 1 deletions

diff --git a/src/internal/syscall/unix/getrandom_freebsd.go b/src/internal/syscall/unix/getrandom_freebsd.go
new file mode 100644
index 0000000000..fc241f2345
--- /dev/null
+++ b/src/internal/syscall/unix/getrandom_freebsd.go
@@ -0,0 +1,51 @@
+// Copyright 2018 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 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 (
+	// GRND_NONBLOCK means return EAGAIN rather than blocking.
+	GRND_NONBLOCK GetRandomFlag = 0x0001
+
+	// 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 randomTrap == 0 {
+		return 0, syscall.ENOSYS
+	}
+	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_generic.go b/src/internal/syscall/unix/getrandom_linux_generic.go
index 8425800b6d..f8490ce978 100644
--- a/src/internal/syscall/unix/getrandom_linux_generic.go
+++ b/src/internal/syscall/unix/getrandom_linux_generic.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 arm64
+// +build linux,arm64
 
 package unix