cgo: fix GoBytes

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/4956051

misc/cgo/test/Makefile

@@ -12,6 +12,7 @@ CGOFILES=\
 	callback.go\
 	env.go\
 	exports.go\
+	helpers.go\
 	issue1222.go\
 	issue1328.go\
 	issue1560.go\

misc/cgo/test/callback.go

@@ -65,7 +65,7 @@ func testCallbackPanic(t *testing.T) {
 func testCallbackPanicLoop(t *testing.T) {
 	// Make sure we don't blow out m->g0 stack.
 	for i := 0; i < 100000; i++ {
-		TestCallbackPanic(t)
+		testCallbackPanic(t)
 	}
 }
 

misc/cgo/test/cgo_test.go

@@ -26,5 +26,6 @@ func TestBlocking(t *testing.T)            { testBlocking(t) }
 func Test1328(t *testing.T)                { test1328(t) }
 func TestParallelSleep(t *testing.T)       { testParallelSleep(t) }
 func TestSetEnv(t *testing.T)              { testSetEnv(t) }
+func TestHelpers(t *testing.T)             { testHelpers(t) }
 
 func BenchmarkCgoCall(b *testing.B) { benchCgoCall(b) }

misc/cgo/test/helpers.go

+// Copyright 2011 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 cgotest
+
+// const char *greeting = "hello, world";
+import "C"
+
+import (
+	"reflect"
+	"testing"
+	"unsafe"
+)
+
+const greeting = "hello, world"
+
+type testPair struct {
+	Name string
+	Got, Want interface{}
+}
+
+var testPairs = []testPair{
+	{"GoString", C.GoString(C.greeting), greeting},
+	{"GoStringN", C.GoStringN(C.greeting, 5), greeting[:5]},
+	{"GoBytes", C.GoBytes(unsafe.Pointer(C.greeting), 5), []byte(greeting[:5])},
+}
+
+func testHelpers(t *testing.T) {
+	for _, pair := range testPairs {
+		if !reflect.DeepEqual(pair.Got, pair.Want) {
+			t.Errorf("%s: got %#v, want %#v", pair.Got, pair.Want)
+		}
+	}
+}

src/pkg/runtime/string.goc

@@ -80,6 +80,8 @@ runtime·gobytes(byte *p, int32 n)
 	Slice sl;
 
 	sl.array = runtime·mallocgc(n, FlagNoPointers, 1, 0);
+	sl.len = n;
+	sl.cap = n;
 	runtime·memmove(sl.array, p, n);
 	return sl;
 }