cmd/cgo: omit misaligned struct fields, like we omit bitfields

Fixes issue 7560.

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://codereview.appspot.com/96300045

2 files changed, 45 insertions, 0 deletions

diff --git a/misc/cgo/test/cgo_test.go b/misc/cgo/test/cgo_test.go
index f015ec9fa..eb237725a 100644
--- a/misc/cgo/test/cgo_test.go
+++ b/misc/cgo/test/cgo_test.go
@@ -52,5 +52,6 @@ func Test6390(t *testing.T)                { test6390(t) }
 func Test5986(t *testing.T)                { test5986(t) }
 func Test7665(t *testing.T)                { test7665(t) }
 func TestNaming(t *testing.T)              { testNaming(t) }
+func Test7560(t *testing.T)                { test7560(t) }
 
 func BenchmarkCgoCall(b *testing.B) { benchCgoCall(b) }
diff --git a/misc/cgo/test/issue7560.go b/misc/cgo/test/issue7560.go
new file mode 100644
index 000000000..4bea6e357
--- /dev/null
+++ b/misc/cgo/test/issue7560.go
@@ -0,0 +1,44 @@
+// 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.
+
+package cgotest
+
+/*
+#include <stdint.h>
+
+typedef struct {
+	char x;
+	long y;
+} __attribute__((__packed__)) misaligned;
+
+int
+offset7560(void)
+{
+	return (uintptr_t)&((misaligned*)0)->y;
+}
+*/
+import "C"
+
+import (
+	"reflect"
+	"testing"
+)
+
+func test7560(t *testing.T) {
+	// some mingw don't implement __packed__ correctly.
+	if C.offset7560() != 1 {
+		t.Skip("C compiler did not pack struct")
+	}
+
+	// C.misaligned should have x but then a padding field to get to the end of the struct.
+	// There should not be a field named 'y'.
+	var v C.misaligned
+	rt := reflect.TypeOf(&v).Elem()
+	if rt.NumField() != 2 || rt.Field(0).Name != "x" || rt.Field(1).Name != "_" {
+		t.Errorf("unexpected fields in C.misaligned:\n")
+		for i := 0; i < rt.NumField(); i++ {
+			t.Logf("%+v\n", rt.Field(i))
+		}
+	}
+}