cmd/cgo: fix default alignment for empty structs

Fixes issue 5242.

LGTM=iant
R=iant
CC=golang-codereviews
https://codereview.appspot.com/125120043

Committer: Ian Lance Taylor <iant@golang.org>

2 files changed, 32 insertions, 0 deletions

diff --git a/misc/cgo/test/cgo_test.go b/misc/cgo/test/cgo_test.go
index eb237725a..3c6d5cb59 100644
--- a/misc/cgo/test/cgo_test.go
+++ b/misc/cgo/test/cgo_test.go
@@ -53,5 +53,6 @@ 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 Test5242(t *testing.T)                { test5242(t) }
 
 func BenchmarkCgoCall(b *testing.B) { benchCgoCall(b) }
diff --git a/misc/cgo/test/issue5242.go b/misc/cgo/test/issue5242.go
new file mode 100644
index 000000000..fe0a6321c
--- /dev/null
+++ b/misc/cgo/test/issue5242.go
@@ -0,0 +1,31 @@
+// 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.
+
+// Issue 5242.  Cgo incorrectly computed the alignment of structs
+// with no Go accessible fields as 0, and then panicked on
+// modulo-by-zero computations.
+
+package cgotest
+
+/*
+typedef struct {
+} foo;
+
+typedef struct {
+	int x : 1;
+} bar;
+
+int issue5242(foo f, bar b) {
+	return 5242;
+}
+*/
+import "C"
+
+import "testing"
+
+func test5242(t *testing.T) {
+	if got := C.issue5242(C.foo{}, C.bar{}); got != 5242 {
+		t.Errorf("got %v", got)
+	}
+}