runtime: fix _cgo_allocate(0)

Fixes a SWIG bug reported off-list.

LGTM=iant
R=iant
CC=golang-codereviews
https://codereview.appspot.com/155990043

2 files changed, 17 insertions, 0 deletions

diff --git a/misc/cgo/test/callback_c_gc.c b/misc/cgo/test/callback_c_gc.c
index 32bfed0c0..28a62c6db 100644
--- a/misc/cgo/test/callback_c_gc.c
+++ b/misc/cgo/test/callback_c_gc.c
@@ -39,6 +39,16 @@ callCgoAllocate(void)
 	int i;
 	struct { size_t n; void *ret; } a;
 	List *l, *head, **tail;
+
+	// Make sure this doesn't crash.
+	// And make sure it returns non-nil.
+	a.n = 0;
+	a.ret = 0;
+	crosscall2(_cgo_allocate, &a, sizeof a);
+	if(a.ret == 0) {
+		fprintf(stderr, "callCgoAllocate: alloc 0 returned nil\n");
+		exit(2);
+	}
 	
 	head = 0;
 	tail = &head;
diff --git a/misc/cgo/test/callback_c_gccgo.c b/misc/cgo/test/callback_c_gccgo.c
index d92dca009..d367b7b68 100644
--- a/misc/cgo/test/callback_c_gccgo.c
+++ b/misc/cgo/test/callback_c_gccgo.c
@@ -35,6 +35,13 @@ callCgoAllocate(void)
 	int i;
 	List *l, *head, **tail;
 	
+	// Make sure this doesn't crash.
+	// And make sure it returns non-nil.
+	if(_cgo_allocate(0) == 0) {
+		fprintf(stderr, "callCgoAllocate: alloc 0 returned nil\n");
+		exit(2);
+	}
+
 	head = 0;
 	tail = &head;
 	for(i=0; i<100; i++) {