cmd/cgo: throw if C.malloc returns nil

Change-Id: If7740ac7b6c4190db5a1ab4100d12cf16dc79c84
Reviewed-on: https://go-review.googlesource.com/31768
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

misc/cgo/errors/malloc.go

+// Copyright 2016 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.
+
+// Test that C.malloc does not return nil.
+
+package main
+
+// #include <stdlib.h>
+import "C"
+
+import (
+	"fmt"
+)
+
+func main() {
+	p := C.malloc(C.size_t(^uintptr(0)))
+	if p == nil {
+		fmt.Println("malloc: C.malloc returned nil")
+		// Just exit normally--the test script expects this
+		// program to crash, so exiting normally indicates failure.
+	}
+}

misc/cgo/errors/test.bash

@@ -59,5 +59,15 @@ if ! go run ptr.go; then
 	exit 1
 fi
 
+# The malloc.go test should crash.
+rm -f malloc.out
+if go run malloc.go >malloc.out 2>&1; then
+	echo "`go run malloc.go` succeeded unexpectedly"
+	cat malloc.out
+	rm -f malloc.out
+	exit 1
+fi
+rm -f malloc.out
+
 rm -rf errs _obj
 exit 0

src/cmd/cgo/out.go

@@ -1463,9 +1463,15 @@ const cMallocDefGo = `
 var __cgofn__cgoPREFIX_Cfunc__Cmalloc byte
 var _cgoPREFIX_Cfunc__Cmalloc = unsafe.Pointer(&__cgofn__cgoPREFIX_Cfunc__Cmalloc)
 
+//go:linkname runtime_throw runtime.throw
+func runtime_throw(string)
+
 //go:cgo_unsafe_args
 func _cgo_cmalloc(p0 uint64) (r1 unsafe.Pointer) {
 	_cgo_runtime_cgocall(_cgoPREFIX_Cfunc__Cmalloc, uintptr(unsafe.Pointer(&p0)))
+	if r1 == nil {
+		runtime_throw("runtime: C malloc failed")
+	}
 	return
 }
 `