Add a minimal binary target for escape analysis on go-marshal.

Note that this is not an automated test.

PiperOrigin-RevId: 295238672

tools/go_marshal/test/BUILD

@@ -1,4 +1,4 @@
-load("//tools:defs.bzl", "go_library", "go_test")
+load("//tools:defs.bzl", "go_binary", "go_library", "go_test")
 
 licenses(["notice"])
 
@@ -27,3 +27,15 @@ go_library(
     marshal = True,
     deps = ["//tools/go_marshal/test/external"],
 )
+
+go_binary(
+    name = "escape",
+    testonly = 1,
+    srcs = ["escape.go"],
+    gc_goopts = ["-m"],
+    deps = [
+        ":test",
+        "//pkg/usermem",
+        "//tools/go_marshal/marshal",
+    ],
+)

tools/go_marshal/test/benchmark_test.go

@@ -24,7 +24,7 @@ import (
 	"gvisor.dev/gvisor/pkg/binary"
 	"gvisor.dev/gvisor/pkg/usermem"
 	"gvisor.dev/gvisor/tools/go_marshal/analysis"
-	test "gvisor.dev/gvisor/tools/go_marshal/test"
+	"gvisor.dev/gvisor/tools/go_marshal/test"
 )
 
 // Marshalling using the standard encoding/binary package.

tools/go_marshal/test/escape.go

@@ -0,0 +1,114 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// This binary provides a convienient target for analyzing how the go-marshal
+// API causes its various arguments to escape to the heap. To use, build and
+// observe the output from the go compiler's escape analysis:
+//
+// $ bazel build :escape
+// ...
+// escape.go:67:2: moved to heap: task
+// escape.go:77:31: make([]byte, size) escapes to heap
+// escape.go:87:31: make([]byte, size) escapes to heap
+// escape.go:96:6: moved to heap: stat
+// ...
+//
+// This is not an automated test, but simply a minimal binary for easy analysis.
+package main
+
+import (
+	"gvisor.dev/gvisor/pkg/usermem"
+	"gvisor.dev/gvisor/tools/go_marshal/marshal"
+	"gvisor.dev/gvisor/tools/go_marshal/test"
+)
+
+// dummyTask implements marshal.Task.
+type dummyTask struct {
+}
+
+func (*dummyTask) CopyScratchBuffer(size int) []byte {
+	return make([]byte, size)
+}
+
+func (*dummyTask) CopyOutBytes(addr usermem.Addr, b []byte) (int, error) {
+	return len(b), nil
+}
+
+func (*dummyTask) CopyInBytes(addr usermem.Addr, b []byte) (int, error) {
+	return len(b), nil
+}
+
+func (task *dummyTask) MarshalBytes(addr usermem.Addr, marshallable marshal.Marshallable) {
+	buf := task.CopyScratchBuffer(marshallable.SizeBytes())
+	marshallable.MarshalBytes(buf)
+	task.CopyOutBytes(addr, buf)
+}
+
+func (task *dummyTask) MarshalUnsafe(addr usermem.Addr, marshallable marshal.Marshallable) {
+	buf := task.CopyScratchBuffer(marshallable.SizeBytes())
+	marshallable.MarshalUnsafe(buf)
+	task.CopyOutBytes(addr, buf)
+}
+
+// Expected escapes:
+// - task: passed to marshal.Marshallable.CopyOut as the marshal.Task interface.
+func doCopyOut() {
+	task := dummyTask{}
+	var stat test.Stat
+	stat.CopyOut(&task, usermem.Addr(0xf000ba12))
+}
+
+// Expected escapes:
+// - buf: make allocates on the heap.
+func doMarshalBytesDirect() {
+	task := dummyTask{}
+	var stat test.Stat
+	buf := task.CopyScratchBuffer(stat.SizeBytes())
+	stat.MarshalBytes(buf)
+	task.CopyOutBytes(usermem.Addr(0xf000ba12), buf)
+}
+
+// Expected escapes:
+// - buf: make allocates on the heap.
+func doMarshalUnsafeDirect() {
+	task := dummyTask{}
+	var stat test.Stat
+	buf := task.CopyScratchBuffer(stat.SizeBytes())
+	stat.MarshalUnsafe(buf)
+	task.CopyOutBytes(usermem.Addr(0xf000ba12), buf)
+}
+
+// Expected escapes:
+// - stat: passed to dummyTask.MarshalBytes as the marshal.Marshallable interface.
+func doMarshalBytesViaMarshallable() {
+	task := dummyTask{}
+	var stat test.Stat
+	task.MarshalBytes(usermem.Addr(0xf000ba12), &stat)
+}
+
+// Expected escapes:
+// - stat: passed to dummyTask.MarshalUnsafe as the marshal.Marshallable interface.
+func doMarshalUnsafeViaMarshallable() {
+	task := dummyTask{}
+	var stat test.Stat
+	task.MarshalUnsafe(usermem.Addr(0xf000ba12), &stat)
+}
+
+func main() {
+	doCopyOut()
+	doMarshalBytesDirect()
+	doMarshalUnsafeDirect()
+	doMarshalBytesViaMarshallable()
+	doMarshalUnsafeViaMarshallable()
+}