src/runtime/gcinfo_test.go

// 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 runtime_test

import (
	"bytes"
	"runtime"
	"testing"
)

const (
	typeScalar  = 0
	typePointer = 1
)

// TestGCInfo tests that various objects in heap, data and bss receive correct GC pointer type info.
func TestGCInfo(t *testing.T) {
	verifyGCInfo(t, "bss Ptr", &bssPtr, infoPtr)
	verifyGCInfo(t, "bss ScalarPtr", &bssScalarPtr, infoScalarPtr)
	verifyGCInfo(t, "bss PtrScalar", &bssPtrScalar, infoPtrScalar)
	verifyGCInfo(t, "bss BigStruct", &bssBigStruct, infoBigStruct())
	verifyGCInfo(t, "bss string", &bssString, infoString)
	verifyGCInfo(t, "bss slice", &bssSlice, infoSlice)
	verifyGCInfo(t, "bss eface", &bssEface, infoEface)
	verifyGCInfo(t, "bss iface", &bssIface, infoIface)

	verifyGCInfo(t, "data Ptr", &dataPtr, infoPtr)
	verifyGCInfo(t, "data ScalarPtr", &dataScalarPtr, infoScalarPtr)
	verifyGCInfo(t, "data PtrScalar", &dataPtrScalar, infoPtrScalar)
	verifyGCInfo(t, "data BigStruct", &dataBigStruct, infoBigStruct())
	verifyGCInfo(t, "data string", &dataString, infoString)
	verifyGCInfo(t, "data slice", &dataSlice, infoSlice)
	verifyGCInfo(t, "data eface", &dataEface, infoEface)
	verifyGCInfo(t, "data iface", &dataIface, infoIface)

	verifyGCInfo(t, "stack Ptr", new(Ptr), infoPtr)
	verifyGCInfo(t, "stack ScalarPtr", new(ScalarPtr), infoScalarPtr)
	verifyGCInfo(t, "stack PtrScalar", new(PtrScalar), infoPtrScalar)
	verifyGCInfo(t, "stack BigStruct", new(BigStruct), infoBigStruct())
	verifyGCInfo(t, "stack string", new(string), infoString)
	verifyGCInfo(t, "stack slice", new([]string), infoSlice)
	verifyGCInfo(t, "stack eface", new(interface{}), infoEface)
	verifyGCInfo(t, "stack iface", new(Iface), infoIface)

	for i := 0; i < 10; i++ {
		verifyGCInfo(t, "heap Ptr", escape(new(Ptr)), trimDead(padDead(infoPtr)))
		verifyGCInfo(t, "heap PtrSlice", escape(&make([]*byte, 10)[0]), trimDead(infoPtr10))
		verifyGCInfo(t, "heap ScalarPtr", escape(new(ScalarPtr)), trimDead(infoScalarPtr))
		verifyGCInfo(t, "heap ScalarPtrSlice", escape(&make([]ScalarPtr, 4)[0]), trimDead(infoScalarPtr4))
		verifyGCInfo(t, "heap PtrScalar", escape(new(PtrScalar)), trimDead(infoPtrScalar))
		verifyGCInfo(t, "heap BigStruct", escape(new(BigStruct)), trimDead(infoBigStruct()))
		verifyGCInfo(t, "heap string", escape(new(string)), trimDead(infoString))
		verifyGCInfo(t, "heap eface", escape(new(interface{})), trimDead(infoEface))
		verifyGCInfo(t, "heap iface", escape(new(Iface)), trimDead(infoIface))
	}
}

func verifyGCInfo(t *testing.T, name string, p interface{}, mask0 []byte) {
	mask := runtime.GCMask(p)
	if !bytes.Equal(mask, mask0) {
		t.Errorf("bad GC program for %v:\nwant %+v\ngot  %+v", name, mask0, mask)
		return
	}
}

func padDead(mask []byte) []byte {
	// Because the dead bit isn't encoded in the second word,
	// and because on 32-bit systems a one-word allocation
	// uses a two-word block, the pointer info for a one-word
	// object needs to be expanded to include an extra scalar
	// on 32-bit systems to match the heap bitmap.
	if runtime.PtrSize == 4 && len(mask) == 1 {
		return []byte{mask[0], 0}
	}
	return mask
}

func trimDead(mask []byte) []byte {
	for len(mask) > 2 && mask[len(mask)-1] == typeScalar {
		mask = mask[:len(mask)-1]
	}
	if len(mask) == 2 && mask[0] == typeScalar && mask[1] == typeScalar {
		mask = mask[:0]
	}
	return mask
}

var gcinfoSink interface{}

func escape(p interface{}) interface{} {
	gcinfoSink = p
	return p
}

var infoPtr = []byte{typePointer}

type Ptr struct {
	*byte
}

var infoPtr10 = []byte{typePointer, typePointer, typePointer, typePointer, typePointer, typePointer, typePointer, typePointer, typePointer, typePointer}

type ScalarPtr struct {
	q int
	w *int
	e int
	r *int
	t int
	y *int
}

var infoScalarPtr = []byte{typeScalar, typePointer, typeScalar, typePointer, typeScalar, typePointer}

var infoScalarPtr4 = append(append(append(append([]byte(nil), infoScalarPtr...), infoScalarPtr...), infoScalarPtr...), infoScalarPtr...)

type PtrScalar struct {
	q *int
	w int
	e *int
	r int
	t *int
	y int
}

var infoPtrScalar = []byte{typePointer, typeScalar, typePointer, typeScalar, typePointer, typeScalar}

type BigStruct struct {
	q *int
	w byte
	e [17]byte
	r []byte
	t int
	y uint16
	u uint64
	i string
}

func infoBigStruct() []byte {
	switch runtime.GOARCH {
	case "386", "arm", "mips", "mipsle":
		return []byte{
			typePointer,                                                // q *int
			typeScalar, typeScalar, typeScalar, typeScalar, typeScalar, // w byte; e [17]byte
			typePointer, typeScalar, typeScalar, // r []byte
			typeScalar, typeScalar, typeScalar, typeScalar, // t int; y uint16; u uint64
			typePointer, typeScalar, // i string
		}
	case "arm64", "amd64", "mips64", "mips64le", "ppc64", "ppc64le", "s390x", "wasm":
		return []byte{
			typePointer,                        // q *int
			typeScalar, typeScalar, typeScalar, // w byte; e [17]byte
			typePointer, typeScalar, typeScalar, // r []byte
			typeScalar, typeScalar, typeScalar, // t int; y uint16; u uint64
			typePointer, typeScalar, // i string
		}
	case "amd64p32":
		return []byte{
			typePointer,                                                // q *int
			typeScalar, typeScalar, typeScalar, typeScalar, typeScalar, // w byte; e [17]byte
			typePointer, typeScalar, typeScalar, // r []byte
			typeScalar, typeScalar, typeScalar, typeScalar, typeScalar, // t int; y uint16; u uint64
			typePointer, typeScalar, // i string
		}
	default:
		panic("unknown arch")
	}
}

type Iface interface {
	f()
}

type IfaceImpl int

func (IfaceImpl) f() {
}

var (
	// BSS
	bssPtr       Ptr
	bssScalarPtr ScalarPtr
	bssPtrScalar PtrScalar
	bssBigStruct BigStruct
	bssString    string
	bssSlice     []string
	bssEface     interface{}
	bssIface     Iface

	// DATA
	dataPtr                   = Ptr{new(byte)}
	dataScalarPtr             = ScalarPtr{q: 1}
	dataPtrScalar             = PtrScalar{w: 1}
	dataBigStruct             = BigStruct{w: 1}
	dataString                = "foo"
	dataSlice                 = []string{"foo"}
	dataEface     interface{} = 42
	dataIface     Iface       = IfaceImpl(42)

	infoString = []byte{typePointer, typeScalar}
	infoSlice  = []byte{typePointer, typeScalar, typeScalar}
	infoEface  = []byte{typeScalar, typePointer}
	infoIface  = []byte{typeScalar, typePointer}
)