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cmd/internal/gc: add and test write barrier debug output
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We can expand the test cases as we discover problems.
This is some basic tests plus all the things I got wrong
in some recent work.

Change-Id: Id875fcfaf74eb087ae42b441fe47a34c5b8ccb39
Reviewed-on: https://go-review.googlesource.com/9158
Reviewed-by: Rick Hudson <[email protected]>
Reviewed-by: Austin Clements <[email protected]>
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rsc committed Apr 24, 2015
1 parent 80f575b commit 9406f68
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Showing 3 changed files with 116 additions and 0 deletions.
3 changes: 3 additions & 0 deletions src/cmd/internal/gc/lex.go
Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,8 @@ var goarch string

var goroot string

var Debug_wb int

// Debug arguments.
// These can be specified with the -d flag, as in "-d nil"
// to set the debug_checknil variable. In general the list passed
Expand All @@ -46,6 +48,7 @@ var debugtab = []struct {
{"nil", &Debug_checknil}, // print information about nil checks
{"typeassert", &Debug_typeassert}, // print information about type assertion inlining
{"disablenil", &Disable_checknil}, // disable nil checks
{"wb", &Debug_wb}, // print information about write barriers
}

// Our own isdigit, isspace, isalpha, isalnum that take care
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3 changes: 3 additions & 0 deletions src/cmd/internal/gc/walk.go
Original file line number Diff line number Diff line change
Expand Up @@ -2218,6 +2218,9 @@ func applywritebarrier(n *Node, init **NodeList) *Node {
if Curfn != nil && Curfn.Func.Nowritebarrier {
Yyerror("write barrier prohibited")
}
if Debug_wb > 0 {
Warnl(int(n.Lineno), "write barrier")
}
t := n.Left.Type
l := Nod(OADDR, n.Left, nil)
l.Etype = 1 // addr does not escape
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110 changes: 110 additions & 0 deletions test/writebarrier.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,110 @@
// errorcheck -0 -l -d=wb

// Copyright 2015 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 where write barriers are and are not emitted.

package p

import "unsafe"

func f(x **byte, y *byte) {
*x = y // ERROR "write barrier"

z := y // no barrier
*x = z // ERROR "write barrier"
}

func f1(x *[]byte, y []byte) {
*x = y // ERROR "write barrier"

z := y // no barrier
*x = z // ERROR "write barrier"
}

func f1a(x *[]byte, y *[]byte) {
*x = *y // ERROR "write barrier"

z := *y // no barrier
*x = z // ERROR "write barrier"
}

func f2(x *interface{}, y interface{}) {
*x = y // ERROR "write barrier"

z := y // no barrier
*x = z // ERROR "write barrier"
}

func f2a(x *interface{}, y *interface{}) {
*x = *y // ERROR "write barrier"

z := y // no barrier
*x = z // ERROR "write barrier"
}

func f3(x *string, y string) {
*x = y // ERROR "write barrier"

z := y // no barrier
*x = z // ERROR "write barrier"
}

func f3a(x *string, y *string) {
*x = *y // ERROR "write barrier"

z := *y // no barrier
*x = z // ERROR "write barrier"
}

func f4(x *[2]string, y [2]string) {
*x = y // ERROR "write barrier"

z := y // no barrier
*x = z // ERROR "write barrier"
}

func f4a(x *[2]string, y *[2]string) {
*x = *y // ERROR "write barrier"

z := *y // no barrier
*x = z // ERROR "write barrier"
}

type T struct {
X *int
Y int
M map[int]int
}

func f5(t, u *T) {
t.X = &u.Y // ERROR "write barrier"
}

func f6(t *T) {
t.M = map[int]int{1: 2} // ERROR "write barrier"
}

func f7(x, y *int) []*int {
var z [3]*int
i := 0
z[i] = x // ERROR "write barrier"
i++
z[i] = y // ERROR "write barrier"
i++
return z[:i]
}

func f9(x *interface{}, v *byte) {
*x = v // ERROR "write barrier"
}

func f10(x *byte, f func(interface{})) {
f(x)
}

func f11(x *unsafe.Pointer, y unsafe.Pointer) {
*x = unsafe.Pointer(uintptr(y) + 1) // ERROR "write barrier"
}

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