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cmd/compile: for arm, zero unaligned memory 1 byte at a time
If memory might be unaligned, zero it one byte at a time instead of 4 bytes at a time. Fixes #15902 Change-Id: I4eff0840e042e2f137c1a4028f08793eb7dfd703 Reviewed-on: https://go-review.googlesource.com/23587 Run-TryBot: Keith Randall <khr@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Minux Ma <minux@golang.org>
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@ -341,6 +341,11 @@ func clearfat(nl *gc.Node) {
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c := w % 4 // bytes
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q := w / 4 // quads
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if nl.Type.Align < 4 {
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q = 0
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c = w
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}
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var r0 gc.Node
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r0.Op = gc.OREGISTER
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@ -395,6 +400,27 @@ func clearfat(nl *gc.Node) {
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}
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}
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if c > 4 {
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// Loop to zero unaligned memory.
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var end gc.Node
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gc.Regalloc(&end, gc.Types[gc.Tptr], nil)
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p := gins(arm.AMOVW, &dst, &end)
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p.From.Type = obj.TYPE_ADDR
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p.From.Offset = int64(c)
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p = gins(arm.AMOVB, &nz, &dst)
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p.To.Type = obj.TYPE_MEM
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p.To.Offset = 1
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p.Scond |= arm.C_PBIT
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pl := p
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p = gins(arm.ACMP, &dst, nil)
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raddr(&end, p)
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gc.Patch(gc.Gbranch(arm.ABNE, nil, 0), pl)
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gc.Regfree(&end)
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c = 0
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}
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var p *obj.Prog
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for c > 0 {
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p = gins(arm.AMOVB, &nz, &dst)
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27
test/fixedbugs/issue15902.go
Normal file
27
test/fixedbugs/issue15902.go
Normal file
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@ -0,0 +1,27 @@
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// run
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// Copyright 2016 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// This test makes sure we don't use 4-byte unaligned writes
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// to zero memory on architectures that don't support them.
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package main
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type T struct {
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a byte
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b [10]byte
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}
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//go:noinline
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func f(t *T) {
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// t will be aligned, so &t.b won't be.
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t.b = [10]byte{}
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}
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var t T
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func main() {
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f(&t)
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}
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