From 85a7c090c4f831b6d29556c36bbe0a6cd8e8da6d Mon Sep 17 00:00:00 2001 From: Daniel Morsing Date: Wed, 17 Jul 2013 11:04:34 +0200 Subject: [PATCH] cmd/8g: Make clearfat non-interleaved with pointer calculations. clearfat (used to zero initialize structures) will use AX for x86 block ops. If we write to AX while calculating the dest pointer, we will fill the structure with incorrect values. Since 64-bit arithmetic uses AX to synthesize a 64-bit register, getting an adress by indexing with 64-bit ops can clobber the register. Fixes #5820. R=golang-dev, rsc CC=golang-dev https://golang.org/cl/11383043 --- src/cmd/8g/ggen.c | 2 +- test/fixedbugs/issue5820.go | 18 ++++++++++++++++++ 2 files changed, 19 insertions(+), 1 deletion(-) create mode 100644 test/fixedbugs/issue5820.go diff --git a/src/cmd/8g/ggen.c b/src/cmd/8g/ggen.c index 1095d5e441d..5570e128559 100644 --- a/src/cmd/8g/ggen.c +++ b/src/cmd/8g/ggen.c @@ -78,9 +78,9 @@ clearfat(Node *nl) c = w % 4; // bytes q = w / 4; // quads - gconreg(AMOVL, 0, D_AX); nodreg(&n1, types[tptr], D_DI); agen(nl, &n1); + gconreg(AMOVL, 0, D_AX); if(q >= 4) { gconreg(AMOVL, q, D_CX); diff --git a/test/fixedbugs/issue5820.go b/test/fixedbugs/issue5820.go new file mode 100644 index 00000000000..94de06d57db --- /dev/null +++ b/test/fixedbugs/issue5820.go @@ -0,0 +1,18 @@ +// run + +// Copyright 2013 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. + +// issue 5820: register clobber when clearfat and 64 bit arithmetic is interleaved. + +package main + +func main() { + array := make([][]int, 2) + index := uint64(1) + array[index] = nil + if array[1] != nil { + panic("array[1] != nil") + } +}