[release-branch.go1.1] cmd/8g: Make clearfat non-interleaved with pointer calculations.

««« CL 11383043 / dc24634de6c5
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
»»»

Update #5928

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/11698043

diff --git a/src/cmd/8g/ggen.c b/src/cmd/8g/ggen.c
index 70148106c4058f31c5bef7b81a1a28dbb8e2cf9a..b0154bb80c100d7702425c2139395094b6d7fc51 100644 (file)
--- 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 (file)
index 0000000..94de06d
--- /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")
+       }
+}