mirror
/
go
mirror of https://github.com/golang/go.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

cmd/ld: fix bug with "runtime/cgo" in external link mode 

In external link mode the linker explicitly adds the string
constant "runtime/cgo".  It adds the string constant using the
same symbol name as the compiler, but a different format.  The
compiler assumes that the string data immediately follows the
string header, but the linker puts the two in different
sections.  The result is bad string data when the compiler
sees "runtime/cgo" used as a string constant.

The compiler assumption is in datastring in [568]g/gobj.c.
The linker layout is in addstrdata in ld/data.c.  The compiler
assumption is valid for string literals.  The linker is not
creating a string literal, so its assumption is also valid.

There are a few ways to avoid this problem.  This patch fixes
it by only doing the fake import of runtime/cgo if necessary,
and by only creating the string symbol if necessary.

Fixes #7234.

LGTM=dvyukov
R=golang-codereviews, dvyukov, bradfitz
CC=golang-codereviews
https://golang.org/cl/58410043
This commit is contained in:
Ian Lance Taylor 2014-01-30 09:25:47 -08:00
parent 73b0d84c83
commit 1683dab725
2 changed files with 42 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
misc/cgo/test/issue7234_test.go Normal file
View File

@ -0,0 +1,21 @@
// 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 cgotest
import "testing"
// This test actually doesn't have anything to do with cgo. It is a
// test of http://golang.org/issue/7234, a compiler/linker bug in
// handling string constants when using -linkmode=external. The test
// is in this directory because we routinely test -linkmode=external
// here.
var v7234 = [...]string{"runtime/cgo"}
func TestIssue7234(t *testing.T) {
if v7234[0] != "runtime/cgo" {
t.Errorf("bad string constant %q", v7234[0])
}
}

39
src/cmd/ld/lib.c
View File

@ -164,6 +164,7 @@ loadlib(void)
{
int i, w, x;
LSym *s, *gmsym;
char* cgostrsym;
if(flag_shared) {
s = linklookup(ctxt, "runtime.islibrary", 0);
@ -176,24 +177,6 @@ loadlib(void)
loadinternal("math");
if(flag_race)
loadinternal("runtime/race");
if(linkmode == LinkExternal) {
// This indicates a user requested -linkmode=external.
// The startup code uses an import of runtime/cgo to decide
// whether to initialize the TLS. So give it one. This could
// be handled differently but it's an unusual case.
loadinternal("runtime/cgo");
// Pretend that we really imported the package.
// This will do no harm if we did in fact import it.
s = linklookup(ctxt, "go.importpath.runtime/cgo.", 0);
s->type = SDATA;
s->dupok = 1;
s->reachable = 1;
// Provided by the code that imports the package.
// Since we are simulating the import, we have to provide this string.
addstrdata("go.string.\"runtime/cgo\"", "runtime/cgo");
}
for(i=0; i<ctxt->libraryp; i++) {
if(debug['v'] > 1)
@ -202,6 +185,26 @@ loadlib(void)
objfile(ctxt->library[i].file, ctxt->library[i].pkg);
}
if(linkmode == LinkExternal && !iscgo) {
// This indicates a user requested -linkmode=external.
// The startup code uses an import of runtime/cgo to decide
// whether to initialize the TLS. So give it one. This could
// be handled differently but it's an unusual case.
loadinternal("runtime/cgo");
// Pretend that we really imported the package.
s = linklookup(ctxt, "go.importpath.runtime/cgo.", 0);
s->type = SDATA;
s->dupok = 1;
s->reachable = 1;
// Provided by the code that imports the package.
// Since we are simulating the import, we have to provide this string.
cgostrsym = "go.string.\"runtime/cgo\"";
if(linkrlookup(ctxt, cgostrsym, 0) == nil)
addstrdata(cgostrsym, "runtime/cgo");
}
if(linkmode == LinkAuto) {
if(iscgo && externalobj)
linkmode = LinkExternal;