runtime: Mark runtime_goexit function as noinline.

runtime: Mark runtime_goexit function as noinline.

If the compiler inlines this function into kickoff, it may reuse
the TLS block address to load g. However, this is not necessarily
correct, as the call to g->entry in kickoff may cause the TLS
address to change. If the wrong value is loaded for g->status in
runtime_goexit, it may cause a runtime panic.

By marking the function as noinline we prevent the compiler from
reusing the TLS address.

[iant, 2014-09-22 20:23:18]

Thanks for finding this.  Do you have a test case?  Or does it happen for your
compiler with the regular testsuite?

https://codereview.appspot.com/146100043/diff/20001/libgo/runtime/proc.c
File libgo/runtime/proc.c (right):

https://codereview.appspot.com/146100043/diff/20001/libgo/runtime/proc.c#newc...
libgo/runtime/proc.c:1893: void
Write this on a single line, and put it just before the function definition,
like the other uses of noinline.

[pcc, 2014-09-22 20:40:34]

I do not. The issue caused several test failures in the regular test suite when
proc.c is compiled with Clang.

See also https://github.com/go-llvm/llgo/pull/202 which is the corresponding
llgo issue.

https://codereview.appspot.com/146100043/diff/20001/libgo/runtime/proc.c
File libgo/runtime/proc.c (right):

https://codereview.appspot.com/146100043/diff/20001/libgo/runtime/proc.c#newc...
libgo/runtime/proc.c:1893: void
On 2014/09/22 20:23:18, iant wrote:
> Write this on a single line, and put it just before the function definition,
> like the other uses of noinline.

Done.

[iant, 2014-09-22 21:00:22]

LGTM

[iant, 2014-09-22 21:14:28]

*** Submitted as
https://code.google.com/p/gofrontend/source/detail?r=225a208260a6 ***

runtime: Mark runtime_goexit function as noinline.

If the compiler inlines this function into kickoff, it may reuse
the TLS block address to load g. However, this is not necessarily
correct, as the call to g->entry in kickoff may cause the TLS
address to change. If the wrong value is loaded for g->status in
runtime_goexit, it may cause a runtime panic.

By marking the function as noinline we prevent the compiler from
reusing the TLS address.

LGTM=iant
R=iant
CC=gofrontend-dev
https://codereview.appspot.com/146100043

Committer: Ian Lance Taylor <iant@golang.org>