linux-kernel - Re: Is gcc thread-unsafe?

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Date:	Sun, 4 Nov 2007 19:06:28 +0100
From:	"Bart Van Assche" <bart.vanassche@...il.com>
To:	"Linus Torvalds" <torvalds@...ux-foundation.org>
Cc:	"Andrew Haley" <aph@...hat.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Tomash Brechko" <tomash.brechko@...il.com>
Subject: Re: Is gcc thread-unsafe?

On 11/4/07, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>
> On Sun, 4 Nov 2007, Bart Van Assche wrote:
> >
> > Has it already been decided who will do this audit, and when this
> > audit will happen ? Has a target date been set when this audit should
> > be complete, or is the completion of this audit a requirement for the
> > release of a specific gcc version ?
>
> I am told that the gcc people realized that was indeed a bug (people were
> able to show problems even in non-threaded environments with mprotect()),
> and have now fixed it in the current gcc sources. That still leaves the
> old versions with potential problems, but I think it makes it much less
> interesting to audit for these things.
>
>                 Linus

What I understood from the gcc mailing list is that a patch has been
applied to the gcc sources that solves the issue with speculative
stores that was already discussed here on the LKML
(http://gcc.gnu.org/ml/gcc/2007-10/msg00554.html).

But the issue I am referring to is a different issue: namely that a
compiler optimization called register promotion can introduce data
races. Hans J. Boehm has a clear explanation of this -- see also
paragraph 4.3 in
http://www.hpl.hp.com/techreports/2004/HPL-2004-209.pdf or
http://portal.acm.org/citation.cfm?id=1064978.1065042 .

Bart Van Assche.
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