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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <p73d4v1pq50.fsf@bingen.suse.de>
Date:	Fri, 26 Oct 2007 22:39:07 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	"Bart Van Assche" <bart.vanassche@...il.com>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Andrew Haley" <aph@...hat.com>
Subject: Re: Is gcc thread-unsafe?

Alan Cox <alan@...rguk.ukuu.org.uk> writes:
>
> You can stop the compiler but not the CPU - and some processors will
> certainly speculatively load across conditionals, reorder writes etc

The difference is that the CPU knows how to cancel most[1] side effects
of these speculative accesses (e.g. by not issuing exceptions[2] etc.). 

The compiler doesn't normally (except on some architectures with special support like IA64;
but I'm not sure gcc supports it there) 

[1] In some it can't and we've had problems with that in the past. e.g. in
a few cases speculative reads can be a problem. But we generally fix or
workaround those cases in the code.
[2] Modulo hardware bugs -- see the hall of shame in x86_64 fault.c

-Andi
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/