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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/
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