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Date: Mon, 15 Nov 2010 11:42:31 -0700 From: Jeff Law <law@...hat.com> To: Andreas Schwab <schwab@...ux-m68k.org> CC: Andi Kleen <andi@...stfloor.org>, Jim <jim876@...all.nl>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, gcc@....gnu.org Subject: Re: gcc 4.5.1 / as 2.20.51.0.11 miscompiling drivers/char/i8k.c ? On 11/07/10 15:41, Andreas Schwab wrote: > Andi Kleen<andi@...stfloor.org> writes: > >> Jim<jim876@...all.nl> writes: >> >>> After upgrading my Dell laptop, both OS+kernel the i8k interface was giving >>> nonsensical output. As it turned out it's not the kernel but compiler >>> upgrade which broke this. >>> >>> Guys at Archlinux have found the underlying cause (but don't seem to have >>> submitted a patch yet): >>> https://bbs.archlinux.org/viewtopic.php?pid=780692#p780692 >>> gcc seems to optimize the assembly statements away. >>> >>> And indeed, applying this patch makes the i8k interface work again, >>> i.e. replacing the asm(..) construct by asm volatile(..) >> The compiler really should not optimize the asm away, because >> it has both input and output arguments which are later used. >> "asm volatile" normally just means "don't move significantly" > The asm fails to mention that it modifies *regs. But there's a memory clobber, that should be sufficient to indicate *regs is modified. jeff -- 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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