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SubjectRe: gcc 4.5.1 / as miscompiling drivers/char/i8k.c ?
On 11/07/10 15:41, Andreas Schwab wrote:
> Andi Kleen<> writes:
>> Jim<> 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):
>>> 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.


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