gcc 4.5.1 / as 2.20.51.0.11 miscompiling drivers/char/i8k.c ?

[Jeff Law]

On 11/07/10 15:41, Andreas Schwab wrote:
> Andi Kleen<andi@firstfloor.org>  writes:
>
>> Jim<jim876@xs4all.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