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

[Andreas Schwab]

Andi Kleen <andi@xxxxxxxxxxxxxx> writes:

> Jim <jim876@xxxxxxxxx> 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.

Andreas.

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Andreas Schwab, schwab@xxxxxxxxxxxxxx
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