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

    Andreas.

    --
    Andreas Schwab, schwab@linux-m68k.org
    GPG Key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5
    "And now for something completely different."


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