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    SubjectRe: 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@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



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