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    SubjectRe: [PATCH 1 of 4] mm: add a ptep_modify_prot transaction abstraction

    * Linus Torvalds <torvalds@linux-foundation.org> wrote:

    > On Fri, 20 Jun 2008, Jeremy Fitzhardinge wrote:
    > >
    > > Blows up on "gcc version 3.4.4 20050314 (prerelease) (Debian 3.4.3-13)":
    >
    > Yeah, I was a bit worried about that. Gcc sometimes does insane
    > things.
    >
    > We literally just tested that the asm should only _ever_ be generated
    > with a constant value, but if some gcc dead-code removal thing doesn't
    > work, it will then screw up and try to generate the asm even for a
    > non-constant thing.
    >
    > The fairly trivial fix is probably to just change the "i" to "ir",
    > safe in the knowledge that any _sane_ case will never use the "r"
    > possibility. I suspect even your insane case will end up then killing
    > the bad choice later.

    okay - Jeremy, could you try the fix below? (or tip/master, i just
    pushed this out)

    (i dont use gcc 3.x myself to build the kernel, had way too many
    miscompilations in randconfig tests in the past.)

    Ingo

    -------------->
    commit b68b80b8ab39c42707dc126c41e87d46edc97c27
    Author: Ingo Molnar <mingo@elte.hu>
    Date: Fri Jun 20 21:50:20 2008 +0200

    x86, bitops: make constant-bit set/clear_bit ops faster, gcc workaround

    Jeremy Fitzhardinge reported this compiler bug:

    Suggestion from Linus: add "r" to the input constraint of the
    set_bit()/clear_bit()'s constant 'nr' branch:

    Blows up on "gcc version 3.4.4 20050314 (prerelease) (Debian 3.4.3-13)":

    CC init/main.o
    include2/asm/bitops.h: In function `start_kernel':
    include2/asm/bitops.h:59: warning: asm operand 1 probably doesn't match constraints
    include2/asm/bitops.h:59: warning: asm operand 1 probably doesn't match constraints
    include2/asm/bitops.h:59: warning: asm operand 1 probably doesn't match constraints
    include2/asm/bitops.h:59: error: impossible constraint in `asm'
    include2/asm/bitops.h:59: error: impossible constraint in `asm'
    include2/asm/bitops.h:59: error: impossible constraint in `asm'

    Reported-by: Jeremy Fitzhardinge <jeremy@goop.org>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>

    diff --git a/include/asm-x86/bitops.h b/include/asm-x86/bitops.h
    index 6c50548..4575de4 100644
    --- a/include/asm-x86/bitops.h
    +++ b/include/asm-x86/bitops.h
    @@ -58,7 +58,7 @@ static inline void set_bit(unsigned int nr, volatile unsigned long *addr)
    if (IS_IMMEDIATE(nr)) {
    asm volatile(LOCK_PREFIX "orb %1,%0"
    : CONST_MASK_ADDR(nr, addr)
    - : "i" (CONST_MASK(nr))
    + : "ir" (CONST_MASK(nr))
    : "memory");
    } else {
    asm volatile(LOCK_PREFIX "bts %1,%0"
    @@ -95,7 +95,7 @@ static inline void clear_bit(int nr, volatile unsigned long *addr)
    if (IS_IMMEDIATE(nr)) {
    asm volatile(LOCK_PREFIX "andb %1,%0"
    : CONST_MASK_ADDR(nr, addr)
    - : "i" (~CONST_MASK(nr)));
    + : "ir" (~CONST_MASK(nr)));
    } else {
    asm volatile(LOCK_PREFIX "btr %1,%0"
    : BITOP_ADDR(addr)

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