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    Subject[tip:x86/urgent] x86: Use correct byte-sized register constraint in __xchg_op()
    Commit-ID:  2ca052a3710fac208eee690faefdeb8bbd4586a1
    Gitweb: http://git.kernel.org/tip/2ca052a3710fac208eee690faefdeb8bbd4586a1
    Author: Jeremy Fitzhardinge <jeremy@goop.org>
    AuthorDate: Mon, 2 Apr 2012 16:15:33 -0700
    Committer: H. Peter Anvin <hpa@zytor.com>
    CommitDate: Fri, 6 Apr 2012 09:39:39 -0700

    x86: Use correct byte-sized register constraint in __xchg_op()

    x86-64 can access the low half of any register, but i386 can only do
    it with a subset of registers. 'r' causes compilation failures on i386,
    but 'q' expresses the constraint properly.

    Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org>
    Link: http://lkml.kernel.org/r/4F7A3315.501@goop.org
    Reported-by: Leigh Scott <leigh123linux@googlemail.com>
    Tested-by: Thomas Reitmayr <treitmayr@devbase.at>
    Signed-off-by: H. Peter Anvin <hpa@zytor.com>
    Cc: <stable@vger.kernel.org> v3.3
    ---
    arch/x86/include/asm/cmpxchg.h | 2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)

    diff --git a/arch/x86/include/asm/cmpxchg.h b/arch/x86/include/asm/cmpxchg.h
    index b3b7332..bc18d0e 100644
    --- a/arch/x86/include/asm/cmpxchg.h
    +++ b/arch/x86/include/asm/cmpxchg.h
    @@ -43,7 +43,7 @@ extern void __add_wrong_size(void)
    switch (sizeof(*(ptr))) { \
    case __X86_CASE_B: \
    asm volatile (lock #op "b %b0, %1\n" \
    - : "+r" (__ret), "+m" (*(ptr)) \
    + : "+q" (__ret), "+m" (*(ptr)) \
    : : "memory", "cc"); \
    break; \
    case __X86_CASE_W: \

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