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    Subject[PATCH 86/91] Fix gcc 4.5.1 miscompiling drivers/char/i8k.c (again)
    2.6.27-longterm review patch.  If anyone has any objections, please let us know.

    ------------------

    commit 22d3243de86bc92d874abb7c5b185d5c47aba323 upstream.

    The fix in commit 6b4e81db2552 ("i8k: Tell gcc that *regs gets
    clobbered") to work around the gcc miscompiling i8k.c to add "+m
    (*regs)" caused register pressure problems and a build failure.

    Changing the 'asm' statement to 'asm volatile' instead should prevent
    that and works around the gcc bug as well, so we can remove the "+m".

    [ Background on the gcc bug: a memory clobber fails to mark the function
    the asm resides in as non-pure (aka "__attribute__((const))"), so if
    the function does nothing else that triggers the non-pure logic, gcc
    will think that that function has no side effects at all. As a result,
    callers will be mis-compiled.

    Adding the "+m" made gcc see that it's not a pure function, and so
    does "asm volatile". The problem was never really the need to mark
    "*regs" as changed, since the memory clobber did that part - the
    problem was just a bug in the gcc "pure" function analysis - Linus ]

    Signed-off-by: Jim Bos <jim876@xs4all.nl>
    Acked-by: Jakub Jelinek <jakub@redhat.com>
    Cc: Andi Kleen <andi@firstfloor.org>
    Cc: Andreas Schwab <schwab@linux-m68k.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
    ---
    drivers/char/i8k.c | 8 ++++----
    1 files changed, 4 insertions(+), 4 deletions(-)

    Index: longterm-2.6.27/drivers/char/i8k.c
    ===================================================================
    --- longterm-2.6.27.orig/drivers/char/i8k.c 2012-02-05 22:34:47.002916726 +0100
    +++ longterm-2.6.27/drivers/char/i8k.c 2012-02-05 22:34:47.136914619 +0100
    @@ -119,7 +119,7 @@
    int eax = regs->eax;

    #if defined(CONFIG_X86_64)
    - asm("pushq %%rax\n\t"
    + asm volatile("pushq %%rax\n\t"
    "movl 0(%%rax),%%edx\n\t"
    "pushq %%rdx\n\t"
    "movl 4(%%rax),%%ebx\n\t"
    @@ -141,11 +141,11 @@
    "lahf\n\t"
    "shrl $8,%%eax\n\t"
    "andl $1,%%eax\n"
    - :"=a"(rc), "+m" (*regs)
    + :"=a"(rc)
    : "a"(regs)
    : "%ebx", "%ecx", "%edx", "%esi", "%edi", "memory");
    #else
    - asm("pushl %%eax\n\t"
    + asm volatile("pushl %%eax\n\t"
    "movl 0(%%eax),%%edx\n\t"
    "push %%edx\n\t"
    "movl 4(%%eax),%%ebx\n\t"
    @@ -167,7 +167,7 @@
    "lahf\n\t"
    "shrl $8,%%eax\n\t"
    "andl $1,%%eax\n"
    - :"=a"(rc), "+m" (*regs)
    + :"=a"(rc)
    : "a"(regs)
    : "%ebx", "%ecx", "%edx", "%esi", "%edi", "memory");
    #endif



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