From: "Michael S. Tsirkin" <[email protected]> ADDL clobbers flags (such as CF) but barrier.h didn't tell this to gcc. Historically, gcc doesn't need them on x86, and always considers flags clobbered. We are probably missing the cc clobber in a *lot* of places for this reason.
But even if not necessary, it's probably a good thing to add for documentation, and in case gcc semantics ever change. Reported-by: Borislav Petkov <[email protected]> Signed-off-by: Michael S. Tsirkin <[email protected]> Cc: Andrey Konovalov <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Arnd Bergmann <[email protected]> Cc: Davidlohr Bueso <[email protected]> Cc: "H. Peter Anvin" <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: "Paul E. McKenney" <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: virtualization <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Borislav Petkov <[email protected]> --- arch/x86/include/asm/barrier.h | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h index 0681d2532527..5bce7865b623 100644 --- a/arch/x86/include/asm/barrier.h +++ b/arch/x86/include/asm/barrier.h @@ -15,9 +15,12 @@ * Some non-Intel clones support out of order store. wmb() ceases to be a * nop for these. */ -#define mb() alternative("lock; addl $0,0(%%esp)", "mfence", X86_FEATURE_XMM2) -#define rmb() alternative("lock; addl $0,0(%%esp)", "lfence", X86_FEATURE_XMM2) -#define wmb() alternative("lock; addl $0,0(%%esp)", "sfence", X86_FEATURE_XMM) +#define mb() asm volatile(ALTERNATIVE("lock; addl $0,0(%%esp)", "mfence", \ + X86_FEATURE_XMM2) ::: "memory", "cc") +#define rmb() asm volatile(ALTERNATIVE("lock; addl $0,0(%%esp)", "lfence", \ + X86_FEATURE_XMM2) ::: "memory", "cc") +#define wmb() asm volatile(ALTERNATIVE("lock; addl $0,0(%%esp)", "sfence", \ + X86_FEATURE_XMM2) ::: "memory", "cc") #else #define mb() asm volatile("mfence":::"memory") #define rmb() asm volatile("lfence":::"memory") -- 2.3.5
