On 10/06/2015 11:54 AM, Pranith Kumar wrote:
> We are reading from memory locations pointed to by p1 and p2 in the asm
> block. Add a memory clobber flag to make gcc aware of this.
>
> Signed-off-by: Pranith Kumar <[email protected]>
> ---
> arch/x86/include/asm/cmpxchg.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/cmpxchg.h b/arch/x86/include/asm/cmpxchg.h
> index 4a2e5bc..3e83949 100644
> --- a/arch/x86/include/asm/cmpxchg.h
> +++ b/arch/x86/include/asm/cmpxchg.h
> @@ -214,7 +214,8 @@ extern void __add_wrong_size(void)
> : "=a" (__ret), "+d" (__old2), \
> "+m" (*(p1)), "+m" (*(p2)) \
> : "i" (2 * sizeof(long)), "a" (__old1), \
> - "b" (__new1), "c" (__new2)); \
> + "b" (__new1), "c" (__new2) \
> + : "memory"); \
> __ret; \
> })
NAK. We already have the "+m" for exactly this reason; adding an
explicit memory clobber should only be used to prevent movement of
*other* memory operations around this one (i.e. a barrier).
-hpa
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