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Re: [Xen-devel] [PATCH] linux/x86: avoid casting hypercall arguments to long

On 21/1/08 15:18, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

> -  : "1" ((long)(a1))    \
> +  : "1" ((a1)?:0)     \

Most of the patch seems to be placing this construct all over the place.
What's it for? How is x?:0 different from x?

> + register typeof((a4)?:0) __arg4 asm("r10") = (a4); \
> + register typeof((a5)?:0) __arg5 asm("r8") = (a5); \
> +    "=d" (__ign3), "+r" (__arg4), "+r" (__arg5) \

Is it guaranteed that gcc will keep the register variables in their assigned
registers across the inline asm?

 -- Keir



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