Re: [Xen-devel] [PATCH 16/17] xen: arm: refactor xchg and cmpxchg into their own headers

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Ian,

On 03/20/2014 03:46 PM, Ian Campbell wrote:
> diff --git a/xen/include/asm-arm/arm32/cmpxchg.h 
> b/xen/include/asm-arm/arm32/cmpxchg.h
> new file mode 100644
> index 0000000..70c6090
> --- /dev/null
> +++ b/xen/include/asm-arm/arm32/cmpxchg.h
> +static always_inline unsigned long __cmpxchg(
> +    volatile void *ptr, unsigned long old, unsigned long new, int size)
> +{
> +     unsigned long oldval, res;
> +
> +     switch (size) {
> +     case 1:
> +             do {
> +                     asm volatile("@ __cmpxchg1\n"
> +                     "       ldrexb  %1, [%2]\n"
> +                     "       mov     %0, #0\n"
> +                     "       teq     %1, %3\n"
> +                     "       strexbeq %0, %4, [%2]\n"
> +                             : "=&r" (res), "=&r" (oldval)
> +                             : "r" (ptr), "Ir" (old), "r" (new)
> +                             : "memory", "cc");
> +             } while (res);
> +             break;
> +     case 2:
> +             do {
> +                     asm volatile("@ __cmpxchg2\n"
> +                     "       ldrexh  %1, [%2]\n"
> +                     "       mov     %0, #0\n"
> +                     "       teq     %1, %3\n"
> +                     "       strexheq %0, %4, [%2]\n"
> +                             : "=&r" (res), "=&r" (oldval)
> +                             : "r" (ptr), "Ir" (old), "r" (new)
> +                             : "memory", "cc");
> +             } while (res);
> +             break;
> +     case 4:
> +             do {
> +                     asm volatile("@ __cmpxchg4\n"
> +                     "       ldrex   %1, [%2]\n"
> +                     "       mov     %0, #0\n"
> +                     "       teq     %1, %3\n"
> +                     "       strexeq %0, %4, [%2]\n"
> +                             : "=&r" (res), "=&r" (oldval)
> +                             : "r" (ptr), "Ir" (old), "r" (new)
> +                             : "memory", "cc");
> +         } while (res);
> +         break;
> +#if 0
> +     case 8:
> +             do {
> +                     asm volatile("@ __cmpxchg8\n"
> +                     "       ldrexd  %1, [%2]\n"
> +                     "       mov     %0, #0\n"
> +                     "       teq     %1, %3\n"
> +                     "       strexdeq %0, %4, [%2]\n"
> +                             : "=&r" (res), "=&r" (oldval)
> +                             : "r" (ptr), "Ir" (old), "r" (new)
> +                             : "memory", "cc");
> +             } while (res);
> +             break;
> +#endif

Is it really useful to let the dead code in the header?

Regards,

-- 
Julien Grall

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