On May 10, 2016 10:23:13 AM PDT, Peter Zijlstra <pet...@infradead.org> wrote:
>On Tue, May 10, 2016 at 06:53:18PM +0200, Borislav Petkov wrote:
>> static __always_inline unsigned int __arch_hweight32(unsigned int w)
>> {
>> - unsigned int res = 0;
>> + unsigned int res;
>>
>> - asm (ALTERNATIVE("call __sw_hweight32", POPCNT32,
>X86_FEATURE_POPCNT)
>> - : "="REG_OUT (res)
>> - : REG_IN (w));
>> + if (likely(static_cpu_has(X86_FEATURE_POPCNT))) {
>> + /* popcnt %eax, %eax */
>> + asm volatile(POPCNT32
>> + : "="REG_OUT (res)
>> + : REG_IN (w));
>>
>> - return res;
>> + return res;
>> + }
>> + return __sw_hweight32(w);
>> }
>
>So what was wrong with using the normal thunk_*.S wrappers for the
>calls? That would allow you to use the alternative() stuff which does
>generate smaller code.
Also, to be fair... if the problem is with these being in C then we could just
do it in assembly easily enough.
--
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