x86: bitops asm constraint fixes
This (simplified) piece of code didn't behave as expected due to incorrect constraints in some of the bitops functions, when X86_FEATURE_xxx is referring to other than the first long: int test(struct cpuinfo_x86 *c) { if (cpu_has(c, X86_FEATURE_xxx)) clear_cpu_cap(c, X86_FEATURE_xxx); return cpu_has(c, X86_FEATURE_xxx); } I'd really like understand, though, what the policy of (not) having a "memory" clobber in these operations is - currently, this appears to be totally inconsistent. Also, many comments of the non-atomic functions say those may also be re-ordered - this contradicts the use of "asm volatile" in there, which again I'd like to understand. As much as all of these, using 'int' for the 'nr' parameter and 'void *' for the 'addr' one is in conflict with Documentation/atomic_ops.txt, especially because bt{,c,r,s} indeed take the bit index as signed (which hence would really need special precaution) and access the full 32 bits (if 'unsigned long' was used properly here, 64 bits for x86-64) pointed at, so invalid uses like referencing a 'char' array cannot currently be caught. Finally, the code with and without this patch relies heavily on the -fno-strict-aliasing compiler switch and I'm not certain this really is a good idea. In the light of all of this I'm sending this as RFC, as fixing the above might warrant a much bigger patch... Signed-off-by: Jan Beulich <jbeulich@novell.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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