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Re: V2 [PATCH] x86: Use _rdtsc intrinsic for HP_TIMING_NOW
On Tue, 2 Oct 2018, Adhemerval Zanella wrote:
> > NB: Checking if __i686__ isn't sufficient since __i686__ may not be
> > defined when building for i686 class processors.
>
> Right, it seems gcc does not define it for -march newer than pentium4.
Specifically, you need a negative test (testing not building for an older
processor) as in sysdeps/x86/cpu-features.h. (There's probably a case for
factoring it out so there's a single header, usable from assembly sources
as well as from C code, that defines a macro, suitable for #if tests, that
can be used to test "known to be i686 or later".)
--
Joseph S. Myers
joseph@codesourcery.com