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Re: PATCH: Update CPUID feature check
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Ulrich Drepper <drepper at redhat dot com>
- Cc: GNU C Library <libc-alpha at sourceware dot org>
- Date: Fri, 29 May 2009 13:59:17 -0700
- Subject: Re: PATCH: Update CPUID feature check
- References: <20090526003810.GA13254@lucon.org> <4A204989.8020907@redhat.com>
On Fri, May 29, 2009 at 1:46 PM, Ulrich Drepper <drepper@redhat.com> wrote:
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> H.J. Lu wrote:
>> The CPUID feature bits in x86 processors from Intel and AMD indicate
>> the availability of the same CPU feature. ?There is no need to check
>> the same CPU feature separately for Intel and AMD processors.
>
> I see nowhere that this is really guaranteed. ?It's a best effort thing
> from where I stand. ?Will we really never see conflicts because of some
> agreements which are in place?
>
Intel and AMD processors use to the same CPU feature bits.
They also use the same opcode for the same instruction. There
are cases in the past, like popcnt, where both Intel and AMD
would implement the same instruction in the future processors
with different opcodes. Intel and AMD agreed to the same
opcode and the same cpuid feature bit for it. I don't believe
it will be different in the future.
--
H.J.