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From: "H. Peter Anvin" <hpa@zytor.com>
To: Jike Song <albcamus@gmail.com>
Cc: gcosta@redhat.com, linux-kernel@vger.kernel.org
Subject: Re: questions about rd{msr|tsc|pmc} instruction with x86-64
Date: Wed, 15 Oct 2008 23:39:35 -0700	[thread overview]
Message-ID: <48F6E1A7.2070602@zytor.com> (raw)
In-Reply-To: <df9815e70810152330h7886c77arb01e1fd308b4a7ae@mail.gmail.com>

Jike Song wrote:
> 
> By my reading of Intel & AMD manuals, this comment is wrong.  rdmsr of
> x86-64 has the same behavior as i386, namely the high 32bit returns in
> edx and the low 32bit in eax, not "returns at rax".  And the gcc
> constraint "A" does mean edx:eax in x86-64 also, at least when testing
> on my AMD Turion 64 processor.
> 

"A" means rdx:rax on x86-64, not edx:eax.  For a 64-bit number, it 
means, literally, "one of rdx or rax"!  As you correctly point out, this 
is not how rdmsr works.

	-hpa

  reply	other threads:[~2008-10-16  6:40 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-10-16  6:30 Jike Song
2008-10-16  6:39 ` H. Peter Anvin [this message]
2008-10-16 16:31   ` Jike Song
     [not found]     ` <48F76FA3.1000602@zytor.com>
2008-10-17  5:25       ` Jike Song
2008-10-20 13:47         ` Ingo Molnar

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