Messages in this thread | | | Date | Wed, 15 Oct 2008 23:39:35 -0700 | From | "H. Peter Anvin" <> | Subject | Re: questions about rd{msr|tsc|pmc} instruction with x86-64 |
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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
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