Messages in this thread Patch in this message | | | Date | Fri, 17 Oct 2008 13:25:07 +0800 | From | Jike Song <> | Subject | Re: questions about rd{msr|tsc|pmc} instruction with x86-64 |
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H. Peter Anvin wrote: > Jike Song wrote: > > Thanks, Peter! So I misunderstood the gcc constraint 'A' for x86-64, > > but seems the comment "while x86_64 returns at rax" still wrong, > > should this be fixed? > > Yes, feel free to submit a patch. > > -hpa Here you go... CC trivial@kernel.org as well.
From 6eed2948d41f959dc113eb3ff30927bcacf34d08 Mon Sep 17 00:00:00 2001 From: Jike Song <albcamus@gmail.com> Date: Fri, 17 Oct 2008 10:51:13 +0800 Subject: [PATCH] x86: correct wrong comment
The rdmsr instruction(et al) for i386 and x86-64 are semantically same. The only difference is how gcc interpret constraint "A" for these targets.
Signed-off-by: Jike Song <albcamus@gmail.com> --- include/asm-x86/msr.h | 8 ++++---- 1 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/include/asm-x86/msr.h b/include/asm-x86/msr.h index 530af1f..fd0e1a1 100644 --- a/include/asm-x86/msr.h +++ b/include/asm-x86/msr.h @@ -22,10 +22,10 @@ static inline unsigned long long native_read_tscp(unsigned int *aux) } /* - * i386 calling convention returns 64-bit value in edx:eax, while - * x86_64 returns at rax. Also, the "A" constraint does not really - * mean rdx:rax in x86_64, so we need specialized behaviour for each - * architecture + * both i386 and x86_64 returns 64-bit value in edx:eax, but gcc's "A" + * constraint has different meanings. For i386, "A" means exactly + * edx:eax, while for x86_64 it doesn't mean rdx:rax or edx:eax. Instead, + * it means rax *or* rdx. */ #ifdef CONFIG_X86_64 #define DECLARE_ARGS(val, low, high) unsigned low, high -- 1.6.0.1
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