From: Jeffrey Walton <noloader@gmail.com>
To: "孙世龙 sunshilong" <sunshilong369@gmail.com>
Cc: kernelnewbies <Kernelnewbies@kernelnewbies.org>
Subject: Re: How to comprehend this code snippet: __asm__ __volatile__("rdtsc" : "=A"(t))?
Date: Thu, 16 Jul 2020 09:42:18 -0400 [thread overview]
Message-ID: <CAH8yC8mniGumUqRU2BBEw2aS=LwkAx3YGt10jKtUSX0CwG2VOQ@mail.gmail.com> (raw)
In-Reply-To: <CAAvDm6aQc4E1mo468Bw9KHLsGvvzvkdUe87qJTSTq4yV_8t83A@mail.gmail.com>
On Thu, Jul 16, 2020 at 9:25 AM 孙世龙 sunshilong <sunshilong369@gmail.com> wrote:
>
> >The 'A' is the constraint EAX:RDX register pair.
> >Also see https://gcc.gnu.org/onlinedocs/gcc/Machine-Constraints.html
> >and https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html.
> Thanks to your attached document, I find a lot of useful information.
> BTW, What does "The A register", "The B register" and etc mean?
> I googled but didn't get any useful information.
> Could you please give me a few brief explanations or suggest some
> documents for me to go through?
See the docs for the various constraints. Also see
https://gcc.gnu.org/onlinedocs/gcc/Constraints.html#Constraints.
Jeff
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prev parent reply other threads:[~2020-07-16 13:44 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-16 12:20 How to comprehend this code snippet: __asm__ __volatile__("rdtsc" : "=A"(t))? 孙世龙 sunshilong
2020-07-16 12:52 ` Jeffrey Walton
2020-07-16 13:24 ` 孙世龙 sunshilong
2020-07-16 13:42 ` Jeffrey Walton [this message]
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