linux-kernel - Re: How to move two valuables to x86 CPU register ebx, ecx by using AT&A inline asm.

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Message-ID: <73c1f2160911222143j196fac7cqf0464c4ad9c35cfc@mail.gmail.com>
Date:	Mon, 23 Nov 2009 00:43:47 -0500
From:	Brian Gerst <brgerst@...il.com>
To:	Johnny Hung <johnny.hacking@...il.com>
Cc:	Jiri Slaby <jirislaby@...il.com>, kernelnewbies@...linux.org,
	linux-kernel@...r.kernel.org, linux-embedded@...r.kernel.org
Subject: Re: How to move two valuables to x86 CPU register ebx, ecx by using 
	AT&A inline asm.

On Sun, Nov 22, 2009 at 10:14 PM, Johnny Hung <johnny.hacking@...il.com> wrote:
> After testing:
>
> # gcc inlineasm.c
> inlineasm.c: Assembler messages:
> inlineasm.c:7: Error: suffix or operands invalid for `out'
> [root@...ian-johnny] ~/workspace/test
>
> # cat inlineasm.c
> #include <stdio.h>
>
> int main ()
> {
>    unsigned int val = 5, tmp = 10;
>    asm volatile ("outb $0x27, %%al"
>     :
>     : "a" (0xb2), "b"(val), "c" (tmp)
>    );
> }
>
>    It seems the source of outb instruction cannot be a constant. Is
> there a AT&T instructions document for x86?

In AT&T syntax, the source register comes first.  So it should be
"outb %%al, $0x27", assuming that 0x27 is the port number you are
trying to write to.

--
Brian Gerst
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