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

[Brian Gerst <brgerst@gmail.com>]

On Sun, Nov 22, 2009 at 10:14 PM, Johnny Hung <johnny.hacking@gmail.com> wrote:
> After testing:
>
> # gcc inlineasm.c
> inlineasm.c: Assembler messages:
> inlineasm.c:7: Error: suffix or operands invalid for `out'
> [root@debian-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