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

[Brian Gerst]

On Sun, Nov 22, 2009 at 10:14 PM, Johnny Hung <johnny.hacking@xxxxxxxxx> 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 ()
> {
> Â Âunsigned int val = 5, tmp = 10;
> Â Âasm volatile ("outb $0x27, %%al"
> Â Â :
> Â Â : "a" (0xb2), "b"(val), "c" (tmp)
> Â Â);
> }
>
> Â ÂIt 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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