gas: inconsistencies w/ immediates

gas: inconsistencies w/ immediates

[Andrew Morton]

Using HJ's 2.9.5.0.34 binutils release (x86):

The handling of immediate constants appears to be inconsistent:


	movl	$1234,%eax

OK, this moves an immediate into eax.


	movl	$1234/$10,%eax

This fails because it is treating $10 as a label, not as a constant.


	.equ	some_label,$1234

Here, the assembler treats $1234 as a label!



This bizarre handling of $NNN really bites because this is the format in
which compiler-generated constants come out of GCC. For example, suppose
you wish to do this:


foo()
{
        asm(".equ SIZEOF_FOO,%0" :: "i" (sizeof foo));
}

bar()
{
        asm("movl $SIZEOF_FOO,%eax");
}

main()
{}

mnm:/home/morton> gcc -O x.c
/tmp/cc86xNLu1.o: In function `bar':
/tmp/cc86xNLu1.o(.text+0xc): undefined reference to `$1'


I'm unaware of any workaround which will allow the above to be done.


So is it possible to make the following changes:

1: Support $NN in gas expressions (I don't need this, but it
   seems sensible) and

2: Support $NN as integers (not labels) in pseudo-ops.

Thanks.

Re: gas: inconsistencies w/ immediates

[Andreas Schwab]

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Andrew Morton <andrewm@uow.edu.au> writes:

|> Using HJ's 2.9.5.0.34 binutils release (x86):
|> 
|> The handling of immediate constants appears to be inconsistent:
|> 
|> 
|> 	movl	$1234,%eax
|> 
|> OK, this moves an immediate into eax.
|> 
|> 
|> 	movl	$1234/$10,%eax
|> 
|> This fails because it is treating $10 as a label, not as a constant.

Isn't `$' part of the insn syntax (immediate prefix)?  IMHO this should be
written as:

        movl    $1234/10,%eax

|> This bizarre handling of $NNN really bites because this is the format in
|> which compiler-generated constants come out of GCC. For example, suppose
|> you wish to do this:
|> 
|> 
|> foo()
|> {
|>         asm(".equ SIZEOF_FOO,%0" :: "i" (sizeof foo));
                                ^^
Try %c0.

Andreas.

-- 
Andreas Schwab                                  "And now for something
SuSE Labs                                        completely different."
Andreas.Schwab@suse.de
SuSE GmbH, Schanzäckerstr. 10, D-90443 Nürnberg

Re: gas: inconsistencies w/ immediates

[Alan Modra]

On Mon, 31 Jul 2000, Andreas Schwab wrote:

> Andrew Morton <andrewm@uow.edu.au> writes:
> 
> |> 	movl	$1234/$10,%eax
> |> 
> |> This fails because it is treating $10 as a label, not as a constant.
> 
> Isn't `$' part of the insn syntax (immediate prefix)?

Yes.  Strictly speaking, it's part of the operand.

> IMHO this should be written as:
> 
>         movl    $1234/10,%eax

Correct again.  Watch out for versions of x86 gas that define `/' to start
the beginning of a comment, with disastrous results for division
expressions.

-- 
Linuxcare.  Support for the Revolution.

Re: gas: inconsistencies w/ immediates

[Andrew Morton]

Andreas wrote:
> 
|> foo()
|> {
|>         asm(".equ SIZEOF_FOO,%0" :: "i" (sizeof foo));
                                ^^
Try %c0.

Perfect.  Many thanks.