Re: dubious use of O_subtract in gas/config/tc-ia64.c

[James E Wilson <wilson at specifixinc dot com>]

On Tue, 2005-02-01 at 06:46, Jan Beulich wrote:
> Could anyone shed some light on the relevance of the two instances of
> checks for O_subtract within operand_match(), cases IA64_OPND_IMMU64,
> IA64_OPND_IMM14, and IA64_OPND_IMM22?

This code is present in the first check in, so it was probably needed
for the linux kernel port.

I see in your example that you are subtracting two symbols in different
sections, which isn't something that we can easily compute.

If I write an example that subtracts two symbols in the same section,
then I get a reasonable result.  This testcase does not work if I
comment out the O_subtract checks.  Perhaps what we need is just a check
to verify that the symbols are in the same section?

        .data
bsym:   data8 0
esym:
        .text
start:
        mov             r1 = esym-bsym
        movl            r1 = esym-bsym

I tried a quick linux kernel build with a hacked assembler and found a
similar but slightly different testcase.  This occurs twice in the
arch/ia64/kernel/pal.S file.
        .text
1:
        adds r8 = 1f-1b,r8
1:

I didn't try looking for other examples.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com