ia64: add option to suppress warnings about A/B-step errata

[Jim Wilson]

On Sat, 2004-04-10 at 11:48, Zack Weinberg wrote:
> Unfortunately the assembler does not ignore unrecognized -m options,
> so there is a compatibility issue if I make GCC 3.4 (say) start
> passing -mb-step along to the assembler, but it will only affect
> people who want to use brand new GCC to generate code for these old
> chips - I think it can be handled with a release note.

This means the linux kernel may be silently miscompiled/misassembled,
when configured with B-step support, which is not a very good option.  I
think it would be better to have gcc emit the new assembler option, and
if someone complains, we tell them to update their assembler.  That way,
the error is not silent.  Use of the -mb-step option is rare enough that
I think this will not cause much trouble.  We probably still need a
linux patch though, to add the new -mb-step to aflags.  This isn't your
problem though.  I suppose we could add a linux patch that adds
-Wa,-mb-step to cflags, but I think it makes more sense to fix gcc to
pass through the flag itself.

Alternatively, perhaps we can remove the B-step support if the IA-64
linux kernel maintainers don't think we need it anymore.  I don't know
of any other place where the -mb-step option is used.

> If this patch is approved I would like it to be included on the 2.15
> release branch as well as mainline.

Thanks should be no problem.

> Comments?  Where should this be documented?  How do I add test cases?

Document it in gas/doc/c-ia64.texi.

Test cases are added like we do for gcc.  You add a file that is similar
to existing ones.  See gas/testsuite/gas/ia64.

The patch looks fine to me, except the part about silently breaking
linux kernel builds configured with B-step support.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com