Re: proposed gcc/gas -mb-step changes

David Mosberger
2004-04-13T22:48:09Z

>>>>> On 13 Apr 2004 00:17:32 -0700, Jim Wilson <wilson@specifixinc.com> said:

Jim> Zack Weinberg of CodeSourcery sent mail to the binutils mailing
Jim> list which proposes to add a new -mb-step option to the
Jim> assembler. Currently, gas will always give warnings if given
Jim> code which triggers an Itanium (Merced) B-step errata. The
Jim> proposal is to only warn when the new -mb-step option is used.
Jim> Also, this means that the existing gcc option -mb-step will
Jim> have to pass -mb-step to the assembler. The discussion is here
Jim> http://sources.redhat.com/ml/binutils/2004-04/msg00187.html

Jim> The linux kernel is the only code I know of that uses the gcc
Jim> -mb-step option. This is used if you configure with B-step
Jim> support enabled. This change means that the kernel should be
Jim> modified to add -mb-step to aflags when the B-step support is
Jim> enabled, just like it currently does for cflags. Gas will fail
Jim> if given a -m option it doesn't recognize, so this means that
Jim> these changes will only work with new assembler versions. I am
Jim> assuming that use of the B-step support is rare enough that
Jim> this won't be a problem.

Seems like an acceptable solution to me.

IIRC, the Errata being worked around by -mb-step was exceedingly rare
to trigger and I'm not even sure it was ever observed to trigger in a
realworld situation. If so, perhaps it would be OK to drop -mb-step
entirely. That would cause a small risk for users of B-step Itanium
(Merced) CPUs, but I can't imagine anyone is doing anything
"mission-critical" on prototype machines anyhow. For testing etc.,
the a kernel compiled without -mb-step should still be usable, AFAIK.

--david