[Linux-ia64] -ma-step and -mconstant-gp options for gcc?

[Linux-ia64] -ma-step and -mconstant-gp options for gcc?

[Francis Galiegue]

I wonder what the two options in $subject do...

For -ma-step, I can guess this assumes that the code will run on an A stepping
CPU, but in this case, will it run on a B? If I want to compile a kernel for a
B stepping processor, I guess I have to remove this option?

The second I really don't know...

-- 
Francis Galiegue, fg@mandrakesoft.com
"Programming is a race between programmers, who try and make more and more
idiot-proof software, and universe, which produces more and more remarkable
idiots. Until now, universe leads the race"  -- R. Cook

Re: [Linux-ia64] -ma-step and -mconstant-gp options for gcc?

[Jes Sorensen]

>>>>> "Francis" = Francis Galiegue <fg@mandrakesoft.com> writes:

Francis> I wonder what the two options in $subject do...  For
Francis> -ma-step, I can guess this assumes that the code will run on
Francis> an A stepping CPU, but in this case, will it run on a B? If I
Francis> want to compile a kernel for a B stepping processor, I guess
Francis> I have to remove this option?

The first one enables workarounds in the compiler so it doesn't
generate code that triggers problems on the A-step's.

The second tells the compiler that the gp is constant so it doesn't
constantly reload it when calling functions. It's used by the kernel.

Jes

Re: [Linux-ia64] -ma-step and -mconstant-gp options for gcc?

[Jim Wilson]

The -ma-step option enables compiler workarounds for A-step and B0-step
errata.  So far it didn't seem worth the trouble to add a -mb0-step option.
This option will likely be removed before the next toolchain release.

There is also a -mb-step option that enables compiler workarounds for B-step
errata.  This should be used if compiling code for B-step machines.  -ma-step
implies -mb-step, so you don't need both.

For -mconstant-gp, see the discussion of the elf header flag EF_IA_64_CONS_GP
in the psABI.

Jim