Re: [PATCH] Set cpu explicitly in kernel compiles

[Tom Rini <trini@kernel.crashing.org>]

On Thu, May 05, 2005 at 10:12:42AM -0500, Kumar Gala wrote:
> 
> On May 5, 2005, at 9:23 AM, Tom Rini wrote:
> 
> >On Thu, May 05, 2005 at 09:00:50AM -0500, Kumar Gala wrote:
> > >
> >> On May 5, 2005, at 7:24 AM, Dan Malek wrote:
> > >
> >> >
> > > >
> > > >On May 5, 2005, at 1:22 AM, Paul Mackerras wrote:
> > > > > If you think we should have -mcpu=xxx on the command line for 
> >4xx,
> > > > > 44x, 8xx, etc., then that's fine, but that is a separate problem
> >> >from
> > > > > what my patch was addressing (one which my patch might make it
> >> >easier
> > > > > to fix, though).
> > > >
> > > >I think that is exactly what we want, although I don't know how 
> >that is
> > > > separate from the patch you sent.? My original comment was the 
> >patch
> > > > fixes the problem for only one of the cpu cores, not all of them.?
> >> >Which
> > > > then led into the subsequent suggestion of making the biarch work
> > > > like the past compilers, and we must specific the flags for POWER4
> > > > instead of the other way around.? Without explicit -mcpu flags, 
> >the
> > > > existing compiler behavior is just fine .....? but, I guess I'd be
> > > >standing
> > > > in the way of progress to want this :-)
> > >
> >> I agree with Dan here.? I think we should go ahead and extend the 
> >patch
> >> to set -mcpu and -mtune flags for the list of processors we have in
> >> "Processor Type".? If I'm building a kernel for e500 or 4xx I might 
> >as
> >> well get a kernel that is tuned a bit more for the subarch.?
> >
> > This is fine.
> >
> >> Additionally, there should be some expert override ability, so if I
> >> really want to do -mcpu=7455 -mtune=7455 I can.
> >
> >Gack, no!? It's quite a pain to go from CONFIG_FOO="string" into 
> >useable
> > Makefile bits that the one we did have back in 2.4 is gone.? That also
> > implies gcc finally knows something about these cores that might be
> > useful, which I don't think is the case, nor is it likely to be.? But 
> >if
> > we did want it, we'd probably go the route x86 has.
> 
> I'm not saying it has to be done via a CONFIG option, all I'm saying is 
> if I want to explicitly use GCC then I would hope we could somehow 
> disable it being override.

If you're not doing it via CONFIG, that leaves manual (which is always
an option) or seeing if passing CFLAGS on the cmdline overrides things,
or adds to them.

-- 
Tom Rini
http://gate.crashing.org/~trini/