[PATCH] Set cpu explicitly in kernel compiles

[Tom Rini]

On Fri, May 06, 2005 at 04:44:33PM +0200, Segher Boessenkool wrote:
> >Well, say you are compiling for 405.  You either need to have a gcc
> >that was configured with --with-cpu=405, or you need to have hacked
> >arch/ppc/Makefile to add -mcpu=405.  In both cases the problem doesn't
> >arise.  It only arises if you have a biarch gcc4 that was configured
> >without any --with-cpu=xxx option and is run without any -mcpu=xxx
> >option.
> 
> It happens for any installation where the default chosen by the GCC
> used is not the -mcpu=XXX flag you need used for your kernel.  Which
> is a much more general statement than the biarch one.  Most people just
> get lucky, because they compile code with a compiler that is defaulted
> for their target, and userland and kernel use (about) the same options
> on most targets.  Not so in biarch land (bleeech).

Note that up until very recently (and just a bit before conflicting
opcodes were added), no -mcpu=XXX was required.  For example, I compiled
a 44x kernel with a -mcpu=750 toolchain no problems shortly after Paul
posted this.  The only exception to this rule I can possibly think of is
85xx.  But even that would be the "very recently" thing I mentioned as
I know you can use an 82xx-set toolchain to build for 85xx.

Having said that..

> >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).
> 
> Please always use -mcpu=XXX (and perhaps -mtune=XXX), that's the only
> "correct" way to fix this.  Or _never_ do any -mcpu=, and let users
> override it in the CC setting in the Makefile.  But I like the first
> option better.

We should setup cpu-opt-$(CONFIG_every choice) to fix new gcc breakage
(and I guess we shouldn't have removed the do-nothing ones we had a few
years ago).

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