Re: [PATCH] Set cpu explicitly in kernel compiles

[Paul Mackerras <paulus@samba.org>]

Tom Rini writes:

> So here's where the confusion comes in.  You're saying that even though
> (except .S files) no ppc32 kernel config was passing in explicit
> -mcpu=... or similar, only CONFIG_6xx is hurt by the gcc4 biarch thingy?

Indeed, we were never using -mcpu, and maybe we should be.

The problem only comes up if you configure gcc4 as biarch.  I can't
imagine anyone building a biarch compiler for 4xx or 8xx. :)

Alan Modra tells me that gcc4 can support all the ppc families in the
one binary, and that you can specify what cpu to use as the assumed
default at configure time.  If you specify --with-cpu=xxx at configure
time you get scheduling for that particular cpu.

So yes, only CONFIG_6xx is affected by biarch gcc4 assuming POWER4.
Other families would only be affected if you were using a generic
gcc4, which won't work at present anyway, since we don't add
-mcpu=xxx.

Paul.