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Date: Wed, 4 May 2005 21:47:37 -0700
From: Tom Rini <trini@kernel.crashing.org>
To: Paul Mackerras <paulus@samba.org>
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Subject: Re: [PATCH] Set cpu explicitly in kernel compiles
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On Thu, May 05, 2005 at 02:44:08PM +1000, Paul Mackerras wrote:
> 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. :)

I can, quite easily.  Think someone like Dan doing dev from their nice
shiney G5.

> 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.

Why won't it work with generic gcc4 ?  Will something more than a lot of
extra nops be added?

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