linux-kernel - Re: [PATCH] powerpc: e500: Fix compilation with gcc e500 compiler

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Message-ID: <20220524185247.GK25951@gate.crashing.org>
Date:   Tue, 24 May 2022 13:52:47 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Pali Rohár <pali@...nel.org>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc: e500: Fix compilation with gcc e500 compiler

On Tue, May 24, 2022 at 08:12:55PM +0200, Pali Rohár wrote:
> On Tuesday 24 May 2022 12:59:55 Segher Boessenkool wrote:
> > On Tue, May 24, 2022 at 11:39:39AM +0200, Pali Rohár wrote:
> > > gcc e500 compiler does not support -mcpu=powerpc option. When it is
> > > specified then gcc throws compile error:
> > > 
> > >   gcc: error: unrecognized argument in option ‘-mcpu=powerpc’
> > >   gcc: note: valid arguments to ‘-mcpu=’ are: 8540 8548 native
> > 
> > What?  Are you using some modified version of GCC, perhaps?
> 
> Hello! I'm using official gcc version, no special modification.
> 
> > No version of GCC that isn't hamstrung can have this output.
> 
> gcc for e500 cores has really this output when you pass -mcpu=powerpc.
> 
> Upstream gcc dropped support for e500 cores during development of
> version 9.

This isn't true.  The SPE instruction extension is no longer supported
(because it wasn't maintained).  Everything else still works.

> But you can still compile and install gcc 8.5.0 (last version
> of gcc 8) which has this full e500 support.
> 
> Really, you can easily try it. Debian 10 (Buster) has gcc 8.3.0 in its
> default installation and also provides packages with cross compilers.
> Just run 'sudo apt install gcc-powerpc-linux-gnuspe' on desktop amd64
> version of Debian 10, it will install e500 cross compiler.
> 
> -mcpu=8540 specify e500v1 and -mcpu=8548 specify e500v2

Aha.  Right, because this config forces -mspe it requires one of these
CPUs.

You can use a powerpc-linux compiler instead, and everything will just
work.  These CPUs are still supported, in all of GCC 9 .. GCC 12 :-)


Segher