linux-kernel - Re: [PATCH] arch/mips/kernel/traps: add CONFIG_MIPS_FP_SUPPORT when using handle

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Message-ID: <alpine.DEB.2.21.2204280951510.9383@angie.orcam.me.uk>
Date:   Thu, 28 Apr 2022 10:00:13 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     Stephen Zhang <starzhangzsd@...il.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Joshua Kinard <kumba@...too.org>
cc:     liam.howlett@...cle.com, ebiederm@...ssion.com, dbueso@...e.de,
        alobakin@...me, f.fainelli@...il.com,
        zhangshida <zhangshida@...inos.cn>, linux-kernel@...r.kernel.org,
        linux-mips@...r.kernel.org
Subject: Re: [PATCH] arch/mips/kernel/traps: add CONFIG_MIPS_FP_SUPPORT when
 using handle_fpe

On Thu, 28 Apr 2022, Stephen Zhang wrote:

> >  Please send me .config causing it and tell me what compiler and version
> > you have seen this error with.  We rely on things being optimised away
> > heavily throughout the Linux kernel, so this is certainly something to
> > investigate.  I have built such a config just fine, but maybe there's a
> > bug somewhere my setup does not trigger.
> 
> Okay. The compiler we used is:
> 
> Compiler gcc
> Compiler version 10
> Compiler string mips-linux-gnu-gcc (Debian 10.2.1-6) 10.2.1 20210110
> Cross-compile  mips-linux-gnu
> 
> the  commit id of kernel is c00c5e1d157bec0ef0b0b59aa5482eb8dc7e8e49
> 
> and the .config file is sent as an attachment.

 Thanks.

 The bug is in arch/mips/include/asm/mach-ip27/cpu-feature-overrides.h, 
which has:

#define cpu_has_fpu			1

(and similarly arch/mips/include/asm/mach-ip30/cpu-feature-overrides.h).
This is not supported, as noted in arch/mips/include/asm/cpu-features.h:

/* Don't override `cpu_has_fpu' to 1 or the "nofpu" option won't work.  */

Perhaps we should explicitly undefine `cpu_has_fpu' if set to 1?

  Maciej