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

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Message-ID: <alpine.DEB.2.21.2204271156190.9383@angie.orcam.me.uk>
Date:   Wed, 27 Apr 2022 11:57:35 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     Stephen Zhang <starzhangzsd@...il.com>
cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        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 Wed, 27 Apr 2022, Stephen Zhang wrote:

> Thanks for your comment. Do you mean  the following code:
> 
>  if (0 && !0)
>     set_except_vector(15, handle_fpe);
> 
> will be optimised away if !CONFIG_MIPS_FP_SUPPORT?

 Yes.  Or more specifically the LHS of the conditional expression will be
0 then, as shown above, and the whole statement will be gone.

> But we did get “undefined reference to `handle_fpe”  error when compiled with
> !CONFIG_MIPS_FP_SUPPORT.

 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.

  Maciej