linux-kernel - Re: [PATCH 2/2] MIPS: make kgdb depend on FPU support

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Message-ID: <alpine.DEB.2.21.2102081748280.35623@angie.orcam.me.uk>
Date:   Mon, 8 Feb 2021 18:03:08 +0100 (CET)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     Arnd Bergmann <arnd@...nel.org>
cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Arnd Bergmann <arnd@...db.de>,
        kernel test robot <lkp@...el.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Paul Cercueil <paul@...pouillou.net>,
        Paul Burton <paulburton@...nel.org>,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] MIPS: make kgdb depend on FPU support

On Fri, 22 Jan 2021, Arnd Bergmann wrote:

> From: Arnd Bergmann <arnd@...db.de>
> 
> kgdb fails to build when the FPU support is disabled:
> 
> arch/mips/kernel/kgdb.c: In function 'dbg_set_reg':
> arch/mips/kernel/kgdb.c:147:35: error: 'struct thread_struct' has no member named 'fpu'
>   147 |    memcpy((void *)&current->thread.fpu.fcr31, mem,
>       |                                   ^
> arch/mips/kernel/kgdb.c:155:34: error: 'struct thread_struct' has no member named 'fpu'
>   155 |   memcpy((void *)&current->thread.fpu.fpr[fp_reg], mem,
> 
> This is only relevant for CONFIG_EXPERT=y, so disallowing it
> in Kconfig is an easier workaround than fixing it properly.

 Wrapping the relevant parts of this file into #ifdef MIPS_FP_SUPPORT 
would be as easy though and would qualify as a proper fix given that we 
have no XML description support for the MIPS target (so we need to supply 
the inexistent registers in the protocol; or maybe we can return NULL in 
`dbg_get_reg' to get them padded out in the RSP packet, I haven't checked 
if generic KGDB code supports this feature).

  Maciej