linux-kernel - Re: [PATCH v2] MIPS: Fix MAX_REG_OFFSET and remove zero-length struct member

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Message-ID: <CAAhV-H4x4oQEtvk4Ah0WNBWtaQysj00k_Pybs=+r37oriJxVPA@mail.gmail.com>
Date: Sat, 19 Apr 2025 10:56:50 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Thorsten Blum <thorsten.blum@...ux.dev>
Cc: "Maciej W. Rozycki" <macro@...am.me.uk>, Thomas Bogendoerfer <tsbogend@...ha.franken.de>, 
	Oleg Nesterov <oleg@...hat.com>, linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] MIPS: Fix MAX_REG_OFFSET and remove zero-length struct member

On Sat, Apr 19, 2025 at 4:22 AM Thorsten Blum <thorsten.blum@...ux.dev> wrote:
>
> On 18. Apr 2025, at 22:18, Thorsten Blum wrote:
> > On 18. Apr 2025, at 17:14, Maciej W. Rozycki wrote:
> >> On Fri, 18 Apr 2025, Thorsten Blum wrote:
> >>>>> Does regs_get_register() even work for CPU_CAVIUM_OCTEON when accessing
> >>>>> the last two registers because they're both ULL, not UL? (independent of
> >>>>> my patch)
> >>>>
> >>>> Or rather two arrays of registers.  With 32-bit configurations their
> >>>> contents have to be retrieved by pieces.  I don't know if it's handled by
> >>>> the caller(s) though as I'm not familiar with this interface.
> >>>
> >>> Ah, CPU_CAVIUM_OCTEON seems to be 64-bit only, so there's no difference
> >>> between UL and ULL. Then both my patch and your suggestion:
> >>
> >> So it seems odd to use `long long int' here, but I can't be bothered to
> >> check history.  There could be a valid reason or it could be just sloppy
> >> coding.
> >>
> >>> I still prefer my approach without '__last[0]' because it also silences
> >>> the following false-positive Coccinelle warning, which is how I stumbled
> >>> upon this in the first place:
> >>>
> >>> ./ptrace.h:51:15-21: WARNING use flexible-array member instead
> >>
> >> So make `__last' a flexible array instead?  With a separate patch.
> >
> > No, '__last[0]' is a fake flexible array and the Coccinelle warning is
> > wrong. We should either ignore the warning or silence it by removing the
> > marker, but turning it into a real flexible array doesn't make sense.
> > I'd prefer to just remove it from the struct.
> >
> > Stefan or Oleg, do you have any preference?
>
> Sorry, I meant Thomas, not Stefan.
In my opinion just changing __last[0] to __last[] is OK, no other
actions needed.

Huacai
>
>