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

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Message-ID: <alpine.DEB.2.21.2504181608420.18253@angie.orcam.me.uk>
Date: Fri, 18 Apr 2025 16:14:16 +0100 (BST)
From: "Maciej W. Rozycki" <macro@...am.me.uk>
To: Thorsten Blum <thorsten.blum@...ux.dev>
cc: 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 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.

> Would it make sense to also change the register arrays 'mpl' and 'mtp'
> from ULL to UL? ULL seems unnecessarily confusing to me.

 Maybe, but I'm not familiar enough with the Cavium Octeon platform to 
decide offhand and I won't dive into it, sorry.

  Maciej