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

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Message-Id: <A08BC566-5F6D-4FA5-B315-34D2FCA55A6E@linux.dev>
Date: Fri, 18 Apr 2025 22:21:22 +0200
From: Thorsten Blum <thorsten.blum@...ux.dev>
To: "Maciej W. Rozycki" <macro@...am.me.uk>
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 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.