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

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Message-Id: <DAD22E95-6D33-43D5-B5E5-3A7B45A63944@linux.dev>
Date: Fri, 18 Apr 2025 12:06:18 +0200
From: Thorsten Blum <thorsten.blum@...ux.dev>
To: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc: Oleg Nesterov <oleg@...hat.com>,
 "Maciej W. Rozycki" <macro@...am.me.uk>,
 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 09:57, Thomas Bogendoerfer wrote:
> On Thu, Apr 17, 2025 at 07:47:13PM +0200, Thorsten Blum wrote:
>> Remove the unnecessary zero-length struct member '__last' and fix
>> MAX_REG_OFFSET to point to the last register in 'pt_regs'.
>> 
>> Fixes: 40e084a506eba ("MIPS: Add uprobes support.")
> 
> what does it fix ?

The value of MAX_REG_OFFSET and thus how regs_get_register() behaves.

From my understanding, MAX_REG_OFFSET points to the marker '__last[0]'
instead of the actual last register in 'pt_regs', which could allow
regs_get_register() to return an invalid offset.

Let me know if I'm missing anything.

Thanks,
Thorsten