linux-kernel - Re: [PATCH] MIPS: Remove unnecessary zero-length struct member

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Message-ID: <alpine.DEB.2.21.2504170903020.18253@angie.orcam.me.uk>
Date: Thu, 17 Apr 2025 09:09:39 +0100 (BST)
From: "Maciej W. Rozycki" <macro@...am.me.uk>
To: Thorsten Blum <thorsten.blum@...ux.dev>
cc: Oleg Nesterov <oleg@...hat.com>, 
    Thomas Bogendoerfer <tsbogend@...ha.franken.de>, 
    linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MIPS: Remove unnecessary zero-length struct member

On Thu, 17 Apr 2025, Thorsten Blum wrote:

> > Also this is broken anyway: if you use MAX_REG_OFFSET for `offset' passed 
> > to `regs_get_register', then data past the end of `regs' will be accessed.
> 
> Yes, true. It seems like
> 
> 	if (unlikely(offset >= MAX_REG_OFFSET))
> 		return 0;
> 
> should do the trick.

 No, other platforms use the same (offset > MAX_REG_OFFSET) check that we 
do and just set MAX_REG_OFFSET correctly to point at the last register in 
`struct pt_regs'.

> The comment also says "If @offset is bigger than MAX_REG_OFFSET", rather
> than "is bigger than or equal to".

 And quite correctly so.

> Happy to add it to v2 or a separate patch, if this is actually correct?!

 Yes, please send v2.  There's no point in changing MAX_REG_OFFSET twice.

  Maciej