linux-kernel - Re: [PATCH] objtool: Fix UNWIND_HINT_{SAVE,RESTORE} across basic blocks

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Date: Thu, 29 Feb 2024 22:33:13 -0800
From: Kees Cook <keescook@...omium.org>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, oe-kbuild-all@...ts.linux.dev,
	kernel test robot <lkp@...el.com>,
	Alexander Lobakin <aleksander.lobakin@...el.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] objtool: Fix UNWIND_HINT_{SAVE,RESTORE} across basic
 blocks

On Mon, Feb 26, 2024 at 11:35:27PM -0800, Josh Poimboeuf wrote:
> On Fri, Feb 23, 2024 at 04:45:22PM -0800, Kees Cook wrote:
> > Josh, Peter, can you give a clue about what's happened here? For
> > added context, the referenced commit is changing a noreturn function
> > prototype[1], which I know gets some special objtool handling, but it's
> > converting a pointer arg to a u8... I can't imagine what has gone weird
> > here. :P
> 
> I think this convinced GCC to reshuffle some basic blocks, which
> uncovered an objtool bug.  Or, objtool just wasn't smart enough, as the
> warning says ;-)
> 
> This should fix it, absent any more warnings.  Kees, feel free to take
> it in your branch if that helps.

Thanks very much! I'll carry it in my tree.

-Kees

-- 
Kees Cook