linux-kernel - Re: [PATCH] fs/select: rework stack allocation hack for clang

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Message-ID: <202402161321.B0B1D6F@keescook>
Date: Fri, 16 Feb 2024 13:21:49 -0800
From: Kees Cook <keescook@...omium.org>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Arnd Bergmann <arnd@...db.de>, Jan Kara <jack@...e.cz>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...ux.intel.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] fs/select: rework stack allocation hack for clang

On Fri, Feb 16, 2024 at 09:23:34PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> A while ago, we changed the way that select() and poll() preallocate
> a temporary buffer just under the size of the static warning limit of
> 1024 bytes, as clang was frequently going slightly above that limit.
> 
> The warnings have recently returned and I took another look. As it turns
> out, clang is not actually inherently worse at reserving stack space,
> it just happens to inline do_select() into core_sys_select(), while gcc
> never inlines it.
> 
> Annotate do_select() to never be inlined and in turn remove the special
> case for the allocation size. This should give the same behavior for
> both clang and gcc all the time and once more avoids those warnings.
> 
> Fixes: ad312f95d41c ("fs/select: avoid clang stack usage warning")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook