linux-kernel - Re: [PATCH] kunit/fortify: Add back "volatile" for sizeof() constants

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Message-ID: <CAG48ez0n1E0iuOxPe=jq4MuuP3w2wMSNixmfNmBbB89jyJBSbA@mail.gmail.com>
Date: Tue, 1 Jul 2025 15:41:35 +0200
From: Jann Horn <jannh@...gle.com>
To: Kees Cook <kees@...nel.org>
Cc: Jannik Glückert <jannik.glueckert@...il.com>, 
	Nathan Chancellor <nathan@...nel.org>, linux-hardening@...r.kernel.org, 
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] kunit/fortify: Add back "volatile" for sizeof() constants

On Sun, Jun 29, 2025 at 1:40 AM Kees Cook <kees@...nel.org> wrote:
> It seems the Clang can see through OPTIMIZER_HIDE_VAR when the constant
> is coming from sizeof.

Wait, what? That sounds extremely implausible/broken to me.

https://godbolt.org/z/ndeP5chcb also suggests that clang does not
generally "see through OPTIMIZER_HIDE_VAR when the constant is coming
from sizeof".

Do you have a minimal reproducer of what you're talking about?