linux-kernel - Re: [PATCH 2/2] kbuild: Add option to fail build on vmlinux objtool issues

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Message-ID: <20241214005223.f2fansikbwovm3oo@jpoimboe>
Date: Fri, 13 Dec 2024 16:52:23 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Brendan Jackman <jackmanb@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Nicolas Schier <nicolas@...sle.eu>, linux-kernel@...r.kernel.org,
	linux-kbuild@...r.kernel.org
Subject: Re: [PATCH 2/2] kbuild: Add option to fail build on vmlinux objtool
 issues

On Fri, Dec 13, 2024 at 11:31:31AM +0000, Brendan Jackman wrote:
> NOINSTR_VALIDATION is pretty helpful for detecting bugs, I would like
> my build to fail when those bugs arise.
> 
> If we wanted to we could enable this for individual warnings, it seems
> unlikely there's a use-case for that though. So for now I've just added
> a global setting for vmlinux.
> 
> Signed-off-by: Brendan Jackman <jackmanb@...gle.com>

Note that *any* objtool warning has a good change of being a major bug
in the kernel or compiler which could result in crashing the kernel or
breaking the livepatch consistency model.  So the option shouldn't be
restricted to noinstr builds only.  In which case it should be called
CONFIG_OBJTOOL_WERROR, analagous to CONFIG_WERROR.

We definitely need this, though it will likely break a lot of robot
builds, so it wouldn't be a good idea to merge it until after the
holidays.  Though once the patches are ready I could throw it on a git
branch to see how bad the robot breakage is.

-- 
Josh