linux-kernel - Re: [PATCH 13/13] objtool: Add CONFIG_OBJTOOL

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Message-ID: <isd5ptllbyya5rqzyr75w7b6vasnpyomnub22prdegr2jdodrv@75qx5eg5bppn>
Date: Sat, 15 Mar 2025 18:49:54 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Ingo Molnar <mingo@...nel.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, 
	Peter Zijlstra <peterz@...radead.org>, Brendan Jackman <jackmanb@...gle.com>, 
	Nathan Chancellor <nathan@...nel.org>, Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 13/13] objtool: Add CONFIG_OBJTOOL_WERROR

On Sun, Mar 16, 2025 at 01:41:43AM +0100, Ingo Molnar wrote:
> > +config OBJTOOL_WERROR
> > +	bool "Upgrade objtool warnings to errors"
> > +	default y
> > +	depends on OBJTOOL && !COMPILE_TEST
> > +	help
> > +	  Fail the build on objtool warnings.
> 
> This is *way* too aggressive: objtool false positives are still common, 

I'm not sure what false positives you'd be referring to, these days the
vast majority of warnings I see are actual bugs.

> and an 'allmodconfig' should not fail the build IMO.

In fact it doesn't: allmodconfig sets COMPILE_TEST which prevents
OBJTOOL_WERROR.

I've had complaints from people who spent days debugging a broken kernel
only to discover it was related to an ignored objtool warning.

For non-bot builds which actually get run on a system, many of the
warnings should most definitely not be ignored.  Especially since
objtool is directly involved in some critical kernel infrastructure like
static calls/jumps and CPU mitigations.

All that said, I really don't know whether this default is too
aggressive.  But I do wonder if running it through a linux-next cycle
after the next merge window might help answer that question.

-- 
Josh