linux-kernel - Re: [tip: objtool/urgent] objtool, pwm: mediatek: Prevent theoretical divide-by-zero in pwm_mediatek

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Message-ID: <5i7cbgl7vza4bktquqbr7mvkrypbzmoeoys76wpzo4efmwze32@uwasrdhgsejo>
Date: Wed, 26 Mar 2025 22:44:04 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Uwe Kleine-König <ukleinek@...nel.org>
Cc: Ingo Molnar <mingo@...nel.org>, linux-tip-commits@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org
Subject: Re: [tip: objtool/urgent] objtool, pwm: mediatek: Prevent
 theoretical divide-by-zero in pwm_mediatek_config()

On Wed, Mar 26, 2025 at 11:35:28AM +0100, Uwe Kleine-König wrote:
> I wonder a bit about procedures here. While I like that warnings that
> pop up in drivers/pwm (and elsewhere) are cared for, I think that the
> sensible way to change warning related settings is to make it hard to
> enable them first (harder than "depends on !COMPILE_TEST" "To avoid
> breaking bots too badly") and then work on the identified problems
> before warning broadly. The way chosen here instead seems to be enabling
> the warning immediately and then post fixes to the warnings and merge
> them without respective maintainer feedback in less than 12 hours.

Actually, this type of warning has existed for years.  Nothing in the
recent objtool patches enabled it.

I only discovered this particular one a few days ago.  I suspect it only
exists with newer compilers.

> I fail to reproduce the warning here for an x86_64 build on
> 1e26c5e28ca5. I have:
> 
>         $ grep -E 'CONFIG_(CLK|PWM_MEDIATEK|OBJTOOL_WERROR)\>' .config
>         CONFIG_PWM_MEDIATEK=m
>         CONFIG_OBJTOOL_WERROR=y
> 
> and the build works fine for me and there is no warning about
> drivers/pwm/pwm-mediatek.o. What am I missing?

Sorry, I should have given more details about that.  It was likely
something with KCOV and/or UBSAN, though I can't seem to recreate it at
the moment either :-/

-- 
Josh