linux-kernel - Re: [PATCH] x86/boot: Address clang -Wimplicit-fallthrough in vsprintf()

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Message-ID: <20240524163956.GBZlDC3DH_OqvAjSBC@fat_crate.local>
Date: Fri, 24 May 2024 18:39:56 +0200
From: Borislav Petkov <bp@...en8.de>
To: Kees Cook <keescook@...omium.org>
Cc: Nathan Chancellor <nathan@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>, linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev, patches@...ts.linux.dev,
	kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] x86/boot: Address clang -Wimplicit-fallthrough in
 vsprintf()

On Thu, May 23, 2024 at 04:12:25PM -0700, Kees Cook wrote:
> There isn't a bug _here_, but this is about making the code unambiguous
> everywhere in the kernel. We've already done the work to get rid of
> all these warnings; this one is newly introduced, so let's get it fixed.

Nah, it has been there since forever (forever == 2007 in this case). It
fires because I enabled the warning in the decompressor.

> We don't want to have the same flow-control statement reachable from two
> different "case"s where the resulting behaviors are different. Otherwise
> we can't determine if a "fallthrough" is missing or intentional.

I'd agree if this warning wasn't enabled by default but were a W=123...
diagnostic thing which does the additional checks. But right now clang
is warning for a perfectly valid, albeit a bit confusing C.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette