linux-kernel - Re: [PATCH 00/12] Clang -Wformat warning fixes

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Message-ID: <cd59f3eab3d2b4f069f4ebf169b33307eaa9e50d.camel@perches.com>
Date:   Fri, 10 Jun 2022 05:44:18 -0700
From:   Joe Perches <joe@...ches.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bill Wendling <morbo@...gle.com>
Cc:     Jan Engelhardt <jengelh@...i.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Bill Wendling <isanbard@...il.com>,
        Tony Luck <tony.luck@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Phillip Potter <phil@...lpotter.co.uk>,
        Arnd Bergmann <arnd@...db.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Jan Kara <jack@...e.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        Ross Philipson <ross.philipson@...cle.com>,
        Daniel Kiper <daniel.kiper@...cle.com>,
        linux-edac@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        linux-mm@...ck.org, netfilter-devel@...r.kernel.org,
        coreteam@...filter.org, Networking <netdev@...r.kernel.org>,
        alsa-devel@...a-project.org,
        clang-built-linux <llvm@...ts.linux.dev>
Subject: Re: [PATCH 00/12] Clang -Wformat warning fixes

On Fri, 2022-06-10 at 07:20 +0200, Greg Kroah-Hartman wrote:
> On Thu, Jun 09, 2022 at 04:16:16PM -0700, Bill Wendling wrote:
> > On Thu, Jun 9, 2022 at 4:03 PM Jan Engelhardt <jengelh@...i.de> wrote:
> > > On Friday 2022-06-10 00:49, Bill Wendling wrote:
> > > > On Thu, Jun 9, 2022 at 3:25 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
> > > > > On Thu,  9 Jun 2022 22:16:19 +0000 Bill Wendling <morbo@...gle.com> wrote:
> > > > > 
> > > > > > This patch set fixes some clang warnings when -Wformat is enabled.
> > > > > 
> > > > > tldr:
> > > > > 
> > > > > -       printk(msg);
> > > > > +       printk("%s", msg);
> > > > > 
> > > > > Otherwise these changes are a
> > > > > useless consumer of runtime resources.

> > > > Calling a "printf" style function is already insanely expensive.

I expect the printk code itself dominates, not the % scan cost.

> > > Perhaps you can split vprintk_store in the middle (after the call to
> > > vsnprintf), and offer the second half as a function of its own (e.g.
> > > "puts"). Then the tldr could be
> > > 
> > > - printk(msg);
> > > + puts(msg);
> > 
> > That might be a nice compromise. Andrew, what do you think?
> 
> You would need to do that for all of the dev_printk() variants, so I
> doubt that would ever be all that useful as almost no one should be
> using a "raw" printk() these days.

True.  The kernel has ~20K variants like that.

$ git grep -P '\b(?:(?:\w+_){1,3}(?:alert|emerg|crit|err|warn|notice|info|cont|debug|dbg)|printk)\s*\(".*"\s*\)\s*;' | wc -l
21160

That doesn't include the ~3K uses like

#define foo "bar"
	printk(foo);

$ git grep -P '\b(?:(?:\w+_){1,3}(?:alert|emerg|crit|err|warn|info|notice|debug|dbg|cont)|printk)\s*\((?:\s*\w+){1,3}\s*\)\s*;'|wc -l
2922

There are apparently only a few hundred uses of variants like:

	printk("%s", foo)

$ git grep -P '\b(?:(?:\w+_){1,3}(?:alert|emerg|crit|err|warn|info|notice|debug|dbg|cont)|printk)\s*\(\s*"%s(?:\\n)?"\s*,\s*(?:".*"|\w+)\s*\)\s*;' | wc -l
305

unless I screwed up my greps (which of course is quite possible)