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

From: Joe Perches <joe@perches.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Bill Wendling <morbo@google.com>
Cc: Jan Engelhardt <jengelh@inai.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	 Bill Wendling <isanbard@gmail.com>,
	Tony Luck <tony.luck@intel.com>, Borislav Petkov <bp@alien8.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
	Phillip Potter <phil@philpotter.co.uk>,
	 Arnd Bergmann <arnd@arndb.de>,
	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
	Jan Kara <jack@suse.com>, Pablo Neira Ayuso <pablo@netfilter.org>,
	Jozsef Kadlecsik <kadlec@netfilter.org>,
	Florian Westphal <fw@strlen.de>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Jaroslav Kysela <perex@perex.cz>, Takashi Iwai <tiwai@suse.com>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Tom Rix <trix@redhat.com>,
	Ross Philipson <ross.philipson@oracle.com>,
	Daniel Kiper <daniel.kiper@oracle.com>,
	linux-edac@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
	ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
	linux-mm@kvack.org,  netfilter-devel@vger.kernel.org,
	coreteam@netfilter.org, Networking <netdev@vger.kernel.org>,
	alsa-devel@alsa-project.org,
	clang-built-linux <llvm@lists.linux.dev>
Subject: Re: [PATCH 00/12] Clang -Wformat warning fixes
Date: Fri, 10 Jun 2022 05:44:18 -0700	[thread overview]
Message-ID: <cd59f3eab3d2b4f069f4ebf169b33307eaa9e50d.camel@perches.com> (raw)
In-Reply-To: <YqLUn3RdZ9HAKZKu@kroah.com>

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@inai.de> wrote:
> > > On Friday 2022-06-10 00:49, Bill Wendling wrote:
> > > > On Thu, Jun 9, 2022 at 3:25 PM Andrew Morton <akpm@linux-foundation.org> wrote:
> > > > > On Thu,  9 Jun 2022 22:16:19 +0000 Bill Wendling <morbo@google.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)