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

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Message-ID: <724889aa6a8d4d41b8557733610c7657@AcuMS.aculab.com>
Date:   Fri, 10 Jun 2022 09:14:45 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Jan Engelhardt' <jengelh@...i.de>
CC:     'Bill Wendling' <morbo@...gle.com>,
        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>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Jan Kara <jack@...e.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
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        Takashi Iwai <tiwai@...e.com>,
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        clang-built-linux <llvm@...ts.linux.dev>
Subject: RE: [PATCH 00/12] Clang -Wformat warning fixes

From: Jan Engelhardt
> Sent: 10 June 2022 09:32
> 
> 
> On Friday 2022-06-10 10:17, David Laight wrote:
> >>
> >> Calling a "printf" style function is already insanely expensive. :-) I
> >> understand that it's not okay blithely to increase runtime resources
> >> simply because it's already slow, but in this case it's worthwhile.
> >
> >Yep, IMHO definitely should be fixed.
> >It is even possible that using "%s" is faster because the printf
> >code doesn't have to scan the string for format effectors.
> 
> I see no special handling; the vsnprintf function just loops
> over fmt as usual and I see no special casing of fmt by
> e.g. strcmp(fmt, "%s") == 0 to take a shortcut.

Consider the difference between:
	printf("fubar");
and
	printf("%s", "fubar");
In the former all of "fubar" is checked for '%'.
In the latter only the length of "fubar" has to be counted.

FWIW the patch description should probably by:
	use "%s" when formatting a single string.
(or something to that effect).

	David

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