linux-kernel - Re: [PATCH v2 next 05/11] tools/nolibc/printf: Simplify __nolibc

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Message-ID: <aYebFp495HrbbDbZ@1wt.eu>
Date: Sat, 7 Feb 2026 21:05:42 +0100
From: Willy Tarreau <w@....eu>
To: david.laight.linux@...il.com
Cc: Thomas Weißschuh <linux@...ssschuh.net>,
        linux-kernel@...r.kernel.org, Cheng Li <lechain@...il.com>
Subject: Re: [PATCH v2 next 05/11] tools/nolibc/printf: Simplify
 __nolibc_printf()

On Fri, Feb 06, 2026 at 07:11:15PM +0000, david.laight.linux@...il.com wrote:
> From: David Laight <david.laight.linux@...il.com>
> 
> Move the check for the length modifiers into the format processing
> between the field width and conversion specifier.
> This lets the loop be simplified and a 'fast scan' for a format start
> used.
> 
> If an error is detected (eg an invalid conversion specifier) then
> copy the invalid format to the output buffer.
> 
> Reduces code size by about 10% on x86-64.

I'm surprised, because for me it's the opposite:

  $ size hello-patch*
     text    data     bss     dec     hex filename
     1859      48      24    1931     78b hello-patch1
     2071      48      24    2143     85f hello-patch2
     2091      48      24    2163     873 hello-patch3
     2422      48      24    2494     9be hello-patch4

The whole program grew by almost 16%, and that's a 30% increase since
the first patch. This is with gcc 15 -Oz. aarch64 however decreased by
15 bytes since previous patch.

I have not figured what makes this change yet, I'm still digging.

Willy