Re: [PATCH v5 next 00/17] Enhance printf()

[David Laight <david.laight.linux@gmail.com>]

On Sun, 8 Mar 2026 22:01:19 +0100
Thomas Weißschuh <linux@weissschuh.net> wrote:

> Hi David,
> 
> thanks again for your patches!
> 
> On 2026-03-08 11:37:25+0000, david.laight.linux@gmail.com wrote:
> > From: David Laight <david.laight.linux@gmail.com>
> > David Laight (17):
> >   tools/nolibc: Add _NOLIBC_OPTIMIZER_HIDE_VAR() to compiler.h
> >   selftests/nolibc: Rename w to written in expect_vfprintf()
> >   tools/nolibc: Implement strerror() in terms of strerror_r()
> >   tools/nolibc: Rename the 'errnum' parameter to strerror()
> >   tools/nolibc/printf: Output pad characters in 16 byte chunks
> >   tools/nolibc/printf: Simplify __nolibc_printf()
> >   tools/nolibc/printf: Use goto and reduce indentation
> >   tools/nolibc/printf: Use bit-masks to hold requested flag, length and
> >     conversion chars
> >   tools/nolibc/printf: Add support for length modifiers tzqL and formats
> >     iX
> >   tools/nolibc/printf: Handle "%s" with the numeric formats
> >   tools/nolibc/printf: Prepend sign to converted number
> >   tools/nolibc/printf: Add support for conversion flags space and plus
> >   tools/nolibc/printf: Special case 0 and add support for %#x
> >   tools/nolibc/printf: Add support for left aligning fields
> >   tools/nolibc/printf: Add support for zero padding and field precision
> >   tools/nolibc/printf: Add support for octal output  
> 
> Beginning from here we have another sign-compare warning:
> 
> /home/t-8ch/.cache/crosstools/gcc-13.2.0-nolibc/i386-linux/bin/i386-linux-gcc -Os -fno-ident -fno-asynchronous-unwind-tables -std=c89 -W -Wall -Wextra -fno-stack-protector -Wmissing-prototypes  -fstack-protector-all -mstack-protector-guard=global -fsanitize=undefined -fsanitize-trap=all -m32 -Werror -Wl,--fatal-warnings  -o nolibc-test \
>   -nostdlib -nostdinc -static -Isysroot/i386/include nolibc-test.c nolibc-test-linkage.c -lgcc
> In file included from sysroot/i386/include/nolibc.h:123,
>                  from sysroot/i386/include/stdio.h:8,
>                  from nolibc-test.c:12:
> sysroot/i386/include/stdio.h: In function '__nolibc_printf':
> sysroot/i386/include/stdio.h:569:41: error: comparison of integer expressions of different signedness: 'unsigned int' and 'char' [-Werror=sign-compare]
>   569 |                         if (sign_prefix != *out) {
>       |                                         ^~
> cc1: all warnings being treated as errors
> 
> I have applied all of the patches *before*
> "tools/nolibc/printf: Prepend sign to converted number", which
> introduced the sign_prefix variable.
> 
> Could you fix this up and repost the remaining patches?

I hate 'sign compare' ...
I dislike using casts to 'fix' it - random 'integer' casts have caused me
grief in the past.
I don't want to make 'sign_prefix' signed - stops you adding 4 characters
(should you so desire); not to mention >> being either UB or implementation
defined on signed values (or maybe just negative ones).

The two obvious fixes are:
	if (sign_prefix - *out)
or:
	if (sign_prefix != *out + 0u) 

Your pick :-)

At least it is only the last couple of patches.

	David

> 
> 
> Thomas
> 
> >   selftests/nolibc: Use printf variable field widths and precisions
> > 
> >  tools/include/nolibc/compiler.h              |   3 +
> >  tools/include/nolibc/stdio.h                 | 427 ++++++++++++++-----
> >  tools/testing/selftests/nolibc/nolibc-test.c |  99 +++--
> >  3 files changed, 371 insertions(+), 158 deletions(-)