[Bug c/95130] GCC ignoring attribute(format(gnu_printf)) on printf in mingw

["tomas.kalibera at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95130

--- Comment #22 from Tomas Kalibera <tomas.kalibera at gmail dot com> ---
(In reply to CVS Commits from comment #21)
> The master branch has been updated by Jonathan Yong <jyong@gcc.gnu.org>:
> 
> https://gcc.gnu.org/g:966f3c134bb4802ac7ba0517de4e8e3f6384cfa3
> 
> commit r14-3334-g966f3c134bb4802ac7ba0517de4e8e3f6384cfa3
> Author: Tomas Kalibera <tomas.kalibera@gmail.com>
> Date:   Sun Aug 20 02:16:16 2023 +0000
> 
>     Fix format attribute for printf
>     
>     Since a long time (GCC 4.4?) GCC does support annotating functions
>     with either the format attribute "gnu_printf" or "ms_printf" to
>     distinguish between different format string interpretations.
>     
>     However, it seems like the attribute is ignored for the "printf"
>     symbol; regardless what the function declaration says, GCC treats
>     it as "ms_printf". This has become an issue now that mingw-w64
>     supports using the UCRT instead of msvcrt.dll, and in this case
>     the stdio functions are declared with the gnu_printf attribute,
>     and inttypes.h uses the same format specifiers as in GNU mode.
>     
>     A reproducible example of the problem:
>     
>     $ cat format.c
>     __attribute__((__format__ (gnu_printf, 1, 2))) int printf (const char
> *__format, ...);
>     __attribute__((__format__ (gnu_printf, 1, 2))) int othername (const char
> *__format, ...);
>     
>     void function(void) {
>         long long unsigned x = 42;
>         othername("%llu\n", x);
>         printf("%llu\n", x);
>     }
>     $ x86_64-w64-mingw32-gcc -c -Wformat format.c
>     format.c: In function 'function':
>     format.c:7:15: warning: unknown conversion type character 'l' in format
> [-Wformat=]
>         7 |     printf("%llu\n", x);
>           |               ^
>     format.c:7:12: warning: too many arguments for format
> [-Wformat-extra-args]
>         7 |     printf("%llu\n", x);
>           |            ^~~~~~~~
>     
>     Note how both functions, printf and othername, are declare with
>     identical gnu_printf format attributes - GCC does take this into
>     account for "othername" and doesn't produce a warning, but GCC
>     seems to disregard the attribute in the printf declaration and
>     behave as if it was declared as ms_printf.
>     
>     If the printf function declaration is changed into a static inline
>     function, the actual attribute used is honored though.
>     
>     gcc/c-family/ChangeLog:
>     
>             PR c/95130
>             * c-format.cc: skip default format for printf symbol if
>             explicitly declared by prototype.
>     
>     Signed-off-by: Tomas Kalibera <tomas.kalibera@gmail.com>
>     Signed-off-by: Jonathan Yong <10walls@gmail.com>

Great, thanks a lot for finishing and adding this,
Tomas