pointer() is using printf() type of format, and GCC compiler
(Debian 14.2.0-17) is not happy about this:

lib/vsprintf.c:2466:17: error: function ‘pointer’ might be a candidate for ‘gnu_printf’ format attribute [-Werror=suggest-attribute=format]

Fix the compilation errors (`make W=1` when CONFIG_WERROR=y, which is default)
by adding __printf() attribute.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 lib/vsprintf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 56fe96319292..8ebb5f866b08 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2419,7 +2419,7 @@ char *rust_fmt_argument(char *buf, char *end, void *ptr);
  * from Rust code to format core::fmt::Arguments. Do *not* use it from C.
  * See rust/kernel/print.rs for details.
  */
-static noinline_for_stack
+static noinline_for_stack __printf(1, 0)
 char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 	      struct printf_spec spec)
 {
-- 
2.47.2

On Thu, Mar 20 2025, Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:

> pointer() is using printf() type of format, and GCC compiler
> (Debian 14.2.0-17) is not happy about this:
>
> lib/vsprintf.c:2466:17: error: function ‘pointer’ might be a candidate for ‘gnu_printf’ format attribute [-Werror=suggest-attribute=format]
>
> Fix the compilation errors (`make W=1` when CONFIG_WERROR=y, which is default)
> by adding __printf() attribute.
>

I had quite a bit of trouble reproducing, until I realized I had to
apply your patches in reverse order, because adding the attribute to one
function will then "taint" its callers.

So this one seems to be self-inflicted pain by the annotation of
va_format (which is completely broken, I'll reply separately to that
one). This doesn't solve the false warning for va_format(), but how
about we at least do

 static char *va_format(char *buf, char *end, struct va_format *va_fmt,
-                      struct printf_spec spec, const char *fmt)
+                      struct printf_spec spec)
 {

        case 'V':
-               return va_format(buf, end, ptr, spec, fmt);
+               return va_format(buf, end, ptr, spec);
        case 'K':

because va_format() doesn't use that fmt argument at all.

Rasmus

On Fri, Mar 21, 2025 at 02:43:18PM +0100, Rasmus Villemoes wrote:
> On Thu, Mar 20 2025, Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:
> > pointer() is using printf() type of format, and GCC compiler
> > (Debian 14.2.0-17) is not happy about this:
> >
> > lib/vsprintf.c:2466:17: error: function ‘pointer’ might be a candidate for ‘gnu_printf’ format attribute [-Werror=suggest-attribute=format]
> >
> > Fix the compilation errors (`make W=1` when CONFIG_WERROR=y, which is default)
> > by adding __printf() attribute.
> >
> 
> I had quite a bit of trouble reproducing, until I realized I had to
> apply your patches in reverse order, because adding the attribute to one
> function will then "taint" its callers.

Exactly, that's why cover letter has "strict order" mention.

> So this one seems to be self-inflicted pain by the annotation of
> va_format (which is completely broken, I'll reply separately to that
> one). This doesn't solve the false warning for va_format(), but how
> about we at least do
> 
>  static char *va_format(char *buf, char *end, struct va_format *va_fmt,
> -                      struct printf_spec spec, const char *fmt)
> +                      struct printf_spec spec)
>  {
> 
>         case 'V':
> -               return va_format(buf, end, ptr, spec, fmt);
> +               return va_format(buf, end, ptr, spec);
>         case 'K':
> 
> because va_format() doesn't use that fmt argument at all.

Yes, I was thinking about this. I'll do it in a separate patch in v2.

-- 
With Best Regards,
Andy Shevchenko