Re: [PATCH 1/2] tracing: work around -Wmissing-format-attribute warning

[Arnd Bergmann]

On Tue, Jun 2, 2026, at 20:59, Andy Shevchenko wrote:
> On Tue, Jun 02, 2026 at 05:07:05PM +0200, Arnd Bergmann wrote:
>> 
>> A number of tracing headers turn off -Wsuggest-attribute=format for
>> gcc, but they don't turn it off for clang, so the same warning still
>> happens on new versions of clang that support the format attribute.
>> 
>> To avoid duplicating the same thing in each tracing header, as well
>> as changing all of them to also turn it off for clang, add a new
>> __vsnprintf() helper that is not annotated this way in linux/sprintf.h
>> but is defined to work the same way as the regular vsprintf.
>
> vsprintf()

Fixed now

> Why the __printf() annotation is in the C file and not here?
> Is this all about headers as the second paragraph in the commit message 
> explains?
> I would add a comment to explain it here, otherwise we might see false 
> patches to "make things consistent" in a wrong way.

I've tried to come up with a kerneldoc comment now, similar to
the one for the vsnprintf() function, and added a separate prototype
in the header. Does this address your concern?

      Arnd

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 3caf0796f54d..7c696aea2ed3 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2975,7 +2975,23 @@ int vsnprintf(char *buf, size_t size, const char *fmt_str, va_list args)
 }
 EXPORT_SYMBOL(vsnprintf);
 
-int __printf(3, 0) __vsnprintf(char *buf, size_t size, const char *fmt_str, va_list args)
+/**
+ * __vsnprintf - vsnprintf() wrapper without __printf() attribute
+ * @buf: The buffer to place the result into
+ * @size: The size of the buffer, including the trailing null space
+ * @fmt_str: The format string to use
+ * @args: Arguments for the format string
+ *
+ * This has the exact same behavior as vsnprintf() but can be used in call
+ * sites that are missing a __printf() annotation, e.g. because they
+ * get a 'va_format' argument instead of format and varargs.
+ *
+ * For this to work, the attribute is added to the declaration here but
+ * not in the header.
+ */
+int __printf(3, 0) __vsnprintf(char *buf, size_t size, const char *fmt_str, va_list args);
+
+int __vsnprintf(char *buf, size_t size, const char *fmt_str, va_list args)
 {
 	return vsnprintf(buf, size, fmt_str, args);
 }