Re: [PATCH] printf: add __printf attribute

[Andy Shevchenko]

On Sat, Dec 06, 2025 at 12:13:34PM -0500, Tamir Duberstein wrote:
> On Sat, Dec 6, 2025 at 11:11 AM Andy Shevchenko
> <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
> > On Sat, Dec 06, 2025 at 08:19:09AM -0500, Tamir Duberstein wrote:

...

> > > -static void
> > > +static void __printf(2, 3)
> >
> > 3?!
> >
> > I think it should be (2, 0). Yes, the both users call it with "%p..." in format
> > string, but the second parameter tells compiler to check the variadic
> > arguments, which are absent here. Changing 'const void *p' to '...' will align
> > it with the given __printf() attribute, but I don't know if this what we want.
> 
> The second parameter is the first-to-check, it is not specific to
> variadic arguments. Using 0 means that no arguments are checkable, so
> the compiler only validates the format string itself and won’t
> diagnose mismatches with `p`. This works whether or not we later
> change `const void *p` to `...`.

Yes, but this is fragile. As I explained it works only because we supply
the format string stuck to "%p", anything else will require reconsidering
the function prototypes. So, strictly speaking this should be (2, 0) if
we leave const void *p as is.

-- 
With Best Regards,
Andy Shevchenko