Re: linux-next: build warning after merge of the landlock tree

[Geert Uytterhoeven]

Hi Mickaël,

On Tue, Oct 3, 2023 at 3:15 PM Mickaël Salaün <mic@xxxxxxxxxxx> wrote:
> On Tue, Oct 03, 2023 at 02:27:37PM +1100, Stephen Rothwell wrote:
> > After merging the landlock tree, today's linux-next build (powerpc
> > allyesconfig) produced this warning:
> >
> > samples/landlock/sandboxer.c: In function 'populate_ruleset_net':
> > samples/landlock/sandboxer.c:170:78: warning: format '%llu' expects argument of type 'long long unsigned int', but argument 3 has type '__u64' {aka 'long unsigned int'} [-Wformat=]
> >   170 |                                 "Failed to update the ruleset with port \"%llu\": %s\n",
> >       |                                                                           ~~~^
> >       |                                                                              |
> >       |                                                                              long long unsigned int
> >       |                                                                           %lu
> >   171 |                                 net_port.port, strerror(errno));
> >       |                                 ~~~~~~~~~~~~~
> >       |                                         |
> >       |                                         __u64 {aka long unsigned int}
> >
> > Introduced by commit
> >
> >   24889e7a2079 ("samples/landlock: Add network demo")
>
> PowerPC-64 follows the LP64 data model and then uses int-l64.h (instead of
> int-ll64.h like most architectures) for user space code.
>
> Here is the same code with the (suggested) "%lu" token on x86_86:
>
>   samples/landlock/sandboxer.c: In function ‘populate_ruleset_net’:
>   samples/landlock/sandboxer.c:170:77: error: format ‘%lu’ expects argument of type ‘long unsigned int’, but argument 3 has type ‘__u64’ {aka ‘long long unsigned int’} [-Werror=format=]
>     170 |                                 "Failed to update the ruleset with port \"%lu\": %s\n",
>         |                                                                           ~~^
>         |                                                                             |
>         |                                                                             long unsigned int
>         |                                                                           %llu
>     171 |                                 net_port.port, strerror(errno));
>         |                                 ~~~~~~~~~~~~~
>         |                                         |
>         |                                         __u64 {aka long long unsigned int}
>
>
> We would then need to cast __u64 to unsigned long long to avoid this warning,
> which may look useless, of even buggy, for people taking a look at this sample.

In userspace code, you are supposed to #include <inttypes.h>
and use PRIu64.

> Anyway, it makes more sense to cast it to __u16 because it is the
> expected type for a TCP port. I'm updating the patch with that.
> Konstantin, please take this fix for the next series:
> https://git.kernel.org/mic/c/fc9de206a61a

Until someone passes a too large number, and it becomes truncated...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds