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

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Message-Id: <0174c612-ed97-44f3-bec5-1f512f135d21@app.fastmail.com>
Date:   Tue, 03 Oct 2023 15:40:23 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     Mickaël Salaün <mic@...ikod.net>,
        "Stephen Rothwell" <sfr@...b.auug.org.au>
Cc:     "Konstantin Meskhidze" <konstantin.meskhidze@...wei.com>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        linux-next <linux-next@...r.kernel.org>,
        "Willem de Bruijn" <willemdebruijn.kernel@...il.com>,
        gnoack3000@...il.com, linux-security-module@...r.kernel.org,
        Netdev <netdev@...r.kernel.org>, netfilter-devel@...r.kernel.org,
        yusongping@...wei.com, artem.kuzin@...wei.com,
        "Geert Uytterhoeven" <geert@...ux-m68k.org>,
        "Randy Dunlap" <rdunlap@...radead.org>
Subject: Re: linux-next: build warning after merge of the landlock tree

On Tue, Oct 3, 2023, at 15:15, Mickaël Salaün wrote:
> 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.
>
> 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
>
>
> On Tue, Oct 03, 2023 at 02:27:37PM +1100, Stephen Rothwell wrote:
>> Hi all,
>> 
>> 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"

I think defining the __SANE_USERSPACE_TYPES__ macro should take care of this,
then __u64 has the same type as it does in the kernel.

        Arnd