linux-kernel - Re: [PATCH] wireguard (gcc13): cast enum limits members to int in prints

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Date:   Mon, 31 Oct 2022 14:07:45 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     "Jiri Slaby (SUSE)" <jirislaby@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Martin Liska <mliska@...e.cz>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, wireguard@...ts.zx2c4.com,
        netdev@...r.kernel.org
Subject: Re: [PATCH] wireguard (gcc13): cast enum limits members to int in
 prints

Hi Jiri,

On Mon, Oct 31, 2022 at 12:44:24PM +0100, Jiri Slaby (SUSE) wrote:
> Since gcc13, each member of an enum has the same type as the enum [1]. And
> that is inherited from its members. Provided "REKEY_AFTER_MESSAGES = 1ULL
> << 60", the named type is unsigned long.
> 
> This generates warnings with gcc-13:
>   error: format '%d' expects argument of type 'int', but argument 6 has type 'long unsigned int'
> 
> Cast the enum members to int when printing them.
> 
> Alternatively, we can cast it to ulong (to silence gcc < 12) and use %lu.
> Alternatively, we can move REKEY_AFTER_MESSAGES away from the enum.
> 
> [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=36113

Huh, interesting situation. It's interesting that 1<<60 even works at
all on old gccs. I guess that in this case, it just takes the type of
the actual constant, rather than of the enum type?

Either way, I'll apply (a version of) your patch and push it back out on
the next wireguard fixup series.

Thanks for this.

Jason