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Subject: Re: [PATCH] printf: fix Woverride-init warning for EDEADLK errno
To:     Arnd Bergmann <arnd@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Petr Mladek <pmladek@suse.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Andy Shevchenko <andy.shevchenko@gmail.com>
Cc:     Arnd Bergmann <arnd@arndb.de>, linux-kernel@vger.kernel.org
References: <20201026215004.3893088-1-arnd@kernel.org>
From:   =?UTF-8?Q?Uwe_Kleine-K=c3=b6nig?= <uwe@kleine-koenig.org>
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Message-ID: <b185c2d6-e890-6e56-3349-2ab023637af0@kleine-koenig.org>
Date:   Tue, 27 Oct 2020 07:55:47 +0100
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From: =?UTF-8?Q?Uwe_Kleine-K=c3=b6nig?= <uwe@kleine-koenig.org>
To: Arnd Bergmann <arnd@kernel.org>, Andrew Morton
 <akpm@linux-foundation.org>, Petr Mladek <pmladek@suse.com>,
 Rasmus Villemoes <linux@rasmusvillemoes.dk>,
 Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>, linux-kernel@vger.kernel.org
Message-ID: <b185c2d6-e890-6e56-3349-2ab023637af0@kleine-koenig.org>
Subject: Re: [PATCH] printf: fix Woverride-init warning for EDEADLK errno
References: <20201026215004.3893088-1-arnd@kernel.org>
In-Reply-To: <20201026215004.3893088-1-arnd@kernel.org>

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Content-Type: text/plain; charset=utf-8
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Good morning Arnd,

On 10/26/20 10:49 PM, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
>=20
> On most architectures, gcc -Wextra warns about the list of error
> numbers containing both EDEADLK and EDEADLOCK:
>=20
> lib/errname.c:15:67: warning: initialized field overwritten [-Woverride=
-init]
>    15 | #define E(err) [err + BUILD_BUG_ON_ZERO(err <=3D 0 || err > 300=
)] =3D "-" #err
>       |                                                                =
   ^~~
> lib/errname.c:172:2: note: in expansion of macro 'E'
>   172 |  E(EDEADLK), /* EDEADLOCK */
>       |  ^
> lib/errname.c:15:67: note: (near initialization for 'names_0[35]')
>    15 | #define E(err) [err + BUILD_BUG_ON_ZERO(err <=3D 0 || err > 300=
)] =3D "-" #err
>       |                                                                =
   ^~~
> lib/errname.c:172:2: note: in expansion of macro 'E'
>   172 |  E(EDEADLK), /* EDEADLOCK */
>       |  ^

bad performance of gcc to warn twice about the same line and not
mentioning the line that has E(EDEADLOCK).

> Make that line conditional on the two values being distinct.
>=20
> Fixes: 57f5677e535b ("printf: add support for printing symbolic error n=
ames")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  lib/errname.c | 2 ++
>  1 file changed, 2 insertions(+)
>=20
> diff --git a/lib/errname.c b/lib/errname.c
> index 0c4d3e66170e..6adff0bf2445 100644
> --- a/lib/errname.c
> +++ b/lib/errname.c
> @@ -169,7 +169,9 @@ static const char *names_0[] =3D {
>  	E(ECANCELED), /* ECANCELLED */
>  	E(EAGAIN), /* EWOULDBLOCK */
>  	E(ECONNREFUSED), /* EREFUSED */
> +#if EDEADLK !=3D EDEADLOCK
>  	E(EDEADLK), /* EDEADLOCK */
> +#endif

The comments suggest that duplicates are expected. Would it make sense
to add similar conditions to the other three entries?

Best regards
Uwe

>  };
>  #undef E
> =20


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