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From:   Alexander Lochmann <alexander.lochmann@tu-dortmund.de>
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Subject: Re: [x86] BUG()/BUG_ON() macros cannot be disabled
Message-ID: <cb93221b-d4b3-d442-7c8d-97022cfdbe80@tu-dortmund.de>
Date:   Tue, 25 Sep 2018 14:58:26 +0200
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From: Alexander Lochmann <alexander.lochmann@tu-dortmund.de>
To: Arnd Bergmann <arnd@arndb.de>
Cc: linux-arch <linux-arch@vger.kernel.org>,
 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Message-ID: <cb93221b-d4b3-d442-7c8d-97022cfdbe80@tu-dortmund.de>
Subject: Re: [x86] BUG()/BUG_ON() macros cannot be disabled
References: <9516e4b3-f9f2-b150-f019-8b1ef465efb3@tu-dortmund.de>
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Am 25.09.2018 um 14:20 schrieb Arnd Bergmann:
>=20
> I think it's the most reasonable implementation, otherwise a
> function like
>=20
> int something(void)
> {
>       if (x)
>          return 0;
>      else
>           BUG();
> }
>=20
> will return an uninitialized value.
>=20
> The arch specific implementations usually just contain a trapping
> instruction. With CONFIG_BUG() you get a nice console output
> that indicates where this happened, but without CONFIG_BUG(),
> this is just reported as an invalid instruction (if CONFIG_PRINTK
> is still enabled), killing the current process.
>=20
>        Arnd
>=20
I see. In that case, you should really update the documentation and help
page of CONFIG_BUG. In its current version it is misleading. It can be
understood as 'It disables that macro completely.'.

Although I know what the purpose of BUG()/BUG_ON() is, I would not
consider the above example as valid C code....
Defining BUG as an endless loop to overcome GCC warnings about not
returning a value is a dirty hack for me.

- Alex

--=20
Technische Universit=C3=A4t Dortmund
Alexander Lochmann                PGP key: 0xBC3EF6FD
Otto-Hahn-Str. 16                 phone:  +49.231.7556141
D-44227 Dortmund                  fax:    +49.231.7556116
http://ess.cs.tu-dortmund.de/Staff/al


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