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To:     Arnd Bergmann <arnd@arndb.de>
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        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
References: <9516e4b3-f9f2-b150-f019-8b1ef465efb3@tu-dortmund.de>
 <CAK8P3a1sO9HtJPo0S=s3MFK4TN0s_raNTWRTYCYBTGiyHuXg_A@mail.gmail.com>
From:   Alexander Lochmann <alexander.lochmann@tu-dortmund.de>
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Subject: Re: [x86] BUG()/BUG_ON() macros cannot be disabled
Message-ID: <649d3c5c-3d96-0ed3-cd4d-57641f0ee614@tu-dortmund.de>
Date:   Tue, 25 Sep 2018 14:13:30 +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: <649d3c5c-3d96-0ed3-cd4d-57641f0ee614@tu-dortmund.de>
Subject: Re: [x86] BUG()/BUG_ON() macros cannot be disabled
References: <9516e4b3-f9f2-b150-f019-8b1ef465efb3@tu-dortmund.de>
 <CAK8P3a1sO9HtJPo0S=s3MFK4TN0s_raNTWRTYCYBTGiyHuXg_A@mail.gmail.com>
In-Reply-To: <CAK8P3a1sO9HtJPo0S=s3MFK4TN0s_raNTWRTYCYBTGiyHuXg_A@mail.gmail.com>

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Am 25.09.2018 um 14:06 schrieb Arnd Bergmann:
> On Tue, Sep 25, 2018 at 1:35 PM Alexander Lochmann
> <alexander.lochmann@tu-dortmund.de> wrote:
>>
>> Hi Arnd,
>>
>> I recently tried to disable the BUG macros on x86-32. I disabled the
>> config item in 'General Setup -> Configure standard kernel features
>> (expert users) -> BUG() support'.
>> However, BUG/BUG_ON is still defined. In the !CONFIG_BUG branch in
>> include/asm-generic/bug.h (line 181) the code checks for the existence=

>> of architecture-specific variants of those macros.
>> Since x86 defines its own version of BUG(), line 182 is *not* used.
>> In the following, the x86 variant of BUG() is then used to define the
>> BUG_ON() macro.
>>
>> I propose a patch that really disables both macros if the developer
>> wants it.
>> It undefines the respective x86 variants, and defines both macros as
>> 'empty' macros.
>=20
> Maybe we should update the documentation instead. Note that the
> generic version is using 'while (1)' rather than 'while (0)', so this i=
s
> not an empty macro but rather one that does more than the
> arch-specific one-instruction version does.
>=20
> We don't really want an empty macro any more, this was used in
> the past, but causes compile-time warnings and undefined behavior
> for no good reason
I see. So the documentation of the CONFIG_BUG option is wrong?
It currently states that 'Disabling this option eliminates support for
BUG and WARN'.
Is the current implemention (an endless loop) desired behavior?

- Alex
>=20
>        Arnd
>=20

--=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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