linux-kernel - Re: [x86] BUG()/BUG_ON() macros cannot be disabled

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Date:   Tue, 25 Sep 2018 14:13:30 +0200
From:   Alexander Lochmann <alexander.lochmann@...dortmund.de>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [x86] BUG()/BUG_ON() macros cannot be disabled



Am 25.09.2018 um 14:06 schrieb Arnd Bergmann:
> On Tue, Sep 25, 2018 at 1:35 PM Alexander Lochmann
> <alexander.lochmann@...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.
> 
> Maybe we should update the documentation instead. Note that the
> generic version is using 'while (1)' rather than 'while (0)', so this is
> not an empty macro but rather one that does more than the
> arch-specific one-instruction version does.
> 
> 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
> 
>        Arnd
> 

-- 
Technische Universität Dortmund
Alexander Lochmann                PGP key: 0xBC3EF6FD
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