linux-kernel - Re: [PATCH] MIPS: Make BUG() _

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Message-ID: <20081122093935.GA31703@linux-mips.org>
Date:	Sat, 22 Nov 2008 09:39:35 +0000
From:	Ralf Baechle <ralf@...ux-mips.org>
To:	David Daney <ddaney@...iumnetworks.com>
Cc:	linux-mips <linux-mips@...ux-mips.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MIPS: Make BUG() __noreturn.

On Thu, Nov 20, 2008 at 05:26:36PM -0800, David Daney wrote:
> From: David Daney <ddaney@...iumnetworks.com>
> Date: Thu, 20 Nov 2008 17:26:36 -0800
> To: linux-mips <linux-mips@...ux-mips.org>
> CC: linux-kernel@...r.kernel.org
> Subject: [PATCH] MIPS: Make BUG() __noreturn.
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> 
> MIPS: Make BUG() __noreturn.

Please don't repeat the subject in the body of a patch email.  Git takes
the subject followed by the body upto the --- line as the log message so
this is just duplication that will need to be manually deleted again.

> Often we do things like put BUG() in the default clause of a case
> statement.  Since it was not declared __noreturn, this could sometimes
> lead to bogus compiler warnings that variables were used
> uninitialized.
>
> There is a small problem in that we have to put a magic while(1); loop to
> fool GCC into really thinking it is noreturn.  This makes the new
> BUG() function 3 instructions long instead of just 1, but I think it
> is worth it as it is now unnecessary to do extra work to silence the
> 'used uninitialized' warnings.
>
> I also re-wrote BUG_ON so that if it is given a constant condition, it
> just does BUG() instead of loading a constant value in to a register
> and testing it.

I don't like the endless loop in the BUG() macros but at this time it seems
the best solution.  Looking forward to __builtin_noreturn().

Patch applied,

  Ralf
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