linux-kernel - Re: Definition of BUG on x86

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Date:	Thu, 19 Feb 2009 12:07:11 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Ingo Molnar <mingo@...e.hu>, Petr Tesarik <ptesarik@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Definition of BUG on x86

Jeremy Fitzhardinge wrote:
> Ingo Molnar wrote:
>> Well, the important question is thatGCC will optimize out whatever 
>> comes after the __builtin_trap(), right? To guarantee an assert we can 
>> do something like:
>>
>>      __builtin_trap();
>>     panic("should never get here");
>>
>> to guarantee a message. (But realistically GCC will at most generate a 
>> build error.)
>>   
> 
> Ah, right, I remember the problem.  There's no guaranteed way of getting 
> the address of the ud2a instruction __builtin_trap generates to put it 
> into the bug table.
> 

Did we actually run into any instance where that failed?

It's true that it's not guaranteed, but it seems highly unlikely that it 
would happen in real life.  We *could* do a forward search at that 
point, that should catch the vast majority of the failing cases, again, 
but once again there are no guarantees.

I guess I should ask the gcc people...

	-hpa

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