linux-kernel - Re: use of setjmp/longjmp in x86 emulator.

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Message-ID: <4B8C463B.7070900@zytor.com>
Date:	Mon, 01 Mar 2010 14:56:59 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Zachary Amsden <zamsden@...hat.com>
CC:	Gleb Natapov <gleb@...hat.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, avi@...hat.com, mtosatti@...hat.com
Subject: Re: use of setjmp/longjmp in x86 emulator.

On 03/01/2010 02:31 PM, H. Peter Anvin wrote:
> On 03/01/2010 11:18 AM, Zachary Amsden wrote:
>>
>> It's going to be ugly to emulate segmentation, NX and write protect 
>> support without hardware to do this checking for you, but it's just what 
>> you have to do in this slow path - tedious, fully specified emulation.
>>
>> Just because it's tedious doesn't mean we need to use setjmp / longjmp.  
>> Throw / catch might be effective, but it's still pretty bizarre to do 
>> tricks like that in C.
>>
> 
> Well, setjmp/longjmp really is not much more than exception handling in C.
> 

For what it's worth, I think that setjmp/longjmp is not anywhere near as
dangerous as people want to make it out to be.  gcc will warn for
dangerous uses (and a lot of non-dangerous uses), but generally the
difficult problems can be dealt with by moving the setjmp-protected code
into a separate function.

	-hpa
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