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

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Message-ID: <20100302080527.GT16909@redhat.com>
Date:	Tue, 2 Mar 2010 10:05:27 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Zachary Amsden <zamsden@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...or.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 Mon, Mar 01, 2010 at 01:34:42PM -1000, Zachary Amsden wrote:
> On 03/01/2010 12:56 PM, H. Peter Anvin wrote:
> >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.
> 
> I'd be curious to see if it would need to evolve it to preemptsetjmp
> / irqlongjmp or some other more complex forms in time.
> 
Just don't allow stupid usage of longjmp. Like everything else
it can be abused.

> But I'd rather implement a new language where acquisition of
> resources such as locks, dynamically allocated objects, and ref
> counts are predicated in the function typing and are heavily
> encouraged to possess defined inverses.  Then the closure of a
> particular layer of nesting already has enough information to
> provide release upon escape, and the compiler can easily take the
> burden of checking for a large class of lock and resource violation.
> 
> And it would have to be prettier than the current languages that do
> that, meaning operator overloading would be banned.  Although it
> would define rational numbers, super-extended precision arithmetic,
> imaginary numbers, quaternions and matrices as part of the spec, so
> there would be no need to use arithmetic overrides anyway, and then
> all the nonsensical operators could die, die, die, especially the
> function () and logical operator overrides.
> 
Will you language have a lot of parentheses?

--
			Gleb.
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