Re: use of setjmp/longjmp in x86 emulator.

From: Zachary Amsden
Date: Mon Mar 01 2010 - 18:34:59 EST

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.

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.

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