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Article #2682

Re: an optimization I claim is illegal

#2682
From: David Chase
Date: Tue, 21 Nov 1995 03:06
31 lines
2098 bytes
Though I think the programming practices that make the optimization illegal
are relatively vile (*), I think it is a mistake to argue the point in terms
of 486 assembly language.  Furthermore, the situation described

> This machine code may LOOK OK, but it ISNT. Why? Because an
> interrupt may come flying in after the call to f and before the
> return. The machine registers are pushed onto the stack
> in the interrupt. After the interrupt has done its job
> it pops the register back. WOOPS!!! A segment register
> gets loaded with an invalid address. A general protection
> fault ensues.

sounds odd to me -- to me, this sounds like quality of OS
implementation, not standards stuff (why would an interrupt handler
fail to put the registers back?  Is this some DOS thing?).  I'd be
interested to see just how this could be disallowed without banning
other things that people find useful and not so vile.
It-would-be-nice, from a taste point of view, if whatever prohibition
emerges could be checked at compile-time, though I suppose my employer
would be perfectly happy if the bug could only (practically) be
detected by running the code through a debugging interpeter.

(*) Relative, of course, to what I already think of C++ code in general.

speaking for myself,

David Chase
---
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Path: arc1-ca.pugleaf.net!in2.uu.net!bounce-back
Date: 21 Nov 95 03:06:55 GMT
Approved: fjh@cs.mu.oz.au
From: chase@centerline.com (David Chase)
Newsgroups: comp.std.c++
Subject: Re: an optimization I claim is illegal
X-Original-Date: 20 Nov 1995 22:43:53 GMT
Organization: CenterLine Software
Message-ID: <48r0b9$d07@wcap.centerline.com>
References: <48ngom$r5f@oznet07.ozemail.com.au>
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