Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!zephyr.ens.tek.com!tekcrl!tekgvs!toma
From: toma@tekgvs.LABS.TEK.COM (Tom Almy)
Newsgroups: comp.lang.lisp.x
Subject: Re: xscheme,xlisp save/restore bug?
Keywords: xscheme xlisp bug
Message-ID: <6206@tekgvs.LABS.TEK.COM>
Date: 21 Oct 89 19:28:59 GMT
References: <363@nyit.UUCP>
Reply-To: toma@tekgvs.LABS.TEK.COM (Tom Almy)
Organization: Tektronix, Inc., Beaverton,  OR.
Lines: 41

In article <363@nyit.UUCP> zilla@nyit.UUCP (John Lewis) writes:
>There is a major bug in the xscheme (0.17) save/restore functions.
>Since this code was adapted directly from Xlisp2.0, i'm wondering
>whether there is a similar problem in Xlisp (& a fix, hopefully),
>or why it isn't a problem.

I thought the same, but it turns out the problems are different, although
related to garbage collection.
Here are the restore function fixes for xlisp 2.0:


*******************
Problem: "restore" corrupts system.
Diagnosis: argument stack not being reset -- initial garbage collect
 "marks" random memory!

Solution: Add to "initialize" in xlirestore:


	xlfp = xlsp = xlargstkbase;
	*xlsp++ = NIL;

Problem: "restore" corrupts system with 8086 compilers.
Diagnosis: cvoptr is doing improper arithmetic.

Solution: CVPTR in xlisp.h needs to be defined as 
#define CVPTR(x)	((((unsigned long)(x) >> 16) << 4) + ((unsigned) x))
	return statement in cvoptr() (xlimage.c) needs to be changed from:
return (off + (OFFTYPE)((p - seg->sg_nodes) << 1));
	to:
return (off+(((CVPTR(p)-CVPTR(seg->sg_nodes))/sizeof(struct node))<<1));


Note: for this to work with non-8086 compilers, the default in xlisp.h for 
CVPTR should be changed from (x) to ((OFFTYPE)(x)).



Tom Almy
toma@tekgvs.labs.tek.com
Standard Disclaimers Apply