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From: bolosky@cs.rochester.edu (Bill Bolosky)
Newsgroups: rec.games.hack,comp.sources.games.bugs
Subject: Re: Nethack crashes after picking character
Keywords: GEC 63, Sys V, UX63 portable CC
Message-ID: <1989Aug22.075948.22553@cs.rochester.edu>
Date: 22 Aug 89 07:59:48 GMT
References: <97@castle.ed.ac.uk> <1021@ks.UUCP>
Reply-To: bolosky@cs.rochester.edu.UUCP (Bill Bolosky)
Organization: U of Rochester, CS Dept, Rochester, NY
Lines: 32

In article <1021@ks.UUCP> jriegel@cstemp2.almaden.ibm.com (Jeff Riegel) writes:
>In article <97@castle.ed.ac.uk>, emct35@castle.ed.ac.uk (Jason Smith) writes:
>> 
>> We can start the program up, it allows us to pick a character, then there is
>> a dramatic pause, followed by a segmentation (memory) fault.
>> 
>  I'm having the same problem using an IBM RT running AIX 2.2.1.  I'd appreciate finding out what this problem is.  I compiled the program with SYS V defined.
>Thanks in advance.
>
>
>-Jeff
>jriegel@ibm.com


This problem has been around on RTs for several older versions of nethack,
also.  It's not operating system dependant, because it also happens under
Mach.  My (fairly strong) suspicion is that it's related to pointer
rounding.  The RT has (half and) fullword load and store operations that oly
work when aligned on a (half or) fullword boundary.  When you try to make an
unaligned reference, it simply rounds the pointer down rather than
generating an error, thus postponing the eventual crash to sometime more
obscure and annoying.  malloc and the compiler do their best to align
everything on 32-bit boundaries, but it is quite possible to foil them.  For
example, if you do foo = malloc(100); *(int *)(foo+2) = x;, x will be
written at *foo, not *(foo + 2).

I have been meaning to look into the sources to find out who does this and
fix it, but I'm far too busy (and lazy).  If someone who's more familiar
with the code knows where something like this might happen, and would let me
know, I'd be happy to fix it.

Bill