Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!tank!eecae!cps3xx!usenet
From: usenet@cps3xx.UUCP (Usenet file owner)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Catching free memory violations
Keywords: FreeMem monitor debug memory spam
Message-ID: <3965@cps3xx.UUCP>
Date: 28 Jul 89 00:50:05 GMT
References: <7408@ecsvax.UUCP>
Reply-To: porkka@frith.UUCP (Joe Porkka)
Organization: Michigan State University
Lines: 33

In article <7408@ecsvax.UUCP> utoddl@ecsvax.UUCP (Todd M. Lewis) writes:
>
>I have a program which seems to use memory it doesn't own
>from time to time, and I'd like some way to catch it in the act.
>I've been thinking about a method to see if/when it messes up free
>memory, and I'd like to know why this wouldn't work:
>
>    * Zap FreeMem() to zero out memory whenever it is freed.
>    * Zero out all memory which is already freed.
>    * Periodically scan all free memory to see if it is still
>       zero'd out.  If it isn't, report the address range that
>       has been munged (so you know about it) and optionally 
>       zero that RAM (and see who dies:).

SOunds good.

Easy way to Zap FreeMem is make a function called "freemem"
and then for every other module in the program, #define FreeMem freemem

To help solve my memory trashing problems, I have sometimes replace
AllocMem & FreeMem with the above method with routines
that did the same, but tracked each Alloc and Free. The FreeMem
routine would print an error (with name of the function that called it)
if something tried to free an unalloced block or a block of the
wrong size. TO help debugging without rebooting, then you can
run thru your memory alloc list and actually free blocks that
did not otherwise get freed.

If your memory mismangement is more complicated than messing up
Alloc/Free, then I suggest as a first cut to just check
memory that you have used then freed.

REAL NAME: Joe Porkka   jap@frith.cl.msu.edu