From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID
	autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,939bba6defed3e0d
X-Google-Attributes: gid103376,public
From: Tucker Taft <stt@averstar.com>
Subject: Re: problem solved,
 but I don't know why (was: GNAT implementation bug)
Date: 2000/04/14
Message-ID: <38F79277.84A3262E@averstar.com>#1/1
X-Deja-AN: 611289003
Content-Transfer-Encoding: 7bit
References: <8d7n1a$ee6@journal.concentric.net>
X-Accept-Language: en
Content-Type: text/plain; charset=us-ascii
X-Complaints-To: usenet@inmet2.burl.averstar.com
X-Trace: inmet2.burl.averstar.com 955748983 5053 141.199.8.164 (14 Apr 2000
 21:49:43 GMT)
Organization: AverStar (formerly Intermetrics)  Burlington, MA  USA
Mime-Version: 1.0
NNTP-Posting-Date: 14 Apr 2000 21:49:43 GMT
Newsgroups: comp.lang.ada
Date: 2000-04-14T21:49:43+00:00
List-Id: <comp.lang.ada>

Steve Arnold wrote:
> 
> It looks like I solved the problem, but I still have no idea why there was a
> problem in the first place (being a newbie, it seems like it *should've*
> worked).
> 
> When I replaced the following (in Remove):
> 
>        if List.Count = 1 then
>           Clear(List) ;
>        elsif List.Cursor = List.Head then...
> 
> with the actual code from Clear:
> 
>        if List.Count = 1 then
>           List := (Count => 0, Traversing => False, others => null) ;
>        elsif List.Cursor = List.Head then...
> 
> it started working correctly.  But I still have at least two questions (on
> this particular issue, anyway ;)
> 
> 1) Why did this code behave differently when running under Linux than when
> running under windoze?  (obvious answer: windoze is brain-dead)

It could be a bug in the gcc back end for Linux, or it
could be a problem with a small default stack size.

> 
> 2) Why did my trivial change fix it?

You "hand-inlined" one function, which conceivably might lessen
the stack requirements.  Or it is a codegenerator bug, and you
made a small change which happened to eliminate the combination
of constructs which hit the latent bug.

> 
> In other parts of these packages, I call functions/procedures that were
> defined in the same package, and it always worked...

It sounds like a bug in the run-time system, the code generator,
or a too-small default stack size.  I wouldn't try to figure
out what *you* did wrong.  It is probably someone else's fault.

> ... Just what is going on here?  When is it safe to do
> this (if ever) and when is it not safe?

You seem to have been unlucky enough to bump into a compiler or run-time
bug.

-- 
-Tucker Taft   stt@averstar.com   http://www.averstar.com/~stt/
Technical Director, Distributed IT Solutions  (www.averstar.com/tools)
AverStar (formerly Intermetrics, Inc.)   Burlington, MA  USA