From: Thomas Demmer <demmer AT LSTM DOT Ruhr-UNI-Bochum DOT De>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Getting useful information from the traceback
Date: Tue, 16 Dec 1997 10:29:14 +0100
Organization: Lehrstuhl fuer Stroemungsmechanik
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To: djgpp AT delorie DOT com
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Chris Frolik wrote:
> 
> I am writing a program with DJGPP + Allegro, and I have a bug in my
> program which causes the program to crash and print the registers and
> traceback onto the screen.  Thanks to the wonderful symify utility, I
> can locate exactly which line number and which file the problem occurs
> in.  However, now that I know *where* the problem occurs, I am still not
[...] 
> Shutting down Allegro
> Exiting due to signal SIGSEGV
This is the magic line: SIGSEGV means you access memory that is
not within your program's data space. Usually this is a 
NULL pointer access or something similar.

Dividing by zero would get you a SIGFPE, FloatinPointError. 
IIRC, try 
info libc alpha signal
I think there is a description of Signal DJGPP knows. Or 
grep SIGSEGV /djgpp/info/*
to find the location.


[...]
> 
> Call frame traceback EIPs:
>   0x0000e5c7   _test_seg_size__12galaxy_tableiii+131, line 162 of tiles.cc

Triggered here. What does this line say?

>   0x0000e65b   _select_seg_size__12galaxy_tableii+55, line 178 of
> tiles.cc
>   0x00005fc8   _save_map__FP8PACKFILEPc+228, line 40 of save.cc
>   0x000041b6   _save_file__Fv+382, line 386 of file.cc
Poking in the fog I'd wildly guess opening a file and not checking
for a NULL return because of invalid file names or alikes.


-- 
Ciao
Tom

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* Thomas Demmer                                             *
* Lehrstuhl fuer Stroemungsmechanik                         *
* Ruhr-Uni-Bochum                                           *
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