[mercury-users] Tcl/Tk

[Ralph Becket]

Tomas, Wednesday,  6 June 2007:
> Hello all,
> 
> I am using the Mercury Tcl/Tk code from `extras' and am having a couple of
> problems:
> 
> 1) Seg faults:
> 
> *** Mercury runtime: caught segmentation violation ***
> PC at signal: 136059738 (81c1b5a)
> address involved: 0xc
> This may have been caused by a stack overflow, due to unbounded recursion.
> exiting from signal handler
> 
> These seem to happen after a while when I am using the GUI. There is also
> a largish data file (Prolog syntax) that cannot be read from the GUI
> without causing a segmentation fault. Reading it before the widgets are
> created works fine.
> 
> I tried increasing the "detstack" and "heap" with no effect. Any ideas how
> I can start to try to debug this?

Compile in a debugging grade then run the program to completion under
mdb.  mdb should report the last trace event number reached before the
program terminated.  Then re-run the program under mdb and `goto n'
where n is that event number.  Step through the program until you get to
the call that segfaults.  Also, try running `stack' to see if there are
obvious problems there (you can probably ignore stack trace items saying
"2978 calls to foo/7" because in a non-debugging grade these will be
turned into while loops, but if you see a long stack trace with repeated
patterns, you've probably got a tail-call optimisation failure.)

-- Ralph
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