[PPL-devel] Re: Segfault consulting a very simple program

[Roberto Bagnara]

Dear all,

thanks for the workaround.  The patch below allowed me to get around
the XSB bug I reported some time ago.  I can thus continue developing
an XSB interface for the Parma Polyhedra Library (http://www.cs.unipr.it/ppl/).
All the best

     Roberto


Luis Fernando Pias de Castro wrote:
> Hi,
> 
> well, it seems both Kostis and David were right. ;)
> 
> The problem is due to a use of numbervars *inside* the singleton
> checks. The patch below seems to eliminate the segfault in this case,
> even though it has the side-effect of missing the warning. Any
> suggestions of how to deal with this better? Or should I commit this?
> 
> Thanks,
> -Luis
> 
> ===================================================================
> RCS file: /cvsroot/xsb/XSB/cmplib/singlton.P,v
> retrieving revision 1.3
> diff -c -r1.3 singlton.P
> *** singlton.P	18 Aug 1999 22:05:23 -0000	1.3
> --- singlton.P	22 Jul 2002 20:33:20 -0000
> ***************
> *** 78,83 ****
> --- 78,85 ----
>   	arg(NewN, Term, Arg),	% We cannot use ll_arg/3 here (Term may be a list)
>   	( Arg = '$VAR'(Number) ->
>   		( integer(Number) ->
> + 		        Number > 0,
> + 		        Number =< Arity,
>   			ll_arg(Number, Occurences, OccCount),
>   			( var(OccCount) -> OccCount = found(_)
>   			; OccCount = found(Times) -> 
> 
> 
> Kostis Sagonas <kostis at csd.uu.se> writes:
> 
> 
>>David wrote:
>>
>> > Yup, it's a bug.  I'm quite sure it arises because the compiler is
>> > using numbervars, and gets confused about your use of $VAR(0) and its
>> > use of $VAR(0) for the variable A.
>>
>>Not quite.  Just in case it was not clear from my previous message,
>>the problem is due to the singleton check pass of the XSB compiler,
>>not the use of numbervars.
>>
>>I bet that in XSB a similar problem can be observed in compiling
>>something like:
>>
>> p :- A = '$VAR'(87456).
>>
>>Or using some other big number.  NOT related to numbervars!
>>
>>Kostis.

-- 
Prof. Roberto Bagnara
Computer Science Group
Department of Mathematics, University of Parma, Italy
http://www.cs.unipr.it/~bagnara/
mailto:bagnara at cs.unipr.it