[PD-dev] Segfault without messages

[Claude Heiland-Allen]

On 24/10/10 00:22, Brian Neltner wrote:
> Thanks for the info Claude,
>
> Here is what gdb eventually spit out.
>
> I read the documentation page, but I'm afraid I don't really see what I
> should do from that. Is it trying to do a trace with #0 being the
> immediate call that crashed, while #1 is what called #0 and #2 called #1
> and so on? If so, it seems that maxlib history is what is causing the
> problem.

Yes, in the absence of symbol information from 'history.pd_linux', I 
would guess that it is these lines that are the problem:

http://pure-data.svn.sourceforge.net/viewvc/pure-data/branches/pd-extended/0.42/externals/maxlib/history.c?revision=13589&view=markup#l155

155 	 if(++x->x_inpointer > MAX_ARG)
156 	{
157 	x->x_inpointer = 0;
158 	}

Possibly it should be >= instead of >, otherwise the code might end up 
reading/writing past the end of the 0-indexed arrays of size MAX_ARG, 
causing all kinds of memory corruption and random crashes, but I don't 
suggest making the change without checking whether it is correct - the 
code doesn't have any comments indicating the data invariants.

> Sorry, I wish I knew more about programming...
> Brian
>
> On Sat, 2010-10-23 at 21:13 +0100, Claude Heiland-Allen wrote:
>> On 23/10/10 20:36, Brian Neltner wrote:
>>> I have attached the offending script.
>>
>> Seems quite simple, but I don't have pd-extended and miss the required
>> libraries to test.
>>
>>> pd gui; pd process exited
>>> Segmentation Fault
>>>
>>> Not very useful...
>>
>> You could try 'gdb' or 'valgrind' to get more useful output.
>>
>> $ gdb --args pd-extended blah blah
>>   >  run
>> Segmentation Fault
>>   >  bt
>> (tells you where the error is, hopefully)
>>   >  quit
>> $
>>
>> See also:
>>
>> http://puredata.info/docs/developer/DebuggingPdExternals
>>
>>
>> Claude
>


Claude