Re: XML::LibXML-1.56

On Wednesday 10 December 2003 13:06, Petr Pajas wrote:
> Hi Joachim, All,
>
> can you please try to reproduce the problem with latest CVS version of
> LibXML and LibXSLT?
>
> cvs -z3 -d:pserver:anonymous@xxxxxxxxx:/home/cvs co XML-LibXML
>
> PmmREFCNT_dec is the most usual place of crashes because most freeing
> happens there. It doesn't imply the problem is in PmmREFCNT_dec.

OK I will give that a try and report back if it still persists ....

>
> Maybe I didn't follow this thread carefully enough, but I think the
> subject isn't correct here. If the sigsegv happens within LibXSLT's
> self tests on functions, it is most probably problem related to
> LibXSLT not LibXML.

See my last message. (The subject should have been different.)

However the segfault is being caused by running:
XML-LibXSLT-1.53/t/10functions.t

but:

the position of the segfault is:

(gdb) bt
#0  0x402fdc23 in PmmREFCNT_dec () from 
/usr/local/lib/perl/5.6.1/auto/XML/LibXML/LibXML.so

.. which is a function in:
XML-LibXML-1.56/perl-libxml-mm.c
(and not XML-LibXML-1.56) as one might think ...

Regards,
~/joachim

>
> -- Petr
>
> Joachim Bauernberger <jbauernberger@xxxxxxxxxxxxxxxx> writes:
> > Hi,
> >
> > sill me!!!
> >
> > <duh>I got the subject of this thread wrong....</duh>
> >
> > What I'm are debugging here is XML::LibXML-1.56 + XML::LibXSLT-1.53
> > (XML::LibXML-1.53 is probably fine I dunno ...)
> >
> > Regards,
> > ~/joachim
> >
> > On Wednesday 10 December 2003 12:24, Joachim Bauernberger wrote:
> >> Hi,
> >>
> >> i just had some spare time and was able to confine the problem further
> >> to the PmmREFCNT_dec() function in perl-libxml-mm.c of XML-LibXML-1.56:
> >>
> >> I have added some debug printf statements to demonstrate where it
> >> crashes
> >>
> >> /* decrements the proxy counter. if the counter becomes zero or less,
> >>    this method will free the proxy node. If the node is part of a
> >>    subtree, PmmREFCNT_def will fix the reference counts and delete
> >>    the subtree if it is not required any more.
> >>  */
> >> int
> >> PmmREFCNT_dec( ProxyNodePtr node )
> >> {
> >>     xmlNodePtr libnode = NULL;
> >>     ProxyNodePtr owner = NULL;
> >>     int retval = 0;
> >>
> >>     if ( node != NULL && node) {
> >>         printf("## Before PmmREFCNT(node)\n");
> >>         retval = PmmREFCNT(node)--;
> >>         printf("## node->count=%d\n",node->count);
> >>         printf("## PmmREFCNT(node)=%d\n",PmmREFCNT(node));
> >>         printf("## retval=%d\n",retval);
> >>         if ( PmmREFCNT(node) <= 0 ) {
> >>             xs_warn( "NODE DELETATION\n" );
> >>             libnode = PmmNODE( node );
> >>             if ( libnode != NULL ) {
> >>                 if ( libnode->_private != node ) {
> >>                     xs_warn( "lost node\n" );
> >>                     libnode = NULL;
> >>                 }
> >>                 else {
> >>                     libnode->_private = NULL;
> >>                 }
> >>             }
> >>
> >>             PmmNODE( node ) = NULL;
> >>             if ( PmmOWNER(node) && PmmOWNERPO(node) ) {
> >>                 xs_warn( "DOC NODE!\n" );
> >>                 owner = PmmOWNERPO(node);
> >>                 PmmOWNER( node ) = NULL;
> >>                 if( libnode != NULL && libnode->parent == NULL ) {
> >>                     /* this is required if the node does not directly
> >>                      * belong to the document tree
> >>                      */
> >>                     xs_warn( "REAL DELETE" );
> >>                     PmmFreeNode( libnode );
> >>                 }
> >>                 xs_warn( "decrease owner" );
> >>
> >>            /*
> >>
> >> At this point owner is a dangling pointer which will crash when
> >> dereferencing it in the next call to PmmREFCNT_dec( ) -> remember this
> >> func is recursive ...
> >>            */
> >>
> >>                 printf("## Before 1 PmmREFCNT_dec(owner)\n");
> >>                 PmmREFCNT_dec( owner );
> >>
> >>            /* we won't get here */
> >>                 printf("## After 1 PmmREFCNT_dec()\n");
> >>             }
> >>             else if ( libnode != NULL ) {
> >>                 xs_warn( "STANDALONE REAL DELETE" );
> >>                 PmmFreeNode( libnode );
> >>             }
> >>             Safefree( node );
> >>             /* free( node ); */
> >>         }
> >>     }
> >>     else {
> >>         xs_warn("lost node" );
> >>     }
> >>     printf ("Returning retval=%d\n",retval);
> >>     return retval;
> >> }
> >>
> >>
> >> ~~~~~~~~~~~~~~~~~~~~~
> >> ~~~~~~~~~~~~~~~~~~~~~
> >>
> >> Having a quick look at the state of "owner" shows that it is probably
> >> not fit for being passwd around:
> >>
> >> (gdb) p *node->owner
> >> $10 = {_private = 0x30312f74, type = 1668183398, name = 0x6e6f6974
> >> <Address 0x6e6f6974 out of bounds>, children = 0x742e73, last =
> >> 0x4015a6e8, parent = 0x41, next = 0x0,
> >>   prev = 0x0, doc = 0x0, ns = 0x0, content = 0x0, properties = 0x0,
> >> nsDef = 0x82eb5e8}
> >>
> >> But where does owner get srewed up in the first place? I doubt that it's
> >> anywhere in perl-libxml-mm.c !!
> >>
> >> I will try to look deeper into this when I have more time at hand, ->
> >> also I am not familiar with the code so the person who wrote this might
> >> be able to spot the problem faster than me ...
> >>
> >> Note that you have to add the -g switch to CFLAGS in the XML-LibXML
> >> Makefile to get any meaningful debugging with gdb.
> >>
> >> Cheers,
> >> ~/joachim
> >>
> >> On Tuesday 09 December 2003 08:55, Joachim Bauernberger wrote:
> >> > Hi Grant,
> >> >
> >> > On Monday 08 December 2003 18:49, Grant McLean wrote:
> >> > <snip/>
> >> >
> >> > > > [t][jmbdev]# perl ./10functions.t
> >> > > > 1..14
> >> > > > ok 1
> >> > > > ok 2
> >> > > > ok 3
> >> > > > ok 4
> >> > > > ok 5
> >> > > > ok 6
> >> > > > Segmentation fault
> >> > >
> >> > > One obvious difference between running 'make test' and running the
> >> > > test directly is that make test uses the recently built version of
> >> > > LibXML sitting in the blib directory whereas your simple perl
> >> > > command to run the test script uses the version of LibXML installed
> >> > > on your system.
> >> >
> >> > That version of LibXML was already installed from before, so it should
> >> > not make a difference (I also double checked by using the -Include
> >> > switches as you did below but it's all the same...)
> >> >
> >> > cheers,
> >> > ~/joachim
> >> >
> >> > > You could try editing the command line generated by 'make test':
> >> > >
> >> > > PERL_DL_NONLAZY=1 /usr/bin/perl -Iblib/arch -Iblib/lib \
> >> > > -I/usr/lib/perl/5.6.1  -I/usr/share/perl/5.6.1 t/10functions.t
> >> > >
> >> > > or you could use the 'prove' script that comes with recent versions
> >> > > of Test::Harness to achieve a similar thing.
> >> > >
> >> > > Of course if you've already run 'make install' then the files from
> >> > > blib should have been copied to /usr/local/lib already.
> >> > >
> >> > > Cheers
> >> > > Grant

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