Re: [xslt] Segmentation fault with an infinite loop

["William M. Brack" <wbrack mmm com hk>]

Mike Hommey said:
> Here we go, copy/paste from gdb output of a full backtrace:
> (Note that I cut after #49, and it goes up to #21807...)
>
> Program received signal SIGSEGV, Segmentation fault.
> [Switching to Thread 16384 (LWP 16779)]
> 0x4013d56d in xmlXPathObjectCopy__internal_alias (val=0x804fc18)
>      at xpath.c:3291
> 3291    xmlXPathObjectCopy(xmlXPathObjectPtr val) {
> #0  0x4013d56d in xmlXPathObjectCopy__internal_alias (val=0x804fc18)
>      at xpath.c:3291
>          ret = 0x0
> #1  0x4014b261 in xmlXPathCompOpEval (ctxt=0x80b0180, op=0x804fa70)
>      at xpath.c:10289
<snip>
>
>
> Mike


Hi Mike,

  I spent quite a bit of time chasing after this, trying on
different systems, different software versions, etc. etc., but was
initially unable to reproduce the problem (similarly to the others
who have responded on the list).  I then went through the gdb dump
you posted and unfortunately (through something known as Saud's
law) worked backwards.  There was nothing amiss until I got to
frame 0 - the crash was not on an executable line of code, but
rather on the arrival to a called routine, before any work had
begun.  This tends to indicate that the actual cause of the crash
was not a problem within the library, but rather was due to the
fact that your process did not have sufficient stack space
allocated to it.

  Despite a couple of queries, I don't believe you have ever told us
which OS and/or distribution you are using.  On two of my systems,
by default (using a generic Linux 2.4 or 2.6 kernel) a process has
8192KB of stack space allocated to it (as can be displayed using
the "ulimit -a" command).  On my Fedora Core 1 system, the default
stack space is 10240KB.  With either of those settings, everything
works properly.  If I manually change that, downwards, to a bit
less that 2000KB, I get exactly the symptoms you have described,
including a standalone crash, runs ok under valgrind, and a gdb
backtrace of just over 20K frames.

  Could you please let the list know more details about your
configuration, and also a copy of your "ulimit -a" output?  If, in
fact, your stack space is less than 8192KB, I would suggest you
change it up to that figure and see if the problem is solved.

HTH,

Bill