Need help in understanding GDB stack trace

[ying lcs]

All,

I need help in understadning Gdb stack trace:

[Switching to Thread 0xb73b4700 (LWP 28041)]
0x00000000 in ?? ()
(gdb) bt
#0  0x00000000 in ?? ()
#1  0xb5bfc9a6 in DefaultSerializeElementRule::serializeStart (this=0xa450e40,
    domElement=0xa03e104, fd=0xa450ab0)
    at /media/storage/working/content/serializer/src/DefaultSerializeElementRule.cpp:55

And here is my method:

void DefaultSerializeElementRule::serializeStart(nsIDOMElement*
domElement, FILE* fd) {

  nsAutoString tagName;

  domElement->GetTagName(tagName);

  fprintf(fd, "<%s", NS_ConvertUTF16toUTF8(tagName).get());
  // this is line 55:
  serializeAttribute(domElement, fd);

}


I don't understand what is the meaning of :
0x00000000 in ?? ()

from the stack trace, both my domElement, fd are not null. So why my
program crashes?

Thank you.