How it is diagnosed:
We did not reproduce the failure. Relied on source & discussion ananlysis.
Squid crashes with randomly, with log message: xstrdup: tried to dup a NULL pointer!
Null pointer dereference!
Actually, it is not caused by source code bug, but because the binary was broken by a 3rd party patch. After recompile, the crash disappeared.
The developers diagnosed the failure based on stack trace.
Is there any log message?:
Can Errlog anticipate?
Yes. Errlog can print a msg and the BT in the SIGSEGV handler, we can handle this case.