[Python-Dev] Issue #8863 adds a new PYTHONNOFAULTHANDLER environment variable

James Y Knight foom at fuhm.net
Sat Dec 18 14:50:49 CET 2010

On Dec 17, 2010, at 7:55 PM, Victor Stinner wrote:

> Hi,
> In 2008, I proposed a patch to raise a Python exception on SIGSEVG signal. In some cases, it's possible to catch the exception, log it, and continue the execution. But because in some cases, the Python internal state is corrupted, the idea was rejected (see the issue #3999).
> Someone asked me to display the Python backtrace on SIGSEGV, instead of raising an exception. I implemented this idea in issue #8863. After 9 versions, I think that the patch is ready for inclusion. It catchs SIGSEGV, SIGFPE, SIGBUS and SIGILL signals, and also display the Python backtrace on fatal errors. Because some operating systems have their own fault handler (eg. Ubuntu with apport), Dave Malcolm asked me to add an option disable the Python handler. 

I think instead of calling abort() to kill the process, you should:
- install the signal handler with SA_NODEFER|SA_RESETHAND (or if sigaction is not present, explicitly reset the action to SIG_DFL and unblock first thing upon entering the handler), and then,
- at the end of the handler, kill(getpid(), orig_signal) in order to abort the process.

This has two advantages: 1) the process's exit code will actually show the correct signal, 2) it might let the OS fault handlers work properly as well -- I'm not sure. If it does, you may want to experiment with whether having or omitting SA_NODEFER gives a better backtrace (from the OS mechanism) in that case.

If #2 actually works, you may not even need the env var, which would be nice. 


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