[Python-Dev] Trap SIGSEGV and SIGFPE (original) (raw)

Victor Stinner victor.stinner at haypocalc.com
Wed Dec 10 12:06:49 CET 2008

Hi,

I published a new version of my fault handler: it installs an handler for signals SIGFPE and SIGSEGV. Using it, it's possible to catch them and continue the execution of your Python program. Example:

try: call_evil_code() except MemoryError: print "A segfault? Haha, I don't care!" print "continue the execution"

(yes, it's possible to continue the execution after a segmentation fault!)

Handled errors:

Such errors may occurs from external libraries (written in C)... or Python builtin libraries (eg. imageop). The handler is now only used in Py_EvalFrameEx(), but it could be used anywhere.

The patch uses sigsetjmp() in Py_EvalFrameEx() to set a "check point", and siglongjmp() in the signal handler to go back to the check point. It also uses a separated stack for the signal handler, because on stack overflow you can not use the stack (ex: unable to call any function!). With MAXDEPTH=100, the memory footprint is ~20 KB. If you call Py_EvalFrameEx() more than MAXDEPTH times, the handler will go back to the frame #MAXDEPTH on error (you loose the last entries in the Python traceback).

sigsetjmp()/siglongjmp() should be available on many OS. I just know that it works perfectly on Linux. sigaltstack() is needed to recover after a stack overflow, but other errors can be catched without it.

I didn't run any benchmark yet, but it would be interresting ;-) Changing MAXDEPTH constant may changes the speed with many recursive calls (eg. MAXDEPTH=1 only set a check for the first call to Py_EvalFrameEx()).

I would appreciate a review, especially for the patch in Python/ceval.c.

-- Victor Stinner aka haypo http://www.haypocalc.com/blog/

More information about the Python-Dev mailing list