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:
- Segmentation fault:
* invalid memory read
* invalid memory write
* stack overflow (stack pointer outside the stack memory)
- SIGFPE
* division by zero
* floating point error?
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/
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