| msg284196 - (view) |
Author: Ted Meyer (Ted Meyer) |
Date: 2016-12-28 20:38 |
| Using this simple snippit of code: import signal import signal def sig_hdlr(signum, frame): raise ValueError() def faulty(): local_var = "" signal.signal(signal.SIGALRM, sig_hdlr) signal.alarm(1) try: while True: local_var += "!" except ValueError: print (local_val) faulty() I can reliably get a crash: tmathmeyer@tmathmeyer-linuxstation:~$ python --version Python 2.7.6 tmathmeyer@tmathmeyer-linuxstation:~$ python pybug.py Traceback (most recent call last): File "pybug.py", line 16, in faulty() File "pybug.py", line 14, in faulty print local_val NameError: global name 'local_val' is not defined tmathmeyer@tmathmeyer-linuxstation:~$ python3.4 pybug.py Traceback (most recent call last): File "pybug.py", line 12, in faulty local_var += "!" File "pybug.py", line 4, in sig_hdlr raise ValueError() ValueError During handling of the above exception, another exception occurred: Traceback (most recent call last): File "pybug.py", line 16, in faulty() File "pybug.py", line 14, in faulty print (local_val) NameError: name 'local_val' is not defined I can repro this on 2.7.6 and 3.4, but do not have other versions to test on. |
|
|
| msg284197 - (view) |
Author: Ted Meyer (Ted Meyer) |
Date: 2016-12-28 20:46 |
| Sorry everyone, it appears I made a mistake pasting the code in here. There was a type where I was trying to print local_val instead of local_var. the code should be this: import signal def sig_hdlr(signum, frame): raise ValueError() def faulty(): local_var = "" signal.signal(signal.SIGALRM, sig_hdlr) signal.alarm(1) try: while True: local_var += "!" except ValueError: print (local_var) faulty() and the crash should be this: Traceback (most recent call last): File "pybug.py", line 12, in faulty local_var += "!" File "pybug.py", line 4, in sig_hdlr raise ValueError() ValueError During handling of the above exception, another exception occurred: Traceback (most recent call last): File "pybug.py", line 16, in faulty() File "pybug.py", line 14, in faulty print (local_var) UnboundLocalError: local variable 'local_var' referenced before assignment |
|
|
| msg284198 - (view) |
Author: Joe Jevnik (llllllllll) * |
Date: 2016-12-28 20:48 |
| The issue appears to be in ceval.c:unicode_concatenate (or the py2 equivalent) The code sets the local variable on the lhs to NULL before doing a potentially inplace append to the string. This means that if a signal is raised during the concat, we never hit the STORE_FAST instruction following the INPLACE_ADD so the local or cell still holds NULL, triggering an error. I am not really sure what can be done to prevent the failure while still allowing the optimization. |
|
|
| msg284710 - (view) |
Author: Armin Rigo (arigo) *  |
Date: 2017-01-05 07:03 |
| The signal handler is called between the INPLACE_ADD and the following STORE_FAST opcode, never from string_concatenate() itself. A fix would be to make sure signal handlers are not called between these two opcodes. See the minimal, proof-of-concept patch #1. A possibly better fix, which at least should match the SETUP_FINALLY handling in the ticker handler, is attached as patch #2. (Patches against 2.7.13) |
|
|