[ python-Bugs-975387 ] Python and segfaulting extension modules

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Bugs item #975387, was opened at 2004-06-18 16:32
Message generated for change (Comment added) made by loewis
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Category: Python Interpreter Core
Group: Python 2.3
>Status: Closed
>Resolution: Wont Fix
Priority: 5
Submitted By: Folke Lemaitre (zypher)
Assigned to: Nobody/Anonymous (nobody)
Summary: Python and segfaulting extension modules

Initial Comment:
Normally when a segfault occurs in a python thread 
(mainly in extension modules), two things can happen:
 * Python segfaults
 * Python uses 99% CPU while Garbage Collecting the 
same INVALID object over and over again

The second result is reported as a bug somewhere else.

In a python program with lots of threads and lots of 
loaded extension modules it is almost impossible to find 
the cause of a segfault.

Wouldn't it be possible to have some traceback printed 
when a SIGSEGV occurs? Would be really very handy.

There even exists an extension module that does just 
that, but unfortunately only intercepts problems from 
the main thread. (http://systems.cs.uchicago.edu/wad/)

I think something similar should be standard behaviour of 
python.

Even nicer would be if python just raises an exception 
encapsulating the c stacktrace or even converting a c 
trace to a python traceback

Example WAD output:

WAD can either be imported as a Python extension 
module or linked to an extension module. To illustrate, 
consider the earlier example: 

  % python foo.py
  Segmentation Fault (core dumped)
  %

To identify the problem, a programmer can run Python 
interactively and import WAD as follows: 
  % python
  Python 2.0 (#1, Oct 27 2000, 14:34:45) 
  [GCC 2.95.2 19991024 (release)] on sunos5
  Type "copyright", "credits" or "license" for more   
information.
  >>> import libwadpy
  WAD Enabled
  >>> execfile("foo.py")
  Traceback (most recent call last):
    File "", line 1, in ?
    File "foo.py", line 16, in ?
      foo()
    File "foo.py", line 13, in foo
      bar()
    File "foo.py", line 10, in bar
      spam()
    File "foo.py", line 7, in spam
      doh.doh(a,b,c)
  SegFault: [ C stack trace ]
  
  #2   0x00027774 in call_builtin   
(func=0x1c74f0,arg=0x1a1ccc,kw=0x0)
  #1   0xff022f7c in _wrap_doh
(0x0,0x1a1ccc,0x160ef4,0x9c,0x56b44,0x1aa3d8)
  #0   0xfe7e0568 in doh(a=0x3,b=0x4,c=0x0) in 'foo.c', 
line 28

/u0/beazley/Projects/WAD/Python/foo.c, line 28

    int doh(int a, int b, int *c) {
 =>   *c = a + b;
      return *c;
    }

>>>



----------------------------------------------------------------------

>Comment By: Martin v. Löwis (loewis)
Date: 2004-06-20 23:10

Message:
Logged In: YES 
user_id=21627

This is not a bug report: there is no specific bug being
reported.

Instead, it is a feature request, but I'd like to reject it,
as it is unimplementable, in a generic, platform-independent
way. The fact that WAD only works for the main thread should
be reported as a bug report to the WAD maintainers.

If you think something should be done about this, please
contribute patches. I personally prefer to use a
fully-featured debugger to analyse problems in extension
modules.

----------------------------------------------------------------------

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