[New-bugs-announce] [issue25562] Python 2 & 3 don't allow the user to disable ctypes SEH in windows

[tzickel]

New submission from tzickel:

In Windows, there is a mechanizm called SEH that allows C/C++ programs to catch OS Exceptions (such as divide by zero, page faults, etc..).

Python's ctypes module for some reason forces the user to wrap all ctypes FFI calls with a special SEH wrapper that converts those exceptions to Python exceptions.

For the UNIX people think about it that python installs a signal handler without you asking (or being able to remove it) when calling FFI functions.

The main issue with this, is that when you want to debug why a DLL behaves badly and you want a process dump (or catch the stack trace in the DLL) you can't without attaching a debugger and catching first-chance exceptions (because the ctypes SEH handling masks the issue).

My proposal is to have both in python 2 and in python 3 an option to call an FFI function with selectively using or not SEH.

Here is the SEH wrap (as you can see it's not optional in runtime):
https://github.com/python/cpython/blob/master/Modules/_ctypes/callproc.c#L806

----------
components: ctypes
messages: 254143
nosy: amaury.forgeotdarc, belopolsky, meador.inge, tzickel
priority: normal
severity: normal
status: open
title: Python 2 & 3 don't allow the user to disable ctypes SEH in windows
type: behavior
versions: Python 2.7, Python 3.6

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue25562>
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