Python: Fix UB in Inputs Passing (#2726)

Trying to fix the macOS PyPy 3.7 error seen in https://github.com/conda-forge/warpx-feedstock/issues/37
Testing in https://github.com/conda-forge/warpx-feedstock/pull/38

After googling for a while, the original implementation was likely based on https://code.activestate.com/lists/python-list/704158, which contains bugs.

1) Bug: `create_string_buffer`

Allocating new, null-terminated char arrays with `ctypes.create_string_buffer` does lead to scrambled arrays in pypy3.7.
As far as I can see, this [should have also worked](https://docs.python.org/3/library/ctypes.html), but maybe there is a bug in the upstream implementation or the original code created some kind of use-after-free on a temporary while the new implementation just shares the existing byte address.

This leads to errors such as the ones here:
https://github.com/conda-forge/warpx-feedstock/pull/38#issuecomment-1010160519

The call `argvC[i] = ctypes.c_char_p(enc_arg)` is equivalent in creating a `NULL`-terminated char array.

2) Bug: Last Argv Argument

The last argument in the array of char arrays `argv` in ANSII C needs to be a plain `NULL` ptr.
Before this PR, this has been allocated but never initialized, leading to undefined behavior (read as: crashes).

Reference: https://stackoverflow.com/a/39096006/2719194

3) Cleanup: there is a pre-defined `ctypes.c_char_p` we can use for pointer of char.

0 files changed, 0 insertions, 0 deletions