[Python-Dev] Issue #8863 adds a new PYTHONNOFAULTHANDLER environment variable

["Martin v. Löwis"]

> Functions used by the fault handler:
>  - write()
>  - PyUnicode_Check()
>  - PyFrame_GetLineNumber()
>  - DebugBreak() (Windows, in debug mode, only)
>  - abort()
>  - (macro) PyUnicode_GET_SIZE() and PyUnicode_AS_UNICODE()
>  - PyUnicode_Check(), PyFrame_Check()
>  - PyFrame_GetLineNumber()
>  - _Py_atomic_load_relaxed()
>  - _PyThreadState_GetFrame()
> 
> I suppose that all *Py*() functions are POSIX compliants.

The problem is that merely being POSIX compliant would not be enough
to allow calling a function in a signal handler. Instead, the function
*also* needs to be async-signal safe. However,

>  - abort() conforms to SVr4, POSIX.1-2001, 4.3BSD, C89, C99.
>  - write() conforms to SVr4, 4.3BSD, POSIX.1-2001

These two functions are indeed async-signal safe. So assuming that
none of the functions above indirectly calls a non-async-signal-safe
function, this part is fine.

Looking at your function list, my other concern is that you are calling
Python API without holding the GIL, IIUC. In particular, you are
accessing _PyThreadState_Current, which may not point to the current
thread if the current thread has released the GIL.

Regards,
Martin