POSIX_SPAWN_CHDIR can be passed multiple times with different arguments. In thet case the temporary bytes object saved in*cwd can be deallocated, and theposix_spawn_file_actions_addchdir_np() argument can became a bad pointer.

I think that we need to usetemp_buffer here.

Please add a test forposix_spawn() with multiplePOSIX_SPAWN_CHDIR actions.

Yeah, I am not sure how to handle multiplePOSIX_SPAWN_CHDIR actions.

We can either:

1. callposix_spawn_file_actions_addchdir_np for eachPOSIX_SPAWN_CHDIR in which caseposix_spawn will fail when any of those doesn't exist (or when other error occurs as you pointed out below) even if that one wouldn't be the final one. In such case, the error message might be pretty big.

2. we can omit all but the last one, in which case it will not behave as some might expect. But we would have only two paths to display in the error message.

As for the bad pointer, it's possible, butcwd always holds the latest one so whether it's called with one or muliple ones shouldn't matter here? But I might be completely wrong. Also, if we want to save all the paths (in case 1. is the prefered one), that might change.

posix_spawn_file_actions_addchdir_np also affects how files are found for laterposix_spawn_file_actions_add_open, so you need to do them all.

This is not the only common error possible here. For example, you can get EPERM or EACCES if any of the executable or the cwd paths are not readable for the user, or ENAMETOOLONG if they are too long, or ELOOP if they contain symlink loops, or ENOTDIR if any of intermediate path component is not a directory. It is not possible to handle all errors.

Maybe usePyErr_SetFromErrnoWithFilenameObjects() (notes at end) with too path arguments? It will perhaps not work if there are multiplePOSIX_SPAWN_CHDIR actions, but this is an extremely uncommon case.

The problem withPyErr_SetFromErrnoWithFilenameObjects is that the exception looks like this:

  File "/usr/lib/python3.13/subprocess.py", line 1799, in _posix_spawn    self.pid = os.posix_spawn(executable, args, env, **kwargs)               ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^FileNotFoundError: [Errno 2] No such file or directory: '/usr/bin/ls' -> b'/nonexistent'

and I don't like the arrow, which is why I used thePyErr_Format. But otherwise it works nicely and the change is simpler:

-PyErr_SetFromErrnoWithFilenameObject(PyExc_OSError, path->object);+PyErr_SetFromErrnoWithFilenameObjects(PyExc_OSError, path->object, cwd);

MultiplePOSIX_SPAWN_CHDIR actions make it more complicated...