bpo-37926: Fix PySys_SetArgvEx(0, NULL, 0) crash (GH-15415)

empty_argv is no longer static in Python 3.8, but it is declared in a temporary scope, whereas argv keeps a reference to it. empty_argv memory (allocated on the stack) is reused by make_sys_argv() code which is inlined when using gcc -O3. Define empty_argv in PySys_SetArgvEx() body, to ensure that it remains valid for the whole lifetime of the PySys_SetArgvEx() call.

Author: vstinner

Misc/NEWS.d/next/C API/2019-08-23-11-35-55.bpo-37926.hnI5IQ.rst

@@ -0,0 +1 @@
+Fix a crash in ``PySys_SetArgvEx(0, NULL, 0)``.

Python/sysmodule.c

@@ -3058,11 +3058,11 @@ make_sys_argv(int argc, wchar_t * const * argv)
 void
 PySys_SetArgvEx(int argc, wchar_t **argv, int updatepath)
 {
+ wchar_t* empty_argv[1] = {L""};
  PyThreadState *tstate = _PyThreadState_GET();
 
  if (argc < 1 || argv == NULL) {
  /* Ensure at least one (empty) argument is seen */
- wchar_t* empty_argv[1] = {L""};
  argv = empty_argv;
  argc = 1;
  }