00343: Fix test_faulthandler on GCC 10

bpo-38965: Fix faulthandler._stack_overflow() on GCC 10
Fixed upstream and backported from the 3.7 branch:
https://bugs.python.org/issue38965
python@f4a21d3

bpo-21131: Fix faulthandler.register(chain=True) stack (pythonGH-15276)
https://bugs.python.org/issue21131
python@ac827ed

Author: vstinner

Modules/faulthandler.c

@@ -952,18 +952,15 @@ faulthandler_fatal_error_py(PyObject *self, PyObject *args)
 }
 
 #if defined(HAVE_SIGALTSTACK) && defined(HAVE_SIGACTION)
-#ifdef __INTEL_COMPILER
-   /* Issue #23654: Turn off ICC's tail call optimization for the
-    * stack_overflow generator. ICC turns the recursive tail call into
-    * a loop. */
-#  pragma intel optimization_level 0
-#endif
 static
 Py_uintptr_t
 stack_overflow(Py_uintptr_t min_sp, Py_uintptr_t max_sp, size_t *depth)
 {
-    /* allocate 4096 bytes on the stack at each call */
-    unsigned char buffer[4096];
+    /* Allocate (at least) 4096 bytes on the stack at each call.
+
+       bpo-23654, bpo-38965: use volatile keyword to prevent tail call
+       optimization. */
+    volatile unsigned char buffer[4096];
     Py_uintptr_t sp = (Py_uintptr_t)&buffer;
     *depth += 1;
     if (sp < min_sp || max_sp < sp)
@@ -1146,7 +1143,11 @@ int _PyFaulthandler_Init(void)
      * be able to allocate memory on the stack, even on a stack overflow. If it
      * fails, ignore the error. */
     stack.ss_flags = 0;
-    stack.ss_size = SIGSTKSZ;
+    /* bpo-21131: allocate dedicated stack of SIGSTKSZ*2 bytes, instead of just
+       SIGSTKSZ bytes. Calling the previous signal handler in faulthandler
+       signal handler uses more than SIGSTKSZ bytes of stack memory on some
+       platforms. */
+    stack.ss_size = SIGSTKSZ * 2;
     stack.ss_sp = PyMem_Malloc(stack.ss_size);
     if (stack.ss_sp != NULL) {
         err = sigaltstack(&stack, &old_stack);