Set the minimum size to _PyOS_STACK_MARGIN_BYTES*3

Author: vstinner

Modules/_testinternalcapi.c

@@ -2438,9 +2438,8 @@ test_threadstate_set_stack(PyObject *self, PyObject *Py_UNUSED(args))
     PyThreadState *tstate = PyThreadState_GET();
     assert(!PyErr_Occurred());
 
-    // Test a size smaller than _PyOS_STACK_MARGIN_BYTES
-    size_t size = 4096;
-    assert(size < _PyOS_STACK_MARGIN_BYTES);
+    // Test the minimum stack size
+    size_t size = _PyOS_STACK_MARGIN_BYTES * 3;
     void *start = (void*)(_Py_get_machine_stack_pointer() - size);
     check_threadstate_set_stack(tstate, start, size);
 
@@ -2449,6 +2448,13 @@ test_threadstate_set_stack(PyObject *self, PyObject *Py_UNUSED(args))
     start = (void*)(_Py_get_machine_stack_pointer() - size);
     check_threadstate_set_stack(tstate, start, size);
 
+    // Test invalid size (too small)
+    size = 5;
+    start = (void*)(_Py_get_machine_stack_pointer() - size);
+    assert(PyUnstable_ThreadState_SetStack(tstate, start, size) == -1);
+    assert(PyErr_ExceptionMatches(PyExc_ValueError));
+    PyErr_Clear();
+
     PyUnstable_ThreadState_ResetStack(tstate);
     Py_RETURN_NONE;
 }

Python/ceval.c

@@ -444,20 +444,19 @@ tstate_set_stack(PyThreadState *tstate,
                  void *stack_start_addr, size_t stack_size)
 {
     assert(stack_size > 0);
+    assert(stack_size >= (_PyOS_STACK_MARGIN_BYTES * 3));
 
     _PyThreadStateImpl *ts = (_PyThreadStateImpl *)tstate;
     ts->c_stack_hard_limit = (uintptr_t)stack_start_addr;
     ts->c_stack_top = (uintptr_t)stack_start_addr + stack_size;
 
     uintptr_t soft_limit = ts->c_stack_hard_limit;
-    if (stack_size >= _PyOS_STACK_MARGIN_BYTES) {
 #ifdef _Py_THREAD_SANITIZER
-        // Thread sanitizer crashes if we use a bit more than half the stack.
-        soft_limit += (stack_size / 2);
+    // Thread sanitizer crashes if we use a bit more than half the stack.
+    soft_limit += (stack_size / 2);
 #else
-        soft_limit += _PyOS_STACK_MARGIN_BYTES;
+    soft_limit += _PyOS_STACK_MARGIN_BYTES;
 #endif
-    }
     ts->c_stack_soft_limit = soft_limit;
 
     // Sanity checks
@@ -477,8 +476,10 @@ int
 PyUnstable_ThreadState_SetStack(PyThreadState *tstate,
                                 void *stack_start_addr, size_t stack_size)
 {
-    if (stack_size == 0) {
-        PyErr_SetString(PyExc_ValueError, "stack_size must be greater than 0");
+    if (stack_size < (_PyOS_STACK_MARGIN_BYTES * 3)) {
+        PyErr_Format(PyExc_ValueError,
+                     "stack_size must be at least %zu bytes",
+                     _PyOS_STACK_MARGIN_BYTES * 3);
         return -1;
     }