gh-139653: Add PyUnstable_ThreadState_SetStackProtection() (#139668)

Add PyUnstable_ThreadState_SetStackProtection() and
PyUnstable_ThreadState_ResetStackProtection() functions
to set the stack base address and stack size of a Python
thread state.

Co-authored-by: Petr Viktorin <encukou@gmail.com>

Include/cpython/pystate.h

@@ -276,6 +276,18 @@ PyAPI_FUNC(int) PyGILState_Check(void);
 */
 PyAPI_FUNC(PyObject*) _PyThread_CurrentFrames(void);
 
+// Set the stack protection start address and stack protection size
+// of a Python thread state
+PyAPI_FUNC(int) PyUnstable_ThreadState_SetStackProtection(
+    PyThreadState *tstate,
+    void *stack_start_addr,  // Stack start address
+    size_t stack_size);      // Stack size (in bytes)
+
+// Reset the stack protection start address and stack protection size
+// of a Python thread state
+PyAPI_FUNC(void) PyUnstable_ThreadState_ResetStackProtection(
+    PyThreadState *tstate);
+
 /* Routines for advanced debuggers, requested by David Beazley.
    Don't use unless you know what you are doing! */
 PyAPI_FUNC(PyInterpreterState *) PyInterpreterState_Main(void);

Include/internal/pycore_pythonrun.h

@@ -60,6 +60,12 @@ extern PyObject * _Py_CompileStringObjectWithModule(
 #  define _PyOS_STACK_MARGIN_SHIFT (_PyOS_LOG2_STACK_MARGIN + 2)
 #endif
 
+#ifdef _Py_THREAD_SANITIZER
+#  define _PyOS_MIN_STACK_SIZE (_PyOS_STACK_MARGIN_BYTES * 6)
+#else
+#  define _PyOS_MIN_STACK_SIZE (_PyOS_STACK_MARGIN_BYTES * 3)
+#endif
+
 
 #ifdef __cplusplus
 }

Include/internal/pycore_tstate.h

@@ -37,6 +37,10 @@ typedef struct _PyThreadStateImpl {
     uintptr_t c_stack_soft_limit;
     uintptr_t c_stack_hard_limit;
 
+    // PyUnstable_ThreadState_ResetStackProtection() values
+    uintptr_t c_stack_init_base;
+    uintptr_t c_stack_init_top;
+
     PyObject *asyncio_running_loop; // Strong reference
     PyObject *asyncio_running_task; // Strong reference