vm: Support strict stackless mode, with proper exception reporting.

I.e. in this mode, C stack will never be used to call a Python function,
but if there's no free heap for a call, it will be reported as
RuntimeError (as expected), not MemoryError.

py/mpconfig.h

@@ -125,11 +125,19 @@
 #define MICROPY_QSTR_BYTES_IN_LEN (1)
 #endif
 
-// Avoid using C stack when making Python function calls.
+// Avoid using C stack when making Python function calls. C stack still
+// may be used if there's no free heap.
 #ifndef MICROPY_STACKLESS
 #define MICROPY_STACKLESS (0)
 #endif
 
+// Never use C stack when making Python function calls. This may break
+// testsuite as will subtly change which exception is thrown in case
+// of too deep recursion and other similar cases.
+#ifndef MICROPY_STACKLESS_STRICT
+#define MICROPY_STACKLESS_STRICT (0)
+#endif
+
 /*****************************************************************************/
 /* Micro Python emitters                                                     */
 

py/runtime.h

@@ -130,6 +130,7 @@ void mp_import_all(mp_obj_t module);
 
 // Raise NotImplementedError with given message
 NORETURN void mp_not_implemented(const char *msg);
+NORETURN void mp_exc_recursion_depth(void);
 
 // helper functions for native/viper code
 mp_uint_t mp_convert_obj_to_native(mp_obj_t obj, mp_uint_t type);

py/stackctrl.c

@@ -27,6 +27,7 @@
 #include "py/mpstate.h"
 #include "py/nlr.h"
 #include "py/obj.h"
+#include "py/runtime.h"
 #include "py/stackctrl.h"
 
 void mp_stack_ctrl_init(void) {
@@ -46,11 +47,15 @@ void mp_stack_set_limit(mp_uint_t limit) {
     MP_STATE_VM(stack_limit) = limit;
 }
 
-void mp_stack_check(void) {
-    if (mp_stack_usage() >= MP_STATE_VM(stack_limit)) {
+void mp_exc_recursion_depth(void) {
     nlr_raise(mp_obj_new_exception_arg1(&mp_type_RuntimeError,
         MP_OBJ_NEW_QSTR(MP_QSTR_maximum_space_recursion_space_depth_space_exceeded)));
 }
+
+void mp_stack_check(void) {
+    if (mp_stack_usage() >= MP_STATE_VM(stack_limit)) {
+        mp_exc_recursion_depth();
+    }
 }
 
 #endif // MICROPY_STACK_CHECK

py/vm.c

@@ -880,6 +880,12 @@ unwind_jump:;
                             nlr_pop();
                             goto run_code_state;
                         }
+                        #if MICROPY_STACKLESS_STRICT
+                        else {
+                        deep_recursion_error:
+                            mp_exc_recursion_depth();
+                        }
+                        #endif
                     }
                     #endif
                     SET_TOP(mp_call_function_n_kw(*sp, unum & 0xff, (unum >> 8) & 0xff, sp + 1));
@@ -912,6 +918,11 @@ unwind_jump:;
                             nlr_pop();
                             goto run_code_state;
                         }
+                        #if MICROPY_STACKLESS_STRICT
+                        else {
+                            goto deep_recursion_error;
+                        }
+                        #endif
                     }
                     #endif
                     SET_TOP(mp_call_method_n_kw_var(false, unum, sp));
@@ -941,6 +952,11 @@ unwind_jump:;
                             nlr_pop();
                             goto run_code_state;
                         }
+                        #if MICROPY_STACKLESS_STRICT
+                        else {
+                            goto deep_recursion_error;
+                        }
+                        #endif
                     }
                     #endif
                     SET_TOP(mp_call_method_n_kw(unum & 0xff, (unum >> 8) & 0xff, sp));
@@ -973,6 +989,11 @@ unwind_jump:;
                             nlr_pop();
                             goto run_code_state;
                         }
+                        #if MICROPY_STACKLESS_STRICT
+                        else {
+                            goto deep_recursion_error;
+                        }
+                        #endif
                     }
                     #endif
                     SET_TOP(mp_call_method_n_kw_var(true, unum, sp));