py: Fix reraise logic.

py/vm.c

@@ -51,12 +51,11 @@ typedef enum {
     exc_sp->opcode = op; \
     exc_sp->handler = ip + unum; \
     exc_sp->val_sp = MP_TAGPTR_MAKE(sp, currently_in_except_block); \
-    exc_sp->prev_exc = nlr.ret_val; \
+    exc_sp->prev_exc = MP_OBJ_NULL; \
     currently_in_except_block = 0; /* in a try block now */
 
 #define POP_EXC_BLOCK() \
     currently_in_except_block = MP_TAGPTR_TAG(exc_sp->val_sp); /* restore previous state */ \
-    if (currently_in_except_block) { nlr.ret_val = exc_sp->prev_exc; } \
     exc_sp--; /* pop back to previous exception handler */
 
 mp_vm_return_kind_t mp_execute_byte_code(const byte *code, const mp_obj_t *args, uint n_args, const mp_obj_t *args2, uint n_args2, mp_obj_t *ret) {
@@ -701,12 +700,17 @@ unwind_return:
                         unum = *ip++;
                         assert(unum <= 1);
                         if (unum == 0) {
-                            if (!currently_in_except_block) {
+                            // search for the inner-most previous exception, to reraise it
+                            obj1 = MP_OBJ_NULL;
+                            for (mp_exc_stack *e = exc_sp; e >= exc_stack; e--) {
+                                if (e->prev_exc != MP_OBJ_NULL) {
+                                    obj1 = e->prev_exc;
+                                    break;
+                                }
+                            }
+                            if (obj1 == MP_OBJ_NULL) {
                                 nlr_jump(mp_obj_new_exception_msg(&mp_type_RuntimeError, "No active exception to reraise"));
                             }
-                            // This assumes that nlr.ret_val holds last raised
-                            // exception and is not overwritten since then.
-                            obj1 = nlr.ret_val;
                         } else {
                             obj1 = POP();
                         }
@@ -844,6 +848,8 @@ yield:
                 // catch exception and pass to byte code
                 sp = MP_TAGPTR_PTR(exc_sp->val_sp);
                 ip = exc_sp->handler;
+                // save this exception in the stack so it can be used in a reraise, if needed
+                exc_sp->prev_exc = nlr.ret_val;
                 // push(traceback, exc-val, exc-type)
                 PUSH(mp_const_none);
                 PUSH(nlr.ret_val);