xref: /openbmc/linux/drivers/acpi/acpica/dswexec.c (revision ae213c44)
1 // SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0
2 /******************************************************************************
3  *
4  * Module Name: dswexec - Dispatcher method execution callbacks;
5  *                        dispatch to interpreter.
6  *
7  * Copyright (C) 2000 - 2019, Intel Corp.
8  *
9  *****************************************************************************/
10 
11 #include <acpi/acpi.h>
12 #include "accommon.h"
13 #include "acparser.h"
14 #include "amlcode.h"
15 #include "acdispat.h"
16 #include "acinterp.h"
17 #include "acnamesp.h"
18 #include "acdebug.h"
19 
20 #define _COMPONENT          ACPI_DISPATCHER
21 ACPI_MODULE_NAME("dswexec")
22 
23 /*
24  * Dispatch table for opcode classes
25  */
26 static acpi_execute_op acpi_gbl_op_type_dispatch[] = {
27 	acpi_ex_opcode_0A_0T_1R,
28 	acpi_ex_opcode_1A_0T_0R,
29 	acpi_ex_opcode_1A_0T_1R,
30 	acpi_ex_opcode_1A_1T_0R,
31 	acpi_ex_opcode_1A_1T_1R,
32 	acpi_ex_opcode_2A_0T_0R,
33 	acpi_ex_opcode_2A_0T_1R,
34 	acpi_ex_opcode_2A_1T_1R,
35 	acpi_ex_opcode_2A_2T_1R,
36 	acpi_ex_opcode_3A_0T_0R,
37 	acpi_ex_opcode_3A_1T_1R,
38 	acpi_ex_opcode_6A_0T_1R
39 };
40 
41 /*****************************************************************************
42  *
43  * FUNCTION:    acpi_ds_get_predicate_value
44  *
45  * PARAMETERS:  walk_state      - Current state of the parse tree walk
46  *              result_obj      - if non-zero, pop result from result stack
47  *
48  * RETURN:      Status
49  *
50  * DESCRIPTION: Get the result of a predicate evaluation
51  *
52  ****************************************************************************/
53 
54 acpi_status
55 acpi_ds_get_predicate_value(struct acpi_walk_state *walk_state,
56 			    union acpi_operand_object *result_obj)
57 {
58 	acpi_status status = AE_OK;
59 	union acpi_operand_object *obj_desc;
60 	union acpi_operand_object *local_obj_desc = NULL;
61 
62 	ACPI_FUNCTION_TRACE_PTR(ds_get_predicate_value, walk_state);
63 
64 	walk_state->control_state->common.state = 0;
65 
66 	if (result_obj) {
67 		status = acpi_ds_result_pop(&obj_desc, walk_state);
68 		if (ACPI_FAILURE(status)) {
69 			ACPI_EXCEPTION((AE_INFO, status,
70 					"Could not get result from predicate evaluation"));
71 
72 			return_ACPI_STATUS(status);
73 		}
74 	} else {
75 		status = acpi_ds_create_operand(walk_state, walk_state->op, 0);
76 		if (ACPI_FAILURE(status)) {
77 			return_ACPI_STATUS(status);
78 		}
79 
80 		status =
81 		    acpi_ex_resolve_to_value(&walk_state->operands[0],
82 					     walk_state);
83 		if (ACPI_FAILURE(status)) {
84 			return_ACPI_STATUS(status);
85 		}
86 
87 		obj_desc = walk_state->operands[0];
88 	}
89 
90 	if (!obj_desc) {
91 		ACPI_ERROR((AE_INFO,
92 			    "No predicate ObjDesc=%p State=%p",
93 			    obj_desc, walk_state));
94 
95 		return_ACPI_STATUS(AE_AML_NO_OPERAND);
96 	}
97 
98 	/*
99 	 * Result of predicate evaluation must be an Integer
100 	 * object. Implicitly convert the argument if necessary.
101 	 */
102 	status = acpi_ex_convert_to_integer(obj_desc, &local_obj_desc,
103 					    ACPI_IMPLICIT_CONVERSION);
104 	if (ACPI_FAILURE(status)) {
105 		goto cleanup;
106 	}
107 
108 	if (local_obj_desc->common.type != ACPI_TYPE_INTEGER) {
109 		ACPI_ERROR((AE_INFO,
110 			    "Bad predicate (not an integer) ObjDesc=%p State=%p Type=0x%X",
111 			    obj_desc, walk_state, obj_desc->common.type));
112 
113 		status = AE_AML_OPERAND_TYPE;
114 		goto cleanup;
115 	}
116 
117 	/* Truncate the predicate to 32-bits if necessary */
118 
119 	(void)acpi_ex_truncate_for32bit_table(local_obj_desc);
120 
121 	/*
122 	 * Save the result of the predicate evaluation on
123 	 * the control stack
124 	 */
125 	if (local_obj_desc->integer.value) {
126 		walk_state->control_state->common.value = TRUE;
127 	} else {
128 		/*
129 		 * Predicate is FALSE, we will just toss the
130 		 * rest of the package
131 		 */
132 		walk_state->control_state->common.value = FALSE;
133 		status = AE_CTRL_FALSE;
134 	}
135 
136 	/* Predicate can be used for an implicit return value */
137 
138 	(void)acpi_ds_do_implicit_return(local_obj_desc, walk_state, TRUE);
139 
140 cleanup:
141 
142 	ACPI_DEBUG_PRINT((ACPI_DB_EXEC,
143 			  "Completed a predicate eval=%X Op=%p\n",
144 			  walk_state->control_state->common.value,
145 			  walk_state->op));
146 
147 	/* Break to debugger to display result */
148 
149 	acpi_db_display_result_object(local_obj_desc, walk_state);
150 
151 	/*
152 	 * Delete the predicate result object (we know that
153 	 * we don't need it anymore)
154 	 */
155 	if (local_obj_desc != obj_desc) {
156 		acpi_ut_remove_reference(local_obj_desc);
157 	}
158 	acpi_ut_remove_reference(obj_desc);
159 
160 	walk_state->control_state->common.state = ACPI_CONTROL_NORMAL;
161 	return_ACPI_STATUS(status);
162 }
163 
164 /*****************************************************************************
165  *
166  * FUNCTION:    acpi_ds_exec_begin_op
167  *
168  * PARAMETERS:  walk_state      - Current state of the parse tree walk
169  *              out_op          - Where to return op if a new one is created
170  *
171  * RETURN:      Status
172  *
173  * DESCRIPTION: Descending callback used during the execution of control
174  *              methods. This is where most operators and operands are
175  *              dispatched to the interpreter.
176  *
177  ****************************************************************************/
178 
179 acpi_status
180 acpi_ds_exec_begin_op(struct acpi_walk_state *walk_state,
181 		      union acpi_parse_object **out_op)
182 {
183 	union acpi_parse_object *op;
184 	acpi_status status = AE_OK;
185 	u32 opcode_class;
186 
187 	ACPI_FUNCTION_TRACE_PTR(ds_exec_begin_op, walk_state);
188 
189 	op = walk_state->op;
190 	if (!op) {
191 		status = acpi_ds_load2_begin_op(walk_state, out_op);
192 		if (ACPI_FAILURE(status)) {
193 			goto error_exit;
194 		}
195 
196 		op = *out_op;
197 		walk_state->op = op;
198 		walk_state->opcode = op->common.aml_opcode;
199 		walk_state->op_info =
200 		    acpi_ps_get_opcode_info(op->common.aml_opcode);
201 
202 		if (acpi_ns_opens_scope(walk_state->op_info->object_type)) {
203 			ACPI_DEBUG_PRINT((ACPI_DB_DISPATCH,
204 					  "(%s) Popping scope for Op %p\n",
205 					  acpi_ut_get_type_name(walk_state->
206 								op_info->
207 								object_type),
208 					  op));
209 
210 			status = acpi_ds_scope_stack_pop(walk_state);
211 			if (ACPI_FAILURE(status)) {
212 				goto error_exit;
213 			}
214 		}
215 	}
216 
217 	if (op == walk_state->origin) {
218 		if (out_op) {
219 			*out_op = op;
220 		}
221 
222 		return_ACPI_STATUS(AE_OK);
223 	}
224 
225 	/*
226 	 * If the previous opcode was a conditional, this opcode
227 	 * must be the beginning of the associated predicate.
228 	 * Save this knowledge in the current scope descriptor
229 	 */
230 	if ((walk_state->control_state) &&
231 	    (walk_state->control_state->common.state ==
232 	     ACPI_CONTROL_CONDITIONAL_EXECUTING)) {
233 		ACPI_DEBUG_PRINT((ACPI_DB_EXEC,
234 				  "Exec predicate Op=%p State=%p\n",
235 				  op, walk_state));
236 
237 		walk_state->control_state->common.state =
238 		    ACPI_CONTROL_PREDICATE_EXECUTING;
239 
240 		/* Save start of predicate */
241 
242 		walk_state->control_state->control.predicate_op = op;
243 	}
244 
245 	opcode_class = walk_state->op_info->class;
246 
247 	/* We want to send namepaths to the load code */
248 
249 	if (op->common.aml_opcode == AML_INT_NAMEPATH_OP) {
250 		opcode_class = AML_CLASS_NAMED_OBJECT;
251 	}
252 
253 	/*
254 	 * Handle the opcode based upon the opcode type
255 	 */
256 	switch (opcode_class) {
257 	case AML_CLASS_CONTROL:
258 
259 		status = acpi_ds_exec_begin_control_op(walk_state, op);
260 		break;
261 
262 	case AML_CLASS_NAMED_OBJECT:
263 
264 		if (walk_state->walk_type & ACPI_WALK_METHOD) {
265 			/*
266 			 * Found a named object declaration during method execution;
267 			 * we must enter this object into the namespace. The created
268 			 * object is temporary and will be deleted upon completion of
269 			 * the execution of this method.
270 			 *
271 			 * Note 10/2010: Except for the Scope() op. This opcode does
272 			 * not actually create a new object, it refers to an existing
273 			 * object. However, for Scope(), we want to indeed open a
274 			 * new scope.
275 			 */
276 			if (op->common.aml_opcode != AML_SCOPE_OP) {
277 				status =
278 				    acpi_ds_load2_begin_op(walk_state, NULL);
279 			} else {
280 				status =
281 				    acpi_ds_scope_stack_push(op->named.node,
282 							     op->named.node->
283 							     type, walk_state);
284 				if (ACPI_FAILURE(status)) {
285 					return_ACPI_STATUS(status);
286 				}
287 			}
288 		}
289 		break;
290 
291 	case AML_CLASS_EXECUTE:
292 	case AML_CLASS_CREATE:
293 
294 		break;
295 
296 	default:
297 
298 		break;
299 	}
300 
301 	/* Nothing to do here during method execution */
302 
303 	return_ACPI_STATUS(status);
304 
305 error_exit:
306 	status = acpi_ds_method_error(status, walk_state);
307 	return_ACPI_STATUS(status);
308 }
309 
310 /*****************************************************************************
311  *
312  * FUNCTION:    acpi_ds_exec_end_op
313  *
314  * PARAMETERS:  walk_state      - Current state of the parse tree walk
315  *
316  * RETURN:      Status
317  *
318  * DESCRIPTION: Ascending callback used during the execution of control
319  *              methods. The only thing we really need to do here is to
320  *              notice the beginning of IF, ELSE, and WHILE blocks.
321  *
322  ****************************************************************************/
323 
324 acpi_status acpi_ds_exec_end_op(struct acpi_walk_state *walk_state)
325 {
326 	union acpi_parse_object *op;
327 	acpi_status status = AE_OK;
328 	u32 op_type;
329 	u32 op_class;
330 	union acpi_parse_object *next_op;
331 	union acpi_parse_object *first_arg;
332 
333 	ACPI_FUNCTION_TRACE_PTR(ds_exec_end_op, walk_state);
334 
335 	op = walk_state->op;
336 	op_type = walk_state->op_info->type;
337 	op_class = walk_state->op_info->class;
338 
339 	if (op_class == AML_CLASS_UNKNOWN) {
340 		ACPI_ERROR((AE_INFO, "Unknown opcode 0x%X",
341 			    op->common.aml_opcode));
342 		return_ACPI_STATUS(AE_NOT_IMPLEMENTED);
343 	}
344 
345 	first_arg = op->common.value.arg;
346 
347 	/* Init the walk state */
348 
349 	walk_state->num_operands = 0;
350 	walk_state->operand_index = 0;
351 	walk_state->return_desc = NULL;
352 	walk_state->result_obj = NULL;
353 
354 	/* Call debugger for single step support (DEBUG build only) */
355 
356 	status = acpi_db_single_step(walk_state, op, op_class);
357 	if (ACPI_FAILURE(status)) {
358 		return_ACPI_STATUS(status);
359 	}
360 
361 	/* Decode the Opcode Class */
362 
363 	switch (op_class) {
364 	case AML_CLASS_ARGUMENT:	/* Constants, literals, etc. */
365 
366 		if (walk_state->opcode == AML_INT_NAMEPATH_OP) {
367 			status = acpi_ds_evaluate_name_path(walk_state);
368 			if (ACPI_FAILURE(status)) {
369 				goto cleanup;
370 			}
371 		}
372 		break;
373 
374 	case AML_CLASS_EXECUTE:	/* Most operators with arguments */
375 
376 		/* Build resolved operand stack */
377 
378 		status = acpi_ds_create_operands(walk_state, first_arg);
379 		if (ACPI_FAILURE(status)) {
380 			goto cleanup;
381 		}
382 
383 		/*
384 		 * All opcodes require operand resolution, with the only exceptions
385 		 * being the object_type and size_of operators.
386 		 */
387 		if (!(walk_state->op_info->flags & AML_NO_OPERAND_RESOLVE)) {
388 
389 			/* Resolve all operands */
390 
391 			status = acpi_ex_resolve_operands(walk_state->opcode,
392 							  &(walk_state->
393 							    operands
394 							    [walk_state->
395 							     num_operands - 1]),
396 							  walk_state);
397 		}
398 
399 		if (ACPI_SUCCESS(status)) {
400 			/*
401 			 * Dispatch the request to the appropriate interpreter handler
402 			 * routine. There is one routine per opcode "type" based upon the
403 			 * number of opcode arguments and return type.
404 			 */
405 			status =
406 			    acpi_gbl_op_type_dispatch[op_type] (walk_state);
407 		} else {
408 			/*
409 			 * Treat constructs of the form "Store(LocalX,LocalX)" as noops when the
410 			 * Local is uninitialized.
411 			 */
412 			if ((status == AE_AML_UNINITIALIZED_LOCAL) &&
413 			    (walk_state->opcode == AML_STORE_OP) &&
414 			    (walk_state->operands[0]->common.type ==
415 			     ACPI_TYPE_LOCAL_REFERENCE)
416 			    && (walk_state->operands[1]->common.type ==
417 				ACPI_TYPE_LOCAL_REFERENCE)
418 			    && (walk_state->operands[0]->reference.class ==
419 				walk_state->operands[1]->reference.class)
420 			    && (walk_state->operands[0]->reference.value ==
421 				walk_state->operands[1]->reference.value)) {
422 				status = AE_OK;
423 			} else {
424 				ACPI_EXCEPTION((AE_INFO, status,
425 						"While resolving operands for [%s]",
426 						acpi_ps_get_opcode_name
427 						(walk_state->opcode)));
428 			}
429 		}
430 
431 		/* Always delete the argument objects and clear the operand stack */
432 
433 		acpi_ds_clear_operands(walk_state);
434 
435 		/*
436 		 * If a result object was returned from above, push it on the
437 		 * current result stack
438 		 */
439 		if (ACPI_SUCCESS(status) && walk_state->result_obj) {
440 			status =
441 			    acpi_ds_result_push(walk_state->result_obj,
442 						walk_state);
443 		}
444 		break;
445 
446 	default:
447 
448 		switch (op_type) {
449 		case AML_TYPE_CONTROL:	/* Type 1 opcode, IF/ELSE/WHILE/NOOP */
450 
451 			/* 1 Operand, 0 external_result, 0 internal_result */
452 
453 			status = acpi_ds_exec_end_control_op(walk_state, op);
454 
455 			break;
456 
457 		case AML_TYPE_METHOD_CALL:
458 			/*
459 			 * If the method is referenced from within a package
460 			 * declaration, it is not a invocation of the method, just
461 			 * a reference to it.
462 			 */
463 			if ((op->asl.parent) &&
464 			    ((op->asl.parent->asl.aml_opcode == AML_PACKAGE_OP)
465 			     || (op->asl.parent->asl.aml_opcode ==
466 				 AML_VARIABLE_PACKAGE_OP))) {
467 				ACPI_DEBUG_PRINT((ACPI_DB_DISPATCH,
468 						  "Method Reference in a Package, Op=%p\n",
469 						  op));
470 
471 				op->common.node = (struct acpi_namespace_node *)
472 				    op->asl.value.arg->asl.node;
473 				acpi_ut_add_reference(op->asl.value.arg->asl.
474 						      node->object);
475 				return_ACPI_STATUS(AE_OK);
476 			}
477 
478 			ACPI_DEBUG_PRINT((ACPI_DB_DISPATCH,
479 					  "Method invocation, Op=%p\n", op));
480 
481 			/*
482 			 * (AML_METHODCALL) Op->Asl.Value.Arg->Asl.Node contains
483 			 * the method Node pointer
484 			 */
485 			/* next_op points to the op that holds the method name */
486 
487 			next_op = first_arg;
488 
489 			/* next_op points to first argument op */
490 
491 			next_op = next_op->common.next;
492 
493 			/*
494 			 * Get the method's arguments and put them on the operand stack
495 			 */
496 			status = acpi_ds_create_operands(walk_state, next_op);
497 			if (ACPI_FAILURE(status)) {
498 				break;
499 			}
500 
501 			/*
502 			 * Since the operands will be passed to another control method,
503 			 * we must resolve all local references here (Local variables,
504 			 * arguments to *this* method, etc.)
505 			 */
506 			status = acpi_ds_resolve_operands(walk_state);
507 			if (ACPI_FAILURE(status)) {
508 
509 				/* On error, clear all resolved operands */
510 
511 				acpi_ds_clear_operands(walk_state);
512 				break;
513 			}
514 
515 			/*
516 			 * Tell the walk loop to preempt this running method and
517 			 * execute the new method
518 			 */
519 			status = AE_CTRL_TRANSFER;
520 
521 			/*
522 			 * Return now; we don't want to disturb anything,
523 			 * especially the operand count!
524 			 */
525 			return_ACPI_STATUS(status);
526 
527 		case AML_TYPE_CREATE_FIELD:
528 
529 			ACPI_DEBUG_PRINT((ACPI_DB_EXEC,
530 					  "Executing CreateField Buffer/Index Op=%p\n",
531 					  op));
532 
533 			status = acpi_ds_load2_end_op(walk_state);
534 			if (ACPI_FAILURE(status)) {
535 				break;
536 			}
537 
538 			status =
539 			    acpi_ds_eval_buffer_field_operands(walk_state, op);
540 			break;
541 
542 		case AML_TYPE_CREATE_OBJECT:
543 
544 			ACPI_DEBUG_PRINT((ACPI_DB_EXEC,
545 					  "Executing CreateObject (Buffer/Package) Op=%p Child=%p ParentOpcode=%4.4X\n",
546 					  op, op->named.value.arg,
547 					  op->common.parent->common.
548 					  aml_opcode));
549 
550 			switch (op->common.parent->common.aml_opcode) {
551 			case AML_NAME_OP:
552 				/*
553 				 * Put the Node on the object stack (Contains the ACPI Name
554 				 * of this object)
555 				 */
556 				walk_state->operands[0] = (void *)
557 				    op->common.parent->common.node;
558 				walk_state->num_operands = 1;
559 
560 				status = acpi_ds_create_node(walk_state,
561 							     op->common.parent->
562 							     common.node,
563 							     op->common.parent);
564 				if (ACPI_FAILURE(status)) {
565 					break;
566 				}
567 
568 				/* Fall through */
569 				/*lint -fallthrough */
570 
571 			case AML_INT_EVAL_SUBTREE_OP:
572 
573 				status =
574 				    acpi_ds_eval_data_object_operands
575 				    (walk_state, op,
576 				     acpi_ns_get_attached_object(op->common.
577 								 parent->common.
578 								 node));
579 				break;
580 
581 			default:
582 
583 				status =
584 				    acpi_ds_eval_data_object_operands
585 				    (walk_state, op, NULL);
586 				break;
587 			}
588 
589 			/*
590 			 * If a result object was returned from above, push it on the
591 			 * current result stack
592 			 */
593 			if (walk_state->result_obj) {
594 				status =
595 				    acpi_ds_result_push(walk_state->result_obj,
596 							walk_state);
597 			}
598 			break;
599 
600 		case AML_TYPE_NAMED_FIELD:
601 		case AML_TYPE_NAMED_COMPLEX:
602 		case AML_TYPE_NAMED_SIMPLE:
603 		case AML_TYPE_NAMED_NO_OBJ:
604 
605 			status = acpi_ds_load2_end_op(walk_state);
606 			if (ACPI_FAILURE(status)) {
607 				break;
608 			}
609 
610 			if (op->common.aml_opcode == AML_REGION_OP) {
611 				ACPI_DEBUG_PRINT((ACPI_DB_EXEC,
612 						  "Executing OpRegion Address/Length Op=%p\n",
613 						  op));
614 
615 				status =
616 				    acpi_ds_eval_region_operands(walk_state,
617 								 op);
618 				if (ACPI_FAILURE(status)) {
619 					break;
620 				}
621 			} else if (op->common.aml_opcode == AML_DATA_REGION_OP) {
622 				ACPI_DEBUG_PRINT((ACPI_DB_EXEC,
623 						  "Executing DataTableRegion Strings Op=%p\n",
624 						  op));
625 
626 				status =
627 				    acpi_ds_eval_table_region_operands
628 				    (walk_state, op);
629 				if (ACPI_FAILURE(status)) {
630 					break;
631 				}
632 			} else if (op->common.aml_opcode == AML_BANK_FIELD_OP) {
633 				ACPI_DEBUG_PRINT((ACPI_DB_EXEC,
634 						  "Executing BankField Op=%p\n",
635 						  op));
636 
637 				status =
638 				    acpi_ds_eval_bank_field_operands(walk_state,
639 								     op);
640 				if (ACPI_FAILURE(status)) {
641 					break;
642 				}
643 			}
644 			break;
645 
646 		case AML_TYPE_UNDEFINED:
647 
648 			ACPI_ERROR((AE_INFO,
649 				    "Undefined opcode type Op=%p", op));
650 			return_ACPI_STATUS(AE_NOT_IMPLEMENTED);
651 
652 		case AML_TYPE_BOGUS:
653 
654 			ACPI_DEBUG_PRINT((ACPI_DB_DISPATCH,
655 					  "Internal opcode=%X type Op=%p\n",
656 					  walk_state->opcode, op));
657 			break;
658 
659 		default:
660 
661 			ACPI_ERROR((AE_INFO,
662 				    "Unimplemented opcode, class=0x%X "
663 				    "type=0x%X Opcode=0x%X Op=%p",
664 				    op_class, op_type, op->common.aml_opcode,
665 				    op));
666 
667 			status = AE_NOT_IMPLEMENTED;
668 			break;
669 		}
670 	}
671 
672 	/*
673 	 * ACPI 2.0 support for 64-bit integers: Truncate numeric
674 	 * result value if we are executing from a 32-bit ACPI table
675 	 */
676 	(void)acpi_ex_truncate_for32bit_table(walk_state->result_obj);
677 
678 	/*
679 	 * Check if we just completed the evaluation of a
680 	 * conditional predicate
681 	 */
682 	if ((ACPI_SUCCESS(status)) &&
683 	    (walk_state->control_state) &&
684 	    (walk_state->control_state->common.state ==
685 	     ACPI_CONTROL_PREDICATE_EXECUTING) &&
686 	    (walk_state->control_state->control.predicate_op == op)) {
687 		status =
688 		    acpi_ds_get_predicate_value(walk_state,
689 						walk_state->result_obj);
690 		walk_state->result_obj = NULL;
691 	}
692 
693 cleanup:
694 
695 	if (walk_state->result_obj) {
696 
697 		/* Break to debugger to display result */
698 
699 		acpi_db_display_result_object(walk_state->result_obj,
700 					      walk_state);
701 
702 		/*
703 		 * Delete the result op if and only if:
704 		 * Parent will not use the result -- such as any
705 		 * non-nested type2 op in a method (parent will be method)
706 		 */
707 		acpi_ds_delete_result_if_not_used(op, walk_state->result_obj,
708 						  walk_state);
709 	}
710 #ifdef _UNDER_DEVELOPMENT
711 
712 	if (walk_state->parser_state.aml == walk_state->parser_state.aml_end) {
713 		acpi_db_method_end(walk_state);
714 	}
715 #endif
716 
717 	/* Invoke exception handler on error */
718 
719 	if (ACPI_FAILURE(status)) {
720 		status = acpi_ds_method_error(status, walk_state);
721 	}
722 
723 	/* Always clear the object stack */
724 
725 	walk_state->num_operands = 0;
726 	return_ACPI_STATUS(status);
727 }
728