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psparse.c revision 1.1.1.2
      1 /******************************************************************************
      2  *
      3  * Module Name: psparse - Parser top level AML parse routines
      4  *
      5  *****************************************************************************/
      6 
      7 /*
      8  * Copyright (C) 2000 - 2011, Intel Corp.
      9  * All rights reserved.
     10  *
     11  * Redistribution and use in source and binary forms, with or without
     12  * modification, are permitted provided that the following conditions
     13  * are met:
     14  * 1. Redistributions of source code must retain the above copyright
     15  *    notice, this list of conditions, and the following disclaimer,
     16  *    without modification.
     17  * 2. Redistributions in binary form must reproduce at minimum a disclaimer
     18  *    substantially similar to the "NO WARRANTY" disclaimer below
     19  *    ("Disclaimer") and any redistribution must be conditioned upon
     20  *    including a substantially similar Disclaimer requirement for further
     21  *    binary redistribution.
     22  * 3. Neither the names of the above-listed copyright holders nor the names
     23  *    of any contributors may be used to endorse or promote products derived
     24  *    from this software without specific prior written permission.
     25  *
     26  * Alternatively, this software may be distributed under the terms of the
     27  * GNU General Public License ("GPL") version 2 as published by the Free
     28  * Software Foundation.
     29  *
     30  * NO WARRANTY
     31  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     32  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     33  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR
     34  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
     35  * HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     36  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     37  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     38  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
     39  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
     40  * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     41  * POSSIBILITY OF SUCH DAMAGES.
     42  */
     43 
     44 
     45 /*
     46  * Parse the AML and build an operation tree as most interpreters,
     47  * like Perl, do.  Parsing is done by hand rather than with a YACC
     48  * generated parser to tightly constrain stack and dynamic memory
     49  * usage.  At the same time, parsing is kept flexible and the code
     50  * fairly compact by parsing based on a list of AML opcode
     51  * templates in AmlOpInfo[]
     52  */
     53 
     54 #include "acpi.h"
     55 #include "accommon.h"
     56 #include "acparser.h"
     57 #include "acdispat.h"
     58 #include "amlcode.h"
     59 #include "acinterp.h"
     60 
     61 #define _COMPONENT          ACPI_PARSER
     62         ACPI_MODULE_NAME    ("psparse")
     63 
     64 
     65 /*******************************************************************************
     66  *
     67  * FUNCTION:    AcpiPsGetOpcodeSize
     68  *
     69  * PARAMETERS:  Opcode          - An AML opcode
     70  *
     71  * RETURN:      Size of the opcode, in bytes (1 or 2)
     72  *
     73  * DESCRIPTION: Get the size of the current opcode.
     74  *
     75  ******************************************************************************/
     76 
     77 UINT32
     78 AcpiPsGetOpcodeSize (
     79     UINT32                  Opcode)
     80 {
     81 
     82     /* Extended (2-byte) opcode if > 255 */
     83 
     84     if (Opcode > 0x00FF)
     85     {
     86         return (2);
     87     }
     88 
     89     /* Otherwise, just a single byte opcode */
     90 
     91     return (1);
     92 }
     93 
     94 
     95 /*******************************************************************************
     96  *
     97  * FUNCTION:    AcpiPsPeekOpcode
     98  *
     99  * PARAMETERS:  ParserState         - A parser state object
    100  *
    101  * RETURN:      Next AML opcode
    102  *
    103  * DESCRIPTION: Get next AML opcode (without incrementing AML pointer)
    104  *
    105  ******************************************************************************/
    106 
    107 UINT16
    108 AcpiPsPeekOpcode (
    109     ACPI_PARSE_STATE        *ParserState)
    110 {
    111     UINT8                   *Aml;
    112     UINT16                  Opcode;
    113 
    114 
    115     Aml = ParserState->Aml;
    116     Opcode = (UINT16) ACPI_GET8 (Aml);
    117 
    118     if (Opcode == AML_EXTENDED_OP_PREFIX)
    119     {
    120         /* Extended opcode, get the second opcode byte */
    121 
    122         Aml++;
    123         Opcode = (UINT16) ((Opcode << 8) | ACPI_GET8 (Aml));
    124     }
    125 
    126     return (Opcode);
    127 }
    128 
    129 
    130 /*******************************************************************************
    131  *
    132  * FUNCTION:    AcpiPsCompleteThisOp
    133  *
    134  * PARAMETERS:  WalkState       - Current State
    135  *              Op              - Op to complete
    136  *
    137  * RETURN:      Status
    138  *
    139  * DESCRIPTION: Perform any cleanup at the completion of an Op.
    140  *
    141  ******************************************************************************/
    142 
    143 ACPI_STATUS
    144 AcpiPsCompleteThisOp (
    145     ACPI_WALK_STATE         *WalkState,
    146     ACPI_PARSE_OBJECT       *Op)
    147 {
    148     ACPI_PARSE_OBJECT       *Prev;
    149     ACPI_PARSE_OBJECT       *Next;
    150     const ACPI_OPCODE_INFO  *ParentInfo;
    151     ACPI_PARSE_OBJECT       *ReplacementOp = NULL;
    152     ACPI_STATUS             Status = AE_OK;
    153 
    154 
    155     ACPI_FUNCTION_TRACE_PTR (PsCompleteThisOp, Op);
    156 
    157 
    158     /* Check for null Op, can happen if AML code is corrupt */
    159 
    160     if (!Op)
    161     {
    162         return_ACPI_STATUS (AE_OK);  /* OK for now */
    163     }
    164 
    165     /* Delete this op and the subtree below it if asked to */
    166 
    167     if (((WalkState->ParseFlags & ACPI_PARSE_TREE_MASK) != ACPI_PARSE_DELETE_TREE) ||
    168          (WalkState->OpInfo->Class == AML_CLASS_ARGUMENT))
    169     {
    170         return_ACPI_STATUS (AE_OK);
    171     }
    172 
    173     /* Make sure that we only delete this subtree */
    174 
    175     if (Op->Common.Parent)
    176     {
    177         Prev = Op->Common.Parent->Common.Value.Arg;
    178         if (!Prev)
    179         {
    180             /* Nothing more to do */
    181 
    182             goto Cleanup;
    183         }
    184 
    185         /*
    186          * Check if we need to replace the operator and its subtree
    187          * with a return value op (placeholder op)
    188          */
    189         ParentInfo = AcpiPsGetOpcodeInfo (Op->Common.Parent->Common.AmlOpcode);
    190 
    191         switch (ParentInfo->Class)
    192         {
    193         case AML_CLASS_CONTROL:
    194             break;
    195 
    196         case AML_CLASS_CREATE:
    197 
    198             /*
    199              * These opcodes contain TermArg operands.  The current
    200              * op must be replaced by a placeholder return op
    201              */
    202             ReplacementOp = AcpiPsAllocOp (AML_INT_RETURN_VALUE_OP);
    203             if (!ReplacementOp)
    204             {
    205                 Status = AE_NO_MEMORY;
    206             }
    207             break;
    208 
    209         case AML_CLASS_NAMED_OBJECT:
    210 
    211             /*
    212              * These opcodes contain TermArg operands.  The current
    213              * op must be replaced by a placeholder return op
    214              */
    215             if ((Op->Common.Parent->Common.AmlOpcode == AML_REGION_OP)       ||
    216                 (Op->Common.Parent->Common.AmlOpcode == AML_DATA_REGION_OP)  ||
    217                 (Op->Common.Parent->Common.AmlOpcode == AML_BUFFER_OP)       ||
    218                 (Op->Common.Parent->Common.AmlOpcode == AML_PACKAGE_OP)      ||
    219                 (Op->Common.Parent->Common.AmlOpcode == AML_BANK_FIELD_OP)   ||
    220                 (Op->Common.Parent->Common.AmlOpcode == AML_VAR_PACKAGE_OP))
    221             {
    222                 ReplacementOp = AcpiPsAllocOp (AML_INT_RETURN_VALUE_OP);
    223                 if (!ReplacementOp)
    224                 {
    225                     Status = AE_NO_MEMORY;
    226                 }
    227             }
    228             else if ((Op->Common.Parent->Common.AmlOpcode == AML_NAME_OP) &&
    229                      (WalkState->PassNumber <= ACPI_IMODE_LOAD_PASS2))
    230             {
    231                 if ((Op->Common.AmlOpcode == AML_BUFFER_OP) ||
    232                     (Op->Common.AmlOpcode == AML_PACKAGE_OP) ||
    233                     (Op->Common.AmlOpcode == AML_VAR_PACKAGE_OP))
    234                 {
    235                     ReplacementOp = AcpiPsAllocOp (Op->Common.AmlOpcode);
    236                     if (!ReplacementOp)
    237                     {
    238                         Status = AE_NO_MEMORY;
    239                     }
    240                     else
    241                     {
    242                         ReplacementOp->Named.Data = Op->Named.Data;
    243                         ReplacementOp->Named.Length = Op->Named.Length;
    244                     }
    245                 }
    246             }
    247             break;
    248 
    249         default:
    250 
    251             ReplacementOp = AcpiPsAllocOp (AML_INT_RETURN_VALUE_OP);
    252             if (!ReplacementOp)
    253             {
    254                 Status = AE_NO_MEMORY;
    255             }
    256         }
    257 
    258         /* We must unlink this op from the parent tree */
    259 
    260         if (Prev == Op)
    261         {
    262             /* This op is the first in the list */
    263 
    264             if (ReplacementOp)
    265             {
    266                 ReplacementOp->Common.Parent        = Op->Common.Parent;
    267                 ReplacementOp->Common.Value.Arg     = NULL;
    268                 ReplacementOp->Common.Node          = Op->Common.Node;
    269                 Op->Common.Parent->Common.Value.Arg = ReplacementOp;
    270                 ReplacementOp->Common.Next          = Op->Common.Next;
    271             }
    272             else
    273             {
    274                 Op->Common.Parent->Common.Value.Arg = Op->Common.Next;
    275             }
    276         }
    277 
    278         /* Search the parent list */
    279 
    280         else while (Prev)
    281         {
    282             /* Traverse all siblings in the parent's argument list */
    283 
    284             Next = Prev->Common.Next;
    285             if (Next == Op)
    286             {
    287                 if (ReplacementOp)
    288                 {
    289                     ReplacementOp->Common.Parent    = Op->Common.Parent;
    290                     ReplacementOp->Common.Value.Arg = NULL;
    291                     ReplacementOp->Common.Node      = Op->Common.Node;
    292                     Prev->Common.Next               = ReplacementOp;
    293                     ReplacementOp->Common.Next      = Op->Common.Next;
    294                     Next = NULL;
    295                 }
    296                 else
    297                 {
    298                     Prev->Common.Next = Op->Common.Next;
    299                     Next = NULL;
    300                 }
    301             }
    302             Prev = Next;
    303         }
    304     }
    305 
    306 
    307 Cleanup:
    308 
    309     /* Now we can actually delete the subtree rooted at Op */
    310 
    311     AcpiPsDeleteParseTree (Op);
    312     return_ACPI_STATUS (Status);
    313 }
    314 
    315 
    316 /*******************************************************************************
    317  *
    318  * FUNCTION:    AcpiPsNextParseState
    319  *
    320  * PARAMETERS:  WalkState           - Current state
    321  *              Op                  - Current parse op
    322  *              CallbackStatus      - Status from previous operation
    323  *
    324  * RETURN:      Status
    325  *
    326  * DESCRIPTION: Update the parser state based upon the return exception from
    327  *              the parser callback.
    328  *
    329  ******************************************************************************/
    330 
    331 ACPI_STATUS
    332 AcpiPsNextParseState (
    333     ACPI_WALK_STATE         *WalkState,
    334     ACPI_PARSE_OBJECT       *Op,
    335     ACPI_STATUS             CallbackStatus)
    336 {
    337     ACPI_PARSE_STATE        *ParserState = &WalkState->ParserState;
    338     ACPI_STATUS             Status = AE_CTRL_PENDING;
    339 
    340 
    341     ACPI_FUNCTION_TRACE_PTR (PsNextParseState, Op);
    342 
    343 
    344     switch (CallbackStatus)
    345     {
    346     case AE_CTRL_TERMINATE:
    347         /*
    348          * A control method was terminated via a RETURN statement.
    349          * The walk of this method is complete.
    350          */
    351         ParserState->Aml = ParserState->AmlEnd;
    352         Status = AE_CTRL_TERMINATE;
    353         break;
    354 
    355 
    356     case AE_CTRL_BREAK:
    357 
    358         ParserState->Aml = WalkState->AmlLastWhile;
    359         WalkState->ControlState->Common.Value = FALSE;
    360         Status = AE_CTRL_BREAK;
    361         break;
    362 
    363 
    364     case AE_CTRL_CONTINUE:
    365 
    366         ParserState->Aml = WalkState->AmlLastWhile;
    367         Status = AE_CTRL_CONTINUE;
    368         break;
    369 
    370 
    371     case AE_CTRL_PENDING:
    372 
    373         ParserState->Aml = WalkState->AmlLastWhile;
    374         break;
    375 
    376 #if 0
    377     case AE_CTRL_SKIP:
    378 
    379         ParserState->Aml = ParserState->Scope->ParseScope.PkgEnd;
    380         Status = AE_OK;
    381         break;
    382 #endif
    383 
    384     case AE_CTRL_TRUE:
    385         /*
    386          * Predicate of an IF was true, and we are at the matching ELSE.
    387          * Just close out this package
    388          */
    389         ParserState->Aml = AcpiPsGetNextPackageEnd (ParserState);
    390         Status = AE_CTRL_PENDING;
    391         break;
    392 
    393 
    394     case AE_CTRL_FALSE:
    395         /*
    396          * Either an IF/WHILE Predicate was false or we encountered a BREAK
    397          * opcode.  In both cases, we do not execute the rest of the
    398          * package;  We simply close out the parent (finishing the walk of
    399          * this branch of the tree) and continue execution at the parent
    400          * level.
    401          */
    402         ParserState->Aml = ParserState->Scope->ParseScope.PkgEnd;
    403 
    404         /* In the case of a BREAK, just force a predicate (if any) to FALSE */
    405 
    406         WalkState->ControlState->Common.Value = FALSE;
    407         Status = AE_CTRL_END;
    408         break;
    409 
    410 
    411     case AE_CTRL_TRANSFER:
    412 
    413         /* A method call (invocation) -- transfer control */
    414 
    415         Status = AE_CTRL_TRANSFER;
    416         WalkState->PrevOp = Op;
    417         WalkState->MethodCallOp = Op;
    418         WalkState->MethodCallNode = (Op->Common.Value.Arg)->Common.Node;
    419 
    420         /* Will return value (if any) be used by the caller? */
    421 
    422         WalkState->ReturnUsed = AcpiDsIsResultUsed (Op, WalkState);
    423         break;
    424 
    425 
    426     default:
    427 
    428         Status = CallbackStatus;
    429         if ((CallbackStatus & AE_CODE_MASK) == AE_CODE_CONTROL)
    430         {
    431             Status = AE_OK;
    432         }
    433         break;
    434     }
    435 
    436     return_ACPI_STATUS (Status);
    437 }
    438 
    439 
    440 /*******************************************************************************
    441  *
    442  * FUNCTION:    AcpiPsParseAml
    443  *
    444  * PARAMETERS:  WalkState       - Current state
    445  *
    446  *
    447  * RETURN:      Status
    448  *
    449  * DESCRIPTION: Parse raw AML and return a tree of ops
    450  *
    451  ******************************************************************************/
    452 
    453 ACPI_STATUS
    454 AcpiPsParseAml (
    455     ACPI_WALK_STATE         *WalkState)
    456 {
    457     ACPI_STATUS             Status;
    458     ACPI_THREAD_STATE       *Thread;
    459     ACPI_THREAD_STATE       *PrevWalkList = AcpiGbl_CurrentWalkList;
    460     ACPI_WALK_STATE         *PreviousWalkState;
    461 
    462 
    463     ACPI_FUNCTION_TRACE (PsParseAml);
    464 
    465     ACPI_DEBUG_PRINT ((ACPI_DB_PARSE,
    466         "Entered with WalkState=%p Aml=%p size=%X\n",
    467         WalkState, WalkState->ParserState.Aml,
    468         WalkState->ParserState.AmlSize));
    469 
    470     if (!WalkState->ParserState.Aml)
    471     {
    472         return_ACPI_STATUS (AE_NULL_OBJECT);
    473     }
    474 
    475     /* Create and initialize a new thread state */
    476 
    477     Thread = AcpiUtCreateThreadState ();
    478     if (!Thread)
    479     {
    480         if (WalkState->MethodDesc)
    481         {
    482             /* Executing a control method - additional cleanup */
    483 
    484             AcpiDsTerminateControlMethod (WalkState->MethodDesc, WalkState);
    485         }
    486 
    487         AcpiDsDeleteWalkState (WalkState);
    488         return_ACPI_STATUS (AE_NO_MEMORY);
    489     }
    490 
    491     WalkState->Thread = Thread;
    492 
    493     /*
    494      * If executing a method, the starting SyncLevel is this method's
    495      * SyncLevel
    496      */
    497     if (WalkState->MethodDesc)
    498     {
    499         WalkState->Thread->CurrentSyncLevel = WalkState->MethodDesc->Method.SyncLevel;
    500     }
    501 
    502     AcpiDsPushWalkState (WalkState, Thread);
    503 
    504     /*
    505      * This global allows the AML debugger to get a handle to the currently
    506      * executing control method.
    507      */
    508     AcpiGbl_CurrentWalkList = Thread;
    509 
    510     /*
    511      * Execute the walk loop as long as there is a valid Walk State.  This
    512      * handles nested control method invocations without recursion.
    513      */
    514     ACPI_DEBUG_PRINT ((ACPI_DB_PARSE, "State=%p\n", WalkState));
    515 
    516     Status = AE_OK;
    517     while (WalkState)
    518     {
    519         if (ACPI_SUCCESS (Status))
    520         {
    521             /*
    522              * The ParseLoop executes AML until the method terminates
    523              * or calls another method.
    524              */
    525             Status = AcpiPsParseLoop (WalkState);
    526         }
    527 
    528         ACPI_DEBUG_PRINT ((ACPI_DB_PARSE,
    529             "Completed one call to walk loop, %s State=%p\n",
    530             AcpiFormatException (Status), WalkState));
    531 
    532         if (Status == AE_CTRL_TRANSFER)
    533         {
    534             /*
    535              * A method call was detected.
    536              * Transfer control to the called control method
    537              */
    538             Status = AcpiDsCallControlMethod (Thread, WalkState, NULL);
    539             if (ACPI_FAILURE (Status))
    540             {
    541                 Status = AcpiDsMethodError (Status, WalkState);
    542             }
    543 
    544             /*
    545              * If the transfer to the new method method call worked, a new walk
    546              * state was created -- get it
    547              */
    548             WalkState = AcpiDsGetCurrentWalkState (Thread);
    549             continue;
    550         }
    551         else if (Status == AE_CTRL_TERMINATE)
    552         {
    553             Status = AE_OK;
    554         }
    555         else if ((Status != AE_OK) && (WalkState->MethodDesc))
    556         {
    557             /* Either the method parse or actual execution failed */
    558 
    559             ACPI_ERROR_METHOD ("Method parse/execution failed",
    560                 WalkState->MethodNode, NULL, Status);
    561 
    562             /* Check for possible multi-thread reentrancy problem */
    563 
    564             if ((Status == AE_ALREADY_EXISTS) &&
    565                 (!(WalkState->MethodDesc->Method.InfoFlags & ACPI_METHOD_SERIALIZED)))
    566             {
    567                 /*
    568                  * Method is not serialized and tried to create an object
    569                  * twice. The probable cause is that the method cannot
    570                  * handle reentrancy. Mark as "pending serialized" now, and
    571                  * then mark "serialized" when the last thread exits.
    572                  */
    573                 WalkState->MethodDesc->Method.InfoFlags |=
    574                     ACPI_METHOD_SERIALIZED_PENDING;
    575             }
    576         }
    577 
    578         /* We are done with this walk, move on to the parent if any */
    579 
    580         WalkState = AcpiDsPopWalkState (Thread);
    581 
    582         /* Reset the current scope to the beginning of scope stack */
    583 
    584         AcpiDsScopeStackClear (WalkState);
    585 
    586         /*
    587          * If we just returned from the execution of a control method or if we
    588          * encountered an error during the method parse phase, there's lots of
    589          * cleanup to do
    590          */
    591         if (((WalkState->ParseFlags & ACPI_PARSE_MODE_MASK) == ACPI_PARSE_EXECUTE) ||
    592             (ACPI_FAILURE (Status)))
    593         {
    594             AcpiDsTerminateControlMethod (WalkState->MethodDesc, WalkState);
    595         }
    596 
    597         /* Delete this walk state and all linked control states */
    598 
    599         AcpiPsCleanupScope (&WalkState->ParserState);
    600         PreviousWalkState = WalkState;
    601 
    602         ACPI_DEBUG_PRINT ((ACPI_DB_PARSE,
    603             "ReturnValue=%p, ImplicitValue=%p State=%p\n",
    604             WalkState->ReturnDesc, WalkState->ImplicitReturnObj, WalkState));
    605 
    606         /* Check if we have restarted a preempted walk */
    607 
    608         WalkState = AcpiDsGetCurrentWalkState (Thread);
    609         if (WalkState)
    610         {
    611             if (ACPI_SUCCESS (Status))
    612             {
    613                 /*
    614                  * There is another walk state, restart it.
    615                  * If the method return value is not used by the parent,
    616                  * The object is deleted
    617                  */
    618                 if (!PreviousWalkState->ReturnDesc)
    619                 {
    620                     /*
    621                      * In slack mode execution, if there is no return value
    622                      * we should implicitly return zero (0) as a default value.
    623                      */
    624                     if (AcpiGbl_EnableInterpreterSlack &&
    625                         !PreviousWalkState->ImplicitReturnObj)
    626                     {
    627                         PreviousWalkState->ImplicitReturnObj =
    628                             AcpiUtCreateIntegerObject ((UINT64) 0);
    629                         if (!PreviousWalkState->ImplicitReturnObj)
    630                         {
    631                             return_ACPI_STATUS (AE_NO_MEMORY);
    632                         }
    633                     }
    634 
    635                     /* Restart the calling control method */
    636 
    637                     Status = AcpiDsRestartControlMethod (WalkState,
    638                                 PreviousWalkState->ImplicitReturnObj);
    639                 }
    640                 else
    641                 {
    642                     /*
    643                      * We have a valid return value, delete any implicit
    644                      * return value.
    645                      */
    646                     AcpiDsClearImplicitReturn (PreviousWalkState);
    647 
    648                     Status = AcpiDsRestartControlMethod (WalkState,
    649                                 PreviousWalkState->ReturnDesc);
    650                 }
    651                 if (ACPI_SUCCESS (Status))
    652                 {
    653                     WalkState->WalkType |= ACPI_WALK_METHOD_RESTART;
    654                 }
    655             }
    656             else
    657             {
    658                 /* On error, delete any return object or implicit return */
    659 
    660                 AcpiUtRemoveReference (PreviousWalkState->ReturnDesc);
    661                 AcpiDsClearImplicitReturn (PreviousWalkState);
    662             }
    663         }
    664 
    665         /*
    666          * Just completed a 1st-level method, save the final internal return
    667          * value (if any)
    668          */
    669         else if (PreviousWalkState->CallerReturnDesc)
    670         {
    671             if (PreviousWalkState->ImplicitReturnObj)
    672             {
    673                 *(PreviousWalkState->CallerReturnDesc) =
    674                     PreviousWalkState->ImplicitReturnObj;
    675             }
    676             else
    677             {
    678                  /* NULL if no return value */
    679 
    680                 *(PreviousWalkState->CallerReturnDesc) =
    681                     PreviousWalkState->ReturnDesc;
    682             }
    683         }
    684         else
    685         {
    686             if (PreviousWalkState->ReturnDesc)
    687             {
    688                 /* Caller doesn't want it, must delete it */
    689 
    690                 AcpiUtRemoveReference (PreviousWalkState->ReturnDesc);
    691             }
    692             if (PreviousWalkState->ImplicitReturnObj)
    693             {
    694                 /* Caller doesn't want it, must delete it */
    695 
    696                 AcpiUtRemoveReference (PreviousWalkState->ImplicitReturnObj);
    697             }
    698         }
    699 
    700         AcpiDsDeleteWalkState (PreviousWalkState);
    701     }
    702 
    703     /* Normal exit */
    704 
    705     AcpiExReleaseAllMutexes (Thread);
    706     AcpiUtDeleteGenericState (ACPI_CAST_PTR (ACPI_GENERIC_STATE, Thread));
    707     AcpiGbl_CurrentWalkList = PrevWalkList;
    708     return_ACPI_STATUS (Status);
    709 }
    710 
    711 
    712