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dtutils.c revision 1.1.1.17
      1 /******************************************************************************
      2  *
      3  * Module Name: dtutils.c - Utility routines for the data table compiler
      4  *
      5  *****************************************************************************/
      6 
      7 /*
      8  * Copyright (C) 2000 - 2020, 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 #include "aslcompiler.h"
     45 #include "actables.h"
     46 
     47 #define _COMPONENT          DT_COMPILER
     48         ACPI_MODULE_NAME    ("dtutils")
     49 
     50 /* Local prototypes */
     51 
     52 static void
     53 DtSum (
     54     DT_SUBTABLE             *Subtable,
     55     void                    *Context,
     56     void                    *ReturnValue);
     57 
     58 
     59 /******************************************************************************
     60  *
     61  * FUNCTION:    DtError
     62  *
     63  * PARAMETERS:  Level               - Seriousness (Warning/error, etc.)
     64  *              MessageId           - Index into global message buffer
     65  *              Op                  - Parse node where error happened
     66  *              ExtraMessage        - additional error message
     67  *
     68  * RETURN:      None
     69  *
     70  * DESCRIPTION: Common error interface for data table compiler
     71  *
     72  *****************************************************************************/
     73 
     74 void
     75 DtError (
     76     UINT8                   Level,
     77     UINT16                  MessageId,
     78     DT_FIELD                *FieldObject,
     79     char                    *ExtraMessage)
     80 {
     81     UINT32                  Line = 0;
     82 
     83 
     84     /* Field object could be NULL */
     85 
     86     if (FieldObject)
     87     {
     88         Line = FieldObject->Line;
     89     }
     90 
     91     /* Check if user wants to ignore this exception */
     92 
     93     if (AslIsExceptionIgnored (AslGbl_Files[ASL_FILE_INPUT].Filename,
     94         Line, Level, MessageId))
     95     {
     96         return;
     97     }
     98 
     99     if (FieldObject)
    100     {
    101         AslCommonError (Level, MessageId,
    102             FieldObject->Line,
    103             FieldObject->Line,
    104             FieldObject->ByteOffset,
    105             FieldObject->Column,
    106             AslGbl_Files[ASL_FILE_INPUT].Filename, ExtraMessage);
    107     }
    108     else
    109     {
    110         AslCommonError (Level, MessageId, 0,
    111             0, 0, 0, 0, ExtraMessage);
    112     }
    113 }
    114 
    115 
    116 /******************************************************************************
    117  *
    118  * FUNCTION:    DtNameError
    119  *
    120  * PARAMETERS:  Level               - Seriousness (Warning/error, etc.)
    121  *              MessageId           - Index into global message buffer
    122  *              Op                  - Parse node where error happened
    123  *              ExtraMessage        - additional error message
    124  *
    125  * RETURN:      None
    126  *
    127  * DESCRIPTION: Error interface for named objects
    128  *
    129  *****************************************************************************/
    130 
    131 void
    132 DtNameError (
    133     UINT8                   Level,
    134     UINT16                  MessageId,
    135     DT_FIELD                *FieldObject,
    136     char                    *ExtraMessage)
    137 {
    138 
    139     switch (Level)
    140     {
    141     case ASL_WARNING2:
    142     case ASL_WARNING3:
    143 
    144         if (AslGbl_WarningLevel < Level)
    145         {
    146             return;
    147         }
    148         break;
    149 
    150     default:
    151 
    152         break;
    153     }
    154 
    155     if (FieldObject)
    156     {
    157         AslCommonError (Level, MessageId,
    158             FieldObject->Line,
    159             FieldObject->Line,
    160             FieldObject->ByteOffset,
    161             FieldObject->NameColumn,
    162             AslGbl_Files[ASL_FILE_INPUT].Filename, ExtraMessage);
    163     }
    164     else
    165     {
    166         AslCommonError (Level, MessageId, 0,
    167             0, 0, 0, 0, ExtraMessage);
    168     }
    169 }
    170 
    171 
    172 /*******************************************************************************
    173  *
    174  * FUNCTION:    DtFatal
    175  *
    176  * PARAMETERS:  None
    177  *
    178  * RETURN:      None
    179  *
    180  * DESCRIPTION: Dump the error log and abort the compiler. Used for serious
    181  *              compile or I/O errors
    182  *
    183  ******************************************************************************/
    184 
    185 void
    186 DtFatal (
    187     UINT16                  MessageId,
    188     DT_FIELD                *FieldObject,
    189     char                    *ExtraMessage)
    190 {
    191 
    192     DtError (ASL_ERROR, MessageId, FieldObject, ExtraMessage);
    193 
    194 /*
    195  * TBD: remove this entire function, DtFatal
    196  *
    197  * We cannot abort the compiler on error, because we may be compiling a
    198  * list of files. We must move on to the next file.
    199  */
    200 #ifdef __OBSOLETE
    201     CmCleanupAndExit ();
    202     exit (1);
    203 #endif
    204 }
    205 
    206 
    207 /*******************************************************************************
    208  *
    209  * FUNCTION:    DtDoConstant
    210  *
    211  * PARAMETERS:  String              - Only hex constants are supported,
    212  *                                    regardless of whether the 0x prefix
    213  *                                    is used
    214  *
    215  * RETURN:      Converted Integer
    216  *
    217  * DESCRIPTION: Convert a string to an integer, with overflow/error checking.
    218  *
    219  ******************************************************************************/
    220 
    221 UINT64
    222 DtDoConstant (
    223     char                    *String)
    224 {
    225     UINT64                  ConvertedInteger;
    226 
    227 
    228     /*
    229      * TBD: The ImplicitStrtoul64 function does not report overflow
    230      * conditions. The input string is simply truncated. If it is
    231      * desired to report overflow to the table compiler, this should
    232      * somehow be added here. Note: integers that are prefixed with 0x
    233      * or not are both hex integers.
    234      */
    235     ConvertedInteger = AcpiUtImplicitStrtoul64 (String);
    236     return (ConvertedInteger);
    237 }
    238 
    239 /******************************************************************************
    240  *
    241  * FUNCTION:    DtGetFieldValue
    242  *
    243  * PARAMETERS:  Field               - Current field list pointer
    244  *
    245  * RETURN:      Field value
    246  *
    247  * DESCRIPTION: Get field value
    248  *
    249  *****************************************************************************/
    250 
    251 char *
    252 DtGetFieldValue (
    253     DT_FIELD                *Field)
    254 {
    255     if (!Field)
    256     {
    257         return (NULL);
    258     }
    259 
    260     return (Field->Value);
    261 }
    262 
    263 
    264 /******************************************************************************
    265  *
    266  * FUNCTION:    DtGetFieldType
    267  *
    268  * PARAMETERS:  Info                - Data table info
    269  *
    270  * RETURN:      Field type
    271  *
    272  * DESCRIPTION: Get field type
    273  *
    274  *****************************************************************************/
    275 
    276 UINT8
    277 DtGetFieldType (
    278     ACPI_DMTABLE_INFO       *Info)
    279 {
    280     UINT8                   Type;
    281 
    282 
    283     /* DT_FLAG means that this is the start of a block of flag bits */
    284     /* TBD - we can make these a separate opcode later */
    285 
    286     if (Info->Flags & DT_FLAG)
    287     {
    288         return (DT_FIELD_TYPE_FLAGS_INTEGER);
    289     }
    290 
    291     /* Type is based upon the opcode for this field in the info table */
    292 
    293     switch (Info->Opcode)
    294     {
    295     case ACPI_DMT_FLAG0:
    296     case ACPI_DMT_FLAG1:
    297     case ACPI_DMT_FLAG2:
    298     case ACPI_DMT_FLAG3:
    299     case ACPI_DMT_FLAG4:
    300     case ACPI_DMT_FLAG5:
    301     case ACPI_DMT_FLAG6:
    302     case ACPI_DMT_FLAG7:
    303     case ACPI_DMT_FLAGS0:
    304     case ACPI_DMT_FLAGS1:
    305     case ACPI_DMT_FLAGS2:
    306     case ACPI_DMT_FLAGS4:
    307     case ACPI_DMT_FLAGS4_0:
    308     case ACPI_DMT_FLAGS4_4:
    309     case ACPI_DMT_FLAGS4_8:
    310     case ACPI_DMT_FLAGS4_12:
    311     case ACPI_DMT_FLAGS16_16:
    312 
    313         Type = DT_FIELD_TYPE_FLAG;
    314         break;
    315 
    316     case ACPI_DMT_NAME4:
    317     case ACPI_DMT_SIG:
    318     case ACPI_DMT_NAME6:
    319     case ACPI_DMT_NAME8:
    320     case ACPI_DMT_STRING:
    321 
    322         Type = DT_FIELD_TYPE_STRING;
    323         break;
    324 
    325     case ACPI_DMT_BUFFER:
    326     case ACPI_DMT_RAW_BUFFER:
    327     case ACPI_DMT_BUF7:
    328     case ACPI_DMT_BUF10:
    329     case ACPI_DMT_BUF12:
    330     case ACPI_DMT_BUF16:
    331     case ACPI_DMT_BUF128:
    332     case ACPI_DMT_PCI_PATH:
    333 
    334         Type = DT_FIELD_TYPE_BUFFER;
    335         break;
    336 
    337     case ACPI_DMT_GAS:
    338     case ACPI_DMT_HESTNTFY:
    339     case ACPI_DMT_IORTMEM:
    340 
    341         Type = DT_FIELD_TYPE_INLINE_SUBTABLE;
    342         break;
    343 
    344     case ACPI_DMT_UNICODE:
    345 
    346         Type = DT_FIELD_TYPE_UNICODE;
    347         break;
    348 
    349     case ACPI_DMT_UUID:
    350 
    351         Type = DT_FIELD_TYPE_UUID;
    352         break;
    353 
    354     case ACPI_DMT_DEVICE_PATH:
    355 
    356         Type = DT_FIELD_TYPE_DEVICE_PATH;
    357         break;
    358 
    359     case ACPI_DMT_LABEL:
    360 
    361         Type = DT_FIELD_TYPE_LABEL;
    362         break;
    363 
    364     default:
    365 
    366         Type = DT_FIELD_TYPE_INTEGER;
    367         break;
    368     }
    369 
    370     return (Type);
    371 }
    372 
    373 
    374 /******************************************************************************
    375  *
    376  * FUNCTION:    DtGetBufferLength
    377  *
    378  * PARAMETERS:  Buffer              - List of integers,
    379  *                                    for example "10 3A 4F 2E"
    380  *
    381  * RETURN:      Count of integer
    382  *
    383  * DESCRIPTION: Get length of bytes needed to store the integers
    384  *
    385  *****************************************************************************/
    386 
    387 UINT32
    388 DtGetBufferLength (
    389     char                    *Buffer)
    390 {
    391     UINT32                  ByteLength = 0;
    392 
    393 
    394     while (*Buffer)
    395     {
    396         if (*Buffer == ' ')
    397         {
    398             ByteLength++;
    399 
    400             while (*Buffer == ' ')
    401             {
    402                 Buffer++;
    403             }
    404         }
    405 
    406         Buffer++;
    407     }
    408 
    409     return (++ByteLength);
    410 }
    411 
    412 
    413 /******************************************************************************
    414  *
    415  * FUNCTION:    DtGetFieldLength
    416  *
    417  * PARAMETERS:  Field               - Current field
    418  *              Info                - Data table info
    419  *
    420  * RETURN:      Field length
    421  *
    422  * DESCRIPTION: Get length of bytes needed to compile the field
    423  *
    424  * Note: This function must remain in sync with AcpiDmDumpTable.
    425  *
    426  *****************************************************************************/
    427 
    428 UINT32
    429 DtGetFieldLength (
    430     DT_FIELD                *Field,
    431     ACPI_DMTABLE_INFO       *Info)
    432 {
    433     UINT32                  ByteLength = 0;
    434     char                    *Value;
    435 
    436 
    437     /* Length is based upon the opcode for this field in the info table */
    438 
    439     switch (Info->Opcode)
    440     {
    441     case ACPI_DMT_FLAG0:
    442     case ACPI_DMT_FLAG1:
    443     case ACPI_DMT_FLAG2:
    444     case ACPI_DMT_FLAG3:
    445     case ACPI_DMT_FLAG4:
    446     case ACPI_DMT_FLAG5:
    447     case ACPI_DMT_FLAG6:
    448     case ACPI_DMT_FLAG7:
    449     case ACPI_DMT_FLAGS0:
    450     case ACPI_DMT_FLAGS1:
    451     case ACPI_DMT_FLAGS2:
    452     case ACPI_DMT_FLAGS4:
    453     case ACPI_DMT_FLAGS4_0:
    454     case ACPI_DMT_FLAGS4_4:
    455     case ACPI_DMT_FLAGS4_8:
    456     case ACPI_DMT_FLAGS4_12:
    457     case ACPI_DMT_FLAGS16_16:
    458     case ACPI_DMT_LABEL:
    459     case ACPI_DMT_EXTRA_TEXT:
    460 
    461         ByteLength = 0;
    462         break;
    463 
    464     case ACPI_DMT_UINT8:
    465     case ACPI_DMT_CHKSUM:
    466     case ACPI_DMT_SPACEID:
    467     case ACPI_DMT_ACCWIDTH:
    468     case ACPI_DMT_IVRS:
    469     case ACPI_DMT_GTDT:
    470     case ACPI_DMT_MADT:
    471     case ACPI_DMT_PCCT:
    472     case ACPI_DMT_PMTT:
    473     case ACPI_DMT_PPTT:
    474     case ACPI_DMT_SDEV:
    475     case ACPI_DMT_SRAT:
    476     case ACPI_DMT_ASF:
    477     case ACPI_DMT_HESTNTYP:
    478     case ACPI_DMT_FADTPM:
    479     case ACPI_DMT_EINJACT:
    480     case ACPI_DMT_EINJINST:
    481     case ACPI_DMT_ERSTACT:
    482     case ACPI_DMT_ERSTINST:
    483     case ACPI_DMT_DMAR_SCOPE:
    484 
    485         ByteLength = 1;
    486         break;
    487 
    488     case ACPI_DMT_UINT16:
    489     case ACPI_DMT_DMAR:
    490     case ACPI_DMT_HEST:
    491     case ACPI_DMT_HMAT:
    492     case ACPI_DMT_NFIT:
    493     case ACPI_DMT_PCI_PATH:
    494 
    495         ByteLength = 2;
    496         break;
    497 
    498     case ACPI_DMT_UINT24:
    499 
    500         ByteLength = 3;
    501         break;
    502 
    503     case ACPI_DMT_UINT32:
    504     case ACPI_DMT_NAME4:
    505     case ACPI_DMT_SIG:
    506     case ACPI_DMT_LPIT:
    507     case ACPI_DMT_TPM2:
    508 
    509         ByteLength = 4;
    510         break;
    511 
    512     case ACPI_DMT_UINT40:
    513 
    514         ByteLength = 5;
    515         break;
    516 
    517     case ACPI_DMT_UINT48:
    518     case ACPI_DMT_NAME6:
    519 
    520         ByteLength = 6;
    521         break;
    522 
    523     case ACPI_DMT_UINT56:
    524     case ACPI_DMT_BUF7:
    525 
    526         ByteLength = 7;
    527         break;
    528 
    529     case ACPI_DMT_UINT64:
    530     case ACPI_DMT_NAME8:
    531 
    532         ByteLength = 8;
    533         break;
    534 
    535     case ACPI_DMT_STRING:
    536 
    537         Value = DtGetFieldValue (Field);
    538         if (Value)
    539         {
    540             ByteLength = strlen (Value) + 1;
    541         }
    542         else
    543         {   /* At this point, this is a fatal error */
    544 
    545             sprintf (AslGbl_MsgBuffer, "Expected \"%s\"", Info->Name);
    546             DtFatal (ASL_MSG_COMPILER_INTERNAL, NULL, AslGbl_MsgBuffer);
    547             return (0);
    548         }
    549         break;
    550 
    551     case ACPI_DMT_GAS:
    552 
    553         ByteLength = sizeof (ACPI_GENERIC_ADDRESS);
    554         break;
    555 
    556     case ACPI_DMT_HESTNTFY:
    557 
    558         ByteLength = sizeof (ACPI_HEST_NOTIFY);
    559         break;
    560 
    561     case ACPI_DMT_IORTMEM:
    562 
    563         ByteLength = sizeof (ACPI_IORT_MEMORY_ACCESS);
    564         break;
    565 
    566     case ACPI_DMT_BUFFER:
    567     case ACPI_DMT_RAW_BUFFER:
    568 
    569         Value = DtGetFieldValue (Field);
    570         if (Value)
    571         {
    572             ByteLength = DtGetBufferLength (Value);
    573         }
    574         else
    575         {   /* At this point, this is a fatal error */
    576 
    577             sprintf (AslGbl_MsgBuffer, "Expected \"%s\"", Info->Name);
    578             DtFatal (ASL_MSG_COMPILER_INTERNAL, NULL, AslGbl_MsgBuffer);
    579             return (0);
    580         }
    581         break;
    582 
    583     case ACPI_DMT_BUF10:
    584 
    585         ByteLength = 10;
    586         break;
    587 
    588     case ACPI_DMT_BUF12:
    589 
    590         ByteLength = 12;
    591         break;
    592 
    593     case ACPI_DMT_BUF16:
    594     case ACPI_DMT_UUID:
    595 
    596         ByteLength = 16;
    597         break;
    598 
    599     case ACPI_DMT_BUF128:
    600 
    601         ByteLength = 128;
    602         break;
    603 
    604     case ACPI_DMT_UNICODE:
    605 
    606         Value = DtGetFieldValue (Field);
    607 
    608         /* TBD: error if Value is NULL? (as below?) */
    609 
    610         ByteLength = (strlen (Value) + 1) * sizeof(UINT16);
    611         break;
    612 
    613     default:
    614 
    615         DtFatal (ASL_MSG_COMPILER_INTERNAL, Field, "Invalid table opcode");
    616         return (0);
    617     }
    618 
    619     return (ByteLength);
    620 }
    621 
    622 
    623 /******************************************************************************
    624  *
    625  * FUNCTION:    DtSum
    626  *
    627  * PARAMETERS:  DT_WALK_CALLBACK:
    628  *              Subtable            - Subtable
    629  *              Context             - Unused
    630  *              ReturnValue         - Store the checksum of subtable
    631  *
    632  * RETURN:      Status
    633  *
    634  * DESCRIPTION: Get the checksum of subtable
    635  *
    636  *****************************************************************************/
    637 
    638 static void
    639 DtSum (
    640     DT_SUBTABLE             *Subtable,
    641     void                    *Context,
    642     void                    *ReturnValue)
    643 {
    644     UINT8                   Checksum;
    645     UINT8                   *Sum = ReturnValue;
    646 
    647 
    648     Checksum = AcpiTbChecksum (Subtable->Buffer, Subtable->Length);
    649     *Sum = (UINT8) (*Sum + Checksum);
    650 }
    651 
    652 
    653 /******************************************************************************
    654  *
    655  * FUNCTION:    DtSetTableChecksum
    656  *
    657  * PARAMETERS:  ChecksumPointer     - Where to return the checksum
    658  *
    659  * RETURN:      None
    660  *
    661  * DESCRIPTION: Set checksum of the whole data table into the checksum field
    662  *
    663  *****************************************************************************/
    664 
    665 void
    666 DtSetTableChecksum (
    667     UINT8                   *ChecksumPointer)
    668 {
    669     UINT8                   Checksum = 0;
    670     UINT8                   OldSum;
    671 
    672 
    673     DtWalkTableTree (AslGbl_RootTable, DtSum, NULL, &Checksum);
    674 
    675     OldSum = *ChecksumPointer;
    676     Checksum = (UINT8) (Checksum - OldSum);
    677 
    678     /* Compute the final checksum */
    679 
    680     Checksum = (UINT8) (0 - Checksum);
    681     *ChecksumPointer = Checksum;
    682 }
    683 
    684 
    685 /******************************************************************************
    686  *
    687  * FUNCTION:    DtSetTableLength
    688  *
    689  * PARAMETERS:  None
    690  *
    691  * RETURN:      None
    692  *
    693  * DESCRIPTION: Walk the subtables and set all the length fields
    694  *
    695  *****************************************************************************/
    696 
    697 void
    698 DtSetTableLength (
    699     void)
    700 {
    701     DT_SUBTABLE             *ParentTable;
    702     DT_SUBTABLE             *ChildTable;
    703 
    704 
    705     ParentTable = AslGbl_RootTable;
    706     ChildTable = NULL;
    707 
    708     if (!ParentTable)
    709     {
    710         return;
    711     }
    712 
    713     DtSetSubtableLength (ParentTable);
    714 
    715     while (1)
    716     {
    717         ChildTable = DtGetNextSubtable (ParentTable, ChildTable);
    718         if (ChildTable)
    719         {
    720             if (ChildTable->LengthField)
    721             {
    722                 DtSetSubtableLength (ChildTable);
    723             }
    724 
    725             if (ChildTable->Child)
    726             {
    727                 ParentTable = ChildTable;
    728                 ChildTable = NULL;
    729             }
    730             else
    731             {
    732                 ParentTable->TotalLength += ChildTable->TotalLength;
    733                 if (ParentTable->LengthField)
    734                 {
    735                     DtSetSubtableLength (ParentTable);
    736                 }
    737             }
    738         }
    739         else
    740         {
    741             ChildTable = ParentTable;
    742 
    743             if (ChildTable == AslGbl_RootTable)
    744             {
    745                 break;
    746             }
    747 
    748             ParentTable = DtGetParentSubtable (ParentTable);
    749 
    750             ParentTable->TotalLength += ChildTable->TotalLength;
    751             if (ParentTable->LengthField)
    752             {
    753                 DtSetSubtableLength (ParentTable);
    754             }
    755         }
    756     }
    757 }
    758 
    759 
    760 /******************************************************************************
    761  *
    762  * FUNCTION:    DtWalkTableTree
    763  *
    764  * PARAMETERS:  StartTable          - Subtable in the tree where walking begins
    765  *              UserFunction        - Called during the walk
    766  *              Context             - Passed to user function
    767  *              ReturnValue         - The return value of UserFunction
    768  *
    769  * RETURN:      None
    770  *
    771  * DESCRIPTION: Performs a depth-first walk of the subtable tree
    772  *
    773  *****************************************************************************/
    774 
    775 void
    776 DtWalkTableTree (
    777     DT_SUBTABLE             *StartTable,
    778     DT_WALK_CALLBACK        UserFunction,
    779     void                    *Context,
    780     void                    *ReturnValue)
    781 {
    782     DT_SUBTABLE             *ParentTable;
    783     DT_SUBTABLE             *ChildTable;
    784 
    785 
    786     ParentTable = StartTable;
    787     ChildTable = NULL;
    788 
    789     if (!ParentTable)
    790     {
    791         return;
    792     }
    793 
    794     UserFunction (ParentTable, Context, ReturnValue);
    795 
    796     while (1)
    797     {
    798         ChildTable = DtGetNextSubtable (ParentTable, ChildTable);
    799         if (ChildTable)
    800         {
    801             UserFunction (ChildTable, Context, ReturnValue);
    802 
    803             if (ChildTable->Child)
    804             {
    805                 ParentTable = ChildTable;
    806                 ChildTable = NULL;
    807             }
    808         }
    809         else
    810         {
    811             ChildTable = ParentTable;
    812             if (ChildTable == AslGbl_RootTable)
    813             {
    814                 break;
    815             }
    816 
    817             ParentTable = DtGetParentSubtable (ParentTable);
    818 
    819             if (ChildTable->Peer == StartTable)
    820             {
    821                 break;
    822             }
    823         }
    824     }
    825 }
    826