MdeModulePkg/Core/Pei/Dependency/Dependency.c

   1 /** @file
   2   PEI Dispatcher Dependency Evaluator
   3
   4   This routine evaluates a dependency expression (DEPENDENCY_EXPRESSION) to determine
   5   if a driver can be scheduled for execution.  The criteria for
   6   schedulability is that the dependency expression is satisfied.
   7
   8 Copyright (c) 2006 - 2008, Intel Corporation. All rights reserved.<BR>
   9 This program and the accompanying materials
  10 are licensed and made available under the terms and conditions of the BSD License
  11 which accompanies this distribution.  The full text of the license may be found at
  12 http://opensource.org/licenses/bsd-license.php
  13
  14 THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  15 WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  16
  17 **/
  18
  19 #include "PeiMain.h"
  20 #include "Dependency.h"
  21
  22 /**
  23
  24   This routine determines if a PPI has been installed.
  25   The truth value of a GUID is determined by if the PPI has
  26   been published and can be queried from the PPI database.
  27
  28
  29   @param PeiServices     An indirect pointer to the EFI_PEI_SERVICES table published by the PEI Foundation
  30   @param Stack           Reference to EVAL_STACK_ENTRY that contains PPI GUID to check
  31
  32   @retval TRUE  if the PPI is already installed.
  33   @retval FALSE if the PPI has yet to be installed.
  34
  35 **/
  36 BOOLEAN
  37 IsPpiInstalled (
  38   IN EFI_PEI_SERVICES  **PeiServices,
  39   IN EVAL_STACK_ENTRY  *Stack
  40   )
  41 {
  42   VOID        *PeiInstance;
  43   EFI_STATUS  Status;
  44   EFI_GUID    PpiGuid;
  45
  46   //
  47   // If there is no GUID to evaluate, just return current result on stack.
  48   //
  49   if (Stack->Operator == NULL) {
  50     return Stack->Result;
  51   }
  52
  53   //
  54   // Copy the Guid into a locale variable so that there are no
  55   // possibilities of alignment faults for cross-compilation
  56   // environments such as Intel?Itanium(TM).
  57   //
  58   CopyMem(&PpiGuid, Stack->Operator, sizeof(EFI_GUID));
  59
  60   //
  61   // Check if the PPI is installed.
  62   //
  63   Status = PeiServicesLocatePpi(
  64              &PpiGuid,        // GUID
  65              0,               // INSTANCE
  66              NULL,            // EFI_PEI_PPI_DESCRIPTOR
  67              &PeiInstance     // PPI
  68              );
  69
  70   if (EFI_ERROR(Status)) {
  71     return FALSE;
  72   }
  73
  74   return TRUE;
  75 }
  76
  77 /**
  78
  79   This is the POSTFIX version of the dependency evaluator.  When a
  80   PUSH [PPI GUID] is encountered, a pointer to the GUID is stored on
  81   the evaluation stack.  When that entry is poped from the evaluation
  82   stack, the PPI is checked if it is installed.  This method allows
  83   some time savings as not all PPIs must be checked for certain
  84   operation types (AND, OR).
  85
  86
  87   @param PeiServices            An indirect pointer to the EFI_PEI_SERVICES table published by the PEI Foundation
  88   @param DependencyExpression   Pointer to a dependency expression.  The Grammar adheres to
  89                                 the BNF described above and is stored in postfix notation.
  90
  91   @retval TRUE      if it is a well-formed Grammar
  92   @retval FALSE     if the dependency expression overflows the evaluation stack
  93                     if the dependency expression underflows the evaluation stack
  94                     if the dependency expression is not a well-formed Grammar.
  95
  96 **/
  97 BOOLEAN
  98 PeimDispatchReadiness (
  99   IN EFI_PEI_SERVICES   **PeiServices,
 100   IN VOID               *DependencyExpression
 101   )
 102 {
 103   DEPENDENCY_EXPRESSION_OPERAND  *Iterator;
 104   EVAL_STACK_ENTRY               *StackPtr;
 105   EVAL_STACK_ENTRY               EvalStack[MAX_GRAMMAR_SIZE];
 106
 107   Iterator  = DependencyExpression;
 108
 109   StackPtr = &EvalStack[0];
 110
 111   while (TRUE) {
 112
 113     switch (*(Iterator++)) {
 114
 115       //
 116       // For performance reason we put the frequently used items in front of
 117       // the rarely used  items
 118       //
 119
 120       case (EFI_DEP_PUSH):
 121         //
 122         // Check to make sure the dependency grammar doesn't overflow the
 123         // EvalStack on the push
 124         //
 125         if (StackPtr > &EvalStack[MAX_GRAMMAR_SIZE-1]) {
 126           return FALSE;
 127         }
 128
 129         //
 130         // Push the pointer to the PUSH opcode operator (pointer to PPI GUID)
 131         // We will evaluate if the PPI is insalled on the POP operation.
 132         //
 133         StackPtr->Operator = (VOID *) Iterator;
 134         Iterator = Iterator + sizeof (EFI_GUID);
 135         StackPtr++;
 136         break;
 137
 138       case (EFI_DEP_AND):
 139       case (EFI_DEP_OR):
 140         //
 141         // Check to make sure the dependency grammar doesn't underflow the
 142         // EvalStack on the two POPs for the AND operation.  Don't need to
 143         // check for the overflow on PUSHing the result since we already
 144         // did two POPs.
 145         //
 146         if (StackPtr < &EvalStack[2]) {
 147           return FALSE;
 148         }
 149
 150         //
 151         // Evaluate the first POPed operator only. If the operand is
 152         // EFI_DEP_AND and the POPed operator evaluates to FALSE, or the
 153         // operand is EFI_DEP_OR and the POPed operator evaluates to TRUE,
 154         // we don't need to check the second operator, and the result will be
 155         // evaluation of the POPed operator. Otherwise, don't POP the second
 156         // operator since it will now evaluate to the final result on the
 157         // next operand that causes a POP.
 158         //
 159         StackPtr--;
 160         //
 161         // Iterator has increased by 1 after we retrieve the operand, so here we
 162         // should get the value pointed by (Iterator - 1), in order to obtain the
 163         // same operand.
 164         //
 165         if (*(Iterator - 1) == EFI_DEP_AND) {
 166           if (!(IsPpiInstalled (PeiServices, StackPtr))) {
 167             (StackPtr-1)->Result = FALSE;
 168             (StackPtr-1)->Operator = NULL;
 169           }
 170         } else {
 171           if (IsPpiInstalled (PeiServices, StackPtr)) {
 172             (StackPtr-1)->Result = TRUE;
 173             (StackPtr-1)->Operator = NULL;
 174           }
 175         }
 176         break;
 177
 178       case (EFI_DEP_END):
 179         StackPtr--;
 180         //
 181         // Check to make sure EvalStack is balanced.  If not, then there is
 182         // an error in the dependency grammar, so return EFI_INVALID_PARAMETER.
 183         //
 184         if (StackPtr != &EvalStack[0]) {
 185           return FALSE;
 186         }
 187         return IsPpiInstalled (PeiServices, StackPtr);
 188         break;
 189
 190       case (EFI_DEP_NOT):
 191         //
 192         // Check to make sure the dependency grammar doesn't underflow the
 193         // EvalStack on the POP for the NOT operation.  Don't need to
 194         // check for the overflow on PUSHing the result since we already
 195         // did a POP.
 196         //
 197         if (StackPtr < &EvalStack[1]) {
 198           return FALSE;
 199         }
 200         (StackPtr-1)->Result = (BOOLEAN) !IsPpiInstalled (PeiServices, (StackPtr-1));
 201         (StackPtr-1)->Operator = NULL;
 202         break;
 203
 204       case (EFI_DEP_TRUE):
 205       case (EFI_DEP_FALSE):
 206         //
 207         // Check to make sure the dependency grammar doesn't overflow the
 208         // EvalStack on the push
 209         //
 210         if (StackPtr > &EvalStack[MAX_GRAMMAR_SIZE-1]) {
 211           return FALSE;
 212         }
 213         //
 214         // Iterator has increased by 1 after we retrieve the operand, so here we
 215         // should get the value pointed by (Iterator - 1), in order to obtain the
 216         // same operand.
 217         //
 218         if (*(Iterator - 1) == EFI_DEP_TRUE) {
 219           StackPtr->Result = TRUE;
 220         } else {
 221           StackPtr->Result = FALSE;
 222         }
 223         StackPtr->Operator = NULL;
 224         StackPtr++;
 225         break;
 226
 227       default:
 228         //
 229         // The grammar should never arrive here
 230         //
 231         return FALSE;
 232     }
 233   }
 234 }