aboutsummaryrefslogtreecommitdiff
path: root/src/processor/postfix_evaluator.h
blob: 28d8023d5a50ced2ae530b23c9f178663dd5d2fa (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
// Copyright (C) 2006 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// postfix_evaluator.h: Postfix (reverse Polish) notation expression evaluator.
//
// PostfixEvaluator evaluates an expression, using the expression itself
// in postfix (reverse Polish) notation and a dictionary mapping constants
// and variables to their values.  The evaluator supports standard
// arithmetic operations, assignment into variables, and when an optional
// MemoryRange is provided, dereferencing.  (Any unary key-to-value operation
// may be used with a MemoryRange implementation that returns the appropriate
// values, but PostfixEvaluator was written with dereferencing in mind.)
//
// The expression language is simple.  Expressions are supplied as strings,
// with operands and operators delimited by whitespace.  Operands may be
// either literal values suitable for ValueType, or constants or variables,
// which reference the dictionary.  The supported binary operators are +
// (addition), - (subtraction), * (multiplication), / (quotient of division),
// and % (modulus of division).  The unary ^ (dereference) operator is also
// provided.  These operators allow any operand to be either a literal
// value, constant, or variable.  Assignment (=) of any type of operand into
// a variable is also supported.
//
// The dictionary is provided as a map with string keys.  Keys beginning
// with the '$' character are treated as variables.  All other keys are
// treated as constants.  Any results must be assigned into variables in the
// dictionary.  These variables do not need to exist prior to calling
// Evaluate, unless used in an expression prior to being assigned to.  The
// internal stack state is not made available after evaluation, and any
// values remaining on the stack are treated as evidence of incomplete
// execution and cause the evaluator to indicate failure.
//
// PostfixEvaluator is intended to support evaluation of "program strings"
// obtained from MSVC frame data debugging information in pdb files as
// returned by the DIA APIs.
//
// Author: Mark Mentovai

#ifndef PROCESSOR_POSTFIX_EVALUATOR_H__
#define PROCESSOR_POSTFIX_EVALUATOR_H__


#include <map>
#include <string>
#include <vector>

#include "processor/memory_region.h"

namespace google_airbag {

using std::map;
using std::string;
using std::vector;

class MemoryRegion;

template<typename ValueType>
class PostfixEvaluator {
 public:
  typedef map<string, ValueType> DictionaryType;

  // Create a PostfixEvaluator object that may be used (with Evaluate) on
  // one or more expressions.  PostfixEvaluator does not take ownership of
  // either argument.  |memory| may be NULL, in which case dereferencing
  // (^) will not be supported.  |dictionary| may be NULL, but evaluation
  // will fail in that case unless set_dictionary is used before calling
  // Evaluate.
  PostfixEvaluator(DictionaryType *dictionary, MemoryRegion *memory)
      : dictionary_(dictionary), memory_(memory), stack_() {}

  // Evaluate the expression.  The results of execution will be stored
  // in one (or more) variables in the dictionary.  Returns false if any
  // failures occure during execution, leaving variables in the dictionary
  // in an indeterminate state.
  bool Evaluate(const string &expression);

  DictionaryType* dictionary() const { return dictionary_; }

  // Reset the dictionary.  PostfixEvaluator does not take ownership.
  void set_dictionary(DictionaryType *dictionary) {dictionary_ = dictionary; }

 private:
  // Return values for PopValueOrIdentifier
  enum PopResult {
    POP_RESULT_FAIL = 0,
    POP_RESULT_VALUE,
    POP_RESULT_IDENTIFIER
  };

  // Retrieves the topmost literal value, constant, or variable from the
  // stack.  Returns POP_RESULT_VALUE if the topmost entry is a literal
  // value, and sets |value| accordingly.  Returns POP_RESULT_IDENTIFIER
  // if the topmost entry is a constant or variable identifier, and sets
  // |identifier| accordingly.  Returns POP_RESULT_FAIL on failure, such
  // as when the stack is empty.
  PopResult PopValueOrIdentifier(ValueType *value, string *identifier);

  // Retrieves the topmost value on the stack.  If the topmost entry is
  // an identifier, the dictionary is queried for the identifier's value.
  // Returns false on failure, such as when the stack is empty or when
  // a nonexistent identifier is named.
  bool PopValue(ValueType *value);

  // Retrieves the top two values on the stack, in the style of PopValue.
  // value2 is popped before value1, so that value1 corresponds to the
  // entry that was pushed prior to value2.  Returns false on failure.
  bool PopValues(ValueType *value1, ValueType *value2);

  // Pushes a new value onto the stack.
  void PushValue(const ValueType &value);

  // The dictionary mapping constant and variable identifiers (strings) to
  // values.  Keys beginning with '$' are treated as variable names, and
  // PostfixEvaluator is free to create and modify these keys.  Weak pointer.
  DictionaryType *dictionary_;

  // If non-NULL, the MemoryRegion used for dereference (^) operations.
  // If NULL, dereferencing is unsupported and will fail.  Weak pointer.
  MemoryRegion *memory_;

  // The stack contains state information as execution progresses.  Values
  // are pushed on to it as the expression string is read and as operations
  // yield values; values are popped when used as operands to operators.
  vector<string> stack_;
};

}  // namespace google_airbag


#endif  // PROCESSOR_POSTFIX_EVALUATOR_H__