1 /* Copyright (c) 2015-2022. The SimGrid Team. All rights reserved. */
3 /* This program is free software; you can redistribute it and/or modify it
4 * under the terms of the license (GNU LGPL) which comes with this package. */
6 #ifndef SIMGRID_MC_DWARF_EXPRESSION_HPP
7 #define SIMGRID_MC_DWARF_EXPRESSION_HPP
13 #include <stdexcept> // runtime_error
17 #include <elfutils/libdw.h>
18 #include <libunwind.h>
20 #include "src/mc/inspect/mc_dwarf.hpp"
21 #include "src/mc/mc_forward.hpp"
23 /** @file DwarfExpression.hpp
25 * Evaluation of DWARF location expressions.
31 /** A DWARF expression
33 * DWARF defines a simple stack-based VM for evaluating expressions
34 * (such as locations of variables, etc.): a DWARF expression is
35 * just a sequence of dwarf instructions. We currently directly use
36 * `Dwarf_Op` from `dwarf.h` for dwarf instructions.
38 using DwarfExpression = std::vector<Dwarf_Op>;
40 /** Context of evaluation of a DWARF expression
42 * Some DWARF instructions need to read the CPU registers,
43 * the process memory, etc. All those information are gathered in
44 * the evaluation context.
46 struct ExpressionContext {
47 /** CPU state (registers) */
48 unw_cursor_t* cursor = nullptr;
49 void* frame_base = nullptr;
50 const mc::AddressSpace* address_space = nullptr; /** Address space used to read memory */
51 mc::ObjectInformation* object_info = nullptr;
54 /** When an error happens in the execution of a DWARF expression */
55 class evaluation_error : public std::runtime_error {
57 using std::runtime_error::runtime_error;
60 /** A stack for evaluating a DWARF expression
62 * DWARF expressions work by manipulating a stack of integer values.
64 class ExpressionStack {
66 using value_type = std::uintptr_t;
67 static constexpr std::size_t MAX_SIZE = 64;
70 // Values of the stack (the top is stack_[size_ - 1]):
71 std::array<uintptr_t, MAX_SIZE> stack_{{0}};
76 std::size_t size() const { return size_; }
77 bool empty() const { return size_ == 0; }
78 void clear() { size_ = 0; }
79 uintptr_t& operator[](int i) { return stack_[i]; }
80 uintptr_t const& operator[](int i) const { return stack_[i]; }
82 /** Top of the stack */
86 throw evaluation_error("Empty stack");
87 return stack_[size_ - 1];
90 /** Access the i-th element from the top of the stack */
91 value_type& top(unsigned i)
94 throw evaluation_error("Invalid element");
95 return stack_[size_ - 1 - i];
98 /** Push a value on the top of the stack */
99 void push(value_type value)
101 if (size_ == stack_.size())
102 throw evaluation_error("DWARF stack overflow");
103 stack_[size_] = value;
107 /* Pop a value from the top of the stack */
111 throw evaluation_error("DWARF stack underflow");
113 return stack_[size_];
116 // These are DWARF operations (DW_OP_foo):
118 /* Push a copy of the top-value (DW_OP_dup) */
119 void dup() { push(top()); }
121 /* Swap the two top-most values */
122 void swap() { std::swap(top(), top(1)); }
125 /** Executes a DWARF expression
127 * @param ops DWARF expression instructions
128 * @param n number of instructions
129 * @param context evaluation context (registers, memory, etc.)
130 * @param stack DWARf stack where the operations are executed
132 void execute(const Dwarf_Op* ops, std::size_t n, ExpressionContext const& context, ExpressionStack& stack);
134 /** Executes/evaluates a DWARF expression
136 * @param expression DWARF expression to execute
137 * @param context evaluation context (registers, memory, etc.)
138 * @param stack DWARf stack where the operations are executed
140 inline void execute(simgrid::dwarf::DwarfExpression const& expression, ExpressionContext const& context,
141 ExpressionStack& stack)
143 execute(expression.data(), expression.size(), context, stack);
147 } // namespace simgrid