X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/blobdiff_plain/7f4f03348bd07609e258eb3b545bdafc2c881847..50ac3e136606baf487eedb6d42729c4e46f55386:/src/mc/DwarfExpression.hpp

diff --git a/src/mc/DwarfExpression.hpp b/src/mc/DwarfExpression.hpp
index aa6d888cd6..1bf89d8943 100644
--- a/src/mc/DwarfExpression.hpp
+++ b/src/mc/DwarfExpression.hpp
@@ -1,5 +1,4 @@
-/* Copyright (c) 2015. The SimGrid Team.
- * All rights reserved.                                                     */
+/* Copyright (c) 2015-2017. The SimGrid Team. All rights reserved.          */
 
 /* This program is free software; you can redistribute it and/or modify it
  * under the terms of the license (GNU LGPL) which comes with this package. */
@@ -8,40 +7,71 @@
 #define SIMGRID_MC_DWARF_EXPRESSION_HPP
 
 #include <cstdint>
+#include <cstdlib>
 
-#include <stdexcept>
+#include <stdexcept> // runtime_error
+#include <utility>
+#include <vector>
 
+#include <elfutils/libdw.h>
+
+#include "src/mc/mc_forward.hpp"
 #include "src/mc/AddressSpace.hpp"
 
+/** @file DwarfExpression.hpp
+ *
+ *  Evaluation of DWARF location expressions.
+ */
+
 namespace simgrid {
 namespace dwarf {
 
-class evaluation_error : std::runtime_error {
-public:
-  evaluation_error(const char* what): std::runtime_error(what) {}
-  ~evaluation_error() noexcept(true);
-};
+/** A DWARF expression
+ *
+ *  DWARF defines a simple stack-based VM for evaluating expressions
+ *  (such as locations of variables, etc.): a DWARF expression is
+ *  just a sequence of dwarf instructions. We currently directly use
+ *  `Dwarf_Op` from `dwarf.h` for dwarf instructions.
+ */
+typedef std::vector<Dwarf_Op> DwarfExpression;
 
+/** Context of evaluation of a DWARF expression
+ *
+ *  Some DWARF instructions need to read the CPU registers,
+ *  the process memory, etc. All those informations are gathered in
+ *  the evaluation context.
+ */
 struct ExpressionContext {
   ExpressionContext() :
     cursor(nullptr), frame_base(nullptr), address_space(nullptr),
     object_info(nullptr), process_index(simgrid::mc::ProcessIndexMissing) {}
-    
+  /** CPU state (registers) */
   unw_cursor_t* cursor;
   void* frame_base;
+  /** Address space used to read memory */
   simgrid::mc::AddressSpace* address_space;
   simgrid::mc::ObjectInformation* object_info;
   int process_index;
 };
 
-typedef std::vector<Dwarf_Op> DwarfExpression;
+/** When an error happens in the execution of a DWARF expression */
+class evaluation_error : std::runtime_error {
+public:
+  evaluation_error(const char* what): std::runtime_error(what) {}
+  ~evaluation_error() noexcept(true);
+};
 
+/** A stack for evaluating a DWARF expression
+ *
+ *  DWARF expressions work by manipulating a stack of integer values.
+ */
 class ExpressionStack {
 public:
   typedef std::uintptr_t value_type;
   static const std::size_t max_size = 64;
 private:
-  uintptr_t stack_[max_size];
+  // Values of the stack (the top is stack_[size_ - 1]):
+  uintptr_t stack_[max_size] {0};
   size_t size_;
 public:
   ExpressionStack() : size_(0) {}
@@ -52,12 +82,16 @@ public:
   void clear()             { size_ = 0; }
   uintptr_t&       operator[](int i)       { return stack_[i]; }
   uintptr_t const& operator[](int i) const { return stack_[i]; }
+
+  /** Top of the stack */
   value_type& top()
   {
     if (size_ == 0)
       throw evaluation_error("Empty stack");
     return stack_[size_ - 1];
   }
+
+  /** Access the i-th element from the top of the stack */
   value_type& top(unsigned i)
   {
     if (size_ < i)
@@ -65,27 +99,47 @@ public:
     return stack_[size_ - 1 - i];
   }
 
-  // Push/pop:
+  /** Push a value on the top of the stack */
   void push(value_type value)
   {
     if (size_ == max_size)
-      throw evaluation_error("Dwarf stack overflow");
+      throw evaluation_error("DWARF stack overflow");
     stack_[size_++] = value;
   }
+
+  /* Pop a value from the top of the stack */
   value_type pop()
   {
     if (size_ == 0)
-      throw evaluation_error("Stack underflow");
+      throw evaluation_error("DWARF stack underflow");
     return stack_[--size_];
   }
 
-  // Other operations:
+  // These are DWARF operations (DW_OP_foo):
+
+  /* Push a copy of the top-value (DW_OP_dup) */
   void dup() { push(top()); }
+
+  /* Swap the two top-most values */
+  void swap() { std::swap(top(), top(1)); }
 };
 
+/** Executes a DWARF expression
+ *
+ *  @param ops     DWARF expression instructions
+ *  @param n       number of instructions
+ *  @param context evaluation context (registers, memory, etc.)
+ *  @param stack   DWARf stack where the operations are executed
+ */
 void execute(const Dwarf_Op* ops, std::size_t n,
   ExpressionContext const& context, ExpressionStack& stack);
 
+/** Executes/evaluates a DWARF expression
+ *
+ *  @param expression DWARF expression to execute
+ *  @param context    evaluation context (registers, memory, etc.)
+ *  @param stack      DWARf stack where the operations are executed
+ */
 inline
 void execute(simgrid::dwarf::DwarfExpression const& expression,
   ExpressionContext const& context, ExpressionStack& stack)