Optionalize the results of querying gdb

Not all queried values are sensible if we ask past allocated
memory (malloc_usable_size doesn't return exact values).

Author: Petr Bauch

src/memory-analyzer/gdb_api.cpp

@@ -369,14 +369,23 @@ gdb_apit::pointer_valuet gdb_apit::get_memory(const std::string &expr)
 {
   PRECONDITION(gdb_state == gdb_statet::STOPPED);
 
-  std::string value = eval_expr(expr);
+  std::string value;
+  try
+  {
+    value = eval_expr(expr);
+  }
+  catch(gdb_interaction_exceptiont &e)
+  {
+    return pointer_valuet{};
+  }
 
   std::regex regex(
     r_hex_addr + r_opt(' ' + r_id) + r_opt(' ' + r_or(r_char, r_string)));
 
   std::smatch result;
   const bool b = regex_match(value, result, regex);
-  CHECK_RETURN(b);
+  if(!b)
+    return pointer_valuet{};
 
   optionalt<std::string> opt_string;
   const std::string string = result[4];
@@ -404,14 +413,22 @@ gdb_apit::pointer_valuet gdb_apit::get_memory(const std::string &expr)
     opt_string = string.substr(2, len - 4);
   }
 
-  return pointer_valuet(result[1], result[2], result[3], opt_string);
+  return pointer_valuet(result[1], result[2], result[3], opt_string, true);
 }
 
-std::string gdb_apit::get_value(const std::string &expr)
+optionalt<std::string> gdb_apit::get_value(const std::string &expr)
 {
   PRECONDITION(gdb_state == gdb_statet::STOPPED);
 
-  const std::string value = eval_expr(expr);
+  std::string value;
+  try
+  {
+    value = eval_expr(expr);
+  }
+  catch(gdb_interaction_exceptiont &e)
+  {
+    return {};
+  }
 
   // Get char value
   {
@@ -423,7 +440,7 @@ std::string gdb_apit::get_value(const std::string &expr)
 
     if(b)
     {
-      return result[1];
+      return std::string{result[1]};
     }
   }
 

src/memory-analyzer/gdb_api.h

@@ -69,18 +69,24 @@ class gdb_apit
   {
     pointer_valuet() = delete;
     pointer_valuet(
-      const std::string &address,
-      const std::string &pointee,
-      const std::string &character,
-      const optionalt<std::string> &string)
-      : address(address), pointee(pointee), character(character), string(string)
+      const std::string &address = "",
+      const std::string &pointee = "",
+      const std::string &character = "",
+      const optionalt<std::string> &string = nullopt,
+      const bool valid = false)
+      : address(address),
+        pointee(pointee),
+        character(character),
+        string(string),
+        valid(valid)
     {
     }
 
     const memory_addresst address;
     const std::string pointee;
     const std::string character;
     const optionalt<std::string> string;
+    bool valid;
   };
 
   /// Get the allocated size estimate for a pointer
@@ -103,17 +109,12 @@ class gdb_apit
   /// \param corefile: core dump
   void run_gdb_from_core(const std::string &corefile);
 
-  /// Get value of the given value expression
-  /// \param expr: an expression of non-pointer type or pointer to char
-  /// \return value of the expression; if the expression is of type pointer to
-  ///   char and represents a string, the string value is returned; otherwise
-  ///   the value is returned just as it is printed by gdb
-  std::string get_value(const std::string &expr);
-
   /// Get the memory address pointed to by the given pointer expression
   /// \param expr: an expression of pointer type (e.g., `&x` with `x` being of
   ///   type `int` or `p` with `p` being of type `int *`)
   /// \return memory address in hex format
+  optionalt<std::string> get_value(const std::string &expr);
+
   pointer_valuet get_memory(const std::string &expr);
 
   /// Return the vector of commands that have been written to gdb so far