implement formatted output for reads and writes

src/main.cpp

@@ -86,7 +86,8 @@ int main(int argc, char **argv) {
 
   // Start watching the variable
   Tracer tracer;
-  tracer.watch_variable(exec_path.string(), var_info->address, var_info->size, prog_args);
+  tracer.watch_variable(var_info->name, exec_path.string(), var_info->address,
+                        var_info->size, prog_args);
 
   return 0;
 }

src/tracer.cpp

@@ -50,12 +50,38 @@ void Tracer::setup_hardware_watchpoint(pid_t pid, uint64_t address, size_t size)
   ptrace(PTRACE_POKEUSER, pid, offsetof(struct user, u_debugreg[7]), dr7);
 }
 
-void Tracer::handle_watchpoint_hit(pid_t pid, uint64_t address) {
-  struct user_regs_struct regs;
-  ptrace(PTRACE_GETREGS, pid, 0, &regs);
+int64_t Tracer::read_memory_value(pid_t pid, uint64_t address, size_t size) {
+  int64_t value = 0;
 
-  std::cout << std::format("Variable accessed at RIP: 0x{:x}", regs.rip)
-            << std::endl;
+  if (size == 1) {
+    value = ptrace(PTRACE_PEEKDATA, pid, address, 0) & 0xFF;
+  } else if (size == 2) {
+    value = ptrace(PTRACE_PEEKDATA, pid, address, 0) & 0xFFFF;
+  } else if (size == 4) {
+    value = ptrace(PTRACE_PEEKDATA, pid, address, 0) & 0xFFFFFFFF;
+  } else if (size == 8) {
+    value = ptrace(PTRACE_PEEKDATA, pid, address, 0);
+  }
+
+  return value;
+}
+
+void Tracer::handle_watchpoint_hit(pid_t pid, uint64_t address, size_t size) {
+  int64_t current_value = read_memory_value(pid, address, size);
+
+  if (!prev_value_.has_value()) {
+    // First access - initialize prev_value
+    prev_value_ = current_value;
+    std::cout << var_name_ << "\tread\t" << current_value << std::endl;
+  } else if (prev_value_.value() != current_value) {
+    // Value changed - this was a write
+    std::cout << var_name_ << "\twrite\t" << prev_value_.value()
+              << "->" << current_value << std::endl;
+    prev_value_ = current_value;
+  } else {
+    // Value unchanged - this was a read
+    std::cout << var_name_ << "\tread\t" << current_value << std::endl;
+  }
 }
 
 uint64_t Tracer::get_load_address(pid_t pid, const std::string &exec_path) {
@@ -91,8 +117,12 @@ uint64_t Tracer::get_load_address(pid_t pid, const std::string &exec_path) {
   return 0;
 }
 
-void Tracer::watch_variable(const std::string &exec_path, uint64_t address, size_t size,
+void Tracer::watch_variable(const std::string &var_name, const std::string &exec_path,
+                            uint64_t address, size_t size,
                             const std::vector<std::string> &args) {
+  var_name_ = var_name;
+  prev_value_.reset();
+
   pid_t pid = fork();
 
   if (pid == 0) {
@@ -152,7 +182,7 @@ void Tracer::watch_variable(const std::string &exec_path, uint64_t address, size
                                offsetof(struct user, u_debugreg[6]), 0);
 
           if (dr6 & 0x1) {  // DR0 triggered
-            handle_watchpoint_hit(pid, runtime_addr);
+            handle_watchpoint_hit(pid, runtime_addr, size);
 
             // Clear DR6
             ptrace(PTRACE_POKEUSER, pid,

src/tracer.hpp

@@ -2,18 +2,24 @@
 #define GWATCH_TRACER_HPP
 
 #include <cstdint>
+#include <optional>
 #include <string>
 #include <vector>
 
 class Tracer {
 public:
-  void watch_variable(const std::string &exec_path, uint64_t address, size_t size,
+  void watch_variable(const std::string &var_name, const std::string &exec_path,
+                      uint64_t address, size_t size,
                       const std::vector<std::string> &args = {});
 
 private:
   void setup_hardware_watchpoint(pid_t pid, uint64_t address, size_t size);
-  void handle_watchpoint_hit(pid_t pid, uint64_t address);
+  void handle_watchpoint_hit(pid_t pid, uint64_t address, size_t size);
   uint64_t get_load_address(pid_t pid, const std::string &exec_path);
+  int64_t read_memory_value(pid_t pid, uint64_t address, size_t size);
+
+  std::string var_name_;
+  std::optional<int64_t> prev_value_;
 };
 
 #endif