patch to restore the breakpoint instruction after it is replaced with…

… the original instruction.

debugging-examples/CMakeLists.txt

@@ -3,7 +3,9 @@
 add_executable(helloworld helloworld.cpp)
 add_executable(calculator calculator.cpp)
 add_executable(single-step single-step.cpp)
+add_executable(loop loop.c)
 
 set_target_properties(helloworld PROPERTIES COMPILE_FLAGS "-g")
 set_target_properties(calculator PROPERTIES COMPILE_FLAGS "-g")
-set_target_properties(single-step PROPERTIES COMPILE_FLAGS "-g")
+set_target_properties(single-step PROPERTIES COMPILE_FLAGS "-g")
+set_target_properties(loop PROPERTIES COMPILE_FLAGS "-g")

debugging-examples/loop.c

@@ -0,0 +1,12 @@
+
+void main()
+{
+    int x,y,z;
+    x = y = 4;
+    int i = 5;
+    while(i  > 0)
+    {
+        z = x + y;
+        --i;
+    }
+}

src/debugger.cpp

@@ -37,6 +37,7 @@ void debugger::run() {
     }
 
     char* line = nullptr;
+    this->pLastActivatedBreakPoint = nullptr;
     // use linenoise for making a nice command line prompt for the debugger.
     while((line = linenoise("tdbg> ")) != nullptr) {
         if(!handle_command(line)) break;
@@ -173,6 +174,22 @@ bool debugger::handle_command(const std::string& line) {
  */
 void debugger::continue_execution()
 {
+    // To return the breakpoint INT3 instruction again for the last restored instruction.
+    // Simply, before we go, we return the user breakpoint again.
+    if (pLastActivatedBreakPoint != nullptr)
+    {
+        if (pLastActivatedBreakPoint->is_enabled())
+        {
+            // single step after the restored location.
+            ptrace(PTRACE_SINGLESTEP, m_pid, nullptr, nullptr);
+            // absorb the SIGTRAP due to single step.
+            wait_for_signal();
+            // restore INT3 instruction by inserting a breakpoint again.
+            pLastActivatedBreakPoint->enable();
+        }
+        // return to the origianl status since INT3 is back.
+        pLastActivatedBreakPoint = nullptr;
+    }
     // Resume the execution of the debugee program.
     ptrace(PTRACE_CONT, m_pid, nullptr, nullptr);
     int signal_status = wait_for_signal();
@@ -195,6 +212,17 @@ void debugger::continue_execution()
             // Set RIP reg to the decrement rip value so the debugger points to current restored instruction.
             ptrace(PTRACE_POKEUSER, m_pid, 8 * RIP, rip);
             printf("Process %d stopped at 0x%lx\n", m_pid, rip);
+
+            /* Store the location of breakpoint of the restored instruction in case 
+            the user issued a debugger command "continue" again. And before we continue,
+            we restore the breakpoint INT3 instruction again. 
+
+            Imaging the case of a breakpoint inside a loop ! if we haven't stored the last
+            breakpoint address which we restored its original instruction, we wouldn't able
+            to break at it again. not just a loop, a recursive function as an example 
+            will work ... etc.
+            */
+            this->pLastActivatedBreakPoint = &m_breakpoints[rip];
         }
         else
         {

src/debugger.h

@@ -37,6 +37,8 @@ class debugger {
     /* An un-order map of breakpoint objects to be access by its addresses hashes.
          m_breakpoints[breakpoint address] -> breakpoint object. */
     std::unordered_map<std::intptr_t, breakpoint> m_breakpoints;
+    // For restoring INT3 instruction after we replaced it with the original instruction.
+    breakpoint* pLastActivatedBreakPoint;
     // To determine if traced process is runnable or not.
     bool debuggee_captured;
 
@@ -63,7 +65,7 @@ class debugger {
     // Start the debuggee program 
     bool run_traced_process();
     // Go to the next instruction.
-    void next_instruction(); 
+    void next_instruction();
 };
 
 #endif /* __DEBUGGER_H */

todo

@@ -0,0 +1,10 @@
+# TODO List
+
+- [x] Re-run debuggee after its termination(run command)
+- [x] Disable debugger commands if debuggee is terminated.
+- [ ] debuggee args are not supported(not even been read)
+- [ ] check for debugger command argc (each one in general).
+- [x] make sure the breakpoint work if a loop exist.
+- [ ] improve the displayed format of **register dump** command.
+- [ ] handle mis writting of break 0x**Address** command, if ***0x*** is not exist case and so on.
+- [ ] add command to delete a breakpoint by address.