Implement breakpoints

src/debug.cpp

@@ -2,6 +2,12 @@
 
 #include <netinet/tcp.h>
 
+#include <iomanip>
+#include <iostream>
+#include <sstream>
+#include <stdexcept>
+#include <vector>
+
 GDBStub::GDBStub(VM &vm, int port)
     : server_fd(-1), client_fd(-1), running(false), vm(vm) {
   server_fd = socket(AF_INET, SOCK_STREAM, 0);
@@ -174,6 +180,12 @@ void GDBStub::handle_packet(const std::string &packet) {
       break;
 
     case 'c':
+      try {
+        while (true) {
+          vm.step();
+        }
+      } catch (const EbreakException &ex) {
+      }
       send_packet("S05");  // TODO: continue execution
       break;
 
@@ -189,6 +201,36 @@ void GDBStub::handle_packet(const std::string &packet) {
         send_packet("");  // Empty response
       }
       break;
+    case 'Z': {
+      // Insert breakpoint
+      if (packet[1] == '0') {
+        uint32_t addr =
+            std::stoul(packet.substr(3, packet.find(',')), nullptr, 16);
+
+        if (breakpoints.count(addr) == 0) {
+          uint32_t original_instr = vm.read_memory_word(addr);
+          breakpoints[addr] = original_instr;
+          vm.write_memory_word(addr, 0x00100073);  // 0x00100073 is EBREAK
+        }
+      }
+      send_packet("OK");
+      break;
+    }
+    case 'z': {
+      // Delete breakpoint
+      if (packet[1] == '0') {
+        uint32_t addr =
+            std::stoul(packet.substr(3, packet.find(',')), nullptr, 16);
+
+        if (breakpoints.count(addr) > 0) {
+          // Restore the original instruction
+          vm.write_memory_word(addr, breakpoints[addr]);
+          breakpoints.erase(addr);
+        }
+      }
+      send_packet("OK");
+      break;
+    }
 
     default:
       send_packet("");  // Unsupported packet

src/debug.hpp

@@ -6,12 +6,7 @@
 
 #include <atomic>
 #include <cstring>
-#include <iomanip>
-#include <iostream>
-#include <sstream>
-#include <stdexcept>
-#include <thread>
-#include <vector>
+#include <unordered_map>
 
 #include "vm.hpp"
 
@@ -49,4 +44,6 @@ class GDBStub {
   std::string read_memory(size_t addr, size_t length);
 
   VM &vm;
+
+  std::unordered_map<uint32_t, uint32_t> breakpoints;
 };

src/rve.cpp

@@ -37,6 +37,7 @@ int main(int argc, char *argv[]) {
   if (!debug) {
     try {
       vm.eval();
+    } catch (const EbreakException &e) {
     } catch (const std::exception &e) {
       std::cerr << "Emulator error: " << e.what() << std::endl;
       return 1;

src/vm.cpp

@@ -52,6 +52,12 @@ std::vector<uint8_t> VM::read_memory(size_t start, size_t size) {
                               memory_.begin() + start + size);
 }
 
+uint32_t VM::read_memory_word(size_t pos) { return *(uint32_t*)&memory_[pos]; }
+
+void VM::write_memory_word(size_t pos, uint32_t value) {
+  *(uint32_t*)&memory_[pos] = value;
+}
+
 uint32_t VM::read_register(size_t regnum) {
   if (regnum == 32) return pc;
 
@@ -304,7 +310,8 @@ void VM::step() {
       break;
     }
     case 0x73: {  // EBREAK
-      running = false;  // Flag to stop the emulator
+      pc -= 4;
+      throw EbreakException();
       break;
     }
     default:
@@ -313,7 +320,7 @@ void VM::step() {
 }
 
 void VM::eval() {
-  while (running) {
+  while (true) {
     step();
   }
 }

src/vm.hpp

@@ -5,6 +5,8 @@
 #include <string>
 #include <vector>
 
+class EbreakException : std::exception {};
+
 const int NUM_REGISTERS = 32;  // Standard RISC-V has 32 registers
 
 std::vector<uint8_t> load_program(const std::string& filename,
@@ -18,6 +20,9 @@ class VM {
   void eval();
 
   std::vector<uint8_t> read_memory(size_t start, size_t size);
+  uint32_t read_memory_word(size_t pos);
+  void write_memory_word(size_t pos, uint32_t value);
+
   uint32_t read_register(size_t regnum);
 
  private:
@@ -25,6 +30,4 @@ class VM {
 
   uint32_t registers[NUM_REGISTERS] = {0};
   uint32_t pc = 0;
-
-  bool running = true;
 };