GDBstub base implementation (gdb is happy)

src/gdbstub/gdbstub.c

@@ -1,5 +1,7 @@
 #include "gdbstub.h"
 
+#include "cpu/rv32cpu.h"
+
 #include <errno.h>
 #include <stdlib.h>
 #include <stdio.h>
@@ -16,10 +18,77 @@ typedef struct sockaddr_in sockaddr_in_t;
 typedef struct sockaddr sockaddr_t;
 
 #define GDBSTUB_PORT 1234
+#define PACKET_BUFFER_SIZE 2048
 
 socket_t gdbstub_server_socket;
 socket_t gdb_socket;
 
+void gdbstub_thread_gdb();
+
+/*
+ * Receive a packet from client gdb
+ * Ignores the ACK on the way, and only returns the packet (not initial '$' symbol)
+ */
+static void gdbstub_recv_packet(char* packet, ssize_t* size)
+{
+	char data;
+	recv(gdb_socket, &data, 1, 0);
+
+	// Start of packet symbol is '$'
+	// Skip data that is not packet (should only be ACK '+')
+	if(data != '$')
+		return gdbstub_recv_packet(packet, size);
+
+	// Receive packet until end of packet '#' symbol
+	size_t i = 0;
+	do
+	{
+		recv(gdb_socket, packet + i, 1, 0);
+		i++;
+	} while(packet[i - 1] != '#');
+
+	// Receive checksum after end of packet symbol
+	recv(gdb_socket, packet + i, 1, 0);
+	recv(gdb_socket, packet + i + 1, 1, 0);
+
+	if(size) *size = i + 2;
+}
+
+/*
+ * Send a packet to client gdb
+ * Pass only the packet data as parameter to this function
+ */
+static void gdbstub_send_packet(char* packet, ssize_t size)
+{
+	// Compute packet checksum
+	char end[4] = {0};
+	uint8_t sum = 0;
+	for(size_t i = 0; i < size; i++)
+	{
+		sum += packet[i];
+	}
+	snprintf(end, 4, "#%02x", sum);
+
+	// Send ACK to last packet, and begin of packet symbol
+	char begin[2] = {'+', '$'};
+	send(gdb_socket, begin, 2, 0);
+
+	// Send the actual data of packet
+	send(gdb_socket, packet, size, 0);
+
+	// Send 'end of packet' and checksum
+	send(gdb_socket, end, 3, 0);
+}
+
+/*
+ * Send a packet to client gdb saying we don't support asked feature
+ */
+static void gdbstub_send_unsupported()
+{
+	char unsupported[] = "+$#00";
+	send(gdb_socket, unsupported, 5, 0);
+}
+
 /*
  * Starts a server that will listen for GDB connections
  */
@@ -68,4 +137,44 @@ void gdbstub_wait_for_connection()
 	}
 
 	gdb_socket = c_socket;
+
+	gdbstub_thread_gdb();
+}
+
+void gdbstub_thread_gdb()
+{
+	while(1)
+	{
+		char packet[PACKET_BUFFER_SIZE];
+		ssize_t packet_size;
+		gdbstub_recv_packet(packet, &packet_size);
+		// printf("<-: %.*s\n", (int) packet_size, packet);
+
+		// Analyse packet to respond correctly
+		if(packet[0] == '?')
+		{
+			char* resp = "S05";
+			gdbstub_send_packet(resp, 3);
+		}
+		else if(packet[0] == 'g')
+		{
+			char resp[32 * 8 + 8 + 1] = {0};
+
+			// All general purpose registers in host byte order as chars
+			for(size_t i = 0; i < 32; i++)
+			{
+				uint32_t value = htonl(cpu0->regs.x[i]);
+				snprintf(resp + i * 8, 9, "%08x", value);
+			}
+
+			// PC register
+			uint32_t pc = htonl(cpu0->pc);
+			snprintf(resp + 32 * 8, 9, "%08x", pc);
+
+			// Final packet size, send packet
+			size_t size = 32 * 8 + 8;
+			gdbstub_send_packet(resp, size);
+		}
+		else gdbstub_send_unsupported();
+	}
 }

src/option.c

@@ -181,7 +181,7 @@ static void print_help()
 	printf("  " OPTION_SEPARATOR "h, " OPTION_SEPARATOR "?, --help\t\tPrint this help message\n");
 	printf("  " OPTION_SEPARATOR "v, --version\t\t\tPrint version information\n");
 	printf("  " OPTION_SEPARATOR "m, --memory\t\t\tSet the simulated memory size, in MiB (max 4096)\n");
-	printf("  " OPTION_SEPARATOR "s, --gdb-stub\t\t\tLaunch a gdb stub server, for remote gdb debugging\n");
+	printf("  " OPTION_SEPARATOR "s, --gdb-stub\t\tLaunch a gdb stub server (remote gdb debugging)\n");
 }
 
 static void print_version()