Function gdb_get_command

payloads/libpayload/gdb/transport.c:169–227

/* High-level send/receive functions. */

void gdb_get_command(struct gdb_message *command)
{
	enum command_state {
		STATE_WAITING,
		STATE_COMMAND,
		STATE_CHECKSUM0,
		STATE_CHECKSUM1,
	};

	u8 checksum = 0;
	u8 running_checksum = 0;
	enum command_state state = STATE_WAITING;

	while (1) {
		int c = gdb_raw_getchar();
		if (c < 0) {
			/*
			 * Timeout waiting for a byte. Reset the
			 * state machine.
			 */
			state = STATE_WAITING;
			continue;
		}

		switch (state) {
		case STATE_WAITING:
			if (c == '$') {
				running_checksum = 0;
				command->used = 0;
				state = STATE_COMMAND;
			}
			break;
		case STATE_COMMAND:
			if (c == '#') {
				state = STATE_CHECKSUM0;
				break;
			}
			die_if(command->used >= command->size, "GDB input buf"
			       "fer overrun (try increasing command.size)!\n");
			command->buf[command->used++] = c;
			running_checksum += c;
			break;
		case STATE_CHECKSUM0:
			checksum = from_hex(c) << 4;
			state = STATE_CHECKSUM1;
			break;
		case STATE_CHECKSUM1:
			checksum += from_hex(c);
			if (running_checksum == checksum) {
				gdb_raw_putchar('+');
				return;
			} else {
				state = STATE_WAITING;
				gdb_raw_putchar('-');
			}
			break;
		}
	}