1  /*
  2   * Copyright 2014 Google Inc.
  3   *
  4   * This program is free software; you can redistribute it and/or
  5   * modify it under the terms of the GNU General Public License as
  6   * published by the Free Software Foundation; either version 2 of
  7   * the License, or (at your option) any later version.
  8   *
  9   * This program is distributed in the hope that it will be useful,
 10   * but without any warranty; without even the implied warranty of
 11   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 12   * GNU General Public License for more details.
 13   */
 14  
 15  #include <gdb.h>
 16  #include <libpayload.h>
 17  
 18  struct gdb_state gdb_state;
 19  
 20  static u8 reply_buf[2048];
 21  static u8 command_buf[2048];
 22  
 23  static struct gdb_message command = {
 24  	.buf = command_buf,
 25  	.used = 0,
 26  	.size = sizeof(command_buf),
 27  };
 28  static struct gdb_message reply = {
 29  	.buf = reply_buf,
 30  	.used = 0,
 31  	.size = sizeof(reply_buf),
 32  };
 33  
 34  void gdb_command_loop(u8 signal)
 35  {
 36  	if (gdb_state.resumed) {
 37  		/* We were just running. Send a stop reply. */
 38  		reply.used = 0;
 39  		gdb_message_add_string(&reply, "S");
 40  		gdb_message_encode_bytes(&reply, &signal, 1);
 41  		gdb_send_reply(&reply);
 42  
 43  	}
 44  	gdb_state.signal = signal;
 45  	gdb_state.resumed = 0;
 46  	gdb_state.connected = 1;
 47  
 48  	while (1) {
 49  		int i;
 50  
 51  		gdb_get_command(&command);
 52  
 53  		reply.used = 0;
 54  		for (i = 0; i < gdb_command_count; i++) {
 55  			int clen = strlen(gdb_commands[i].str);
 56  			if (!strncmp(gdb_commands[i].str, (char *)command.buf,
 57  				     MIN(clen, command.used))) {
 58  				gdb_commands[i].handler(&command, clen, &reply);
 59  				break;
 60  			}
 61  		}
 62  
 63  		/* If we're resuming, we won't send a reply until we stop. */
 64  		if (gdb_state.resumed)
 65  			return;
 66  
 67  		gdb_send_reply(&reply);
 68  	}
 69  }
 70  
 71  static void gdb_output_write(const void *buffer, size_t count)
 72  {
 73  	if (!gdb_state.resumed) {
 74  		/* Must be a die_if() in GDB (or a bug), so bail out and die. */
 75  		gdb_exit(-1);
 76  		if (CONFIG(LP_VIDEO_CONSOLE))
 77  			video_console_init();
 78  		puts("GDB died, redirecting its last words to the screen:\n");
 79  		console_write(buffer, count);
 80  	} else {
 81  		reply.used = 0;
 82  		reply.buf[reply.used++] = 'O';
 83  		gdb_message_encode_bytes(&reply, buffer, count);
 84  		gdb_send_reply(&reply);
 85  	}
 86  }
 87  
 88  static struct console_output_driver gdb_output_driver = {
 89  	.write = &gdb_output_write
 90  };
 91  
 92  static void gdb_init(void)
 93  {
 94  	printf("Ready for GDB connection.\n");
 95  	gdb_transport_init();
 96  	gdb_arch_init();
 97  	console_add_output_driver(&gdb_output_driver);
 98  }
 99  
100  void gdb_enter(void)
101  {
102  	if (!gdb_state.connected)
103  		gdb_init();
104  	gdb_arch_enter();
105  }
106  
107  void gdb_exit(s8 exit_status)
108  {
109  	if (!gdb_state.connected)
110  		return;
111  
112  	reply.used = 0;
113  	gdb_message_add_string(&reply, "W");
114  	gdb_message_encode_bytes(&reply, &exit_status, 1);
115  	gdb_send_reply(&reply);
116  
117  	console_remove_output_driver(&gdb_output_write);
118  	gdb_transport_teardown();
119  	gdb_state.connected = 0;
120  	printf("Detached from GDB connection.\n");
121  }
122  
123  /*
124   * This is a check architecture backends can run before entering the GDB command
125   * loop during exception handling. If it returns true, GDB was already running
126   * and must have caused an exception itself, which may happen if the GDB server
127   * tells us to do something stupid (e.g. write to an unmapped address). In that
128   * case, all we can do is blindly send a generic error code (since we're not
129   * sure which command caused the exception) and continue serving commands. When
130   * GDB eventually tells us to resume, we'll return from this function to the
131   * architecture backend which will have to do a "super exception return" that
132   * returns right back from the original (outermost) exception, "jumping over"
133   * all the intermediate exception frames we may have accumulated since. (This is
134   * the best we can do because our architecture backends generally don't support
135   * "full", unlimited exception reentrancy.)
136   */
137  int gdb_handle_reentrant_exception(void)
138  {
139  	if (!gdb_state.connected || gdb_state.resumed)
140  		return 0;	/* This is not a reentrant exception. */
141  
142  	static const char error_code[] = "E22";	/* EINVAL? */
143  	static const struct gdb_message tmp_reply = {
144  		.buf = (u8 *)error_code,
145  		.used = sizeof(error_code),
146  		.size = sizeof(error_code),
147  	};
148  	gdb_send_reply(&tmp_reply);
149  	gdb_command_loop(gdb_state.signal);	/* preserve old signal */
150  	return 1;
151  }