| 1 | /* Event loop machinery for the remote server for GDB. |
| 2 | Copyright (C) 1999-2020 Free Software Foundation, Inc. |
| 3 | |
| 4 | This file is part of GDB. |
| 5 | |
| 6 | This program is free software; you can redistribute it and/or modify |
| 7 | it under the terms of the GNU General Public License as published by |
| 8 | the Free Software Foundation; either version 3 of the License, or |
| 9 | (at your option) any later version. |
| 10 | |
| 11 | This program is distributed in the hope that it will be useful, |
| 12 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 14 | GNU General Public License for more details. |
| 15 | |
| 16 | You should have received a copy of the GNU General Public License |
| 17 | along with this program. If not, see <http://www.gnu.org/licenses/>. */ |
| 18 | |
| 19 | /* Based on src/gdb/event-loop.c. */ |
| 20 | |
| 21 | #include "server.h" |
| 22 | |
| 23 | #include <sys/types.h> |
| 24 | #include "gdbsupport/gdb_sys_time.h" |
| 25 | |
| 26 | #ifdef USE_WIN32API |
| 27 | #include <windows.h> |
| 28 | #include <io.h> |
| 29 | #endif |
| 30 | |
| 31 | #include <unistd.h> |
| 32 | #include <queue> |
| 33 | |
| 34 | typedef int (event_handler_func) (gdb_fildes_t); |
| 35 | |
| 36 | /* Tell create_file_handler what events we are interested in. */ |
| 37 | |
| 38 | #define GDB_READABLE (1<<1) |
| 39 | #define GDB_WRITABLE (1<<2) |
| 40 | #define GDB_EXCEPTION (1<<3) |
| 41 | |
| 42 | /* Events are queued by on the event_queue and serviced later |
| 43 | on by do_one_event. An event can be, for instance, a file |
| 44 | descriptor becoming ready to be read. Servicing an event simply |
| 45 | means that the procedure PROC will be called. We have 2 queues, |
| 46 | one for file handlers that we listen to in the event loop, and one |
| 47 | for the file handlers+events that are ready. The procedure PROC |
| 48 | associated with each event is always the same (handle_file_event). |
| 49 | Its duty is to invoke the handler associated with the file |
| 50 | descriptor whose state change generated the event, plus doing other |
| 51 | cleanups and such. */ |
| 52 | |
| 53 | struct gdb_event |
| 54 | { |
| 55 | /* Procedure to call to service this event. */ |
| 56 | event_handler_func *proc; |
| 57 | |
| 58 | /* File descriptor that is ready. */ |
| 59 | gdb_fildes_t fd; |
| 60 | }; |
| 61 | |
| 62 | /* Information about each file descriptor we register with the event |
| 63 | loop. */ |
| 64 | |
| 65 | typedef struct file_handler |
| 66 | { |
| 67 | /* File descriptor. */ |
| 68 | gdb_fildes_t fd; |
| 69 | |
| 70 | /* Events we want to monitor. */ |
| 71 | int mask; |
| 72 | |
| 73 | /* Events that have been seen since the last time. */ |
| 74 | int ready_mask; |
| 75 | |
| 76 | /* Procedure to call when fd is ready. */ |
| 77 | handler_func *proc; |
| 78 | |
| 79 | /* Argument to pass to proc. */ |
| 80 | gdb_client_data client_data; |
| 81 | |
| 82 | /* Was an error detected on this fd? */ |
| 83 | int error; |
| 84 | |
| 85 | /* Next registered file descriptor. */ |
| 86 | struct file_handler *next_file; |
| 87 | } |
| 88 | file_handler; |
| 89 | |
| 90 | typedef gdb::unique_xmalloc_ptr<gdb_event> gdb_event_up; |
| 91 | |
| 92 | static std::queue<gdb_event_up, std::list<gdb_event_up>> event_queue; |
| 93 | |
| 94 | /* Gdb_notifier is just a list of file descriptors gdb is interested |
| 95 | in. These are the input file descriptor, and the target file |
| 96 | descriptor. Each of the elements in the gdb_notifier list is |
| 97 | basically a description of what kind of events gdb is interested |
| 98 | in, for each fd. */ |
| 99 | |
| 100 | static struct |
| 101 | { |
| 102 | /* Ptr to head of file handler list. */ |
| 103 | file_handler *first_file_handler; |
| 104 | |
| 105 | /* Masks to be used in the next call to select. Bits are set in |
| 106 | response to calls to create_file_handler. */ |
| 107 | fd_set check_masks[3]; |
| 108 | |
| 109 | /* What file descriptors were found ready by select. */ |
| 110 | fd_set ready_masks[3]; |
| 111 | |
| 112 | /* Number of valid bits (highest fd value + 1). (for select) */ |
| 113 | int num_fds; |
| 114 | } |
| 115 | gdb_notifier; |
| 116 | |
| 117 | /* Callbacks are just routines that are executed before waiting for the |
| 118 | next event. In GDB this is struct gdb_timer. We don't need timers |
| 119 | so rather than copy all that complexity in gdbserver, we provide what |
| 120 | we need, but we do so in a way that if/when the day comes that we need |
| 121 | that complexity, it'll be easier to add - replace callbacks with timers |
| 122 | and use a delta of zero (which is all gdb currently uses timers for anyway). |
| 123 | |
| 124 | PROC will be executed before gdbserver goes to sleep to wait for the |
| 125 | next event. */ |
| 126 | |
| 127 | struct callback_event |
| 128 | { |
| 129 | int id; |
| 130 | callback_handler_func *proc; |
| 131 | gdb_client_data data; |
| 132 | struct callback_event *next; |
| 133 | }; |
| 134 | |
| 135 | /* Table of registered callbacks. */ |
| 136 | |
| 137 | static struct |
| 138 | { |
| 139 | struct callback_event *first; |
| 140 | struct callback_event *last; |
| 141 | |
| 142 | /* Id of the last callback created. */ |
| 143 | int num_callbacks; |
| 144 | } |
| 145 | callback_list; |
| 146 | |
| 147 | void |
| 148 | initialize_event_loop (void) |
| 149 | { |
| 150 | } |
| 151 | |
| 152 | /* Process one event. If an event was processed, 1 is returned |
| 153 | otherwise 0 is returned. Scan the queue from head to tail, |
| 154 | processing therefore the high priority events first, by invoking |
| 155 | the associated event handler procedure. */ |
| 156 | |
| 157 | static int |
| 158 | process_event (void) |
| 159 | { |
| 160 | /* Let's get rid of the event from the event queue. We need to |
| 161 | do this now because while processing the event, since the |
| 162 | proc function could end up jumping out to the caller of this |
| 163 | function. In that case, we would have on the event queue an |
| 164 | event which has been processed, but not deleted. */ |
| 165 | if (!event_queue.empty ()) |
| 166 | { |
| 167 | gdb_event_up event_ptr = std::move (event_queue.front ()); |
| 168 | event_queue.pop (); |
| 169 | |
| 170 | event_handler_func *proc = event_ptr->proc; |
| 171 | gdb_fildes_t fd = event_ptr->fd; |
| 172 | |
| 173 | /* Now call the procedure associated with the event. */ |
| 174 | if ((*proc) (fd)) |
| 175 | return -1; |
| 176 | return 1; |
| 177 | } |
| 178 | |
| 179 | /* This is the case if there are no event on the event queue. */ |
| 180 | return 0; |
| 181 | } |
| 182 | |
| 183 | /* Append PROC to the callback list. |
| 184 | The result is the "id" of the callback that can be passed back to |
| 185 | delete_callback_event. */ |
| 186 | |
| 187 | int |
| 188 | append_callback_event (callback_handler_func *proc, gdb_client_data data) |
| 189 | { |
| 190 | struct callback_event *event_ptr = XNEW (struct callback_event); |
| 191 | |
| 192 | event_ptr->id = callback_list.num_callbacks++; |
| 193 | event_ptr->proc = proc; |
| 194 | event_ptr->data = data; |
| 195 | event_ptr->next = NULL; |
| 196 | if (callback_list.first == NULL) |
| 197 | callback_list.first = event_ptr; |
| 198 | if (callback_list.last != NULL) |
| 199 | callback_list.last->next = event_ptr; |
| 200 | callback_list.last = event_ptr; |
| 201 | return event_ptr->id; |
| 202 | } |
| 203 | |
| 204 | /* Delete callback ID. |
| 205 | It is not an error callback ID doesn't exist. */ |
| 206 | |
| 207 | void |
| 208 | delete_callback_event (int id) |
| 209 | { |
| 210 | struct callback_event **p; |
| 211 | |
| 212 | for (p = &callback_list.first; *p != NULL; p = &(*p)->next) |
| 213 | { |
| 214 | struct callback_event *event_ptr = *p; |
| 215 | |
| 216 | if (event_ptr->id == id) |
| 217 | { |
| 218 | *p = event_ptr->next; |
| 219 | if (event_ptr == callback_list.last) |
| 220 | callback_list.last = NULL; |
| 221 | free (event_ptr); |
| 222 | break; |
| 223 | } |
| 224 | } |
| 225 | } |
| 226 | |
| 227 | /* Run the next callback. |
| 228 | The result is 1 if a callback was called and event processing |
| 229 | should continue, -1 if the callback wants the event loop to exit, |
| 230 | and 0 if there are no more callbacks. */ |
| 231 | |
| 232 | static int |
| 233 | process_callback (void) |
| 234 | { |
| 235 | struct callback_event *event_ptr; |
| 236 | |
| 237 | event_ptr = callback_list.first; |
| 238 | if (event_ptr != NULL) |
| 239 | { |
| 240 | callback_handler_func *proc = event_ptr->proc; |
| 241 | gdb_client_data data = event_ptr->data; |
| 242 | |
| 243 | /* Remove the event before calling PROC, |
| 244 | more events may get added by PROC. */ |
| 245 | callback_list.first = event_ptr->next; |
| 246 | if (callback_list.first == NULL) |
| 247 | callback_list.last = NULL; |
| 248 | free (event_ptr); |
| 249 | if ((*proc) (data)) |
| 250 | return -1; |
| 251 | return 1; |
| 252 | } |
| 253 | |
| 254 | return 0; |
| 255 | } |
| 256 | |
| 257 | /* Add a file handler/descriptor to the list of descriptors we are |
| 258 | interested in. FD is the file descriptor for the file/stream to be |
| 259 | listened to. MASK is a combination of READABLE, WRITABLE, |
| 260 | EXCEPTION. PROC is the procedure that will be called when an event |
| 261 | occurs for FD. CLIENT_DATA is the argument to pass to PROC. */ |
| 262 | |
| 263 | static void |
| 264 | create_file_handler (gdb_fildes_t fd, int mask, handler_func *proc, |
| 265 | gdb_client_data client_data) |
| 266 | { |
| 267 | file_handler *file_ptr; |
| 268 | |
| 269 | /* Do we already have a file handler for this file? (We may be |
| 270 | changing its associated procedure). */ |
| 271 | for (file_ptr = gdb_notifier.first_file_handler; |
| 272 | file_ptr != NULL; |
| 273 | file_ptr = file_ptr->next_file) |
| 274 | if (file_ptr->fd == fd) |
| 275 | break; |
| 276 | |
| 277 | /* It is a new file descriptor. Add it to the list. Otherwise, |
| 278 | just change the data associated with it. */ |
| 279 | if (file_ptr == NULL) |
| 280 | { |
| 281 | file_ptr = XNEW (struct file_handler); |
| 282 | file_ptr->fd = fd; |
| 283 | file_ptr->ready_mask = 0; |
| 284 | file_ptr->next_file = gdb_notifier.first_file_handler; |
| 285 | gdb_notifier.first_file_handler = file_ptr; |
| 286 | |
| 287 | if (mask & GDB_READABLE) |
| 288 | FD_SET (fd, &gdb_notifier.check_masks[0]); |
| 289 | else |
| 290 | FD_CLR (fd, &gdb_notifier.check_masks[0]); |
| 291 | |
| 292 | if (mask & GDB_WRITABLE) |
| 293 | FD_SET (fd, &gdb_notifier.check_masks[1]); |
| 294 | else |
| 295 | FD_CLR (fd, &gdb_notifier.check_masks[1]); |
| 296 | |
| 297 | if (mask & GDB_EXCEPTION) |
| 298 | FD_SET (fd, &gdb_notifier.check_masks[2]); |
| 299 | else |
| 300 | FD_CLR (fd, &gdb_notifier.check_masks[2]); |
| 301 | |
| 302 | if (gdb_notifier.num_fds <= fd) |
| 303 | gdb_notifier.num_fds = fd + 1; |
| 304 | } |
| 305 | |
| 306 | file_ptr->proc = proc; |
| 307 | file_ptr->client_data = client_data; |
| 308 | file_ptr->mask = mask; |
| 309 | } |
| 310 | |
| 311 | /* Wrapper function for create_file_handler. */ |
| 312 | |
| 313 | void |
| 314 | add_file_handler (gdb_fildes_t fd, |
| 315 | handler_func *proc, gdb_client_data client_data) |
| 316 | { |
| 317 | create_file_handler (fd, GDB_READABLE | GDB_EXCEPTION, proc, client_data); |
| 318 | } |
| 319 | |
| 320 | /* Remove the file descriptor FD from the list of monitored fd's: |
| 321 | i.e. we don't care anymore about events on the FD. */ |
| 322 | |
| 323 | void |
| 324 | delete_file_handler (gdb_fildes_t fd) |
| 325 | { |
| 326 | file_handler *file_ptr, *prev_ptr = NULL; |
| 327 | int i; |
| 328 | |
| 329 | /* Find the entry for the given file. */ |
| 330 | |
| 331 | for (file_ptr = gdb_notifier.first_file_handler; |
| 332 | file_ptr != NULL; |
| 333 | file_ptr = file_ptr->next_file) |
| 334 | if (file_ptr->fd == fd) |
| 335 | break; |
| 336 | |
| 337 | if (file_ptr == NULL) |
| 338 | return; |
| 339 | |
| 340 | if (file_ptr->mask & GDB_READABLE) |
| 341 | FD_CLR (fd, &gdb_notifier.check_masks[0]); |
| 342 | if (file_ptr->mask & GDB_WRITABLE) |
| 343 | FD_CLR (fd, &gdb_notifier.check_masks[1]); |
| 344 | if (file_ptr->mask & GDB_EXCEPTION) |
| 345 | FD_CLR (fd, &gdb_notifier.check_masks[2]); |
| 346 | |
| 347 | /* Find current max fd. */ |
| 348 | |
| 349 | if ((fd + 1) == gdb_notifier.num_fds) |
| 350 | { |
| 351 | gdb_notifier.num_fds--; |
| 352 | for (i = gdb_notifier.num_fds; i; i--) |
| 353 | { |
| 354 | if (FD_ISSET (i - 1, &gdb_notifier.check_masks[0]) |
| 355 | || FD_ISSET (i - 1, &gdb_notifier.check_masks[1]) |
| 356 | || FD_ISSET (i - 1, &gdb_notifier.check_masks[2])) |
| 357 | break; |
| 358 | } |
| 359 | gdb_notifier.num_fds = i; |
| 360 | } |
| 361 | |
| 362 | /* Deactivate the file descriptor, by clearing its mask, so that it |
| 363 | will not fire again. */ |
| 364 | |
| 365 | file_ptr->mask = 0; |
| 366 | |
| 367 | /* Get rid of the file handler in the file handler list. */ |
| 368 | if (file_ptr == gdb_notifier.first_file_handler) |
| 369 | gdb_notifier.first_file_handler = file_ptr->next_file; |
| 370 | else |
| 371 | { |
| 372 | for (prev_ptr = gdb_notifier.first_file_handler; |
| 373 | prev_ptr->next_file != file_ptr; |
| 374 | prev_ptr = prev_ptr->next_file) |
| 375 | ; |
| 376 | prev_ptr->next_file = file_ptr->next_file; |
| 377 | } |
| 378 | free (file_ptr); |
| 379 | } |
| 380 | |
| 381 | /* Handle the given event by calling the procedure associated to the |
| 382 | corresponding file handler. Called by process_event indirectly, |
| 383 | through event_ptr->proc. EVENT_FILE_DESC is file descriptor of the |
| 384 | event in the front of the event queue. */ |
| 385 | |
| 386 | static int |
| 387 | handle_file_event (gdb_fildes_t event_file_desc) |
| 388 | { |
| 389 | file_handler *file_ptr; |
| 390 | int mask; |
| 391 | |
| 392 | /* Search the file handler list to find one that matches the fd in |
| 393 | the event. */ |
| 394 | for (file_ptr = gdb_notifier.first_file_handler; file_ptr != NULL; |
| 395 | file_ptr = file_ptr->next_file) |
| 396 | { |
| 397 | if (file_ptr->fd == event_file_desc) |
| 398 | { |
| 399 | /* See if the desired events (mask) match the received |
| 400 | events (ready_mask). */ |
| 401 | |
| 402 | if (file_ptr->ready_mask & GDB_EXCEPTION) |
| 403 | { |
| 404 | warning ("Exception condition detected on fd %s", |
| 405 | pfildes (file_ptr->fd)); |
| 406 | file_ptr->error = 1; |
| 407 | } |
| 408 | else |
| 409 | file_ptr->error = 0; |
| 410 | mask = file_ptr->ready_mask & file_ptr->mask; |
| 411 | |
| 412 | /* Clear the received events for next time around. */ |
| 413 | file_ptr->ready_mask = 0; |
| 414 | |
| 415 | /* If there was a match, then call the handler. */ |
| 416 | if (mask != 0) |
| 417 | { |
| 418 | if ((*file_ptr->proc) (file_ptr->error, |
| 419 | file_ptr->client_data) < 0) |
| 420 | return -1; |
| 421 | } |
| 422 | break; |
| 423 | } |
| 424 | } |
| 425 | |
| 426 | return 0; |
| 427 | } |
| 428 | |
| 429 | /* Create a file event, to be enqueued in the event queue for |
| 430 | processing. The procedure associated to this event is always |
| 431 | handle_file_event, which will in turn invoke the one that was |
| 432 | associated to FD when it was registered with the event loop. */ |
| 433 | |
| 434 | static gdb_event * |
| 435 | create_file_event (gdb_fildes_t fd) |
| 436 | { |
| 437 | gdb_event *file_event_ptr; |
| 438 | |
| 439 | file_event_ptr = XNEW (gdb_event); |
| 440 | file_event_ptr->proc = handle_file_event; |
| 441 | file_event_ptr->fd = fd; |
| 442 | |
| 443 | return file_event_ptr; |
| 444 | } |
| 445 | |
| 446 | /* Called by do_one_event to wait for new events on the monitored file |
| 447 | descriptors. Queue file events as they are detected by the poll. |
| 448 | If there are no events, this function will block in the call to |
| 449 | select. Return -1 if there are no files descriptors to monitor, |
| 450 | otherwise return 0. */ |
| 451 | |
| 452 | static int |
| 453 | wait_for_event (void) |
| 454 | { |
| 455 | file_handler *file_ptr; |
| 456 | int num_found = 0; |
| 457 | |
| 458 | /* Make sure all output is done before getting another event. */ |
| 459 | fflush (stdout); |
| 460 | fflush (stderr); |
| 461 | |
| 462 | if (gdb_notifier.num_fds == 0) |
| 463 | return -1; |
| 464 | |
| 465 | gdb_notifier.ready_masks[0] = gdb_notifier.check_masks[0]; |
| 466 | gdb_notifier.ready_masks[1] = gdb_notifier.check_masks[1]; |
| 467 | gdb_notifier.ready_masks[2] = gdb_notifier.check_masks[2]; |
| 468 | num_found = select (gdb_notifier.num_fds, |
| 469 | &gdb_notifier.ready_masks[0], |
| 470 | &gdb_notifier.ready_masks[1], |
| 471 | &gdb_notifier.ready_masks[2], |
| 472 | NULL); |
| 473 | |
| 474 | /* Clear the masks after an error from select. */ |
| 475 | if (num_found == -1) |
| 476 | { |
| 477 | FD_ZERO (&gdb_notifier.ready_masks[0]); |
| 478 | FD_ZERO (&gdb_notifier.ready_masks[1]); |
| 479 | FD_ZERO (&gdb_notifier.ready_masks[2]); |
| 480 | #ifdef EINTR |
| 481 | /* Dont print anything if we got a signal, let gdb handle |
| 482 | it. */ |
| 483 | if (errno != EINTR) |
| 484 | perror_with_name ("select"); |
| 485 | #endif |
| 486 | } |
| 487 | |
| 488 | /* Enqueue all detected file events. */ |
| 489 | |
| 490 | for (file_ptr = gdb_notifier.first_file_handler; |
| 491 | file_ptr != NULL && num_found > 0; |
| 492 | file_ptr = file_ptr->next_file) |
| 493 | { |
| 494 | int mask = 0; |
| 495 | |
| 496 | if (FD_ISSET (file_ptr->fd, &gdb_notifier.ready_masks[0])) |
| 497 | mask |= GDB_READABLE; |
| 498 | if (FD_ISSET (file_ptr->fd, &gdb_notifier.ready_masks[1])) |
| 499 | mask |= GDB_WRITABLE; |
| 500 | if (FD_ISSET (file_ptr->fd, &gdb_notifier.ready_masks[2])) |
| 501 | mask |= GDB_EXCEPTION; |
| 502 | |
| 503 | if (!mask) |
| 504 | continue; |
| 505 | else |
| 506 | num_found--; |
| 507 | |
| 508 | /* Enqueue an event only if this is still a new event for this |
| 509 | fd. */ |
| 510 | |
| 511 | if (file_ptr->ready_mask == 0) |
| 512 | { |
| 513 | gdb_event *file_event_ptr = create_file_event (file_ptr->fd); |
| 514 | |
| 515 | event_queue.emplace (file_event_ptr); |
| 516 | } |
| 517 | file_ptr->ready_mask = mask; |
| 518 | } |
| 519 | |
| 520 | return 0; |
| 521 | } |
| 522 | |
| 523 | /* Start up the event loop. This is the entry point to the event |
| 524 | loop. */ |
| 525 | |
| 526 | void |
| 527 | start_event_loop (void) |
| 528 | { |
| 529 | /* Loop until there is nothing to do. This is the entry point to |
| 530 | the event loop engine. If nothing is ready at this time, wait |
| 531 | for something to happen (via wait_for_event), then process it. |
| 532 | Return when there are no longer event sources to wait for. */ |
| 533 | |
| 534 | while (1) |
| 535 | { |
| 536 | /* Any events already waiting in the queue? */ |
| 537 | int res = process_event (); |
| 538 | |
| 539 | /* Did the event handler want the event loop to stop? */ |
| 540 | if (res == -1) |
| 541 | return; |
| 542 | |
| 543 | if (res) |
| 544 | continue; |
| 545 | |
| 546 | /* Process any queued callbacks before we go to sleep. */ |
| 547 | res = process_callback (); |
| 548 | |
| 549 | /* Did the callback want the event loop to stop? */ |
| 550 | if (res == -1) |
| 551 | return; |
| 552 | |
| 553 | if (res) |
| 554 | continue; |
| 555 | |
| 556 | /* Wait for a new event. If wait_for_event returns -1, we |
| 557 | should get out because this means that there are no event |
| 558 | sources left. This will make the event loop stop, and the |
| 559 | application exit. */ |
| 560 | |
| 561 | if (wait_for_event () < 0) |
| 562 | return; |
| 563 | } |
| 564 | |
| 565 | /* We are done with the event loop. There are no more event sources |
| 566 | to listen to. So we exit gdbserver. */ |
| 567 | } |