1 /* Fork a Unix child process, and set up to debug it, for GDB. 2 3 Copyright (C) 1990-2013 Free Software Foundation, Inc. 4 5 Contributed by Cygnus Support. 6 7 This file is part of GDB. 8 9 This program is free software; you can redistribute it and/or modify 10 it under the terms of the GNU General Public License as published by 11 the Free Software Foundation; either version 3 of the License, or 12 (at your option) any later version. 13 14 This program is distributed in the hope that it will be useful, 15 but WITHOUT ANY WARRANTY; without even the implied warranty of 16 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 17 GNU General Public License for more details. 18 19 You should have received a copy of the GNU General Public License 20 along with this program. If not, see <http://www.gnu.org/licenses/>. */ 21 22 #include "defs.h" 23 #include "gdb_string.h" 24 #include "inferior.h" 25 #include "terminal.h" 26 #include "target.h" 27 #include "gdb_wait.h" 28 #include "gdb_vfork.h" 29 #include "gdbcore.h" 30 #include "terminal.h" 31 #include "gdbthread.h" 32 #include "command.h" /* for dont_repeat () */ 33 #include "gdbcmd.h" 34 #include "solib.h" 35 36 #include <signal.h> 37 38 /* This just gets used as a default if we can't find SHELL. */ 39 #define SHELL_FILE "/bin/sh" 40 41 extern char **environ; 42 43 static char *exec_wrapper; 44 45 /* Break up SCRATCH into an argument vector suitable for passing to 46 execvp and store it in ARGV. E.g., on "run a b c d" this routine 47 would get as input the string "a b c d", and as output it would 48 fill in ARGV with the four arguments "a", "b", "c", "d". */ 49 50 static void 51 breakup_args (char *scratch, char **argv) 52 { 53 char *cp = scratch, *tmp; 54 55 for (;;) 56 { 57 /* Scan past leading separators */ 58 while (*cp == ' ' || *cp == '\t' || *cp == '\n') 59 cp++; 60 61 /* Break if at end of string. */ 62 if (*cp == '\0') 63 break; 64 65 /* Take an arg. */ 66 *argv++ = cp; 67 68 /* Scan for next arg separator. */ 69 tmp = strchr (cp, ' '); 70 if (tmp == NULL) 71 tmp = strchr (cp, '\t'); 72 if (tmp == NULL) 73 tmp = strchr (cp, '\n'); 74 75 /* No separators => end of string => break. */ 76 if (tmp == NULL) 77 break; 78 cp = tmp; 79 80 /* Replace the separator with a terminator. */ 81 *cp++ = '\0'; 82 } 83 84 /* Null-terminate the vector. */ 85 *argv = NULL; 86 } 87 88 /* When executing a command under the given shell, return non-zero if 89 the '!' character should be escaped when embedded in a quoted 90 command-line argument. */ 91 92 static int 93 escape_bang_in_quoted_argument (const char *shell_file) 94 { 95 const int shell_file_len = strlen (shell_file); 96 97 /* Bang should be escaped only in C Shells. For now, simply check 98 that the shell name ends with 'csh', which covers at least csh 99 and tcsh. This should be good enough for now. */ 100 101 if (shell_file_len < 3) 102 return 0; 103 104 if (shell_file[shell_file_len - 3] == 'c' 105 && shell_file[shell_file_len - 2] == 's' 106 && shell_file[shell_file_len - 1] == 'h') 107 return 1; 108 109 return 0; 110 } 111 112 /* Start an inferior Unix child process and sets inferior_ptid to its 113 pid. EXEC_FILE is the file to run. ALLARGS is a string containing 114 the arguments to the program. ENV is the environment vector to 115 pass. SHELL_FILE is the shell file, or NULL if we should pick 116 one. EXEC_FUN is the exec(2) function to use, or NULL for the default 117 one. */ 118 119 /* This function is NOT reentrant. Some of the variables have been 120 made static to ensure that they survive the vfork call. */ 121 122 int 123 fork_inferior (char *exec_file_arg, char *allargs, char **env, 124 void (*traceme_fun) (void), void (*init_trace_fun) (int), 125 void (*pre_trace_fun) (void), char *shell_file_arg, 126 void (*exec_fun)(const char *file, char * const *argv, 127 char * const *env)) 128 { 129 int pid; 130 static char default_shell_file[] = SHELL_FILE; 131 /* Set debug_fork then attach to the child while it sleeps, to debug. */ 132 static int debug_fork = 0; 133 /* This is set to the result of setpgrp, which if vforked, will be visible 134 to you in the parent process. It's only used by humans for debugging. */ 135 static int debug_setpgrp = 657473; 136 static char *shell_file; 137 static char *exec_file; 138 char **save_our_env; 139 int shell = 0; 140 static char **argv; 141 const char *inferior_io_terminal = get_inferior_io_terminal (); 142 struct inferior *inf; 143 int i; 144 int save_errno; 145 146 /* If no exec file handed to us, get it from the exec-file command 147 -- with a good, common error message if none is specified. */ 148 exec_file = exec_file_arg; 149 if (exec_file == 0) 150 exec_file = get_exec_file (1); 151 152 /* STARTUP_WITH_SHELL is defined in inferior.h. If 0,e we'll just 153 do a fork/exec, no shell, so don't bother figuring out what 154 shell. */ 155 shell_file = shell_file_arg; 156 if (STARTUP_WITH_SHELL) 157 { 158 /* Figure out what shell to start up the user program under. */ 159 if (shell_file == NULL) 160 shell_file = getenv ("SHELL"); 161 if (shell_file == NULL) 162 shell_file = default_shell_file; 163 shell = 1; 164 } 165 166 if (!shell) 167 { 168 /* We're going to call execvp. Create argument vector. 169 Calculate an upper bound on the length of the vector by 170 assuming that every other character is a separate 171 argument. */ 172 int argc = (strlen (allargs) + 1) / 2 + 2; 173 174 argv = (char **) alloca (argc * sizeof (*argv)); 175 argv[0] = exec_file; 176 breakup_args (allargs, &argv[1]); 177 } 178 else 179 { 180 /* We're going to call a shell. */ 181 char *shell_command; 182 int len; 183 char *p; 184 int need_to_quote; 185 const int escape_bang = escape_bang_in_quoted_argument (shell_file); 186 187 /* Multiplying the length of exec_file by 4 is to account for the 188 fact that it may expand when quoted; it is a worst-case number 189 based on every character being '. */ 190 len = 5 + 4 * strlen (exec_file) + 1 + strlen (allargs) + 1 + /*slop */ 12; 191 if (exec_wrapper) 192 len += strlen (exec_wrapper) + 1; 193 194 shell_command = (char *) alloca (len); 195 shell_command[0] = '\0'; 196 197 strcat (shell_command, "exec "); 198 199 /* Add any exec wrapper. That may be a program name with arguments, so 200 the user must handle quoting. */ 201 if (exec_wrapper) 202 { 203 strcat (shell_command, exec_wrapper); 204 strcat (shell_command, " "); 205 } 206 207 /* Now add exec_file, quoting as necessary. */ 208 209 /* Quoting in this style is said to work with all shells. But 210 csh on IRIX 4.0.1 can't deal with it. So we only quote it if 211 we need to. */ 212 p = exec_file; 213 while (1) 214 { 215 switch (*p) 216 { 217 case '\'': 218 case '!': 219 case '"': 220 case '(': 221 case ')': 222 case '$': 223 case '&': 224 case ';': 225 case '<': 226 case '>': 227 case ' ': 228 case '\n': 229 case '\t': 230 need_to_quote = 1; 231 goto end_scan; 232 233 case '\0': 234 need_to_quote = 0; 235 goto end_scan; 236 237 default: 238 break; 239 } 240 ++p; 241 } 242 end_scan: 243 if (need_to_quote) 244 { 245 strcat (shell_command, "'"); 246 for (p = exec_file; *p != '\0'; ++p) 247 { 248 if (*p == '\'') 249 strcat (shell_command, "'\\''"); 250 else if (*p == '!' && escape_bang) 251 strcat (shell_command, "\\!"); 252 else 253 strncat (shell_command, p, 1); 254 } 255 strcat (shell_command, "'"); 256 } 257 else 258 strcat (shell_command, exec_file); 259 260 strcat (shell_command, " "); 261 strcat (shell_command, allargs); 262 263 /* If we decided above to start up with a shell, we exec the 264 shell, "-c" says to interpret the next arg as a shell command 265 to execute, and this command is "exec <target-program> 266 <args>". */ 267 argv = (char **) alloca (4 * sizeof (char *)); 268 argv[0] = shell_file; 269 argv[1] = "-c"; 270 argv[2] = shell_command; 271 argv[3] = (char *) 0; 272 } 273 274 /* Retain a copy of our environment variables, since the child will 275 replace the value of environ and if we're vforked, we have to 276 restore it. */ 277 save_our_env = environ; 278 279 /* Tell the terminal handling subsystem what tty we plan to run on; 280 it will just record the information for later. */ 281 new_tty_prefork (inferior_io_terminal); 282 283 /* It is generally good practice to flush any possible pending stdio 284 output prior to doing a fork, to avoid the possibility of both 285 the parent and child flushing the same data after the fork. */ 286 gdb_flush (gdb_stdout); 287 gdb_flush (gdb_stderr); 288 289 /* If there's any initialization of the target layers that must 290 happen to prepare to handle the child we're about fork, do it 291 now... */ 292 if (pre_trace_fun != NULL) 293 (*pre_trace_fun) (); 294 295 /* Create the child process. Since the child process is going to 296 exec(3) shortly afterwards, try to reduce the overhead by 297 calling vfork(2). However, if PRE_TRACE_FUN is non-null, it's 298 likely that this optimization won't work since there's too much 299 work to do between the vfork(2) and the exec(3). This is known 300 to be the case on ttrace(2)-based HP-UX, where some handshaking 301 between parent and child needs to happen between fork(2) and 302 exec(2). However, since the parent is suspended in the vforked 303 state, this doesn't work. Also note that the vfork(2) call might 304 actually be a call to fork(2) due to the fact that autoconf will 305 ``#define vfork fork'' on certain platforms. */ 306 if (pre_trace_fun || debug_fork) 307 pid = fork (); 308 else 309 pid = vfork (); 310 311 if (pid < 0) 312 perror_with_name (("vfork")); 313 314 if (pid == 0) 315 { 316 if (debug_fork) 317 sleep (debug_fork); 318 319 /* Create a new session for the inferior process, if necessary. 320 It will also place the inferior in a separate process group. */ 321 if (create_tty_session () <= 0) 322 { 323 /* No session was created, but we still want to run the inferior 324 in a separate process group. */ 325 debug_setpgrp = gdb_setpgid (); 326 if (debug_setpgrp == -1) 327 perror (_("setpgrp failed in child")); 328 } 329 330 /* Ask the tty subsystem to switch to the one we specified 331 earlier (or to share the current terminal, if none was 332 specified). */ 333 new_tty (); 334 335 /* Changing the signal handlers for the inferior after 336 a vfork can also change them for the superior, so we don't mess 337 with signals here. See comments in 338 initialize_signals for how we get the right signal handlers 339 for the inferior. */ 340 341 /* "Trace me, Dr. Memory!" */ 342 (*traceme_fun) (); 343 344 /* The call above set this process (the "child") as debuggable 345 by the original gdb process (the "parent"). Since processes 346 (unlike people) can have only one parent, if you are debugging 347 gdb itself (and your debugger is thus _already_ the 348 controller/parent for this child), code from here on out is 349 undebuggable. Indeed, you probably got an error message 350 saying "not parent". Sorry; you'll have to use print 351 statements! */ 352 353 /* There is no execlpe call, so we have to set the environment 354 for our child in the global variable. If we've vforked, this 355 clobbers the parent, but environ is restored a few lines down 356 in the parent. By the way, yes we do need to look down the 357 path to find $SHELL. Rich Pixley says so, and I agree. */ 358 environ = env; 359 360 if (exec_fun != NULL) 361 (*exec_fun) (argv[0], argv, env); 362 else 363 execvp (argv[0], argv); 364 365 /* If we get here, it's an error. */ 366 save_errno = errno; 367 fprintf_unfiltered (gdb_stderr, "Cannot exec %s", exec_file); 368 for (i = 1; argv[i] != NULL; i++) 369 fprintf_unfiltered (gdb_stderr, " %s", argv[i]); 370 fprintf_unfiltered (gdb_stderr, ".\n"); 371 fprintf_unfiltered (gdb_stderr, "Error: %s\n", 372 safe_strerror (save_errno)); 373 gdb_flush (gdb_stderr); 374 _exit (0177); 375 } 376 377 /* Restore our environment in case a vforked child clob'd it. */ 378 environ = save_our_env; 379 380 if (!have_inferiors ()) 381 init_thread_list (); 382 383 inf = current_inferior (); 384 385 inferior_appeared (inf, pid); 386 387 /* Needed for wait_for_inferior stuff below. */ 388 inferior_ptid = pid_to_ptid (pid); 389 390 new_tty_postfork (); 391 392 /* We have something that executes now. We'll be running through 393 the shell at this point, but the pid shouldn't change. Targets 394 supporting MT should fill this task's ptid with more data as soon 395 as they can. */ 396 add_thread_silent (inferior_ptid); 397 398 /* Now that we have a child process, make it our target, and 399 initialize anything target-vector-specific that needs 400 initializing. */ 401 if (init_trace_fun) 402 (*init_trace_fun) (pid); 403 404 /* We are now in the child process of interest, having exec'd the 405 correct program, and are poised at the first instruction of the 406 new program. */ 407 return pid; 408 } 409 410 /* Accept NTRAPS traps from the inferior. */ 411 412 void 413 startup_inferior (int ntraps) 414 { 415 int pending_execs = ntraps; 416 int terminal_initted = 0; 417 ptid_t resume_ptid; 418 419 if (target_supports_multi_process ()) 420 resume_ptid = pid_to_ptid (ptid_get_pid (inferior_ptid)); 421 else 422 resume_ptid = minus_one_ptid; 423 424 /* The process was started by the fork that created it, but it will 425 have stopped one instruction after execing the shell. Here we 426 must get it up to actual execution of the real program. */ 427 428 if (exec_wrapper) 429 pending_execs++; 430 431 while (1) 432 { 433 enum gdb_signal resume_signal = GDB_SIGNAL_0; 434 ptid_t event_ptid; 435 436 struct target_waitstatus ws; 437 memset (&ws, 0, sizeof (ws)); 438 event_ptid = target_wait (resume_ptid, &ws, 0); 439 440 if (ws.kind == TARGET_WAITKIND_IGNORE) 441 /* The inferior didn't really stop, keep waiting. */ 442 continue; 443 444 switch (ws.kind) 445 { 446 case TARGET_WAITKIND_SPURIOUS: 447 case TARGET_WAITKIND_LOADED: 448 case TARGET_WAITKIND_FORKED: 449 case TARGET_WAITKIND_VFORKED: 450 case TARGET_WAITKIND_SYSCALL_ENTRY: 451 case TARGET_WAITKIND_SYSCALL_RETURN: 452 /* Ignore gracefully during startup of the inferior. */ 453 switch_to_thread (event_ptid); 454 break; 455 456 case TARGET_WAITKIND_SIGNALLED: 457 target_terminal_ours (); 458 target_mourn_inferior (); 459 error (_("During startup program terminated with signal %s, %s."), 460 gdb_signal_to_name (ws.value.sig), 461 gdb_signal_to_string (ws.value.sig)); 462 return; 463 464 case TARGET_WAITKIND_EXITED: 465 target_terminal_ours (); 466 target_mourn_inferior (); 467 if (ws.value.integer) 468 error (_("During startup program exited with code %d."), 469 ws.value.integer); 470 else 471 error (_("During startup program exited normally.")); 472 return; 473 474 case TARGET_WAITKIND_EXECD: 475 /* Handle EXEC signals as if they were SIGTRAP signals. */ 476 xfree (ws.value.execd_pathname); 477 resume_signal = GDB_SIGNAL_TRAP; 478 switch_to_thread (event_ptid); 479 break; 480 481 case TARGET_WAITKIND_STOPPED: 482 resume_signal = ws.value.sig; 483 switch_to_thread (event_ptid); 484 break; 485 } 486 487 if (resume_signal != GDB_SIGNAL_TRAP) 488 { 489 /* Let shell child handle its own signals in its own way. */ 490 target_resume (resume_ptid, 0, resume_signal); 491 } 492 else 493 { 494 /* We handle SIGTRAP, however; it means child did an exec. */ 495 if (!terminal_initted) 496 { 497 /* Now that the child has exec'd we know it has already 498 set its process group. On POSIX systems, tcsetpgrp 499 will fail with EPERM if we try it before the child's 500 setpgid. */ 501 502 /* Set up the "saved terminal modes" of the inferior 503 based on what modes we are starting it with. */ 504 target_terminal_init (); 505 506 /* Install inferior's terminal modes. */ 507 target_terminal_inferior (); 508 509 terminal_initted = 1; 510 } 511 512 if (--pending_execs == 0) 513 break; 514 515 /* Just make it go on. */ 516 target_resume (resume_ptid, 0, GDB_SIGNAL_0); 517 } 518 } 519 520 /* Mark all threads non-executing. */ 521 set_executing (resume_ptid, 0); 522 } 523 524 /* Implement the "unset exec-wrapper" command. */ 525 526 static void 527 unset_exec_wrapper_command (char *args, int from_tty) 528 { 529 xfree (exec_wrapper); 530 exec_wrapper = NULL; 531 } 532 533 /* Provide a prototype to silence -Wmissing-prototypes. */ 534 extern initialize_file_ftype _initialize_fork_child; 535 536 void 537 _initialize_fork_child (void) 538 { 539 add_setshow_filename_cmd ("exec-wrapper", class_run, &exec_wrapper, _("\ 540 Set a wrapper for running programs.\n\ 541 The wrapper prepares the system and environment for the new program."), 542 _("\ 543 Show the wrapper for running programs."), NULL, 544 NULL, NULL, 545 &setlist, &showlist); 546 547 add_cmd ("exec-wrapper", class_run, unset_exec_wrapper_command, 548 _("Disable use of an execution wrapper."), 549 &unsetlist); 550 } 551