gdb/fork-child.c

   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 <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 #include "filestuff.h"
  36
  37 #include <signal.h>
  38
  39 /* This just gets used as a default if we can't find SHELL.  */
  40 #define SHELL_FILE "/bin/sh"
  41
  42 extern char **environ;
  43
  44 static char *exec_wrapper;
  45
  46 /* Break up SCRATCH into an argument vector suitable for passing to
  47    execvp and store it in ARGV.  E.g., on "run a b c d" this routine
  48    would get as input the string "a b c d", and as output it would
  49    fill in ARGV with the four arguments "a", "b", "c", "d".  */
  50
  51 static void
  52 breakup_args (char *scratch, char **argv)
  53 {
  54   char *cp = scratch, *tmp;
  55
  56   for (;;)
  57     {
  58       /* Scan past leading separators */
  59       while (*cp == ' ' || *cp == '\t' || *cp == '\n')
  60         cp++;
  61
  62       /* Break if at end of string.  */
  63       if (*cp == '\0')
  64         break;
  65
  66       /* Take an arg.  */
  67       *argv++ = cp;
  68
  69       /* Scan for next arg separator.  */
  70       tmp = strchr (cp, ' ');
  71       if (tmp == NULL)
  72         tmp = strchr (cp, '\t');
  73       if (tmp == NULL)
  74         tmp = strchr (cp, '\n');
  75
  76       /* No separators => end of string => break.  */
  77       if (tmp == NULL)
  78         break;
  79       cp = tmp;
  80
  81       /* Replace the separator with a terminator.  */
  82       *cp++ = '\0';
  83     }
  84
  85   /* Null-terminate the vector.  */
  86   *argv = NULL;
  87 }
  88
  89 /* When executing a command under the given shell, return non-zero if
  90    the '!' character should be escaped when embedded in a quoted
  91    command-line argument.  */
  92
  93 static int
  94 escape_bang_in_quoted_argument (const char *shell_file)
  95 {
  96   const int shell_file_len = strlen (shell_file);
  97
  98   /* Bang should be escaped only in C Shells.  For now, simply check
  99      that the shell name ends with 'csh', which covers at least csh
 100      and tcsh.  This should be good enough for now.  */
 101
 102   if (shell_file_len < 3)
 103     return 0;
 104
 105   if (shell_file[shell_file_len - 3] == 'c'
 106       && shell_file[shell_file_len - 2] == 's'
 107       && shell_file[shell_file_len - 1] == 'h')
 108     return 1;
 109
 110   return 0;
 111 }
 112
 113 /* Start an inferior Unix child process and sets inferior_ptid to its
 114    pid.  EXEC_FILE is the file to run.  ALLARGS is a string containing
 115    the arguments to the program.  ENV is the environment vector to
 116    pass.  SHELL_FILE is the shell file, or NULL if we should pick
 117    one.  EXEC_FUN is the exec(2) function to use, or NULL for the default
 118    one.  */
 119
 120 /* This function is NOT reentrant.  Some of the variables have been
 121    made static to ensure that they survive the vfork call.  */
 122
 123 int
 124 fork_inferior (char *exec_file_arg, char *allargs, char **env,
 125                void (*traceme_fun) (void), void (*init_trace_fun) (int),
 126                void (*pre_trace_fun) (void), char *shell_file_arg,
 127                void (*exec_fun)(const char *file, char * const *argv,
 128                                 char * const *env))
 129 {
 130   int pid;
 131   static char default_shell_file[] = SHELL_FILE;
 132   /* Set debug_fork then attach to the child while it sleeps, to debug.  */
 133   static int debug_fork = 0;
 134   /* This is set to the result of setpgrp, which if vforked, will be visible
 135      to you in the parent process.  It's only used by humans for debugging.  */
 136   static int debug_setpgrp = 657473;
 137   static char *shell_file;
 138   static char *exec_file;
 139   char **save_our_env;
 140   int shell = 0;
 141   static char **argv;
 142   const char *inferior_io_terminal = get_inferior_io_terminal ();
 143   struct inferior *inf;
 144   int i;
 145   int save_errno;
 146
 147   /* If no exec file handed to us, get it from the exec-file command
 148      -- with a good, common error message if none is specified.  */
 149   exec_file = exec_file_arg;
 150   if (exec_file == 0)
 151     exec_file = get_exec_file (1);
 152
 153   /* 'startup_with_shell' is declared in inferior.h and bound to the
 154      "set startup-with-shell" option.  If 0, we'll just do a
 155      fork/exec, no shell, so don't bother figuring out what shell.  */
 156   shell_file = shell_file_arg;
 157   if (startup_with_shell)
 158     {
 159       /* Figure out what shell to start up the user program under.  */
 160       if (shell_file == NULL)
 161         shell_file = getenv ("SHELL");
 162       if (shell_file == NULL)
 163         shell_file = default_shell_file;
 164       shell = 1;
 165     }
 166
 167   if (!shell)
 168     {
 169       /* We're going to call execvp.  Create argument vector.
 170          Calculate an upper bound on the length of the vector by
 171          assuming that every other character is a separate
 172          argument.  */
 173       int argc = (strlen (allargs) + 1) / 2 + 2;
 174
 175       argv = (char **) alloca (argc * sizeof (*argv));
 176       argv[0] = exec_file;
 177       breakup_args (allargs, &argv[1]);
 178     }
 179   else
 180     {
 181       /* We're going to call a shell.  */
 182       char *shell_command;
 183       int len;
 184       char *p;
 185       int need_to_quote;
 186       const int escape_bang = escape_bang_in_quoted_argument (shell_file);
 187
 188       /* Multiplying the length of exec_file by 4 is to account for the
 189          fact that it may expand when quoted; it is a worst-case number
 190          based on every character being '.  */
 191       len = 5 + 4 * strlen (exec_file) + 1 + strlen (allargs) + 1 + /*slop */ 12;
 192       if (exec_wrapper)
 193         len += strlen (exec_wrapper) + 1;
 194
 195       shell_command = (char *) alloca (len);
 196       shell_command[0] = '\0';
 197
 198       strcat (shell_command, "exec ");
 199
 200       /* Add any exec wrapper.  That may be a program name with arguments, so
 201          the user must handle quoting.  */
 202       if (exec_wrapper)
 203         {
 204           strcat (shell_command, exec_wrapper);
 205           strcat (shell_command, " ");
 206         }
 207
 208       /* Now add exec_file, quoting as necessary.  */
 209
 210       /* Quoting in this style is said to work with all shells.  But
 211          csh on IRIX 4.0.1 can't deal with it.  So we only quote it if
 212          we need to.  */
 213       p = exec_file;
 214       while (1)
 215         {
 216           switch (*p)
 217             {
 218             case '\'':
 219             case '!':
 220             case '"':
 221             case '(':
 222             case ')':
 223             case '$':
 224             case '&':
 225             case ';':
 226             case '<':
 227             case '>':
 228             case ' ':
 229             case '\n':
 230             case '\t':
 231               need_to_quote = 1;
 232               goto end_scan;
 233
 234             case '\0':
 235               need_to_quote = 0;
 236               goto end_scan;
 237
 238             default:
 239               break;
 240             }
 241           ++p;
 242         }
 243     end_scan:
 244       if (need_to_quote)
 245         {
 246           strcat (shell_command, "'");
 247           for (p = exec_file; *p != '\0'; ++p)
 248             {
 249               if (*p == '\'')
 250                 strcat (shell_command, "'\\''");
 251               else if (*p == '!' && escape_bang)
 252                 strcat (shell_command, "\\!");
 253               else
 254                 strncat (shell_command, p, 1);
 255             }
 256           strcat (shell_command, "'");
 257         }
 258       else
 259         strcat (shell_command, exec_file);
 260
 261       strcat (shell_command, " ");
 262       strcat (shell_command, allargs);
 263
 264       /* If we decided above to start up with a shell, we exec the
 265          shell, "-c" says to interpret the next arg as a shell command
 266          to execute, and this command is "exec <target-program>
 267          <args>".  */
 268       argv = (char **) alloca (4 * sizeof (char *));
 269       argv[0] = shell_file;
 270       argv[1] = "-c";
 271       argv[2] = shell_command;
 272       argv[3] = (char *) 0;
 273     }
 274
 275   /* Retain a copy of our environment variables, since the child will
 276      replace the value of environ and if we're vforked, we have to
 277      restore it.  */
 278   save_our_env = environ;
 279
 280   /* Tell the terminal handling subsystem what tty we plan to run on;
 281      it will just record the information for later.  */
 282   new_tty_prefork (inferior_io_terminal);
 283
 284   /* It is generally good practice to flush any possible pending stdio
 285      output prior to doing a fork, to avoid the possibility of both
 286      the parent and child flushing the same data after the fork.  */
 287   gdb_flush (gdb_stdout);
 288   gdb_flush (gdb_stderr);
 289
 290   /* If there's any initialization of the target layers that must
 291      happen to prepare to handle the child we're about fork, do it
 292      now...  */
 293   if (pre_trace_fun != NULL)
 294     (*pre_trace_fun) ();
 295
 296   /* Create the child process.  Since the child process is going to
 297      exec(3) shortly afterwards, try to reduce the overhead by
 298      calling vfork(2).  However, if PRE_TRACE_FUN is non-null, it's
 299      likely that this optimization won't work since there's too much
 300      work to do between the vfork(2) and the exec(3).  This is known
 301      to be the case on ttrace(2)-based HP-UX, where some handshaking
 302      between parent and child needs to happen between fork(2) and
 303      exec(2).  However, since the parent is suspended in the vforked
 304      state, this doesn't work.  Also note that the vfork(2) call might
 305      actually be a call to fork(2) due to the fact that autoconf will
 306      ``#define vfork fork'' on certain platforms.  */
 307   if (pre_trace_fun || debug_fork)
 308     pid = fork ();
 309   else
 310     pid = vfork ();
 311
 312   if (pid < 0)
 313     perror_with_name (("vfork"));
 314
 315   if (pid == 0)
 316     {
 317       close_most_fds ();
 318
 319       if (debug_fork)
 320         sleep (debug_fork);
 321
 322       /* Create a new session for the inferior process, if necessary.
 323          It will also place the inferior in a separate process group.  */
 324       if (create_tty_session () <= 0)
 325         {
 326           /* No session was created, but we still want to run the inferior
 327              in a separate process group.  */
 328           debug_setpgrp = gdb_setpgid ();
 329           if (debug_setpgrp == -1)
 330             perror (_("setpgrp failed in child"));
 331         }
 332
 333       /* Ask the tty subsystem to switch to the one we specified
 334          earlier (or to share the current terminal, if none was
 335          specified).  */
 336       new_tty ();
 337
 338       /* Changing the signal handlers for the inferior after
 339          a vfork can also change them for the superior, so we don't mess
 340          with signals here.  See comments in
 341          initialize_signals for how we get the right signal handlers
 342          for the inferior.  */
 343
 344       /* "Trace me, Dr. Memory!"  */
 345       (*traceme_fun) ();
 346
 347       /* The call above set this process (the "child") as debuggable
 348         by the original gdb process (the "parent").  Since processes
 349         (unlike people) can have only one parent, if you are debugging
 350         gdb itself (and your debugger is thus _already_ the
 351         controller/parent for this child), code from here on out is
 352         undebuggable.  Indeed, you probably got an error message
 353         saying "not parent".  Sorry; you'll have to use print
 354         statements!  */
 355
 356       /* There is no execlpe call, so we have to set the environment
 357          for our child in the global variable.  If we've vforked, this
 358          clobbers the parent, but environ is restored a few lines down
 359          in the parent.  By the way, yes we do need to look down the
 360          path to find $SHELL.  Rich Pixley says so, and I agree.  */
 361       environ = env;
 362
 363       if (exec_fun != NULL)
 364         (*exec_fun) (argv[0], argv, env);
 365       else
 366         execvp (argv[0], argv);
 367
 368       /* If we get here, it's an error.  */
 369       save_errno = errno;
 370       fprintf_unfiltered (gdb_stderr, "Cannot exec %s", exec_file);
 371       for (i = 1; argv[i] != NULL; i++)
 372         fprintf_unfiltered (gdb_stderr, " %s", argv[i]);
 373       fprintf_unfiltered (gdb_stderr, ".\n");
 374       fprintf_unfiltered (gdb_stderr, "Error: %s\n",
 375                           safe_strerror (save_errno));
 376       gdb_flush (gdb_stderr);
 377       _exit (0177);
 378     }
 379
 380   /* Restore our environment in case a vforked child clob'd it.  */
 381   environ = save_our_env;
 382
 383   if (!have_inferiors ())
 384     init_thread_list ();
 385
 386   inf = current_inferior ();
 387
 388   inferior_appeared (inf, pid);
 389
 390   /* Needed for wait_for_inferior stuff below.  */
 391   inferior_ptid = pid_to_ptid (pid);
 392
 393   new_tty_postfork ();
 394
 395   /* We have something that executes now.  We'll be running through
 396      the shell at this point, but the pid shouldn't change.  Targets
 397      supporting MT should fill this task's ptid with more data as soon
 398      as they can.  */
 399   add_thread_silent (inferior_ptid);
 400
 401   /* Now that we have a child process, make it our target, and
 402      initialize anything target-vector-specific that needs
 403      initializing.  */
 404   if (init_trace_fun)
 405     (*init_trace_fun) (pid);
 406
 407   /* We are now in the child process of interest, having exec'd the
 408      correct program, and are poised at the first instruction of the
 409      new program.  */
 410   return pid;
 411 }
 412
 413 /* Accept NTRAPS traps from the inferior.  */
 414
 415 void
 416 startup_inferior (int ntraps)
 417 {
 418   int pending_execs = ntraps;
 419   int terminal_initted = 0;
 420   ptid_t resume_ptid;
 421
 422   if (startup_with_shell)
 423     {
 424       /* One trap extra for exec'ing the shell.  */
 425       pending_execs++;
 426     }
 427
 428   if (target_supports_multi_process ())
 429     resume_ptid = pid_to_ptid (ptid_get_pid (inferior_ptid));
 430   else
 431     resume_ptid = minus_one_ptid;
 432
 433   /* The process was started by the fork that created it, but it will
 434      have stopped one instruction after execing the shell.  Here we
 435      must get it up to actual execution of the real program.  */
 436
 437   if (exec_wrapper)
 438     pending_execs++;
 439
 440   while (1)
 441     {
 442       enum gdb_signal resume_signal = GDB_SIGNAL_0;
 443       ptid_t event_ptid;
 444
 445       struct target_waitstatus ws;
 446       memset (&ws, 0, sizeof (ws));
 447       event_ptid = target_wait (resume_ptid, &ws, 0);
 448
 449       if (ws.kind == TARGET_WAITKIND_IGNORE)
 450         /* The inferior didn't really stop, keep waiting.  */
 451         continue;
 452
 453       switch (ws.kind)
 454         {
 455           case TARGET_WAITKIND_SPURIOUS:
 456           case TARGET_WAITKIND_LOADED:
 457           case TARGET_WAITKIND_FORKED:
 458           case TARGET_WAITKIND_VFORKED:
 459           case TARGET_WAITKIND_SYSCALL_ENTRY:
 460           case TARGET_WAITKIND_SYSCALL_RETURN:
 461             /* Ignore gracefully during startup of the inferior.  */
 462             switch_to_thread (event_ptid);
 463             break;
 464
 465           case TARGET_WAITKIND_SIGNALLED:
 466             target_terminal_ours ();
 467             target_mourn_inferior ();
 468             error (_("During startup program terminated with signal %s, %s."),
 469                    gdb_signal_to_name (ws.value.sig),
 470                    gdb_signal_to_string (ws.value.sig));
 471             return;
 472
 473           case TARGET_WAITKIND_EXITED:
 474             target_terminal_ours ();
 475             target_mourn_inferior ();
 476             if (ws.value.integer)
 477               error (_("During startup program exited with code %d."),
 478                      ws.value.integer);
 479             else
 480               error (_("During startup program exited normally."));
 481             return;
 482
 483           case TARGET_WAITKIND_EXECD:
 484             /* Handle EXEC signals as if they were SIGTRAP signals.  */
 485             xfree (ws.value.execd_pathname);
 486             resume_signal = GDB_SIGNAL_TRAP;
 487             switch_to_thread (event_ptid);
 488             break;
 489
 490           case TARGET_WAITKIND_STOPPED:
 491             resume_signal = ws.value.sig;
 492             switch_to_thread (event_ptid);
 493             break;
 494         }
 495
 496       if (resume_signal != GDB_SIGNAL_TRAP)
 497         {
 498           /* Let shell child handle its own signals in its own way.  */
 499           target_resume (resume_ptid, 0, resume_signal);
 500         }
 501       else
 502         {
 503           /* We handle SIGTRAP, however; it means child did an exec.  */
 504           if (!terminal_initted)
 505             {
 506               /* Now that the child has exec'd we know it has already
 507                  set its process group.  On POSIX systems, tcsetpgrp
 508                  will fail with EPERM if we try it before the child's
 509                  setpgid.  */
 510
 511               /* Set up the "saved terminal modes" of the inferior
 512                  based on what modes we are starting it with.  */
 513               target_terminal_init ();
 514
 515               /* Install inferior's terminal modes.  */
 516               target_terminal_inferior ();
 517
 518               terminal_initted = 1;
 519             }
 520
 521           if (--pending_execs == 0)
 522             break;
 523
 524           /* Just make it go on.  */
 525           target_resume (resume_ptid, 0, GDB_SIGNAL_0);
 526         }
 527     }
 528
 529   /* Mark all threads non-executing.  */
 530   set_executing (resume_ptid, 0);
 531 }
 532
 533 /* Implement the "unset exec-wrapper" command.  */
 534
 535 static void
 536 unset_exec_wrapper_command (char *args, int from_tty)
 537 {
 538   xfree (exec_wrapper);
 539   exec_wrapper = NULL;
 540 }
 541
 542 static void
 543 show_startup_with_shell (struct ui_file *file, int from_tty,
 544                          struct cmd_list_element *c, const char *value)
 545 {
 546   fprintf_filtered (file,
 547                     _("Use of shell to start subprocesses is %s.\n"),
 548                     value);
 549 }
 550
 551 /* Provide a prototype to silence -Wmissing-prototypes.  */
 552 extern initialize_file_ftype _initialize_fork_child;
 553
 554 void
 555 _initialize_fork_child (void)
 556 {
 557   add_setshow_filename_cmd ("exec-wrapper", class_run, &exec_wrapper, _("\
 558 Set a wrapper for running programs.\n\
 559 The wrapper prepares the system and environment for the new program."),
 560                             _("\
 561 Show the wrapper for running programs."), NULL,
 562                             NULL, NULL,
 563                             &setlist, &showlist);
 564
 565   add_cmd ("exec-wrapper", class_run, unset_exec_wrapper_command,
 566            _("Disable use of an execution wrapper."),
 567            &unsetlist);
 568
 569   add_setshow_boolean_cmd ("startup-with-shell", class_support,
 570                            &startup_with_shell, _("\
 571 Set use of shell to start subprocesses.  The default is on."), _("\
 572 Show use of shell to start subprocesses."), NULL,
 573                            NULL,
 574                            show_startup_with_shell,
 575                            &setlist, &showlist);
 576 }