gdb/fork-child.c

   1 /* Fork a Unix child process, and set up to debug it, for GDB.
   2
   3    Copyright (C) 1990-1996, 1998-2001, 2004-2012 Free Software
   4    Foundation, Inc.
   5
   6    Contributed by Cygnus Support.
   7
   8    This file is part of GDB.
   9
  10    This program is free software; you can redistribute it and/or modify
  11    it under the terms of the GNU General Public License as published by
  12    the Free Software Foundation; either version 3 of the License, or
  13    (at your option) any later version.
  14
  15    This program is distributed in the hope that it will be useful,
  16    but WITHOUT ANY WARRANTY; without even the implied warranty of
  17    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18    GNU General Public License for more details.
  19
  20    You should have received a copy of the GNU General Public License
  21    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  22
  23 #include "defs.h"
  24 #include "gdb_string.h"
  25 #include "inferior.h"
  26 #include "terminal.h"
  27 #include "target.h"
  28 #include "gdb_wait.h"
  29 #include "gdb_vfork.h"
  30 #include "gdbcore.h"
  31 #include "terminal.h"
  32 #include "gdbthread.h"
  33 #include "command.h" /* for dont_repeat () */
  34 #include "gdbcmd.h"
  35 #include "solib.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 defined in inferior.h.  If 0,e we'll just
 154     do a fork/exec, no shell, so don't bother figuring out what
 155     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       if (debug_fork)
 318         sleep (debug_fork);
 319
 320       /* Create a new session for the inferior process, if necessary.
 321          It will also place the inferior in a separate process group.  */
 322       if (create_tty_session () <= 0)
 323         {
 324           /* No session was created, but we still want to run the inferior
 325              in a separate process group.  */
 326           debug_setpgrp = gdb_setpgid ();
 327           if (debug_setpgrp == -1)
 328             perror (_("setpgrp failed in child"));
 329         }
 330
 331       /* Ask the tty subsystem to switch to the one we specified
 332          earlier (or to share the current terminal, if none was
 333          specified).  */
 334       new_tty ();
 335
 336       /* Changing the signal handlers for the inferior after
 337          a vfork can also change them for the superior, so we don't mess
 338          with signals here.  See comments in
 339          initialize_signals for how we get the right signal handlers
 340          for the inferior.  */
 341
 342       /* "Trace me, Dr. Memory!"  */
 343       (*traceme_fun) ();
 344
 345       /* The call above set this process (the "child") as debuggable
 346         by the original gdb process (the "parent").  Since processes
 347         (unlike people) can have only one parent, if you are debugging
 348         gdb itself (and your debugger is thus _already_ the
 349         controller/parent for this child), code from here on out is
 350         undebuggable.  Indeed, you probably got an error message
 351         saying "not parent".  Sorry; you'll have to use print
 352         statements!  */
 353
 354       /* There is no execlpe call, so we have to set the environment
 355          for our child in the global variable.  If we've vforked, this
 356          clobbers the parent, but environ is restored a few lines down
 357          in the parent.  By the way, yes we do need to look down the
 358          path to find $SHELL.  Rich Pixley says so, and I agree.  */
 359       environ = env;
 360
 361       if (exec_fun != NULL)
 362         (*exec_fun) (argv[0], argv, env);
 363       else
 364         execvp (argv[0], argv);
 365
 366       /* If we get here, it's an error.  */
 367       save_errno = errno;
 368       fprintf_unfiltered (gdb_stderr, "Cannot exec %s", exec_file);
 369       for (i = 1; argv[i] != NULL; i++)
 370         fprintf_unfiltered (gdb_stderr, " %s", argv[i]);
 371       fprintf_unfiltered (gdb_stderr, ".\n");
 372       fprintf_unfiltered (gdb_stderr, "Error: %s\n",
 373                           safe_strerror (save_errno));
 374       gdb_flush (gdb_stderr);
 375       _exit (0177);
 376     }
 377
 378   /* Restore our environment in case a vforked child clob'd it.  */
 379   environ = save_our_env;
 380
 381   if (!have_inferiors ())
 382     init_thread_list ();
 383
 384   inf = current_inferior ();
 385
 386   inferior_appeared (inf, pid);
 387
 388   /* Needed for wait_for_inferior stuff below.  */
 389   inferior_ptid = pid_to_ptid (pid);
 390
 391   new_tty_postfork ();
 392
 393   /* We have something that executes now.  We'll be running through
 394      the shell at this point, but the pid shouldn't change.  Targets
 395      supporting MT should fill this task's ptid with more data as soon
 396      as they can.  */
 397   add_thread_silent (inferior_ptid);
 398
 399   /* Now that we have a child process, make it our target, and
 400      initialize anything target-vector-specific that needs
 401      initializing.  */
 402   if (init_trace_fun)
 403     (*init_trace_fun) (pid);
 404
 405   /* We are now in the child process of interest, having exec'd the
 406      correct program, and are poised at the first instruction of the
 407      new program.  */
 408   return pid;
 409 }
 410
 411 /* Accept NTRAPS traps from the inferior.  */
 412
 413 void
 414 startup_inferior (int ntraps)
 415 {
 416   int pending_execs = ntraps;
 417   int terminal_initted = 0;
 418   ptid_t resume_ptid;
 419
 420   if (target_supports_multi_process ())
 421     resume_ptid = pid_to_ptid (ptid_get_pid (inferior_ptid));
 422   else
 423     resume_ptid = minus_one_ptid;
 424
 425   /* The process was started by the fork that created it, but it will
 426      have stopped one instruction after execing the shell.  Here we
 427      must get it up to actual execution of the real program.  */
 428
 429   if (exec_wrapper)
 430     pending_execs++;
 431
 432   while (1)
 433     {
 434       enum gdb_signal resume_signal = GDB_SIGNAL_0;
 435       ptid_t event_ptid;
 436
 437       struct target_waitstatus ws;
 438       memset (&ws, 0, sizeof (ws));
 439       event_ptid = target_wait (resume_ptid, &ws, 0);
 440
 441       if (ws.kind == TARGET_WAITKIND_IGNORE)
 442         /* The inferior didn't really stop, keep waiting.  */
 443         continue;
 444
 445       switch (ws.kind)
 446         {
 447           case TARGET_WAITKIND_SPURIOUS:
 448           case TARGET_WAITKIND_LOADED:
 449           case TARGET_WAITKIND_FORKED:
 450           case TARGET_WAITKIND_VFORKED:
 451           case TARGET_WAITKIND_SYSCALL_ENTRY:
 452           case TARGET_WAITKIND_SYSCALL_RETURN:
 453             /* Ignore gracefully during startup of the inferior.  */
 454             switch_to_thread (event_ptid);
 455             break;
 456
 457           case TARGET_WAITKIND_SIGNALLED:
 458             target_terminal_ours ();
 459             target_mourn_inferior ();
 460             error (_("During startup program terminated with signal %s, %s."),
 461                    gdb_signal_to_name (ws.value.sig),
 462                    gdb_signal_to_string (ws.value.sig));
 463             return;
 464
 465           case TARGET_WAITKIND_EXITED:
 466             target_terminal_ours ();
 467             target_mourn_inferior ();
 468             if (ws.value.integer)
 469               error (_("During startup program exited with code %d."),
 470                      ws.value.integer);
 471             else
 472               error (_("During startup program exited normally."));
 473             return;
 474
 475           case TARGET_WAITKIND_EXECD:
 476             /* Handle EXEC signals as if they were SIGTRAP signals.  */
 477             xfree (ws.value.execd_pathname);
 478             resume_signal = GDB_SIGNAL_TRAP;
 479             switch_to_thread (event_ptid);
 480             break;
 481
 482           case TARGET_WAITKIND_STOPPED:
 483             resume_signal = ws.value.sig;
 484             switch_to_thread (event_ptid);
 485             break;
 486         }
 487
 488       if (resume_signal != GDB_SIGNAL_TRAP)
 489         {
 490           /* Let shell child handle its own signals in its own way.  */
 491           target_resume (resume_ptid, 0, resume_signal);
 492         }
 493       else
 494         {
 495           /* We handle SIGTRAP, however; it means child did an exec.  */
 496           if (!terminal_initted)
 497             {
 498               /* Now that the child has exec'd we know it has already
 499                  set its process group.  On POSIX systems, tcsetpgrp
 500                  will fail with EPERM if we try it before the child's
 501                  setpgid.  */
 502
 503               /* Set up the "saved terminal modes" of the inferior
 504                  based on what modes we are starting it with.  */
 505               target_terminal_init ();
 506
 507               /* Install inferior's terminal modes.  */
 508               target_terminal_inferior ();
 509
 510               terminal_initted = 1;
 511             }
 512
 513           if (--pending_execs == 0)
 514             break;
 515
 516           /* Just make it go on.  */
 517           target_resume (resume_ptid, 0, GDB_SIGNAL_0);
 518         }
 519     }
 520
 521   /* Mark all threads non-executing.  */
 522   set_executing (resume_ptid, 0);
 523 }
 524
 525 /* Implement the "unset exec-wrapper" command.  */
 526
 527 static void
 528 unset_exec_wrapper_command (char *args, int from_tty)
 529 {
 530   xfree (exec_wrapper);
 531   exec_wrapper = NULL;
 532 }
 533
 534 /* Provide a prototype to silence -Wmissing-prototypes.  */
 535 extern initialize_file_ftype _initialize_fork_child;
 536
 537 void
 538 _initialize_fork_child (void)
 539 {
 540   add_setshow_filename_cmd ("exec-wrapper", class_run, &exec_wrapper, _("\
 541 Set a wrapper for running programs.\n\
 542 The wrapper prepares the system and environment for the new program."),
 543                             _("\
 544 Show the wrapper for running programs."), NULL,
 545                             NULL, NULL,
 546                             &setlist, &showlist);
 547
 548   add_cmd ("exec-wrapper", class_run, unset_exec_wrapper_command,
 549            _("Disable use of an execution wrapper."),
 550            &unsetlist);
 551 }