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   /* On some systems an exec will fail if the executable is open.  */
 276   close_exec_file ();
 277
 278   /* Retain a copy of our environment variables, since the child will
 279      replace the value of environ and if we're vforked, we have to
 280      restore it.  */
 281   save_our_env = environ;
 282
 283   /* Tell the terminal handling subsystem what tty we plan to run on;
 284      it will just record the information for later.  */
 285   new_tty_prefork (inferior_io_terminal);
 286
 287   /* It is generally good practice to flush any possible pending stdio
 288      output prior to doing a fork, to avoid the possibility of both
 289      the parent and child flushing the same data after the fork.  */
 290   gdb_flush (gdb_stdout);
 291   gdb_flush (gdb_stderr);
 292
 293   /* If there's any initialization of the target layers that must
 294      happen to prepare to handle the child we're about fork, do it
 295      now...  */
 296   if (pre_trace_fun != NULL)
 297     (*pre_trace_fun) ();
 298
 299   /* Create the child process.  Since the child process is going to
 300      exec(3) shortly afterwards, try to reduce the overhead by
 301      calling vfork(2).  However, if PRE_TRACE_FUN is non-null, it's
 302      likely that this optimization won't work since there's too much
 303      work to do between the vfork(2) and the exec(3).  This is known
 304      to be the case on ttrace(2)-based HP-UX, where some handshaking
 305      between parent and child needs to happen between fork(2) and
 306      exec(2).  However, since the parent is suspended in the vforked
 307      state, this doesn't work.  Also note that the vfork(2) call might
 308      actually be a call to fork(2) due to the fact that autoconf will
 309      ``#define vfork fork'' on certain platforms.  */
 310   if (pre_trace_fun || debug_fork)
 311     pid = fork ();
 312   else
 313     pid = vfork ();
 314
 315   if (pid < 0)
 316     perror_with_name (("vfork"));
 317
 318   if (pid == 0)
 319     {
 320       if (debug_fork)
 321         sleep (debug_fork);
 322
 323       /* Create a new session for the inferior process, if necessary.
 324          It will also place the inferior in a separate process group.  */
 325       if (create_tty_session () <= 0)
 326         {
 327           /* No session was created, but we still want to run the inferior
 328              in a separate process group.  */
 329           debug_setpgrp = gdb_setpgid ();
 330           if (debug_setpgrp == -1)
 331             perror (_("setpgrp failed in child"));
 332         }
 333
 334       /* Ask the tty subsystem to switch to the one we specified
 335          earlier (or to share the current terminal, if none was
 336          specified).  */
 337       new_tty ();
 338
 339       /* Changing the signal handlers for the inferior after
 340          a vfork can also change them for the superior, so we don't mess
 341          with signals here.  See comments in
 342          initialize_signals for how we get the right signal handlers
 343          for the inferior.  */
 344
 345       /* "Trace me, Dr. Memory!"  */
 346       (*traceme_fun) ();
 347
 348       /* The call above set this process (the "child") as debuggable
 349         by the original gdb process (the "parent").  Since processes
 350         (unlike people) can have only one parent, if you are debugging
 351         gdb itself (and your debugger is thus _already_ the
 352         controller/parent for this child), code from here on out is
 353         undebuggable.  Indeed, you probably got an error message
 354         saying "not parent".  Sorry; you'll have to use print
 355         statements!  */
 356
 357       /* There is no execlpe call, so we have to set the environment
 358          for our child in the global variable.  If we've vforked, this
 359          clobbers the parent, but environ is restored a few lines down
 360          in the parent.  By the way, yes we do need to look down the
 361          path to find $SHELL.  Rich Pixley says so, and I agree.  */
 362       environ = env;
 363
 364       if (exec_fun != NULL)
 365         (*exec_fun) (argv[0], argv, env);
 366       else
 367         execvp (argv[0], argv);
 368
 369       /* If we get here, it's an error.  */
 370       save_errno = errno;
 371       fprintf_unfiltered (gdb_stderr, "Cannot exec %s", exec_file);
 372       for (i = 1; argv[i] != NULL; i++)
 373         fprintf_unfiltered (gdb_stderr, " %s", argv[i]);
 374       fprintf_unfiltered (gdb_stderr, ".\n");
 375       fprintf_unfiltered (gdb_stderr, "Error: %s\n",
 376                           safe_strerror (save_errno));
 377       gdb_flush (gdb_stderr);
 378       _exit (0177);
 379     }
 380
 381   /* Restore our environment in case a vforked child clob'd it.  */
 382   environ = save_our_env;
 383
 384   if (!have_inferiors ())
 385     init_thread_list ();
 386
 387   inf = current_inferior ();
 388
 389   inferior_appeared (inf, pid);
 390
 391   /* Needed for wait_for_inferior stuff below.  */
 392   inferior_ptid = pid_to_ptid (pid);
 393
 394   new_tty_postfork ();
 395
 396   /* We have something that executes now.  We'll be running through
 397      the shell at this point, but the pid shouldn't change.  Targets
 398      supporting MT should fill this task's ptid with more data as soon
 399      as they can.  */
 400   add_thread_silent (inferior_ptid);
 401
 402   /* Now that we have a child process, make it our target, and
 403      initialize anything target-vector-specific that needs
 404      initializing.  */
 405   if (init_trace_fun)
 406     (*init_trace_fun) (pid);
 407
 408   /* We are now in the child process of interest, having exec'd the
 409      correct program, and are poised at the first instruction of the
 410      new program.  */
 411   return pid;
 412 }
 413
 414 /* Accept NTRAPS traps from the inferior.  */
 415
 416 void
 417 startup_inferior (int ntraps)
 418 {
 419   int pending_execs = ntraps;
 420   int terminal_initted = 0;
 421   ptid_t resume_ptid;
 422
 423   if (target_supports_multi_process ())
 424     resume_ptid = pid_to_ptid (ptid_get_pid (inferior_ptid));
 425   else
 426     resume_ptid = minus_one_ptid;
 427
 428   /* The process was started by the fork that created it, but it will
 429      have stopped one instruction after execing the shell.  Here we
 430      must get it up to actual execution of the real program.  */
 431
 432   if (exec_wrapper)
 433     pending_execs++;
 434
 435   while (1)
 436     {
 437       enum target_signal resume_signal = TARGET_SIGNAL_0;
 438       ptid_t event_ptid;
 439
 440       struct target_waitstatus ws;
 441       memset (&ws, 0, sizeof (ws));
 442       event_ptid = target_wait (resume_ptid, &ws, 0);
 443
 444       if (ws.kind == TARGET_WAITKIND_IGNORE)
 445         /* The inferior didn't really stop, keep waiting.  */
 446         continue;
 447
 448       switch (ws.kind)
 449         {
 450           case TARGET_WAITKIND_SPURIOUS:
 451           case TARGET_WAITKIND_LOADED:
 452           case TARGET_WAITKIND_FORKED:
 453           case TARGET_WAITKIND_VFORKED:
 454           case TARGET_WAITKIND_SYSCALL_ENTRY:
 455           case TARGET_WAITKIND_SYSCALL_RETURN:
 456             /* Ignore gracefully during startup of the inferior.  */
 457             switch_to_thread (event_ptid);
 458             break;
 459
 460           case TARGET_WAITKIND_SIGNALLED:
 461             target_terminal_ours ();
 462             target_mourn_inferior ();
 463             error (_("During startup program terminated with signal %s, %s."),
 464                    target_signal_to_name (ws.value.sig),
 465                    target_signal_to_string (ws.value.sig));
 466             return;
 467
 468           case TARGET_WAITKIND_EXITED:
 469             target_terminal_ours ();
 470             target_mourn_inferior ();
 471             if (ws.value.integer)
 472               error (_("During startup program exited with code %d."),
 473                      ws.value.integer);
 474             else
 475               error (_("During startup program exited normally."));
 476             return;
 477
 478           case TARGET_WAITKIND_EXECD:
 479             /* Handle EXEC signals as if they were SIGTRAP signals.  */
 480             xfree (ws.value.execd_pathname);
 481             resume_signal = TARGET_SIGNAL_TRAP;
 482             switch_to_thread (event_ptid);
 483             break;
 484
 485           case TARGET_WAITKIND_STOPPED:
 486             resume_signal = ws.value.sig;
 487             switch_to_thread (event_ptid);
 488             break;
 489         }
 490
 491       if (resume_signal != TARGET_SIGNAL_TRAP)
 492         {
 493           /* Let shell child handle its own signals in its own way.  */
 494           target_resume (resume_ptid, 0, resume_signal);
 495         }
 496       else
 497         {
 498           /* We handle SIGTRAP, however; it means child did an exec.  */
 499           if (!terminal_initted)
 500             {
 501               /* Now that the child has exec'd we know it has already
 502                  set its process group.  On POSIX systems, tcsetpgrp
 503                  will fail with EPERM if we try it before the child's
 504                  setpgid.  */
 505
 506               /* Set up the "saved terminal modes" of the inferior
 507                  based on what modes we are starting it with.  */
 508               target_terminal_init ();
 509
 510               /* Install inferior's terminal modes.  */
 511               target_terminal_inferior ();
 512
 513               terminal_initted = 1;
 514             }
 515
 516           if (--pending_execs == 0)
 517             break;
 518
 519           /* Just make it go on.  */
 520           target_resume (resume_ptid, 0, TARGET_SIGNAL_0);
 521         }
 522     }
 523
 524   /* Mark all threads non-executing.  */
 525   set_executing (resume_ptid, 0);
 526 }
 527
 528 /* Implement the "unset exec-wrapper" command.  */
 529
 530 static void
 531 unset_exec_wrapper_command (char *args, int from_tty)
 532 {
 533   xfree (exec_wrapper);
 534   exec_wrapper = NULL;
 535 }
 536
 537 /* Provide a prototype to silence -Wmissing-prototypes.  */
 538 extern initialize_file_ftype _initialize_fork_child;
 539
 540 void
 541 _initialize_fork_child (void)
 542 {
 543   add_setshow_filename_cmd ("exec-wrapper", class_run, &exec_wrapper, _("\
 544 Set a wrapper for running programs.\n\
 545 The wrapper prepares the system and environment for the new program."),
 546                             _("\
 547 Show the wrapper for running programs."), NULL,
 548                             NULL, NULL,
 549                             &setlist, &showlist);
 550
 551   add_cmd ("exec-wrapper", class_run, unset_exec_wrapper_command,
 552            _("Disable use of an execution wrapper."),
 553            &unsetlist);
 554 }