gdb/fork-child.c

   1 /* Fork a Unix child process, and set up to debug it, for GDB.
   2
   3    Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000,
   4    2001, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011
   5    Free Software Foundation, Inc.
   6
   7    Contributed by Cygnus Support.
   8
   9    This file is part of GDB.
  10
  11    This program is free software; you can redistribute it and/or modify
  12    it under the terms of the GNU General Public License as published by
  13    the Free Software Foundation; either version 3 of the License, or
  14    (at your option) any later version.
  15
  16    This program is distributed in the hope that it will be useful,
  17    but WITHOUT ANY WARRANTY; without even the implied warranty of
  18    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19    GNU General Public License for more details.
  20
  21    You should have received a copy of the GNU General Public License
  22    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  23
  24 #include "defs.h"
  25 #include "gdb_string.h"
  26 #include "inferior.h"
  27 #include "terminal.h"
  28 #include "target.h"
  29 #include "gdb_wait.h"
  30 #include "gdb_vfork.h"
  31 #include "gdbcore.h"
  32 #include "terminal.h"
  33 #include "gdbthread.h"
  34 #include "command.h" /* for dont_repeat () */
  35 #include "gdbcmd.h"
  36 #include "solib.h"
  37
  38 #include <signal.h>
  39
  40 /* This just gets used as a default if we can't find SHELL.  */
  41 #define SHELL_FILE "/bin/sh"
  42
  43 extern char **environ;
  44
  45 static char *exec_wrapper;
  46
  47 /* Break up SCRATCH into an argument vector suitable for passing to
  48    execvp and store it in ARGV.  E.g., on "run a b c d" this routine
  49    would get as input the string "a b c d", and as output it would
  50    fill in ARGV with the four arguments "a", "b", "c", "d".  */
  51
  52 static void
  53 breakup_args (char *scratch, char **argv)
  54 {
  55   char *cp = scratch, *tmp;
  56
  57   for (;;)
  58     {
  59       /* Scan past leading separators */
  60       while (*cp == ' ' || *cp == '\t' || *cp == '\n')
  61         cp++;
  62
  63       /* Break if at end of string.  */
  64       if (*cp == '\0')
  65         break;
  66
  67       /* Take an arg.  */
  68       *argv++ = cp;
  69
  70       /* Scan for next arg separator.  */
  71       tmp = strchr (cp, ' ');
  72       if (tmp == NULL)
  73         tmp = strchr (cp, '\t');
  74       if (tmp == NULL)
  75         tmp = strchr (cp, '\n');
  76
  77       /* No separators => end of string => break.  */
  78       if (tmp == NULL)
  79         break;
  80       cp = tmp;
  81
  82       /* Replace the separator with a terminator.  */
  83       *cp++ = '\0';
  84     }
  85
  86   /* Null-terminate the vector.  */
  87   *argv = NULL;
  88 }
  89
  90 /* When executing a command under the given shell, return non-zero if
  91    the '!' character should be escaped when embedded in a quoted
  92    command-line argument.  */
  93
  94 static int
  95 escape_bang_in_quoted_argument (const char *shell_file)
  96 {
  97   const int shell_file_len = strlen (shell_file);
  98
  99   /* Bang should be escaped only in C Shells.  For now, simply check
 100      that the shell name ends with 'csh', which covers at least csh
 101      and tcsh.  This should be good enough for now.  */
 102
 103   if (shell_file_len < 3)
 104     return 0;
 105
 106   if (shell_file[shell_file_len - 3] == 'c'
 107       && shell_file[shell_file_len - 2] == 's'
 108       && shell_file[shell_file_len - 1] == 'h')
 109     return 1;
 110
 111   return 0;
 112 }
 113
 114 /* Start an inferior Unix child process and sets inferior_ptid to its
 115    pid.  EXEC_FILE is the file to run.  ALLARGS is a string containing
 116    the arguments to the program.  ENV is the environment vector to
 117    pass.  SHELL_FILE is the shell file, or NULL if we should pick
 118    one.  EXEC_FUN is the exec(2) function to use, or NULL for the default
 119    one.  */
 120
 121 /* This function is NOT reentrant.  Some of the variables have been
 122    made static to ensure that they survive the vfork call.  */
 123
 124 int
 125 fork_inferior (char *exec_file_arg, char *allargs, char **env,
 126                void (*traceme_fun) (void), void (*init_trace_fun) (int),
 127                void (*pre_trace_fun) (void), char *shell_file_arg,
 128                void (*exec_fun)(const char *file, char * const *argv,
 129                                 char * const *env))
 130 {
 131   int pid;
 132   static char default_shell_file[] = SHELL_FILE;
 133   /* Set debug_fork then attach to the child while it sleeps, to debug.  */
 134   static int debug_fork = 0;
 135   /* This is set to the result of setpgrp, which if vforked, will be visible
 136      to you in the parent process.  It's only used by humans for debugging.  */
 137   static int debug_setpgrp = 657473;
 138   static char *shell_file;
 139   static char *exec_file;
 140   char **save_our_env;
 141   int shell = 0;
 142   static char **argv;
 143   const char *inferior_io_terminal = get_inferior_io_terminal ();
 144   struct inferior *inf;
 145   int i;
 146   int save_errno;
 147
 148   /* If no exec file handed to us, get it from the exec-file command
 149      -- with a good, common error message if none is specified.  */
 150   exec_file = exec_file_arg;
 151   if (exec_file == 0)
 152     exec_file = get_exec_file (1);
 153
 154   /* STARTUP_WITH_SHELL is defined in inferior.h.  If 0,e we'll just
 155     do a fork/exec, no shell, so don't bother figuring out what
 156     shell.  */
 157   shell_file = shell_file_arg;
 158   if (STARTUP_WITH_SHELL)
 159     {
 160       /* Figure out what shell to start up the user program under.  */
 161       if (shell_file == NULL)
 162         shell_file = getenv ("SHELL");
 163       if (shell_file == NULL)
 164         shell_file = default_shell_file;
 165       shell = 1;
 166     }
 167
 168   if (!shell)
 169     {
 170       /* We're going to call execvp.  Create argument vector.
 171          Calculate an upper bound on the length of the vector by
 172          assuming that every other character is a separate
 173          argument.  */
 174       int argc = (strlen (allargs) + 1) / 2 + 2;
 175
 176       argv = (char **) alloca (argc * sizeof (*argv));
 177       argv[0] = exec_file;
 178       breakup_args (allargs, &argv[1]);
 179     }
 180   else
 181     {
 182       /* We're going to call a shell.  */
 183       char *shell_command;
 184       int len;
 185       char *p;
 186       int need_to_quote;
 187       const int escape_bang = escape_bang_in_quoted_argument (shell_file);
 188
 189       /* Multiplying the length of exec_file by 4 is to account for the
 190          fact that it may expand when quoted; it is a worst-case number
 191          based on every character being '.  */
 192       len = 5 + 4 * strlen (exec_file) + 1 + strlen (allargs) + 1 + /*slop */ 12;
 193       if (exec_wrapper)
 194         len += strlen (exec_wrapper) + 1;
 195
 196       shell_command = (char *) alloca (len);
 197       shell_command[0] = '\0';
 198
 199       strcat (shell_command, "exec ");
 200
 201       /* Add any exec wrapper.  That may be a program name with arguments, so
 202          the user must handle quoting.  */
 203       if (exec_wrapper)
 204         {
 205           strcat (shell_command, exec_wrapper);
 206           strcat (shell_command, " ");
 207         }
 208
 209       /* Now add exec_file, quoting as necessary.  */
 210
 211       /* Quoting in this style is said to work with all shells.  But
 212          csh on IRIX 4.0.1 can't deal with it.  So we only quote it if
 213          we need to.  */
 214       p = exec_file;
 215       while (1)
 216         {
 217           switch (*p)
 218             {
 219             case '\'':
 220             case '!':
 221             case '"':
 222             case '(':
 223             case ')':
 224             case '$':
 225             case '&':
 226             case ';':
 227             case '<':
 228             case '>':
 229             case ' ':
 230             case '\n':
 231             case '\t':
 232               need_to_quote = 1;
 233               goto end_scan;
 234
 235             case '\0':
 236               need_to_quote = 0;
 237               goto end_scan;
 238
 239             default:
 240               break;
 241             }
 242           ++p;
 243         }
 244     end_scan:
 245       if (need_to_quote)
 246         {
 247           strcat (shell_command, "'");
 248           for (p = exec_file; *p != '\0'; ++p)
 249             {
 250               if (*p == '\'')
 251                 strcat (shell_command, "'\\''");
 252               else if (*p == '!' && escape_bang)
 253                 strcat (shell_command, "\\!");
 254               else
 255                 strncat (shell_command, p, 1);
 256             }
 257           strcat (shell_command, "'");
 258         }
 259       else
 260         strcat (shell_command, exec_file);
 261
 262       strcat (shell_command, " ");
 263       strcat (shell_command, allargs);
 264
 265       /* If we decided above to start up with a shell, we exec the
 266          shell, "-c" says to interpret the next arg as a shell command
 267          to execute, and this command is "exec <target-program>
 268          <args>".  */
 269       argv = (char **) alloca (4 * sizeof (char *));
 270       argv[0] = shell_file;
 271       argv[1] = "-c";
 272       argv[2] = shell_command;
 273       argv[3] = (char *) 0;
 274     }
 275
 276   /* On some systems an exec will fail if the executable is open.  */
 277   close_exec_file ();
 278
 279   /* Retain a copy of our environment variables, since the child will
 280      replace the value of environ and if we're vforked, we have to
 281      restore it.  */
 282   save_our_env = environ;
 283
 284   /* Tell the terminal handling subsystem what tty we plan to run on;
 285      it will just record the information for later.  */
 286   new_tty_prefork (inferior_io_terminal);
 287
 288   /* It is generally good practice to flush any possible pending stdio
 289      output prior to doing a fork, to avoid the possibility of both
 290      the parent and child flushing the same data after the fork.  */
 291   gdb_flush (gdb_stdout);
 292   gdb_flush (gdb_stderr);
 293
 294   /* If there's any initialization of the target layers that must
 295      happen to prepare to handle the child we're about fork, do it
 296      now...  */
 297   if (pre_trace_fun != NULL)
 298     (*pre_trace_fun) ();
 299
 300   /* Create the child process.  Since the child process is going to
 301      exec(3) shortly afterwards, try to reduce the overhead by
 302      calling vfork(2).  However, if PRE_TRACE_FUN is non-null, it's
 303      likely that this optimization won't work since there's too much
 304      work to do between the vfork(2) and the exec(3).  This is known
 305      to be the case on ttrace(2)-based HP-UX, where some handshaking
 306      between parent and child needs to happen between fork(2) and
 307      exec(2).  However, since the parent is suspended in the vforked
 308      state, this doesn't work.  Also note that the vfork(2) call might
 309      actually be a call to fork(2) due to the fact that autoconf will
 310      ``#define vfork fork'' on certain platforms.  */
 311   if (pre_trace_fun || debug_fork)
 312     pid = fork ();
 313   else
 314     pid = vfork ();
 315
 316   if (pid < 0)
 317     perror_with_name (("vfork"));
 318
 319   if (pid == 0)
 320     {
 321       if (debug_fork)
 322         sleep (debug_fork);
 323
 324       /* Create a new session for the inferior process, if necessary.
 325          It will also place the inferior in a separate process group.  */
 326       if (create_tty_session () <= 0)
 327         {
 328           /* No session was created, but we still want to run the inferior
 329              in a separate process group.  */
 330           debug_setpgrp = gdb_setpgid ();
 331           if (debug_setpgrp == -1)
 332             perror (_("setpgrp failed in child"));
 333         }
 334
 335       /* Ask the tty subsystem to switch to the one we specified
 336          earlier (or to share the current terminal, if none was
 337          specified).  */
 338       new_tty ();
 339
 340       /* Changing the signal handlers for the inferior after
 341          a vfork can also change them for the superior, so we don't mess
 342          with signals here.  See comments in
 343          initialize_signals for how we get the right signal handlers
 344          for the inferior.  */
 345
 346       /* "Trace me, Dr. Memory!"  */
 347       (*traceme_fun) ();
 348
 349       /* The call above set this process (the "child") as debuggable
 350         by the original gdb process (the "parent").  Since processes
 351         (unlike people) can have only one parent, if you are debugging
 352         gdb itself (and your debugger is thus _already_ the
 353         controller/parent for this child), code from here on out is
 354         undebuggable.  Indeed, you probably got an error message
 355         saying "not parent".  Sorry; you'll have to use print
 356         statements!  */
 357
 358       /* There is no execlpe call, so we have to set the environment
 359          for our child in the global variable.  If we've vforked, this
 360          clobbers the parent, but environ is restored a few lines down
 361          in the parent.  By the way, yes we do need to look down the
 362          path to find $SHELL.  Rich Pixley says so, and I agree.  */
 363       environ = env;
 364
 365       if (exec_fun != NULL)
 366         (*exec_fun) (argv[0], argv, env);
 367       else
 368         execvp (argv[0], argv);
 369
 370       /* If we get here, it's an error.  */
 371       save_errno = errno;
 372       fprintf_unfiltered (gdb_stderr, "Cannot exec %s", exec_file);
 373       for (i = 1; argv[i] != NULL; i++)
 374         fprintf_unfiltered (gdb_stderr, " %s", argv[i]);
 375       fprintf_unfiltered (gdb_stderr, ".\n");
 376       fprintf_unfiltered (gdb_stderr, "Error: %s\n",
 377                           safe_strerror (save_errno));
 378       gdb_flush (gdb_stderr);
 379       _exit (0177);
 380     }
 381
 382   /* Restore our environment in case a vforked child clob'd it.  */
 383   environ = save_our_env;
 384
 385   if (!have_inferiors ())
 386     init_thread_list ();
 387
 388   inf = current_inferior ();
 389
 390   inferior_appeared (inf, pid);
 391
 392   /* Needed for wait_for_inferior stuff below.  */
 393   inferior_ptid = pid_to_ptid (pid);
 394
 395   new_tty_postfork ();
 396
 397   /* We have something that executes now.  We'll be running through
 398      the shell at this point, but the pid shouldn't change.  Targets
 399      supporting MT should fill this task's ptid with more data as soon
 400      as they can.  */
 401   add_thread_silent (inferior_ptid);
 402
 403   /* Now that we have a child process, make it our target, and
 404      initialize anything target-vector-specific that needs
 405      initializing.  */
 406   if (init_trace_fun)
 407     (*init_trace_fun) (pid);
 408
 409   /* We are now in the child process of interest, having exec'd the
 410      correct program, and are poised at the first instruction of the
 411      new program.  */
 412   return pid;
 413 }
 414
 415 /* Accept NTRAPS traps from the inferior.  */
 416
 417 void
 418 startup_inferior (int ntraps)
 419 {
 420   int pending_execs = ntraps;
 421   int terminal_initted = 0;
 422   ptid_t resume_ptid;
 423
 424   if (target_supports_multi_process ())
 425     resume_ptid = pid_to_ptid (ptid_get_pid (inferior_ptid));
 426   else
 427     resume_ptid = minus_one_ptid;
 428
 429   /* The process was started by the fork that created it, but it will
 430      have stopped one instruction after execing the shell.  Here we
 431      must get it up to actual execution of the real program.  */
 432
 433   if (exec_wrapper)
 434     pending_execs++;
 435
 436   while (1)
 437     {
 438       enum target_signal resume_signal = TARGET_SIGNAL_0;
 439       ptid_t event_ptid;
 440
 441       struct target_waitstatus ws;
 442       memset (&ws, 0, sizeof (ws));
 443       event_ptid = target_wait (resume_ptid, &ws, 0);
 444
 445       if (ws.kind == TARGET_WAITKIND_IGNORE)
 446         /* The inferior didn't really stop, keep waiting.  */
 447         continue;
 448
 449       switch (ws.kind)
 450         {
 451           case TARGET_WAITKIND_SPURIOUS:
 452           case TARGET_WAITKIND_LOADED:
 453           case TARGET_WAITKIND_FORKED:
 454           case TARGET_WAITKIND_VFORKED:
 455           case TARGET_WAITKIND_SYSCALL_ENTRY:
 456           case TARGET_WAITKIND_SYSCALL_RETURN:
 457             /* Ignore gracefully during startup of the inferior.  */
 458             switch_to_thread (event_ptid);
 459             break;
 460
 461           case TARGET_WAITKIND_SIGNALLED:
 462             target_terminal_ours ();
 463             target_mourn_inferior ();
 464             error (_("During startup program terminated with signal %s, %s."),
 465                    target_signal_to_name (ws.value.sig),
 466                    target_signal_to_string (ws.value.sig));
 467             return;
 468
 469           case TARGET_WAITKIND_EXITED:
 470             target_terminal_ours ();
 471             target_mourn_inferior ();
 472             if (ws.value.integer)
 473               error (_("During startup program exited with code %d."),
 474                      ws.value.integer);
 475             else
 476               error (_("During startup program exited normally."));
 477             return;
 478
 479           case TARGET_WAITKIND_EXECD:
 480             /* Handle EXEC signals as if they were SIGTRAP signals.  */
 481             xfree (ws.value.execd_pathname);
 482             resume_signal = TARGET_SIGNAL_TRAP;
 483             switch_to_thread (event_ptid);
 484             break;
 485
 486           case TARGET_WAITKIND_STOPPED:
 487             resume_signal = ws.value.sig;
 488             switch_to_thread (event_ptid);
 489             break;
 490         }
 491
 492       if (resume_signal != TARGET_SIGNAL_TRAP)
 493         {
 494           /* Let shell child handle its own signals in its own way.  */
 495           target_resume (resume_ptid, 0, resume_signal);
 496         }
 497       else
 498         {
 499           /* We handle SIGTRAP, however; it means child did an exec.  */
 500           if (!terminal_initted)
 501             {
 502               /* Now that the child has exec'd we know it has already
 503                  set its process group.  On POSIX systems, tcsetpgrp
 504                  will fail with EPERM if we try it before the child's
 505                  setpgid.  */
 506
 507               /* Set up the "saved terminal modes" of the inferior
 508                  based on what modes we are starting it with.  */
 509               target_terminal_init ();
 510
 511               /* Install inferior's terminal modes.  */
 512               target_terminal_inferior ();
 513
 514               terminal_initted = 1;
 515             }
 516
 517           if (--pending_execs == 0)
 518             break;
 519
 520           /* Just make it go on.  */
 521           target_resume (resume_ptid, 0, TARGET_SIGNAL_0);
 522         }
 523     }
 524
 525   /* Mark all threads non-executing.  */
 526   set_executing (resume_ptid, 0);
 527 }
 528
 529 /* Implement the "unset exec-wrapper" command.  */
 530
 531 static void
 532 unset_exec_wrapper_command (char *args, int from_tty)
 533 {
 534   xfree (exec_wrapper);
 535   exec_wrapper = NULL;
 536 }
 537
 538 /* Provide a prototype to silence -Wmissing-prototypes.  */
 539 extern initialize_file_ftype _initialize_fork_child;
 540
 541 void
 542 _initialize_fork_child (void)
 543 {
 544   add_setshow_filename_cmd ("exec-wrapper", class_run, &exec_wrapper, _("\
 545 Set a wrapper for running programs.\n\
 546 The wrapper prepares the system and environment for the new program."),
 547                             _("\
 548 Show the wrapper for running programs."), NULL,
 549                             NULL, NULL,
 550                             &setlist, &showlist);
 551
 552   add_cmd ("exec-wrapper", class_run, unset_exec_wrapper_command,
 553            _("Disable use of an execution wrapper."),
 554            &unsetlist);
 555 }