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
   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;
  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       cp = strchr (cp, ' ');
  72       if (cp == NULL)
  73         cp = strchr (cp, '\t');
  74       if (cp == NULL)
  75         cp = strchr (cp, '\n');
  76
  77       /* No separators => end of string => break.  */
  78       if (cp == NULL)
  79         break;
  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.  */
 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 {
 127   int pid;
 128   char *shell_command;
 129   static char default_shell_file[] = SHELL_FILE;
 130   int len;
 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
 144   /* If no exec file handed to us, get it from the exec-file command
 145      -- with a good, common error message if none is specified.  */
 146   exec_file = exec_file_arg;
 147   if (exec_file == 0)
 148     exec_file = get_exec_file (1);
 149
 150   /* STARTUP_WITH_SHELL is defined in inferior.h.  If 0,e we'll just
 151     do a fork/exec, no shell, so don't bother figuring out what
 152     shell.  */
 153   shell_file = shell_file_arg;
 154   if (STARTUP_WITH_SHELL)
 155     {
 156       /* Figure out what shell to start up the user program under.  */
 157       if (shell_file == NULL)
 158         shell_file = getenv ("SHELL");
 159       if (shell_file == NULL)
 160         shell_file = default_shell_file;
 161       shell = 1;
 162     }
 163
 164   /* Multiplying the length of exec_file by 4 is to account for the
 165      fact that it may expand when quoted; it is a worst-case number
 166      based on every character being '.  */
 167   len = 5 + 4 * strlen (exec_file) + 1 + strlen (allargs) + 1 + /*slop */ 12;
 168   if (exec_wrapper)
 169     len += strlen (exec_wrapper) + 1;
 170
 171   shell_command = (char *) alloca (len);
 172   shell_command[0] = '\0';
 173
 174   if (!shell)
 175     {
 176       /* We're going to call execvp.  Create argument vector.
 177          Calculate an upper bound on the length of the vector by
 178          assuming that every other character is a separate
 179          argument.  */
 180       int argc = (strlen (allargs) + 1) / 2 + 2;
 181       argv = (char **) xmalloc (argc * sizeof (*argv));
 182       argv[0] = exec_file;
 183       breakup_args (allargs, &argv[1]);
 184     }
 185   else
 186     {
 187       /* We're going to call a shell.  */
 188
 189       char *p;
 190       int need_to_quote;
 191       const int escape_bang = escape_bang_in_quoted_argument (shell_file);
 192
 193       strcat (shell_command, "exec ");
 194
 195       /* Add any exec wrapper.  That may be a program name with arguments, so
 196          the user must handle quoting.  */
 197       if (exec_wrapper)
 198         {
 199           strcat (shell_command, exec_wrapper);
 200           strcat (shell_command, " ");
 201         }
 202
 203       /* Now add exec_file, quoting as necessary.  */
 204
 205       /* Quoting in this style is said to work with all shells.  But
 206          csh on IRIX 4.0.1 can't deal with it.  So we only quote it if
 207          we need to.  */
 208       p = exec_file;
 209       while (1)
 210         {
 211           switch (*p)
 212             {
 213             case '\'':
 214             case '!':
 215             case '"':
 216             case '(':
 217             case ')':
 218             case '$':
 219             case '&':
 220             case ';':
 221             case '<':
 222             case '>':
 223             case ' ':
 224             case '\n':
 225             case '\t':
 226               need_to_quote = 1;
 227               goto end_scan;
 228
 229             case '\0':
 230               need_to_quote = 0;
 231               goto end_scan;
 232
 233             default:
 234               break;
 235             }
 236           ++p;
 237         }
 238     end_scan:
 239       if (need_to_quote)
 240         {
 241           strcat (shell_command, "'");
 242           for (p = exec_file; *p != '\0'; ++p)
 243             {
 244               if (*p == '\'')
 245                 strcat (shell_command, "'\\''");
 246               else if (*p == '!' && escape_bang)
 247                 strcat (shell_command, "\\!");
 248               else
 249                 strncat (shell_command, p, 1);
 250             }
 251           strcat (shell_command, "'");
 252         }
 253       else
 254         strcat (shell_command, exec_file);
 255
 256       strcat (shell_command, " ");
 257       strcat (shell_command, allargs);
 258     }
 259
 260   /* On some systems an exec will fail if the executable is open.  */
 261   close_exec_file ();
 262
 263   /* Retain a copy of our environment variables, since the child will
 264      replace the value of environ and if we're vforked, we have to
 265      restore it.  */
 266   save_our_env = environ;
 267
 268   /* Tell the terminal handling subsystem what tty we plan to run on;
 269      it will just record the information for later.  */
 270   new_tty_prefork (inferior_io_terminal);
 271
 272   /* It is generally good practice to flush any possible pending stdio
 273      output prior to doing a fork, to avoid the possibility of both
 274      the parent and child flushing the same data after the fork. */
 275   gdb_flush (gdb_stdout);
 276   gdb_flush (gdb_stderr);
 277
 278   /* If there's any initialization of the target layers that must
 279      happen to prepare to handle the child we're about fork, do it
 280      now...  */
 281   if (pre_trace_fun != NULL)
 282     (*pre_trace_fun) ();
 283
 284   /* Create the child process.  Since the child process is going to
 285      exec(3) shortly afterwards, try to reduce the overhead by
 286      calling vfork(2).  However, if PRE_TRACE_FUN is non-null, it's
 287      likely that this optimization won't work since there's too much
 288      work to do between the vfork(2) and the exec(3).  This is known
 289      to be the case on ttrace(2)-based HP-UX, where some handshaking
 290      between parent and child needs to happen between fork(2) and
 291      exec(2).  However, since the parent is suspended in the vforked
 292      state, this doesn't work.  Also note that the vfork(2) call might
 293      actually be a call to fork(2) due to the fact that autoconf will
 294      ``#define vfork fork'' on certain platforms.  */
 295   if (pre_trace_fun || debug_fork)
 296     pid = fork ();
 297   else
 298     pid = vfork ();
 299
 300   if (pid < 0)
 301     perror_with_name (("vfork"));
 302
 303   if (pid == 0)
 304     {
 305       if (debug_fork)
 306         sleep (debug_fork);
 307
 308       /* Create a new session for the inferior process, if necessary.
 309          It will also place the inferior in a separate process group.  */
 310       if (create_tty_session () <= 0)
 311         {
 312           /* No session was created, but we still want to run the inferior
 313              in a separate process group.  */
 314           debug_setpgrp = gdb_setpgid ();
 315           if (debug_setpgrp == -1)
 316             perror ("setpgrp failed in child");
 317         }
 318
 319       /* Ask the tty subsystem to switch to the one we specified
 320          earlier (or to share the current terminal, if none was
 321          specified).  */
 322       new_tty ();
 323
 324       /* Changing the signal handlers for the inferior after
 325          a vfork can also change them for the superior, so we don't mess
 326          with signals here.  See comments in
 327          initialize_signals for how we get the right signal handlers
 328          for the inferior.  */
 329
 330       /* "Trace me, Dr. Memory!" */
 331       (*traceme_fun) ();
 332
 333       /* The call above set this process (the "child") as debuggable
 334         by the original gdb process (the "parent").  Since processes
 335         (unlike people) can have only one parent, if you are debugging
 336         gdb itself (and your debugger is thus _already_ the
 337         controller/parent for this child), code from here on out is
 338         undebuggable.  Indeed, you probably got an error message
 339         saying "not parent".  Sorry; you'll have to use print
 340         statements!  */
 341
 342       /* There is no execlpe call, so we have to set the environment
 343          for our child in the global variable.  If we've vforked, this
 344          clobbers the parent, but environ is restored a few lines down
 345          in the parent.  By the way, yes we do need to look down the
 346          path to find $SHELL.  Rich Pixley says so, and I agree.  */
 347       environ = env;
 348
 349       /* If we decided above to start up with a shell, we exec the
 350          shell, "-c" says to interpret the next arg as a shell command
 351          to execute, and this command is "exec <target-program>
 352          <args>".  */
 353       if (shell)
 354         {
 355           execlp (shell_file, shell_file, "-c", shell_command, (char *) 0);
 356
 357           /* If we get here, it's an error.  */
 358           fprintf_unfiltered (gdb_stderr, "Cannot exec %s: %s.\n", shell_file,
 359                               safe_strerror (errno));
 360           gdb_flush (gdb_stderr);
 361           _exit (0177);
 362         }
 363       else
 364         {
 365           /* Otherwise, we directly exec the target program with
 366              execvp.  */
 367           int i;
 368           char *errstring;
 369
 370           execvp (exec_file, argv);
 371
 372           /* If we get here, it's an error.  */
 373           errstring = safe_strerror (errno);
 374           fprintf_unfiltered (gdb_stderr, "Cannot exec %s ", exec_file);
 375
 376           i = 1;
 377           while (argv[i] != NULL)
 378             {
 379               if (i != 1)
 380                 fprintf_unfiltered (gdb_stderr, " ");
 381               fprintf_unfiltered (gdb_stderr, "%s", argv[i]);
 382               i++;
 383             }
 384           fprintf_unfiltered (gdb_stderr, ".\n");
 385 #if 0
 386           /* This extra info seems to be useless.  */
 387           fprintf_unfiltered (gdb_stderr, "Got error %s.\n", errstring);
 388 #endif
 389           gdb_flush (gdb_stderr);
 390           _exit (0177);
 391         }
 392     }
 393
 394   /* Restore our environment in case a vforked child clob'd it.  */
 395   environ = save_our_env;
 396
 397   if (!have_inferiors ())
 398     init_thread_list ();
 399
 400   inf = current_inferior ();
 401
 402   inferior_appeared (inf, pid);
 403
 404   /* Needed for wait_for_inferior stuff below.  */
 405   inferior_ptid = pid_to_ptid (pid);
 406
 407   new_tty_postfork ();
 408
 409   /* We have something that executes now.  We'll be running through
 410      the shell at this point, but the pid shouldn't change.  Targets
 411      supporting MT should fill this task's ptid with more data as soon
 412      as they can.  */
 413   add_thread_silent (inferior_ptid);
 414
 415   /* Now that we have a child process, make it our target, and
 416      initialize anything target-vector-specific that needs
 417      initializing.  */
 418   if (init_trace_fun)
 419     (*init_trace_fun) (pid);
 420
 421   /* We are now in the child process of interest, having exec'd the
 422      correct program, and are poised at the first instruction of the
 423      new program.  */
 424   return pid;
 425 }
 426
 427 /* Accept NTRAPS traps from the inferior.  */
 428
 429 void
 430 startup_inferior (int ntraps)
 431 {
 432   int pending_execs = ntraps;
 433   int terminal_initted = 0;
 434   ptid_t resume_ptid;
 435
 436   if (target_supports_multi_process ())
 437     resume_ptid = pid_to_ptid (ptid_get_pid (inferior_ptid));
 438   else
 439     resume_ptid = minus_one_ptid;
 440
 441   /* The process was started by the fork that created it, but it will
 442      have stopped one instruction after execing the shell.  Here we
 443      must get it up to actual execution of the real program.  */
 444
 445   if (exec_wrapper)
 446     pending_execs++;
 447
 448   while (1)
 449     {
 450       int resume_signal = TARGET_SIGNAL_0;
 451       ptid_t event_ptid;
 452
 453       struct target_waitstatus ws;
 454       memset (&ws, 0, sizeof (ws));
 455       event_ptid = target_wait (resume_ptid, &ws, 0);
 456
 457       if (ws.kind == TARGET_WAITKIND_IGNORE)
 458         /* The inferior didn't really stop, keep waiting.  */
 459         continue;
 460
 461       switch (ws.kind)
 462         {
 463           case TARGET_WAITKIND_SPURIOUS:
 464           case TARGET_WAITKIND_LOADED:
 465           case TARGET_WAITKIND_FORKED:
 466           case TARGET_WAITKIND_VFORKED:
 467           case TARGET_WAITKIND_SYSCALL_ENTRY:
 468           case TARGET_WAITKIND_SYSCALL_RETURN:
 469             /* Ignore gracefully during startup of the inferior.  */
 470             switch_to_thread (event_ptid);
 471             break;
 472
 473           case TARGET_WAITKIND_SIGNALLED:
 474             target_terminal_ours ();
 475             target_mourn_inferior ();
 476             error (_("During startup program terminated with signal %s, %s."),
 477                    target_signal_to_name (ws.value.sig),
 478                    target_signal_to_string (ws.value.sig));
 479             return;
 480
 481           case TARGET_WAITKIND_EXITED:
 482             target_terminal_ours ();
 483             target_mourn_inferior ();
 484             if (ws.value.integer)
 485               error (_("During startup program exited with code %d."),
 486                      ws.value.integer);
 487             else
 488               error (_("During startup program exited normally."));
 489             return;
 490
 491           case TARGET_WAITKIND_EXECD:
 492             /* Handle EXEC signals as if they were SIGTRAP signals.  */
 493             xfree (ws.value.execd_pathname);
 494             resume_signal = TARGET_SIGNAL_TRAP;
 495             switch_to_thread (event_ptid);
 496             break;
 497
 498           case TARGET_WAITKIND_STOPPED:
 499             resume_signal = ws.value.sig;
 500             switch_to_thread (event_ptid);
 501             break;
 502         }
 503
 504       if (resume_signal != TARGET_SIGNAL_TRAP)
 505         {
 506           /* Let shell child handle its own signals in its own way.  */
 507           target_resume (resume_ptid, 0, resume_signal);
 508         }
 509       else
 510         {
 511           /* We handle SIGTRAP, however; it means child did an exec.  */
 512           if (!terminal_initted)
 513             {
 514               /* Now that the child has exec'd we know it has already
 515                  set its process group.  On POSIX systems, tcsetpgrp
 516                  will fail with EPERM if we try it before the child's
 517                  setpgid.  */
 518
 519               /* Set up the "saved terminal modes" of the inferior
 520                  based on what modes we are starting it with.  */
 521               target_terminal_init ();
 522
 523               /* Install inferior's terminal modes.  */
 524               target_terminal_inferior ();
 525
 526               terminal_initted = 1;
 527             }
 528
 529           if (--pending_execs == 0)
 530             break;
 531
 532           /* Just make it go on.  */
 533           target_resume (resume_ptid, 0, TARGET_SIGNAL_0);
 534         }
 535     }
 536
 537   /* Mark all threads non-executing.  */
 538   set_executing (resume_ptid, 0);
 539 }
 540
 541 /* Implement the "unset exec-wrapper" command.  */
 542
 543 static void
 544 unset_exec_wrapper_command (char *args, int from_tty)
 545 {
 546   xfree (exec_wrapper);
 547   exec_wrapper = NULL;
 548 }
 549
 550 /* Provide a prototype to silence -Wmissing-prototypes.  */
 551 extern initialize_file_ftype _initialize_fork_child;
 552
 553 void
 554 _initialize_fork_child (void)
 555 {
 556   add_setshow_filename_cmd ("exec-wrapper", class_run, &exec_wrapper, _("\
 557 Set a wrapper for running programs.\n\
 558 The wrapper prepares the system and environment for the new program."),
 559                             _("\
 560 Show the wrapper for running programs."), NULL,
 561                             NULL, NULL,
 562                             &setlist, &showlist);
 563
 564   add_cmd ("exec-wrapper", class_run, unset_exec_wrapper_command,
 565            _("Disable use of an execution wrapper."),
 566            &unsetlist);
 567 }