gdb/fork-child.c

   1 /* Fork a Unix child process, and set up to debug it, for GDB.
   2
   3    Copyright (C) 1990-2014 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 "gdbthread.h"
  31 #include "command.h" /* for dont_repeat () */
  32 #include "gdbcmd.h"
  33 #include "solib.h"
  34 #include "filestuff.h"
  35
  36 #include <signal.h>
  37
  38 /* This just gets used as a default if we can't find SHELL.  */
  39 #define SHELL_FILE "/bin/sh"
  40
  41 extern char **environ;
  42
  43 static char *exec_wrapper;
  44
  45 /* Break up SCRATCH into an argument vector suitable for passing to
  46    execvp and store it in ARGV.  E.g., on "run a b c d" this routine
  47    would get as input the string "a b c d", and as output it would
  48    fill in ARGV with the four arguments "a", "b", "c", "d".  */
  49
  50 static void
  51 breakup_args (char *scratch, char **argv)
  52 {
  53   char *cp = scratch, *tmp;
  54
  55   for (;;)
  56     {
  57       /* Scan past leading separators */
  58       while (*cp == ' ' || *cp == '\t' || *cp == '\n')
  59         cp++;
  60
  61       /* Break if at end of string.  */
  62       if (*cp == '\0')
  63         break;
  64
  65       /* Take an arg.  */
  66       *argv++ = cp;
  67
  68       /* Scan for next arg separator.  */
  69       tmp = strchr (cp, ' ');
  70       if (tmp == NULL)
  71         tmp = strchr (cp, '\t');
  72       if (tmp == NULL)
  73         tmp = strchr (cp, '\n');
  74
  75       /* No separators => end of string => break.  */
  76       if (tmp == NULL)
  77         break;
  78       cp = tmp;
  79
  80       /* Replace the separator with a terminator.  */
  81       *cp++ = '\0';
  82     }
  83
  84   /* Null-terminate the vector.  */
  85   *argv = NULL;
  86 }
  87
  88 /* When executing a command under the given shell, return non-zero if
  89    the '!' character should be escaped when embedded in a quoted
  90    command-line argument.  */
  91
  92 static int
  93 escape_bang_in_quoted_argument (const char *shell_file)
  94 {
  95   const int shell_file_len = strlen (shell_file);
  96
  97   /* Bang should be escaped only in C Shells.  For now, simply check
  98      that the shell name ends with 'csh', which covers at least csh
  99      and tcsh.  This should be good enough for now.  */
 100
 101   if (shell_file_len < 3)
 102     return 0;
 103
 104   if (shell_file[shell_file_len - 3] == 'c'
 105       && shell_file[shell_file_len - 2] == 's'
 106       && shell_file[shell_file_len - 1] == 'h')
 107     return 1;
 108
 109   return 0;
 110 }
 111
 112 /* Start an inferior Unix child process and sets inferior_ptid to its
 113    pid.  EXEC_FILE is the file to run.  ALLARGS is a string containing
 114    the arguments to the program.  ENV is the environment vector to
 115    pass.  SHELL_FILE is the shell file, or NULL if we should pick
 116    one.  EXEC_FUN is the exec(2) function to use, or NULL for the default
 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                void (*exec_fun)(const char *file, char * const *argv,
 127                                 char * const *env))
 128 {
 129   int pid;
 130   static char default_shell_file[] = SHELL_FILE;
 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   int i;
 144   int save_errno;
 145
 146   /* If no exec file handed to us, get it from the exec-file command
 147      -- with a good, common error message if none is specified.  */
 148   exec_file = exec_file_arg;
 149   if (exec_file == 0)
 150     exec_file = get_exec_file (1);
 151
 152   /* 'startup_with_shell' is declared in inferior.h and bound to the
 153      "set startup-with-shell" option.  If 0, we'll just do a
 154      fork/exec, no shell, so don't bother figuring out what shell.  */
 155   shell_file = shell_file_arg;
 156   if (startup_with_shell)
 157     {
 158       /* Figure out what shell to start up the user program under.  */
 159       if (shell_file == NULL)
 160         shell_file = getenv ("SHELL");
 161       if (shell_file == NULL)
 162         shell_file = default_shell_file;
 163       shell = 1;
 164     }
 165
 166   if (!shell)
 167     {
 168       /* We're going to call execvp.  Create argument vector.
 169          Calculate an upper bound on the length of the vector by
 170          assuming that every other character is a separate
 171          argument.  */
 172       int argc = (strlen (allargs) + 1) / 2 + 2;
 173
 174       argv = (char **) alloca (argc * sizeof (*argv));
 175       argv[0] = exec_file;
 176       breakup_args (allargs, &argv[1]);
 177     }
 178   else
 179     {
 180       /* We're going to call a shell.  */
 181       char *shell_command;
 182       int len;
 183       char *p;
 184       int need_to_quote;
 185       const int escape_bang = escape_bang_in_quoted_argument (shell_file);
 186
 187       /* Multiplying the length of exec_file by 4 is to account for the
 188          fact that it may expand when quoted; it is a worst-case number
 189          based on every character being '.  */
 190       len = 5 + 4 * strlen (exec_file) + 1 + strlen (allargs) + 1 + /*slop */ 12;
 191       if (exec_wrapper)
 192         len += strlen (exec_wrapper) + 1;
 193
 194       shell_command = (char *) alloca (len);
 195       shell_command[0] = '\0';
 196
 197       strcat (shell_command, "exec ");
 198
 199       /* Add any exec wrapper.  That may be a program name with arguments, so
 200          the user must handle quoting.  */
 201       if (exec_wrapper)
 202         {
 203           strcat (shell_command, exec_wrapper);
 204           strcat (shell_command, " ");
 205         }
 206
 207       /* Now add exec_file, quoting as necessary.  */
 208
 209       /* Quoting in this style is said to work with all shells.  But
 210          csh on IRIX 4.0.1 can't deal with it.  So we only quote it if
 211          we need to.  */
 212       p = exec_file;
 213       while (1)
 214         {
 215           switch (*p)
 216             {
 217             case '\'':
 218             case '!':
 219             case '"':
 220             case '(':
 221             case ')':
 222             case '$':
 223             case '&':
 224             case ';':
 225             case '<':
 226             case '>':
 227             case ' ':
 228             case '\n':
 229             case '\t':
 230               need_to_quote = 1;
 231               goto end_scan;
 232
 233             case '\0':
 234               need_to_quote = 0;
 235               goto end_scan;
 236
 237             default:
 238               break;
 239             }
 240           ++p;
 241         }
 242     end_scan:
 243       if (need_to_quote)
 244         {
 245           strcat (shell_command, "'");
 246           for (p = exec_file; *p != '\0'; ++p)
 247             {
 248               if (*p == '\'')
 249                 strcat (shell_command, "'\\''");
 250               else if (*p == '!' && escape_bang)
 251                 strcat (shell_command, "\\!");
 252               else
 253                 strncat (shell_command, p, 1);
 254             }
 255           strcat (shell_command, "'");
 256         }
 257       else
 258         strcat (shell_command, exec_file);
 259
 260       strcat (shell_command, " ");
 261       strcat (shell_command, allargs);
 262
 263       /* If we decided above to start up with a shell, we exec the
 264          shell, "-c" says to interpret the next arg as a shell command
 265          to execute, and this command is "exec <target-program>
 266          <args>".  */
 267       argv = (char **) alloca (4 * sizeof (char *));
 268       argv[0] = shell_file;
 269       argv[1] = "-c";
 270       argv[2] = shell_command;
 271       argv[3] = (char *) 0;
 272     }
 273
 274   /* Retain a copy of our environment variables, since the child will
 275      replace the value of environ and if we're vforked, we have to
 276      restore it.  */
 277   save_our_env = environ;
 278
 279   /* Tell the terminal handling subsystem what tty we plan to run on;
 280      it will just record the information for later.  */
 281   new_tty_prefork (inferior_io_terminal);
 282
 283   /* It is generally good practice to flush any possible pending stdio
 284      output prior to doing a fork, to avoid the possibility of both
 285      the parent and child flushing the same data after the fork.  */
 286   gdb_flush (gdb_stdout);
 287   gdb_flush (gdb_stderr);
 288
 289   /* If there's any initialization of the target layers that must
 290      happen to prepare to handle the child we're about fork, do it
 291      now...  */
 292   if (pre_trace_fun != NULL)
 293     (*pre_trace_fun) ();
 294
 295   /* Create the child process.  Since the child process is going to
 296      exec(3) shortly afterwards, try to reduce the overhead by
 297      calling vfork(2).  However, if PRE_TRACE_FUN is non-null, it's
 298      likely that this optimization won't work since there's too much
 299      work to do between the vfork(2) and the exec(3).  This is known
 300      to be the case on ttrace(2)-based HP-UX, where some handshaking
 301      between parent and child needs to happen between fork(2) and
 302      exec(2).  However, since the parent is suspended in the vforked
 303      state, this doesn't work.  Also note that the vfork(2) call might
 304      actually be a call to fork(2) due to the fact that autoconf will
 305      ``#define vfork fork'' on certain platforms.  */
 306   if (pre_trace_fun || debug_fork)
 307     pid = fork ();
 308   else
 309     pid = vfork ();
 310
 311   if (pid < 0)
 312     perror_with_name (("vfork"));
 313
 314   if (pid == 0)
 315     {
 316       close_most_fds ();
 317
 318       if (debug_fork)
 319         sleep (debug_fork);
 320
 321       /* Create a new session for the inferior process, if necessary.
 322          It will also place the inferior in a separate process group.  */
 323       if (create_tty_session () <= 0)
 324         {
 325           /* No session was created, but we still want to run the inferior
 326              in a separate process group.  */
 327           debug_setpgrp = gdb_setpgid ();
 328           if (debug_setpgrp == -1)
 329             perror (_("setpgrp failed in child"));
 330         }
 331
 332       /* Ask the tty subsystem to switch to the one we specified
 333          earlier (or to share the current terminal, if none was
 334          specified).  */
 335       new_tty ();
 336
 337       /* Changing the signal handlers for the inferior after
 338          a vfork can also change them for the superior, so we don't mess
 339          with signals here.  See comments in
 340          initialize_signals for how we get the right signal handlers
 341          for the inferior.  */
 342
 343       /* "Trace me, Dr. Memory!"  */
 344       (*traceme_fun) ();
 345
 346       /* The call above set this process (the "child") as debuggable
 347         by the original gdb process (the "parent").  Since processes
 348         (unlike people) can have only one parent, if you are debugging
 349         gdb itself (and your debugger is thus _already_ the
 350         controller/parent for this child), code from here on out is
 351         undebuggable.  Indeed, you probably got an error message
 352         saying "not parent".  Sorry; you'll have to use print
 353         statements!  */
 354
 355       /* There is no execlpe call, so we have to set the environment
 356          for our child in the global variable.  If we've vforked, this
 357          clobbers the parent, but environ is restored a few lines down
 358          in the parent.  By the way, yes we do need to look down the
 359          path to find $SHELL.  Rich Pixley says so, and I agree.  */
 360       environ = env;
 361
 362       if (exec_fun != NULL)
 363         (*exec_fun) (argv[0], argv, env);
 364       else
 365         execvp (argv[0], argv);
 366
 367       /* If we get here, it's an error.  */
 368       save_errno = errno;
 369       fprintf_unfiltered (gdb_stderr, "Cannot exec %s", exec_file);
 370       for (i = 1; argv[i] != NULL; i++)
 371         fprintf_unfiltered (gdb_stderr, " %s", argv[i]);
 372       fprintf_unfiltered (gdb_stderr, ".\n");
 373       fprintf_unfiltered (gdb_stderr, "Error: %s\n",
 374                           safe_strerror (save_errno));
 375       gdb_flush (gdb_stderr);
 376       _exit (0177);
 377     }
 378
 379   /* Restore our environment in case a vforked child clob'd it.  */
 380   environ = save_our_env;
 381
 382   if (!have_inferiors ())
 383     init_thread_list ();
 384
 385   inf = current_inferior ();
 386
 387   inferior_appeared (inf, pid);
 388
 389   /* Needed for wait_for_inferior stuff below.  */
 390   inferior_ptid = pid_to_ptid (pid);
 391
 392   new_tty_postfork ();
 393
 394   /* We have something that executes now.  We'll be running through
 395      the shell at this point, but the pid shouldn't change.  Targets
 396      supporting MT should fill this task's ptid with more data as soon
 397      as they can.  */
 398   add_thread_silent (inferior_ptid);
 399
 400   /* Now that we have a child process, make it our target, and
 401      initialize anything target-vector-specific that needs
 402      initializing.  */
 403   if (init_trace_fun)
 404     (*init_trace_fun) (pid);
 405
 406   /* We are now in the child process of interest, having exec'd the
 407      correct program, and are poised at the first instruction of the
 408      new program.  */
 409   return pid;
 410 }
 411
 412 /* Accept NTRAPS traps from the inferior.  */
 413
 414 void
 415 startup_inferior (int ntraps)
 416 {
 417   int pending_execs = ntraps;
 418   int terminal_initted = 0;
 419   ptid_t resume_ptid;
 420
 421   if (startup_with_shell)
 422     {
 423       /* One trap extra for exec'ing the shell.  */
 424       pending_execs++;
 425     }
 426
 427   if (target_supports_multi_process ())
 428     resume_ptid = pid_to_ptid (ptid_get_pid (inferior_ptid));
 429   else
 430     resume_ptid = minus_one_ptid;
 431
 432   /* The process was started by the fork that created it, but it will
 433      have stopped one instruction after execing the shell.  Here we
 434      must get it up to actual execution of the real program.  */
 435
 436   if (exec_wrapper)
 437     pending_execs++;
 438
 439   while (1)
 440     {
 441       enum gdb_signal resume_signal = GDB_SIGNAL_0;
 442       ptid_t event_ptid;
 443
 444       struct target_waitstatus ws;
 445       memset (&ws, 0, sizeof (ws));
 446       event_ptid = target_wait (resume_ptid, &ws, 0);
 447
 448       if (ws.kind == TARGET_WAITKIND_IGNORE)
 449         /* The inferior didn't really stop, keep waiting.  */
 450         continue;
 451
 452       switch (ws.kind)
 453         {
 454           case TARGET_WAITKIND_SPURIOUS:
 455           case TARGET_WAITKIND_LOADED:
 456           case TARGET_WAITKIND_FORKED:
 457           case TARGET_WAITKIND_VFORKED:
 458           case TARGET_WAITKIND_SYSCALL_ENTRY:
 459           case TARGET_WAITKIND_SYSCALL_RETURN:
 460             /* Ignore gracefully during startup of the inferior.  */
 461             switch_to_thread (event_ptid);
 462             break;
 463
 464           case TARGET_WAITKIND_SIGNALLED:
 465             target_terminal_ours ();
 466             target_mourn_inferior ();
 467             error (_("During startup program terminated with signal %s, %s."),
 468                    gdb_signal_to_name (ws.value.sig),
 469                    gdb_signal_to_string (ws.value.sig));
 470             return;
 471
 472           case TARGET_WAITKIND_EXITED:
 473             target_terminal_ours ();
 474             target_mourn_inferior ();
 475             if (ws.value.integer)
 476               error (_("During startup program exited with code %d."),
 477                      ws.value.integer);
 478             else
 479               error (_("During startup program exited normally."));
 480             return;
 481
 482           case TARGET_WAITKIND_EXECD:
 483             /* Handle EXEC signals as if they were SIGTRAP signals.  */
 484             xfree (ws.value.execd_pathname);
 485             resume_signal = GDB_SIGNAL_TRAP;
 486             switch_to_thread (event_ptid);
 487             break;
 488
 489           case TARGET_WAITKIND_STOPPED:
 490             resume_signal = ws.value.sig;
 491             switch_to_thread (event_ptid);
 492             break;
 493         }
 494
 495       if (resume_signal != GDB_SIGNAL_TRAP)
 496         {
 497           /* Let shell child handle its own signals in its own way.  */
 498           target_resume (resume_ptid, 0, resume_signal);
 499         }
 500       else
 501         {
 502           /* We handle SIGTRAP, however; it means child did an exec.  */
 503           if (!terminal_initted)
 504             {
 505               /* Now that the child has exec'd we know it has already
 506                  set its process group.  On POSIX systems, tcsetpgrp
 507                  will fail with EPERM if we try it before the child's
 508                  setpgid.  */
 509
 510               /* Set up the "saved terminal modes" of the inferior
 511                  based on what modes we are starting it with.  */
 512               target_terminal_init ();
 513
 514               /* Install inferior's terminal modes.  */
 515               target_terminal_inferior ();
 516
 517               terminal_initted = 1;
 518             }
 519
 520           if (--pending_execs == 0)
 521             break;
 522
 523           /* Just make it go on.  */
 524           target_resume (resume_ptid, 0, GDB_SIGNAL_0);
 525         }
 526     }
 527
 528   /* Mark all threads non-executing.  */
 529   set_executing (resume_ptid, 0);
 530 }
 531
 532 /* Implement the "unset exec-wrapper" command.  */
 533
 534 static void
 535 unset_exec_wrapper_command (char *args, int from_tty)
 536 {
 537   xfree (exec_wrapper);
 538   exec_wrapper = NULL;
 539 }
 540
 541 static void
 542 show_startup_with_shell (struct ui_file *file, int from_tty,
 543                          struct cmd_list_element *c, const char *value)
 544 {
 545   fprintf_filtered (file,
 546                     _("Use of shell to start subprocesses is %s.\n"),
 547                     value);
 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
 568   add_setshow_boolean_cmd ("startup-with-shell", class_support,
 569                            &startup_with_shell, _("\
 570 Set use of shell to start subprocesses.  The default is on."), _("\
 571 Show use of shell to start subprocesses."), NULL,
 572                            NULL,
 573                            show_startup_with_shell,
 574                            &setlist, &showlist);
 575 }