gdb/fork-child.c

   1 /* Fork a Unix child process, and set up to debug it, for GDB.
   2    Copyright 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000,
   3    2001 Free Software Foundation, Inc.
   4    Contributed by Cygnus Support.
   5
   6    This file is part of GDB.
   7
   8    This program is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 2 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program; if not, write to the Free Software
  20    Foundation, Inc., 59 Temple Place - Suite 330,
  21    Boston, MA 02111-1307, USA.  */
  22
  23 #include "defs.h"
  24 #include "gdb_string.h"
  25 #include "frame.h"              /* required by inferior.h */
  26 #include "inferior.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
  35 #include <signal.h>
  36
  37 /* This just gets used as a default if we can't find SHELL */
  38 #ifndef SHELL_FILE
  39 #define SHELL_FILE "/bin/sh"
  40 #endif
  41
  42 extern char **environ;
  43
  44 /* This function breaks up an argument string into an argument
  45  * vector suitable for passing to execvp().
  46  * E.g., on "run a b c d" this routine would get as input
  47  * the string "a b c d", and as output it would fill in argv with
  48  * the four arguments "a", "b", "c", "d".
  49  */
  50 static void
  51 breakup_args (char *scratch, char **argv)
  52 {
  53   char *cp = scratch;
  54
  55   for (;;)
  56     {
  57
  58       /* Scan past leading separators */
  59       while (*cp == ' ' || *cp == '\t' || *cp == '\n')
  60         {
  61           cp++;
  62         }
  63
  64       /* Break if at end of string */
  65       if (*cp == '\0')
  66         break;
  67
  68       /* Take an arg */
  69       *argv++ = cp;
  70
  71       /* Scan for next arg separator */
  72       cp = strchr (cp, ' ');
  73       if (cp == NULL)
  74         cp = strchr (cp, '\t');
  75       if (cp == NULL)
  76         cp = strchr (cp, '\n');
  77
  78       /* No separators => end of string => break */
  79       if (cp == NULL)
  80         break;
  81
  82       /* Replace the separator with a terminator */
  83       *cp++ = '\0';
  84     }
  85
  86   /* execv requires a null-terminated arg vector */
  87   *argv = NULL;
  88
  89 }
  90
  91
  92 /* Start an inferior Unix child process and sets inferior_pid to its pid.
  93    EXEC_FILE is the file to run.
  94    ALLARGS is a string containing the arguments to the program.
  95    ENV is the environment vector to pass.  SHELL_FILE is the shell file,
  96    or NULL if we should pick one.  Errors reported with error().  */
  97
  98 /* This function is NOT-REENTRANT.  Some of the variables have been
  99    made static to ensure that they survive the vfork() call.  */
 100
 101 void
 102 fork_inferior (char *exec_file_arg, char *allargs, char **env,
 103                void (*traceme_fun) (void), void (*init_trace_fun) (int),
 104                void (*pre_trace_fun) (void), char *shell_file_arg)
 105 {
 106   int pid;
 107   char *shell_command;
 108   static char default_shell_file[] = SHELL_FILE;
 109   int len;
 110   /* Set debug_fork then attach to the child while it sleeps, to debug. */
 111   static int debug_fork = 0;
 112   /* This is set to the result of setpgrp, which if vforked, will be visible
 113      to you in the parent process.  It's only used by humans for debugging.  */
 114   static int debug_setpgrp = 657473;
 115   static char *shell_file;
 116   static char *exec_file;
 117   char **save_our_env;
 118   int shell = 0;
 119   static char **argv;
 120
 121   /* If no exec file handed to us, get it from the exec-file command -- with
 122      a good, common error message if none is specified.  */
 123   exec_file = exec_file_arg;
 124   if (exec_file == 0)
 125     exec_file = get_exec_file (1);
 126
 127   /* STARTUP_WITH_SHELL is defined in inferior.h.
 128    * If 0, we'll just do a fork/exec, no shell, so don't
 129    * bother figuring out what shell.
 130    */
 131   shell_file = shell_file_arg;
 132   if (STARTUP_WITH_SHELL)
 133     {
 134       /* Figure out what shell to start up the user program under. */
 135       if (shell_file == NULL)
 136         shell_file = getenv ("SHELL");
 137       if (shell_file == NULL)
 138         shell_file = default_shell_file;
 139       shell = 1;
 140     }
 141
 142   /* Multiplying the length of exec_file by 4 is to account for the fact
 143      that it may expand when quoted; it is a worst-case number based on
 144      every character being '.  */
 145   len = 5 + 4 * strlen (exec_file) + 1 + strlen (allargs) + 1 + /*slop */ 12;
 146   /* If desired, concat something onto the front of ALLARGS.
 147      SHELL_COMMAND is the result.  */
 148 #ifdef SHELL_COMMAND_CONCAT
 149   shell_command = (char *) alloca (strlen (SHELL_COMMAND_CONCAT) + len);
 150   strcpy (shell_command, SHELL_COMMAND_CONCAT);
 151 #else
 152   shell_command = (char *) alloca (len);
 153   shell_command[0] = '\0';
 154 #endif
 155
 156   if (!shell)
 157     {
 158       /* We're going to call execvp. Create argv */
 159       /* Largest case: every other character is a separate arg */
 160       argv = (char **) xmalloc (((strlen (allargs) + 1) / (unsigned) 2 + 2) * sizeof (*argv));
 161       argv[0] = exec_file;
 162       breakup_args (allargs, &argv[1]);
 163
 164     }
 165   else
 166     {
 167
 168       /* We're going to call a shell */
 169
 170       /* Now add exec_file, quoting as necessary.  */
 171
 172       char *p;
 173       int need_to_quote;
 174
 175       strcat (shell_command, "exec ");
 176
 177       /* Quoting in this style is said to work with all shells.  But csh
 178          on IRIX 4.0.1 can't deal with it.  So we only quote it if we need
 179          to.  */
 180       p = exec_file;
 181       while (1)
 182         {
 183           switch (*p)
 184             {
 185             case '\'':
 186             case '"':
 187             case '(':
 188             case ')':
 189             case '$':
 190             case '&':
 191             case ';':
 192             case '<':
 193             case '>':
 194             case ' ':
 195             case '\n':
 196             case '\t':
 197               need_to_quote = 1;
 198               goto end_scan;
 199
 200             case '\0':
 201               need_to_quote = 0;
 202               goto end_scan;
 203
 204             default:
 205               break;
 206             }
 207           ++p;
 208         }
 209     end_scan:
 210       if (need_to_quote)
 211         {
 212           strcat (shell_command, "'");
 213           for (p = exec_file; *p != '\0'; ++p)
 214             {
 215               if (*p == '\'')
 216                 strcat (shell_command, "'\\''");
 217               else
 218                 strncat (shell_command, p, 1);
 219             }
 220           strcat (shell_command, "'");
 221         }
 222       else
 223         strcat (shell_command, exec_file);
 224
 225       strcat (shell_command, " ");
 226       strcat (shell_command, allargs);
 227
 228     }
 229
 230   /* exec is said to fail if the executable is open.  */
 231   close_exec_file ();
 232
 233   /* Retain a copy of our environment variables, since the child will
 234      replace the value of  environ  and if we're vforked, we have to
 235      restore it.  */
 236   save_our_env = environ;
 237
 238   /* Tell the terminal handling subsystem what tty we plan to run on;
 239      it will just record the information for later.  */
 240
 241   new_tty_prefork (inferior_io_terminal);
 242
 243   /* It is generally good practice to flush any possible pending stdio
 244      output prior to doing a fork, to avoid the possibility of both the
 245      parent and child flushing the same data after the fork. */
 246
 247   gdb_flush (gdb_stdout);
 248   gdb_flush (gdb_stderr);
 249
 250   /* If there's any initialization of the target layers that must happen
 251      to prepare to handle the child we're about fork, do it now...
 252    */
 253   if (pre_trace_fun != NULL)
 254     (*pre_trace_fun) ();
 255
 256   if (debug_fork)
 257     pid = fork ();
 258   else
 259     pid = vfork ();
 260
 261   if (pid < 0)
 262     perror_with_name ("vfork");
 263
 264   if (pid == 0)
 265     {
 266       if (debug_fork)
 267         sleep (debug_fork);
 268
 269       /* Run inferior in a separate process group.  */
 270       debug_setpgrp = gdb_setpgid ();
 271       if (debug_setpgrp == -1)
 272         perror ("setpgrp failed in child");
 273
 274       /* Ask the tty subsystem to switch to the one we specified earlier
 275          (or to share the current terminal, if none was specified).  */
 276
 277       new_tty ();
 278
 279       /* Changing the signal handlers for the inferior after
 280          a vfork can also change them for the superior, so we don't mess
 281          with signals here.  See comments in
 282          initialize_signals for how we get the right signal handlers
 283          for the inferior.  */
 284
 285       /* "Trace me, Dr. Memory!" */
 286       (*traceme_fun) ();
 287       /* The call above set this process (the "child") as debuggable
 288        * by the original gdb process (the "parent").  Since processes
 289        * (unlike people) can have only one parent, if you are
 290        * debugging gdb itself (and your debugger is thus _already_ the
 291        * controller/parent for this child),  code from here on out
 292        * is undebuggable.  Indeed, you probably got an error message
 293        * saying "not parent".  Sorry--you'll have to use print statements!
 294        */
 295
 296       /* There is no execlpe call, so we have to set the environment
 297          for our child in the global variable.  If we've vforked, this
 298          clobbers the parent, but environ is restored a few lines down
 299          in the parent.  By the way, yes we do need to look down the
 300          path to find $SHELL.  Rich Pixley says so, and I agree.  */
 301       environ = env;
 302
 303       /* If we decided above to start up with a shell,
 304        * we exec the shell,
 305        * "-c" says to interpret the next arg as a shell command
 306        * to execute, and this command is "exec <target-program> <args>".
 307        * "-f" means "fast startup" to the c-shell, which means
 308        * don't do .cshrc file. Doing .cshrc may cause fork/exec
 309        * events which will confuse debugger start-up code.
 310        */
 311       if (shell)
 312         {
 313           execlp (shell_file, shell_file, "-c", shell_command, (char *) 0);
 314
 315           /* If we get here, it's an error */
 316           fprintf_unfiltered (gdb_stderr, "Cannot exec %s: %s.\n", shell_file,
 317                               safe_strerror (errno));
 318           gdb_flush (gdb_stderr);
 319           _exit (0177);
 320         }
 321       else
 322         {
 323           /* Otherwise, we directly exec the target program with execvp. */
 324           int i;
 325           char *errstring;
 326
 327           execvp (exec_file, argv);
 328
 329           /* If we get here, it's an error */
 330           errstring = safe_strerror (errno);
 331           fprintf_unfiltered (gdb_stderr, "Cannot exec %s ", exec_file);
 332
 333           i = 1;
 334           while (argv[i] != NULL)
 335             {
 336               if (i != 1)
 337                 fprintf_unfiltered (gdb_stderr, " ");
 338               fprintf_unfiltered (gdb_stderr, "%s", argv[i]);
 339               i++;
 340             }
 341           fprintf_unfiltered (gdb_stderr, ".\n");
 342           /* This extra info seems to be useless
 343              fprintf_unfiltered (gdb_stderr, "Got error %s.\n", errstring);
 344            */
 345           gdb_flush (gdb_stderr);
 346           _exit (0177);
 347         }
 348     }
 349
 350   /* Restore our environment in case a vforked child clob'd it.  */
 351   environ = save_our_env;
 352
 353   init_thread_list ();
 354
 355   inferior_pid = pid;           /* Needed for wait_for_inferior stuff below */
 356
 357   /* Now that we have a child process, make it our target, and
 358      initialize anything target-vector-specific that needs initializing.  */
 359
 360   (*init_trace_fun) (pid);
 361
 362   /* We are now in the child process of interest, having exec'd the
 363      correct program, and are poised at the first instruction of the
 364      new program.  */
 365
 366   /* Allow target dependent code to play with the new process.  This might be
 367      used to have target-specific code initialize a variable in the new process
 368      prior to executing the first instruction.  */
 369   TARGET_CREATE_INFERIOR_HOOK (pid);
 370
 371 #ifdef SOLIB_CREATE_INFERIOR_HOOK
 372   SOLIB_CREATE_INFERIOR_HOOK (pid);
 373 #endif
 374 }
 375
 376 /* An inferior Unix process CHILD_PID has been created by a call to
 377    fork() (or variants like vfork).  It is presently stopped, and waiting
 378    to be resumed.  clone_and_follow_inferior will fork the debugger,
 379    and that clone will "follow" (attach to) CHILD_PID.  The original copy
 380    of the debugger will not touch CHILD_PID again.
 381
 382    Also, the original debugger will set FOLLOWED_CHILD FALSE, while the
 383    clone will set it TRUE.
 384  */
 385 void
 386 clone_and_follow_inferior (int child_pid, int *followed_child)
 387 {
 388   extern int auto_solib_add;
 389
 390   int debugger_pid;
 391   int status;
 392   char pid_spelling[100];       /* Arbitrary but sufficient length. */
 393
 394   /* This semaphore is used to coordinate the two debuggers' handoff
 395      of CHILD_PID.  The original debugger will detach from CHILD_PID,
 396      and then the clone debugger will attach to it.  (It must be done
 397      this way because on some targets, only one process at a time can
 398      trace another.  Thus, the original debugger must relinquish its
 399      tracing rights before the clone can pick them up.)
 400    */
 401 #define SEM_TALK (1)
 402 #define SEM_LISTEN (0)
 403   int handoff_semaphore[2];     /* Original "talks" to [1], clone "listens" to [0] */
 404   int talk_value = 99;
 405   int listen_value;
 406
 407   /* Set debug_fork then attach to the child while it sleeps, to debug. */
 408   static int debug_fork = 0;
 409
 410   /* It is generally good practice to flush any possible pending stdio
 411      output prior to doing a fork, to avoid the possibility of both the
 412      parent and child flushing the same data after the fork. */
 413
 414   gdb_flush (gdb_stdout);
 415   gdb_flush (gdb_stderr);
 416
 417   /* Open the semaphore pipes.
 418    */
 419   status = pipe (handoff_semaphore);
 420   if (status < 0)
 421     error ("error getting pipe for handoff semaphore");
 422
 423   /* Clone the debugger. */
 424   if (debug_fork)
 425     debugger_pid = fork ();
 426   else
 427     debugger_pid = vfork ();
 428
 429   if (debugger_pid < 0)
 430     perror_with_name ("fork");
 431
 432   /* Are we the original debugger?  If so, we must relinquish all claims
 433      to CHILD_PID. */
 434   if (debugger_pid != 0)
 435     {
 436       char signal_spelling[100];        /* Arbitrary but sufficient length */
 437
 438       /* Detach from CHILD_PID.  Deliver a "stop" signal when we do, though,
 439          so that it remains stopped until the clone debugger can attach
 440          to it.
 441        */
 442       detach_breakpoints (child_pid);
 443
 444       sprintf (signal_spelling, "%d", target_signal_to_host (TARGET_SIGNAL_STOP));
 445       target_require_detach (child_pid, signal_spelling, 1);
 446
 447       /* Notify the clone debugger that it should attach to CHILD_PID. */
 448       write (handoff_semaphore[SEM_TALK], &talk_value, sizeof (talk_value));
 449
 450       *followed_child = 0;
 451     }
 452
 453   /* We're the child. */
 454   else
 455     {
 456       if (debug_fork)
 457         sleep (debug_fork);
 458
 459       /* The child (i.e., the cloned debugger) must now attach to
 460          CHILD_PID.  inferior_pid is presently set to the parent process
 461          of the fork, while CHILD_PID should be the child process of the
 462          fork.
 463
 464          Wait until the original debugger relinquishes control of CHILD_PID,
 465          though.
 466        */
 467       read (handoff_semaphore[SEM_LISTEN], &listen_value, sizeof (listen_value));
 468
 469       /* Note that we DON'T want to actually detach from inferior_pid,
 470          because that would allow it to run free.  The original
 471          debugger wants to retain control of the process.  So, we
 472          just reset inferior_pid to CHILD_PID, and then ensure that all
 473          breakpoints are really set in CHILD_PID.
 474        */
 475       target_mourn_inferior ();
 476
 477       /* Ask the tty subsystem to switch to the one we specified earlier
 478          (or to share the current terminal, if none was specified).  */
 479
 480       new_tty ();
 481
 482       dont_repeat ();
 483       sprintf (pid_spelling, "%d", child_pid);
 484       target_require_attach (pid_spelling, 1);
 485
 486       /* Perform any necessary cleanup, after attachment.  (This form
 487          of attaching can behave differently on some targets than the
 488          standard method, where a process formerly not under debugger
 489          control was suddenly attached to..)
 490        */
 491       target_post_follow_inferior_by_clone ();
 492
 493       *followed_child = 1;
 494     }
 495
 496   /* Discard the handoff sempahore. */
 497   (void) close (handoff_semaphore[SEM_LISTEN]);
 498   (void) close (handoff_semaphore[SEM_TALK]);
 499 }
 500
 501 /* Accept NTRAPS traps from the inferior.  */
 502
 503 void
 504 startup_inferior (int ntraps)
 505 {
 506   int pending_execs = ntraps;
 507   int terminal_initted;
 508
 509   /* The process was started by the fork that created it,
 510      but it will have stopped one instruction after execing the shell.
 511      Here we must get it up to actual execution of the real program.  */
 512
 513   clear_proceed_status ();
 514
 515   init_wait_for_inferior ();
 516
 517   terminal_initted = 0;
 518
 519   if (STARTUP_WITH_SHELL)
 520     inferior_ignoring_startup_exec_events = ntraps;
 521   else
 522     inferior_ignoring_startup_exec_events = 0;
 523   inferior_ignoring_leading_exec_events =
 524     target_reported_exec_events_per_exec_call () - 1;
 525
 526 #ifdef STARTUP_INFERIOR
 527   STARTUP_INFERIOR (pending_execs);
 528 #else
 529   while (1)
 530     {
 531       stop_soon_quietly = 1;    /* Make wait_for_inferior be quiet */
 532       wait_for_inferior ();
 533       if (stop_signal != TARGET_SIGNAL_TRAP)
 534         {
 535           /* Let shell child handle its own signals in its own way */
 536           /* FIXME, what if child has exit()ed?  Must exit loop somehow */
 537           resume (0, stop_signal);
 538         }
 539       else
 540         {
 541           /* We handle SIGTRAP, however; it means child did an exec.  */
 542           if (!terminal_initted)
 543             {
 544               /* Now that the child has exec'd we know it has already set its
 545                  process group.  On POSIX systems, tcsetpgrp will fail with
 546                  EPERM if we try it before the child's setpgid.  */
 547
 548               /* Set up the "saved terminal modes" of the inferior
 549                  based on what modes we are starting it with.  */
 550               target_terminal_init ();
 551
 552               /* Install inferior's terminal modes.  */
 553               target_terminal_inferior ();
 554
 555               terminal_initted = 1;
 556             }
 557
 558           pending_execs = pending_execs - 1;
 559           if (0 == pending_execs)
 560             break;
 561
 562           resume (0, TARGET_SIGNAL_0);  /* Just make it go on */
 563         }
 564     }
 565 #endif /* STARTUP_INFERIOR */
 566   stop_soon_quietly = 0;
 567 }