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