gdb/fork-child.c

   1 /* Fork a Unix child process, and set up to debug it, for GDB.
   2    Copyright 1990, 91, 92, 93, 94, 1996, 1999 Free Software Foundation, Inc.
   3    Contributed by Cygnus Support.
   4
   5    This file is part of GDB.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 2 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program; if not, write to the Free Software
  19    Foundation, Inc., 59 Temple Place - Suite 330,
  20    Boston, MA 02111-1307, USA.  */
  21
  22 #include "defs.h"
  23 #include "gdb_string.h"
  24 #include "frame.h"              /* required by inferior.h */
  25 #include "inferior.h"
  26 #include "target.h"
  27 #include "wait.h"
  28 #include "gdbcore.h"
  29 #include "terminal.h"
  30 #include "gdbthread.h"
  31
  32 #include <signal.h>
  33 #ifdef HAVE_UNISTD_H
  34 #include <unistd.h>
  35 #endif
  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 (
  52                scratch,
  53                argv)
  54      char *scratch;
  55      char **argv;
  56 {
  57   char *cp = scratch;
  58
  59   for (;;)
  60     {
  61
  62       /* Scan past leading separators */
  63       while (*cp == ' ' || *cp == '\t' || *cp == '\n')
  64         {
  65           cp++;
  66         }
  67
  68       /* Break if at end of string */
  69       if (*cp == '\0')
  70         break;
  71
  72       /* Take an arg */
  73       *argv++ = cp;
  74
  75       /* Scan for next arg separator */
  76       cp = strchr (cp, ' ');
  77       if (cp == NULL)
  78         cp = strchr (cp, '\t');
  79       if (cp == NULL)
  80         cp = strchr (cp, '\n');
  81
  82       /* No separators => end of string => break */
  83       if (cp == NULL)
  84         break;
  85
  86       /* Replace the separator with a terminator */
  87       *cp++ = '\0';
  88     }
  89
  90   /* execv requires a null-terminated arg vector */
  91   *argv = NULL;
  92
  93 }
  94
  95
  96 /* Start an inferior Unix child process and sets inferior_pid to its pid.
  97    EXEC_FILE is the file to run.
  98    ALLARGS is a string containing the arguments to the program.
  99    ENV is the environment vector to pass.  SHELL_FILE is the shell file,
 100    or NULL if we should pick one.  Errors reported with error().  */
 101
 102 void
 103 fork_inferior (exec_file, allargs, env, traceme_fun, init_trace_fun,
 104                pre_trace_fun, shell_file)
 105      char *exec_file;
 106      char *allargs;
 107      char **env;
 108      void (*traceme_fun) PARAMS ((void));
 109      void (*init_trace_fun) PARAMS ((int));
 110      void (*pre_trace_fun) PARAMS ((void));
 111      char *shell_file;
 112 {
 113   int pid;
 114   char *shell_command;
 115   static char default_shell_file[] = SHELL_FILE;
 116   int len;
 117   /* Set debug_fork then attach to the child while it sleeps, to debug. */
 118   static int debug_fork = 0;
 119   /* This is set to the result of setpgrp, which if vforked, will be visible
 120      to you in the parent process.  It's only used by humans for debugging.  */
 121   static int debug_setpgrp = 657473;
 122   char **save_our_env;
 123   int shell = 0;
 124   char **argv;
 125
 126   /* If no exec file handed to us, get it from the exec-file command -- with
 127      a good, common error message if none is specified.  */
 128   if (exec_file == 0)
 129     exec_file = get_exec_file (1);
 130
 131   /* STARTUP_WITH_SHELL is defined in inferior.h.
 132    * If 0, we'll just do a fork/exec, no shell, so don't
 133    * bother figuring out what shell.
 134    */
 135   if (STARTUP_WITH_SHELL)
 136     {
 137       /* Figure out what shell to start up the user program under. */
 138       if (shell_file == NULL)
 139         shell_file = getenv ("SHELL");
 140       if (shell_file == NULL)
 141         shell_file = default_shell_file;
 142       shell = 1;
 143     }
 144
 145   /* Multiplying the length of exec_file by 4 is to account for the fact
 146      that it may expand when quoted; it is a worst-case number based on
 147      every character being '.  */
 148   len = 5 + 4 * strlen (exec_file) + 1 + strlen (allargs) + 1 + /*slop */ 12;
 149   /* If desired, concat something onto the front of ALLARGS.
 150      SHELL_COMMAND is the result.  */
 151 #ifdef SHELL_COMMAND_CONCAT
 152   shell_command = (char *) alloca (strlen (SHELL_COMMAND_CONCAT) + len);
 153   strcpy (shell_command, SHELL_COMMAND_CONCAT);
 154 #else
 155   shell_command = (char *) alloca (len);
 156   shell_command[0] = '\0';
 157 #endif
 158
 159   if (!shell)
 160     {
 161       /* We're going to call execvp. Create argv */
 162       /* Largest case: every other character is a separate arg */
 163       argv = (char **) xmalloc (((strlen (allargs) + 1) / (unsigned) 2 + 2) * sizeof (*argv));
 164       argv[0] = exec_file;
 165       breakup_args (allargs, &argv[1]);
 166
 167     }
 168   else
 169     {
 170
 171       /* We're going to call a shell */
 172
 173       /* Now add exec_file, quoting as necessary.  */
 174
 175       char *p;
 176       int need_to_quote;
 177
 178       strcat (shell_command, "exec ");
 179
 180       /* Quoting in this style is said to work with all shells.  But csh
 181          on IRIX 4.0.1 can't deal with it.  So we only quote it if we need
 182          to.  */
 183       p = exec_file;
 184       while (1)
 185         {
 186           switch (*p)
 187             {
 188             case '\'':
 189             case '"':
 190             case '(':
 191             case ')':
 192             case '$':
 193             case '&':
 194             case ';':
 195             case '<':
 196             case '>':
 197             case ' ':
 198             case '\n':
 199             case '\t':
 200               need_to_quote = 1;
 201               goto end_scan;
 202
 203             case '\0':
 204               need_to_quote = 0;
 205               goto end_scan;
 206
 207             default:
 208               break;
 209             }
 210           ++p;
 211         }
 212     end_scan:
 213       if (need_to_quote)
 214         {
 215           strcat (shell_command, "'");
 216           for (p = exec_file; *p != '\0'; ++p)
 217             {
 218               if (*p == '\'')
 219                 strcat (shell_command, "'\\''");
 220               else
 221                 strncat (shell_command, p, 1);
 222             }
 223           strcat (shell_command, "'");
 224         }
 225       else
 226         strcat (shell_command, exec_file);
 227
 228       strcat (shell_command, " ");
 229       strcat (shell_command, allargs);
 230
 231     }
 232
 233   /* exec is said to fail if the executable is open.  */
 234   close_exec_file ();
 235
 236   /* Retain a copy of our environment variables, since the child will
 237      replace the value of  environ  and if we're vforked, we have to
 238      restore it.  */
 239   save_our_env = environ;
 240
 241   /* Tell the terminal handling subsystem what tty we plan to run on;
 242      it will just record the information for later.  */
 243
 244   new_tty_prefork (inferior_io_terminal);
 245
 246   /* It is generally good practice to flush any possible pending stdio
 247      output prior to doing a fork, to avoid the possibility of both the
 248      parent and child flushing the same data after the fork. */
 249
 250   gdb_flush (gdb_stdout);
 251   gdb_flush (gdb_stderr);
 252
 253   /* If there's any initialization of the target layers that must happen
 254      to prepare to handle the child we're about fork, do it now...
 255    */
 256   if (pre_trace_fun != NULL)
 257     (*pre_trace_fun) ();
 258
 259 #if defined(USG) && !defined(HAVE_VFORK)
 260   pid = fork ();
 261 #else
 262   if (debug_fork)
 263     pid = fork ();
 264   else
 265     pid = vfork ();
 266 #endif
 267
 268   if (pid < 0)
 269     perror_with_name ("vfork");
 270
 271   if (pid == 0)
 272     {
 273       if (debug_fork)
 274         sleep (debug_fork);
 275
 276       /* Run inferior in a separate process group.  */
 277       debug_setpgrp = gdb_setpgid ();
 278       if (debug_setpgrp == -1)
 279         perror ("setpgrp failed in child");
 280
 281       /* Ask the tty subsystem to switch to the one we specified earlier
 282          (or to share the current terminal, if none was specified).  */
 283
 284       new_tty ();
 285
 286       /* Changing the signal handlers for the inferior after
 287          a vfork can also change them for the superior, so we don't mess
 288          with signals here.  See comments in
 289          initialize_signals for how we get the right signal handlers
 290          for the inferior.  */
 291
 292       /* "Trace me, Dr. Memory!" */
 293       (*traceme_fun) ();
 294       /* The call above set this process (the "child") as debuggable
 295        * by the original gdb process (the "parent").  Since processes
 296        * (unlike people) can have only one parent, if you are
 297        * debugging gdb itself (and your debugger is thus _already_ the
 298        * controller/parent for this child),  code from here on out
 299        * is undebuggable.  Indeed, you probably got an error message
 300        * saying "not parent".  Sorry--you'll have to use print statements!
 301        */
 302
 303       /* There is no execlpe call, so we have to set the environment
 304          for our child in the global variable.  If we've vforked, this
 305          clobbers the parent, but environ is restored a few lines down
 306          in the parent.  By the way, yes we do need to look down the
 307          path to find $SHELL.  Rich Pixley says so, and I agree.  */
 308       environ = env;
 309
 310       /* If we decided above to start up with a shell,
 311        * we exec the shell,
 312        * "-c" says to interpret the next arg as a shell command
 313        * to execute, and this command is "exec <target-program> <args>".
 314        * "-f" means "fast startup" to the c-shell, which means
 315        * don't do .cshrc file. Doing .cshrc may cause fork/exec
 316        * events which will confuse debugger start-up code.
 317        */
 318       if (shell)
 319         {
 320           execlp (shell_file, shell_file, "-c", shell_command, (char *) 0);
 321
 322           /* If we get here, it's an error */
 323           fprintf_unfiltered (gdb_stderr, "Cannot exec %s: %s.\n", shell_file,
 324                               safe_strerror (errno));
 325           gdb_flush (gdb_stderr);
 326           _exit (0177);
 327         }
 328       else
 329         {
 330           /* Otherwise, we directly exec the target program with execvp. */
 331           int i;
 332           char *errstring;
 333
 334           execvp (exec_file, argv);
 335
 336           /* If we get here, it's an error */
 337           errstring = safe_strerror (errno);
 338           fprintf_unfiltered (gdb_stderr, "Cannot exec %s ", exec_file);
 339
 340           i = 1;
 341           while (argv[i] != NULL)
 342             {
 343               if (i != 1)
 344                 fprintf_unfiltered (gdb_stderr, " ");
 345               fprintf_unfiltered (gdb_stderr, "%s", argv[i]);
 346               i++;
 347             }
 348           fprintf_unfiltered (gdb_stderr, ".\n");
 349           /* This extra info seems to be useless
 350              fprintf_unfiltered (gdb_stderr, "Got error %s.\n", errstring);
 351            */
 352           gdb_flush (gdb_stderr);
 353           _exit (0177);
 354         }
 355     }
 356
 357   /* Restore our environment in case a vforked child clob'd it.  */
 358   environ = save_our_env;
 359
 360   init_thread_list ();
 361
 362   inferior_pid = pid;           /* Needed for wait_for_inferior stuff below */
 363
 364   /* Now that we have a child process, make it our target, and
 365      initialize anything target-vector-specific that needs initializing.  */
 366
 367   (*init_trace_fun) (pid);
 368
 369   /* We are now in the child process of interest, having exec'd the
 370      correct program, and are poised at the first instruction of the
 371      new program.  */
 372
 373   /* Allow target dependant code to play with the new process.  This might be
 374      used to have target-specific code initialize a variable in the new process
 375      prior to executing the first instruction.  */
 376   TARGET_CREATE_INFERIOR_HOOK (pid);
 377
 378 #ifdef SOLIB_CREATE_INFERIOR_HOOK
 379   SOLIB_CREATE_INFERIOR_HOOK (pid);
 380 #endif
 381 }
 382
 383 /* An inferior Unix process CHILD_PID has been created by a call to
 384    fork() (or variants like vfork).  It is presently stopped, and waiting
 385    to be resumed.  clone_and_follow_inferior will fork the debugger,
 386    and that clone will "follow" (attach to) CHILD_PID.  The original copy
 387    of the debugger will not touch CHILD_PID again.
 388
 389    Also, the original debugger will set FOLLOWED_CHILD FALSE, while the
 390    clone will set it TRUE.
 391  */
 392 void
 393 clone_and_follow_inferior (child_pid, followed_child)
 394      int child_pid;
 395      int *followed_child;
 396 {
 397   extern int auto_solib_add;
 398
 399   int debugger_pid;
 400   int status;
 401   char pid_spelling[100];       /* Arbitrary but sufficient length. */
 402
 403   /* This semaphore is used to coordinate the two debuggers' handoff
 404      of CHILD_PID.  The original debugger will detach from CHILD_PID,
 405      and then the clone debugger will attach to it.  (It must be done
 406      this way because on some targets, only one process at a time can
 407      trace another.  Thus, the original debugger must relinquish its
 408      tracing rights before the clone can pick them up.)
 409    */
 410 #define SEM_TALK (1)
 411 #define SEM_LISTEN (0)
 412   int handoff_semaphore[2];     /* Original "talks" to [1], clone "listens" to [0] */
 413   int talk_value = 99;
 414   int listen_value;
 415
 416   /* Set debug_fork then attach to the child while it sleeps, to debug. */
 417   static int debug_fork = 0;
 418
 419   /* It is generally good practice to flush any possible pending stdio
 420      output prior to doing a fork, to avoid the possibility of both the
 421      parent and child flushing the same data after the fork. */
 422
 423   gdb_flush (gdb_stdout);
 424   gdb_flush (gdb_stderr);
 425
 426   /* Open the semaphore pipes.
 427    */
 428   status = pipe (handoff_semaphore);
 429   if (status < 0)
 430     error ("error getting pipe for handoff semaphore");
 431
 432   /* Clone the debugger. */
 433 #if defined(USG) && !defined(HAVE_VFORK)
 434   debugger_pid = fork ();
 435 #else
 436   if (debug_fork)
 437     debugger_pid = fork ();
 438   else
 439     debugger_pid = vfork ();
 440 #endif
 441
 442   if (debugger_pid < 0)
 443     perror_with_name ("fork");
 444
 445   /* Are we the original debugger?  If so, we must relinquish all claims
 446      to CHILD_PID. */
 447   if (debugger_pid != 0)
 448     {
 449       char signal_spelling[100];        /* Arbitrary but sufficient length */
 450
 451       /* Detach from CHILD_PID.  Deliver a "stop" signal when we do, though,
 452          so that it remains stopped until the clone debugger can attach
 453          to it.
 454        */
 455       detach_breakpoints (child_pid);
 456
 457       sprintf (signal_spelling, "%d", target_signal_to_host (TARGET_SIGNAL_STOP));
 458       target_require_detach (child_pid, signal_spelling, 1);
 459
 460       /* Notify the clone debugger that it should attach to CHILD_PID. */
 461       write (handoff_semaphore[SEM_TALK], &talk_value, sizeof (talk_value));
 462
 463       *followed_child = 0;
 464     }
 465
 466   /* We're the child. */
 467   else
 468     {
 469       if (debug_fork)
 470         sleep (debug_fork);
 471
 472       /* The child (i.e., the cloned debugger) must now attach to
 473          CHILD_PID.  inferior_pid is presently set to the parent process
 474          of the fork, while CHILD_PID should be the child process of the
 475          fork.
 476
 477          Wait until the original debugger relinquishes control of CHILD_PID,
 478          though.
 479        */
 480       read (handoff_semaphore[SEM_LISTEN], &listen_value, sizeof (listen_value));
 481
 482       /* Note that we DON'T want to actually detach from inferior_pid,
 483          because that would allow it to run free.  The original
 484          debugger wants to retain control of the process.  So, we
 485          just reset inferior_pid to CHILD_PID, and then ensure that all
 486          breakpoints are really set in CHILD_PID.
 487        */
 488       target_mourn_inferior ();
 489
 490       /* Ask the tty subsystem to switch to the one we specified earlier
 491          (or to share the current terminal, if none was specified).  */
 492
 493       new_tty ();
 494
 495       dont_repeat ();
 496       sprintf (pid_spelling, "%d", child_pid);
 497       target_require_attach (pid_spelling, 1);
 498
 499       /* Perform any necessary cleanup, after attachment.  (This form
 500          of attaching can behave differently on some targets than the
 501          standard method, where a process formerly not under debugger
 502          control was suddenly attached to..)
 503        */
 504       target_post_follow_inferior_by_clone ();
 505
 506       *followed_child = 1;
 507     }
 508
 509   /* Discard the handoff sempahore. */
 510   (void) close (handoff_semaphore[SEM_LISTEN]);
 511   (void) close (handoff_semaphore[SEM_TALK]);
 512 }
 513
 514 /* Accept NTRAPS traps from the inferior.  */
 515
 516 void
 517 startup_inferior (ntraps)
 518      int ntraps;
 519 {
 520   int pending_execs = ntraps;
 521   int terminal_initted;
 522
 523   /* The process was started by the fork that created it,
 524      but it will have stopped one instruction after execing the shell.
 525      Here we must get it up to actual execution of the real program.  */
 526
 527   clear_proceed_status ();
 528
 529   init_wait_for_inferior ();
 530
 531   terminal_initted = 0;
 532
 533   if (STARTUP_WITH_SHELL)
 534     inferior_ignoring_startup_exec_events = ntraps;
 535   else
 536     inferior_ignoring_startup_exec_events = 0;
 537   inferior_ignoring_leading_exec_events =
 538     target_reported_exec_events_per_exec_call () - 1;
 539
 540 #ifdef STARTUP_INFERIOR
 541   STARTUP_INFERIOR (pending_execs);
 542 #else
 543   while (1)
 544     {
 545       stop_soon_quietly = 1;    /* Make wait_for_inferior be quiet */
 546       wait_for_inferior ();
 547       if (stop_signal != TARGET_SIGNAL_TRAP)
 548         {
 549           /* Let shell child handle its own signals in its own way */
 550           /* FIXME, what if child has exit()ed?  Must exit loop somehow */
 551           resume (0, stop_signal);
 552         }
 553       else
 554         {
 555           /* We handle SIGTRAP, however; it means child did an exec.  */
 556           if (!terminal_initted)
 557             {
 558               /* Now that the child has exec'd we know it has already set its
 559                  process group.  On POSIX systems, tcsetpgrp will fail with
 560                  EPERM if we try it before the child's setpgid.  */
 561
 562               /* Set up the "saved terminal modes" of the inferior
 563                  based on what modes we are starting it with.  */
 564               target_terminal_init ();
 565
 566               /* Install inferior's terminal modes.  */
 567               target_terminal_inferior ();
 568
 569               terminal_initted = 1;
 570             }
 571
 572           pending_execs = pending_execs - 1;
 573           if (0 == pending_execs)
 574             break;
 575
 576           resume (0, TARGET_SIGNAL_0);  /* Just make it go on */
 577         }
 578     }
 579 #endif /* STARTUP_INFERIOR */
 580   stop_soon_quietly = 0;
 581 }