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 "gdb_wait.h"
  28 #include "gdbcore.h"
  29 #include "terminal.h"
  30 #include "gdbthread.h"
  31 #include "command.h" /* for dont_repeat () */
  32
  33 #include <signal.h>
  34
  35 /* This just gets used as a default if we can't find SHELL */
  36 #ifndef SHELL_FILE
  37 #define SHELL_FILE "/bin/sh"
  38 #endif
  39
  40 extern char **environ;
  41
  42 /* This function breaks up an argument string into an argument
  43  * vector suitable for passing to execvp().
  44  * E.g., on "run a b c d" this routine would get as input
  45  * the string "a b c d", and as output it would fill in argv with
  46  * the four arguments "a", "b", "c", "d".
  47  */
  48 static void
  49 breakup_args (
  50                scratch,
  51                argv)
  52      char *scratch;
  53      char **argv;
  54 {
  55   char *cp = scratch;
  56
  57   for (;;)
  58     {
  59
  60       /* Scan past leading separators */
  61       while (*cp == ' ' || *cp == '\t' || *cp == '\n')
  62         {
  63           cp++;
  64         }
  65
  66       /* Break if at end of string */
  67       if (*cp == '\0')
  68         break;
  69
  70       /* Take an arg */
  71       *argv++ = cp;
  72
  73       /* Scan for next arg separator */
  74       cp = strchr (cp, ' ');
  75       if (cp == NULL)
  76         cp = strchr (cp, '\t');
  77       if (cp == NULL)
  78         cp = strchr (cp, '\n');
  79
  80       /* No separators => end of string => break */
  81       if (cp == NULL)
  82         break;
  83
  84       /* Replace the separator with a terminator */
  85       *cp++ = '\0';
  86     }
  87
  88   /* execv requires a null-terminated arg vector */
  89   *argv = NULL;
  90
  91 }
  92
  93
  94 /* Start an inferior Unix child process and sets inferior_pid to its pid.
  95    EXEC_FILE is the file to run.
  96    ALLARGS is a string containing the arguments to the program.
  97    ENV is the environment vector to pass.  SHELL_FILE is the shell file,
  98    or NULL if we should pick one.  Errors reported with error().  */
  99
 100 void
 101 fork_inferior (exec_file, allargs, env, traceme_fun, init_trace_fun,
 102                pre_trace_fun, shell_file)
 103      char *exec_file;
 104      char *allargs;
 105      char **env;
 106      void (*traceme_fun) (void);
 107      void (*init_trace_fun) (int);
 108      void (*pre_trace_fun) (void);
 109      char *shell_file;
 110 {
 111   int pid;
 112   char *shell_command;
 113   static char default_shell_file[] = SHELL_FILE;
 114   int len;
 115   /* Set debug_fork then attach to the child while it sleeps, to debug. */
 116   static int debug_fork = 0;
 117   /* This is set to the result of setpgrp, which if vforked, will be visible
 118      to you in the parent process.  It's only used by humans for debugging.  */
 119   static int debug_setpgrp = 657473;
 120   char **save_our_env;
 121   int shell = 0;
 122   char **argv;
 123
 124   /* If no exec file handed to us, get it from the exec-file command -- with
 125      a good, common error message if none is specified.  */
 126   if (exec_file == 0)
 127     exec_file = get_exec_file (1);
 128
 129   /* STARTUP_WITH_SHELL is defined in inferior.h.
 130    * If 0, we'll just do a fork/exec, no shell, so don't
 131    * bother figuring out what shell.
 132    */
 133   if (STARTUP_WITH_SHELL)
 134     {
 135       /* Figure out what shell to start up the user program under. */
 136       if (shell_file == NULL)
 137         shell_file = getenv ("SHELL");
 138       if (shell_file == NULL)
 139         shell_file = default_shell_file;
 140       shell = 1;
 141     }
 142
 143   /* Multiplying the length of exec_file by 4 is to account for the fact
 144      that it may expand when quoted; it is a worst-case number based on
 145      every character being '.  */
 146   len = 5 + 4 * strlen (exec_file) + 1 + strlen (allargs) + 1 + /*slop */ 12;
 147   /* If desired, concat something onto the front of ALLARGS.
 148      SHELL_COMMAND is the result.  */
 149 #ifdef SHELL_COMMAND_CONCAT
 150   shell_command = (char *) alloca (strlen (SHELL_COMMAND_CONCAT) + len);
 151   strcpy (shell_command, SHELL_COMMAND_CONCAT);
 152 #else
 153   shell_command = (char *) alloca (len);
 154   shell_command[0] = '\0';
 155 #endif
 156
 157   if (!shell)
 158     {
 159       /* We're going to call execvp. Create argv */
 160       /* Largest case: every other character is a separate arg */
 161       argv = (char **) xmalloc (((strlen (allargs) + 1) / (unsigned) 2 + 2) * sizeof (*argv));
 162       argv[0] = exec_file;
 163       breakup_args (allargs, &argv[1]);
 164
 165     }
 166   else
 167     {
 168
 169       /* We're going to call a shell */
 170
 171       /* Now add exec_file, quoting as necessary.  */
 172
 173       char *p;
 174       int need_to_quote;
 175
 176       strcat (shell_command, "exec ");
 177
 178       /* Quoting in this style is said to work with all shells.  But csh
 179          on IRIX 4.0.1 can't deal with it.  So we only quote it if we need
 180          to.  */
 181       p = exec_file;
 182       while (1)
 183         {
 184           switch (*p)
 185             {
 186             case '\'':
 187             case '"':
 188             case '(':
 189             case ')':
 190             case '$':
 191             case '&':
 192             case ';':
 193             case '<':
 194             case '>':
 195             case ' ':
 196             case '\n':
 197             case '\t':
 198               need_to_quote = 1;
 199               goto end_scan;
 200
 201             case '\0':
 202               need_to_quote = 0;
 203               goto end_scan;
 204
 205             default:
 206               break;
 207             }
 208           ++p;
 209         }
 210     end_scan:
 211       if (need_to_quote)
 212         {
 213           strcat (shell_command, "'");
 214           for (p = exec_file; *p != '\0'; ++p)
 215             {
 216               if (*p == '\'')
 217                 strcat (shell_command, "'\\''");
 218               else
 219                 strncat (shell_command, p, 1);
 220             }
 221           strcat (shell_command, "'");
 222         }
 223       else
 224         strcat (shell_command, exec_file);
 225
 226       strcat (shell_command, " ");
 227       strcat (shell_command, allargs);
 228
 229     }
 230
 231   /* exec is said to fail if the executable is open.  */
 232   close_exec_file ();
 233
 234   /* Retain a copy of our environment variables, since the child will
 235      replace the value of  environ  and if we're vforked, we have to
 236      restore it.  */
 237   save_our_env = environ;
 238
 239   /* Tell the terminal handling subsystem what tty we plan to run on;
 240      it will just record the information for later.  */
 241
 242   new_tty_prefork (inferior_io_terminal);
 243
 244   /* It is generally good practice to flush any possible pending stdio
 245      output prior to doing a fork, to avoid the possibility of both the
 246      parent and child flushing the same data after the fork. */
 247
 248   gdb_flush (gdb_stdout);
 249   gdb_flush (gdb_stderr);
 250
 251   /* If there's any initialization of the target layers that must happen
 252      to prepare to handle the child we're about fork, do it now...
 253    */
 254   if (pre_trace_fun != NULL)
 255     (*pre_trace_fun) ();
 256
 257 #if defined(USG) && !defined(HAVE_VFORK)
 258   pid = fork ();
 259 #else
 260   if (debug_fork)
 261     pid = fork ();
 262   else
 263     pid = vfork ();
 264 #endif
 265
 266   if (pid < 0)
 267     perror_with_name ("vfork");
 268
 269   if (pid == 0)
 270     {
 271       if (debug_fork)
 272         sleep (debug_fork);
 273
 274       /* Run inferior in a separate process group.  */
 275       debug_setpgrp = gdb_setpgid ();
 276       if (debug_setpgrp == -1)
 277         perror ("setpgrp failed in child");
 278
 279       /* Ask the tty subsystem to switch to the one we specified earlier
 280          (or to share the current terminal, if none was specified).  */
 281
 282       new_tty ();
 283
 284       /* Changing the signal handlers for the inferior after
 285          a vfork can also change them for the superior, so we don't mess
 286          with signals here.  See comments in
 287          initialize_signals for how we get the right signal handlers
 288          for the inferior.  */
 289
 290       /* "Trace me, Dr. Memory!" */
 291       (*traceme_fun) ();
 292       /* The call above set this process (the "child") as debuggable
 293        * by the original gdb process (the "parent").  Since processes
 294        * (unlike people) can have only one parent, if you are
 295        * debugging gdb itself (and your debugger is thus _already_ the
 296        * controller/parent for this child),  code from here on out
 297        * is undebuggable.  Indeed, you probably got an error message
 298        * saying "not parent".  Sorry--you'll have to use print statements!
 299        */
 300
 301       /* There is no execlpe call, so we have to set the environment
 302          for our child in the global variable.  If we've vforked, this
 303          clobbers the parent, but environ is restored a few lines down
 304          in the parent.  By the way, yes we do need to look down the
 305          path to find $SHELL.  Rich Pixley says so, and I agree.  */
 306       environ = env;
 307
 308       /* If we decided above to start up with a shell,
 309        * we exec the shell,
 310        * "-c" says to interpret the next arg as a shell command
 311        * to execute, and this command is "exec <target-program> <args>".
 312        * "-f" means "fast startup" to the c-shell, which means
 313        * don't do .cshrc file. Doing .cshrc may cause fork/exec
 314        * events which will confuse debugger start-up code.
 315        */
 316       if (shell)
 317         {
 318           execlp (shell_file, shell_file, "-c", shell_command, (char *) 0);
 319
 320           /* If we get here, it's an error */
 321           fprintf_unfiltered (gdb_stderr, "Cannot exec %s: %s.\n", shell_file,
 322                               safe_strerror (errno));
 323           gdb_flush (gdb_stderr);
 324           _exit (0177);
 325         }
 326       else
 327         {
 328           /* Otherwise, we directly exec the target program with execvp. */
 329           int i;
 330           char *errstring;
 331
 332           execvp (exec_file, argv);
 333
 334           /* If we get here, it's an error */
 335           errstring = safe_strerror (errno);
 336           fprintf_unfiltered (gdb_stderr, "Cannot exec %s ", exec_file);
 337
 338           i = 1;
 339           while (argv[i] != NULL)
 340             {
 341               if (i != 1)
 342                 fprintf_unfiltered (gdb_stderr, " ");
 343               fprintf_unfiltered (gdb_stderr, "%s", argv[i]);
 344               i++;
 345             }
 346           fprintf_unfiltered (gdb_stderr, ".\n");
 347           /* This extra info seems to be useless
 348              fprintf_unfiltered (gdb_stderr, "Got error %s.\n", errstring);
 349            */
 350           gdb_flush (gdb_stderr);
 351           _exit (0177);
 352         }
 353     }
 354
 355   /* Restore our environment in case a vforked child clob'd it.  */
 356   environ = save_our_env;
 357
 358   init_thread_list ();
 359
 360   inferior_pid = pid;           /* Needed for wait_for_inferior stuff below */
 361
 362   /* Now that we have a child process, make it our target, and
 363      initialize anything target-vector-specific that needs initializing.  */
 364
 365   (*init_trace_fun) (pid);
 366
 367   /* We are now in the child process of interest, having exec'd the
 368      correct program, and are poised at the first instruction of the
 369      new program.  */
 370
 371   /* Allow target dependant code to play with the new process.  This might be
 372      used to have target-specific code initialize a variable in the new process
 373      prior to executing the first instruction.  */
 374   TARGET_CREATE_INFERIOR_HOOK (pid);
 375
 376 #ifdef SOLIB_CREATE_INFERIOR_HOOK
 377   SOLIB_CREATE_INFERIOR_HOOK (pid);
 378 #endif
 379 }
 380
 381 /* An inferior Unix process CHILD_PID has been created by a call to
 382    fork() (or variants like vfork).  It is presently stopped, and waiting
 383    to be resumed.  clone_and_follow_inferior will fork the debugger,
 384    and that clone will "follow" (attach to) CHILD_PID.  The original copy
 385    of the debugger will not touch CHILD_PID again.
 386
 387    Also, the original debugger will set FOLLOWED_CHILD FALSE, while the
 388    clone will set it TRUE.
 389  */
 390 void
 391 clone_and_follow_inferior (child_pid, followed_child)
 392      int child_pid;
 393      int *followed_child;
 394 {
 395   extern int auto_solib_add;
 396
 397   int debugger_pid;
 398   int status;
 399   char pid_spelling[100];       /* Arbitrary but sufficient length. */
 400
 401   /* This semaphore is used to coordinate the two debuggers' handoff
 402      of CHILD_PID.  The original debugger will detach from CHILD_PID,
 403      and then the clone debugger will attach to it.  (It must be done
 404      this way because on some targets, only one process at a time can
 405      trace another.  Thus, the original debugger must relinquish its
 406      tracing rights before the clone can pick them up.)
 407    */
 408 #define SEM_TALK (1)
 409 #define SEM_LISTEN (0)
 410   int handoff_semaphore[2];     /* Original "talks" to [1], clone "listens" to [0] */
 411   int talk_value = 99;
 412   int listen_value;
 413
 414   /* Set debug_fork then attach to the child while it sleeps, to debug. */
 415   static int debug_fork = 0;
 416
 417   /* It is generally good practice to flush any possible pending stdio
 418      output prior to doing a fork, to avoid the possibility of both the
 419      parent and child flushing the same data after the fork. */
 420
 421   gdb_flush (gdb_stdout);
 422   gdb_flush (gdb_stderr);
 423
 424   /* Open the semaphore pipes.
 425    */
 426   status = pipe (handoff_semaphore);
 427   if (status < 0)
 428     error ("error getting pipe for handoff semaphore");
 429
 430   /* Clone the debugger. */
 431 #if defined(USG) && !defined(HAVE_VFORK)
 432   debugger_pid = fork ();
 433 #else
 434   if (debug_fork)
 435     debugger_pid = fork ();
 436   else
 437     debugger_pid = vfork ();
 438 #endif
 439
 440   if (debugger_pid < 0)
 441     perror_with_name ("fork");
 442
 443   /* Are we the original debugger?  If so, we must relinquish all claims
 444      to CHILD_PID. */
 445   if (debugger_pid != 0)
 446     {
 447       char signal_spelling[100];        /* Arbitrary but sufficient length */
 448
 449       /* Detach from CHILD_PID.  Deliver a "stop" signal when we do, though,
 450          so that it remains stopped until the clone debugger can attach
 451          to it.
 452        */
 453       detach_breakpoints (child_pid);
 454
 455       sprintf (signal_spelling, "%d", target_signal_to_host (TARGET_SIGNAL_STOP));
 456       target_require_detach (child_pid, signal_spelling, 1);
 457
 458       /* Notify the clone debugger that it should attach to CHILD_PID. */
 459       write (handoff_semaphore[SEM_TALK], &talk_value, sizeof (talk_value));
 460
 461       *followed_child = 0;
 462     }
 463
 464   /* We're the child. */
 465   else
 466     {
 467       if (debug_fork)
 468         sleep (debug_fork);
 469
 470       /* The child (i.e., the cloned debugger) must now attach to
 471          CHILD_PID.  inferior_pid is presently set to the parent process
 472          of the fork, while CHILD_PID should be the child process of the
 473          fork.
 474
 475          Wait until the original debugger relinquishes control of CHILD_PID,
 476          though.
 477        */
 478       read (handoff_semaphore[SEM_LISTEN], &listen_value, sizeof (listen_value));
 479
 480       /* Note that we DON'T want to actually detach from inferior_pid,
 481          because that would allow it to run free.  The original
 482          debugger wants to retain control of the process.  So, we
 483          just reset inferior_pid to CHILD_PID, and then ensure that all
 484          breakpoints are really set in CHILD_PID.
 485        */
 486       target_mourn_inferior ();
 487
 488       /* Ask the tty subsystem to switch to the one we specified earlier
 489          (or to share the current terminal, if none was specified).  */
 490
 491       new_tty ();
 492
 493       dont_repeat ();
 494       sprintf (pid_spelling, "%d", child_pid);
 495       target_require_attach (pid_spelling, 1);
 496
 497       /* Perform any necessary cleanup, after attachment.  (This form
 498          of attaching can behave differently on some targets than the
 499          standard method, where a process formerly not under debugger
 500          control was suddenly attached to..)
 501        */
 502       target_post_follow_inferior_by_clone ();
 503
 504       *followed_child = 1;
 505     }
 506
 507   /* Discard the handoff sempahore. */
 508   (void) close (handoff_semaphore[SEM_LISTEN]);
 509   (void) close (handoff_semaphore[SEM_TALK]);
 510 }
 511
 512 /* Accept NTRAPS traps from the inferior.  */
 513
 514 void
 515 startup_inferior (ntraps)
 516      int ntraps;
 517 {
 518   int pending_execs = ntraps;
 519   int terminal_initted;
 520
 521   /* The process was started by the fork that created it,
 522      but it will have stopped one instruction after execing the shell.
 523      Here we must get it up to actual execution of the real program.  */
 524
 525   clear_proceed_status ();
 526
 527   init_wait_for_inferior ();
 528
 529   terminal_initted = 0;
 530
 531   if (STARTUP_WITH_SHELL)
 532     inferior_ignoring_startup_exec_events = ntraps;
 533   else
 534     inferior_ignoring_startup_exec_events = 0;
 535   inferior_ignoring_leading_exec_events =
 536     target_reported_exec_events_per_exec_call () - 1;
 537
 538 #ifdef STARTUP_INFERIOR
 539   STARTUP_INFERIOR (pending_execs);
 540 #else
 541   while (1)
 542     {
 543       stop_soon_quietly = 1;    /* Make wait_for_inferior be quiet */
 544       wait_for_inferior ();
 545       if (stop_signal != TARGET_SIGNAL_TRAP)
 546         {
 547           /* Let shell child handle its own signals in its own way */
 548           /* FIXME, what if child has exit()ed?  Must exit loop somehow */
 549           resume (0, stop_signal);
 550         }
 551       else
 552         {
 553           /* We handle SIGTRAP, however; it means child did an exec.  */
 554           if (!terminal_initted)
 555             {
 556               /* Now that the child has exec'd we know it has already set its
 557                  process group.  On POSIX systems, tcsetpgrp will fail with
 558                  EPERM if we try it before the child's setpgid.  */
 559
 560               /* Set up the "saved terminal modes" of the inferior
 561                  based on what modes we are starting it with.  */
 562               target_terminal_init ();
 563
 564               /* Install inferior's terminal modes.  */
 565               target_terminal_inferior ();
 566
 567               terminal_initted = 1;
 568             }
 569
 570           pending_execs = pending_execs - 1;
 571           if (0 == pending_execs)
 572             break;
 573
 574           resume (0, TARGET_SIGNAL_0);  /* Just make it go on */
 575         }
 576     }
 577 #endif /* STARTUP_INFERIOR */
 578   stop_soon_quietly = 0;
 579 }