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_ptid 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   /* Create the child process.  Note that the apparent call to vfork()
 257      below *might* actually be a call to fork() due to the fact that
 258      autoconf will ``#define vfork fork'' on certain platforms.  */
 259   if (debug_fork)
 260     pid = fork ();
 261   else
 262     pid = vfork ();
 263
 264   if (pid < 0)
 265     perror_with_name ("vfork");
 266
 267   if (pid == 0)
 268     {
 269       if (debug_fork)
 270         sleep (debug_fork);
 271
 272       /* Run inferior in a separate process group.  */
 273       debug_setpgrp = gdb_setpgid ();
 274       if (debug_setpgrp == -1)
 275         perror ("setpgrp failed in child");
 276
 277       /* Ask the tty subsystem to switch to the one we specified earlier
 278          (or to share the current terminal, if none was specified).  */
 279
 280       new_tty ();
 281
 282       /* Changing the signal handlers for the inferior after
 283          a vfork can also change them for the superior, so we don't mess
 284          with signals here.  See comments in
 285          initialize_signals for how we get the right signal handlers
 286          for the inferior.  */
 287
 288       /* "Trace me, Dr. Memory!" */
 289       (*traceme_fun) ();
 290       /* The call above set this process (the "child") as debuggable
 291        * by the original gdb process (the "parent").  Since processes
 292        * (unlike people) can have only one parent, if you are
 293        * debugging gdb itself (and your debugger is thus _already_ the
 294        * controller/parent for this child),  code from here on out
 295        * is undebuggable.  Indeed, you probably got an error message
 296        * saying "not parent".  Sorry--you'll have to use print statements!
 297        */
 298
 299       /* There is no execlpe call, so we have to set the environment
 300          for our child in the global variable.  If we've vforked, this
 301          clobbers the parent, but environ is restored a few lines down
 302          in the parent.  By the way, yes we do need to look down the
 303          path to find $SHELL.  Rich Pixley says so, and I agree.  */
 304       environ = env;
 305
 306       /* If we decided above to start up with a shell,
 307        * we exec the shell,
 308        * "-c" says to interpret the next arg as a shell command
 309        * to execute, and this command is "exec <target-program> <args>".
 310        * "-f" means "fast startup" to the c-shell, which means
 311        * don't do .cshrc file. Doing .cshrc may cause fork/exec
 312        * events which will confuse debugger start-up code.
 313        */
 314       if (shell)
 315         {
 316           execlp (shell_file, shell_file, "-c", shell_command, (char *) 0);
 317
 318           /* If we get here, it's an error */
 319           fprintf_unfiltered (gdb_stderr, "Cannot exec %s: %s.\n", shell_file,
 320                               safe_strerror (errno));
 321           gdb_flush (gdb_stderr);
 322           _exit (0177);
 323         }
 324       else
 325         {
 326           /* Otherwise, we directly exec the target program with execvp. */
 327           int i;
 328           char *errstring;
 329
 330           execvp (exec_file, argv);
 331
 332           /* If we get here, it's an error */
 333           errstring = safe_strerror (errno);
 334           fprintf_unfiltered (gdb_stderr, "Cannot exec %s ", exec_file);
 335
 336           i = 1;
 337           while (argv[i] != NULL)
 338             {
 339               if (i != 1)
 340                 fprintf_unfiltered (gdb_stderr, " ");
 341               fprintf_unfiltered (gdb_stderr, "%s", argv[i]);
 342               i++;
 343             }
 344           fprintf_unfiltered (gdb_stderr, ".\n");
 345           /* This extra info seems to be useless
 346              fprintf_unfiltered (gdb_stderr, "Got error %s.\n", errstring);
 347            */
 348           gdb_flush (gdb_stderr);
 349           _exit (0177);
 350         }
 351     }
 352
 353   /* Restore our environment in case a vforked child clob'd it.  */
 354   environ = save_our_env;
 355
 356   init_thread_list ();
 357
 358   inferior_ptid = pid_to_ptid (pid);    /* Needed for wait_for_inferior stuff below */
 359
 360   /* Now that we have a child process, make it our target, and
 361      initialize anything target-vector-specific that needs initializing.  */
 362
 363   (*init_trace_fun) (pid);
 364
 365   /* We are now in the child process of interest, having exec'd the
 366      correct program, and are poised at the first instruction of the
 367      new program.  */
 368
 369   /* Allow target dependent code to play with the new process.  This might be
 370      used to have target-specific code initialize a variable in the new process
 371      prior to executing the first instruction.  */
 372   TARGET_CREATE_INFERIOR_HOOK (pid);
 373
 374 #ifdef SOLIB_CREATE_INFERIOR_HOOK
 375   SOLIB_CREATE_INFERIOR_HOOK (pid);
 376 #endif
 377 }
 378
 379 /* An inferior Unix process CHILD_PID has been created by a call to
 380    fork() (or variants like vfork).  It is presently stopped, and waiting
 381    to be resumed.  clone_and_follow_inferior will fork the debugger,
 382    and that clone will "follow" (attach to) CHILD_PID.  The original copy
 383    of the debugger will not touch CHILD_PID again.
 384
 385    Also, the original debugger will set FOLLOWED_CHILD FALSE, while the
 386    clone will set it TRUE.
 387  */
 388 void
 389 clone_and_follow_inferior (int child_pid, int *followed_child)
 390 {
 391   extern int auto_solib_add;
 392
 393   int debugger_pid;
 394   int status;
 395   char pid_spelling[100];       /* Arbitrary but sufficient length. */
 396
 397   /* This semaphore is used to coordinate the two debuggers' handoff
 398      of CHILD_PID.  The original debugger will detach from CHILD_PID,
 399      and then the clone debugger will attach to it.  (It must be done
 400      this way because on some targets, only one process at a time can
 401      trace another.  Thus, the original debugger must relinquish its
 402      tracing rights before the clone can pick them up.)
 403    */
 404 #define SEM_TALK (1)
 405 #define SEM_LISTEN (0)
 406   int handoff_semaphore[2];     /* Original "talks" to [1], clone "listens" to [0] */
 407   int talk_value = 99;
 408   int listen_value;
 409
 410   /* Set debug_fork then attach to the child while it sleeps, to debug. */
 411   static int debug_fork = 0;
 412
 413   /* It is generally good practice to flush any possible pending stdio
 414      output prior to doing a fork, to avoid the possibility of both the
 415      parent and child flushing the same data after the fork. */
 416
 417   gdb_flush (gdb_stdout);
 418   gdb_flush (gdb_stderr);
 419
 420   /* Open the semaphore pipes.
 421    */
 422   status = pipe (handoff_semaphore);
 423   if (status < 0)
 424     error ("error getting pipe for handoff semaphore");
 425
 426   /* Clone the debugger.  Note that the apparent call to vfork()
 427      below *might* actually be a call to fork() due to the fact that
 428      autoconf will ``#define vfork fork'' on certain platforms.  */
 429   if (debug_fork)
 430     debugger_pid = fork ();
 431   else
 432     debugger_pid = vfork ();
 433
 434   if (debugger_pid < 0)
 435     perror_with_name ("fork");
 436
 437   /* Are we the original debugger?  If so, we must relinquish all claims
 438      to CHILD_PID. */
 439   if (debugger_pid != 0)
 440     {
 441       char signal_spelling[100];        /* Arbitrary but sufficient length */
 442
 443       /* Detach from CHILD_PID.  Deliver a "stop" signal when we do, though,
 444          so that it remains stopped until the clone debugger can attach
 445          to it.
 446        */
 447       detach_breakpoints (child_pid);
 448
 449       sprintf (signal_spelling, "%d", target_signal_to_host (TARGET_SIGNAL_STOP));
 450       target_require_detach (child_pid, signal_spelling, 1);
 451
 452       /* Notify the clone debugger that it should attach to CHILD_PID. */
 453       write (handoff_semaphore[SEM_TALK], &talk_value, sizeof (talk_value));
 454
 455       *followed_child = 0;
 456     }
 457
 458   /* We're the child. */
 459   else
 460     {
 461       if (debug_fork)
 462         sleep (debug_fork);
 463
 464       /* The child (i.e., the cloned debugger) must now attach to
 465          CHILD_PID.  inferior_ptid is presently set to the parent process
 466          of the fork, while CHILD_PID should be the child process of the
 467          fork.
 468
 469          Wait until the original debugger relinquishes control of CHILD_PID,
 470          though.
 471        */
 472       read (handoff_semaphore[SEM_LISTEN], &listen_value, sizeof (listen_value));
 473
 474       /* Note that we DON'T want to actually detach from inferior_ptid,
 475          because that would allow it to run free.  The original
 476          debugger wants to retain control of the process.  So, we
 477          just reset inferior_ptid to CHILD_PID, and then ensure that all
 478          breakpoints are really set in CHILD_PID.
 479        */
 480       target_mourn_inferior ();
 481
 482       /* Ask the tty subsystem to switch to the one we specified earlier
 483          (or to share the current terminal, if none was specified).  */
 484
 485       new_tty ();
 486
 487       dont_repeat ();
 488       sprintf (pid_spelling, "%d", child_pid);
 489       target_require_attach (pid_spelling, 1);
 490
 491       /* Perform any necessary cleanup, after attachment.  (This form
 492          of attaching can behave differently on some targets than the
 493          standard method, where a process formerly not under debugger
 494          control was suddenly attached to..)
 495        */
 496       target_post_follow_inferior_by_clone ();
 497
 498       *followed_child = 1;
 499     }
 500
 501   /* Discard the handoff sempahore. */
 502   (void) close (handoff_semaphore[SEM_LISTEN]);
 503   (void) close (handoff_semaphore[SEM_TALK]);
 504 }
 505
 506 /* Accept NTRAPS traps from the inferior.  */
 507
 508 void
 509 startup_inferior (int ntraps)
 510 {
 511   int pending_execs = ntraps;
 512   int terminal_initted;
 513
 514   /* The process was started by the fork that created it,
 515      but it will have stopped one instruction after execing the shell.
 516      Here we must get it up to actual execution of the real program.  */
 517
 518   clear_proceed_status ();
 519
 520   init_wait_for_inferior ();
 521
 522   terminal_initted = 0;
 523
 524   if (STARTUP_WITH_SHELL)
 525     inferior_ignoring_startup_exec_events = ntraps;
 526   else
 527     inferior_ignoring_startup_exec_events = 0;
 528   inferior_ignoring_leading_exec_events =
 529     target_reported_exec_events_per_exec_call () - 1;
 530
 531 #ifdef STARTUP_INFERIOR
 532   STARTUP_INFERIOR (pending_execs);
 533 #else
 534   while (1)
 535     {
 536       stop_soon_quietly = 1;    /* Make wait_for_inferior be quiet */
 537       wait_for_inferior ();
 538       if (stop_signal != TARGET_SIGNAL_TRAP)
 539         {
 540           /* Let shell child handle its own signals in its own way */
 541           /* FIXME, what if child has exit()ed?  Must exit loop somehow */
 542           resume (0, stop_signal);
 543         }
 544       else
 545         {
 546           /* We handle SIGTRAP, however; it means child did an exec.  */
 547           if (!terminal_initted)
 548             {
 549               /* Now that the child has exec'd we know it has already set its
 550                  process group.  On POSIX systems, tcsetpgrp will fail with
 551                  EPERM if we try it before the child's setpgid.  */
 552
 553               /* Set up the "saved terminal modes" of the inferior
 554                  based on what modes we are starting it with.  */
 555               target_terminal_init ();
 556
 557               /* Install inferior's terminal modes.  */
 558               target_terminal_inferior ();
 559
 560               terminal_initted = 1;
 561             }
 562
 563           pending_execs = pending_execs - 1;
 564           if (0 == pending_execs)
 565             break;
 566
 567           resume (0, TARGET_SIGNAL_0);  /* Just make it go on */
 568         }
 569     }
 570 #endif /* STARTUP_INFERIOR */
 571   stop_soon_quietly = 0;
 572 }