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 (char *scratch, char **argv)
  50 {
  51   char *cp = scratch;
  52
  53   for (;;)
  54     {
  55
  56       /* Scan past leading separators */
  57       while (*cp == ' ' || *cp == '\t' || *cp == '\n')
  58         {
  59           cp++;
  60         }
  61
  62       /* Break if at end of string */
  63       if (*cp == '\0')
  64         break;
  65
  66       /* Take an arg */
  67       *argv++ = cp;
  68
  69       /* Scan for next arg separator */
  70       cp = strchr (cp, ' ');
  71       if (cp == NULL)
  72         cp = strchr (cp, '\t');
  73       if (cp == NULL)
  74         cp = strchr (cp, '\n');
  75
  76       /* No separators => end of string => break */
  77       if (cp == NULL)
  78         break;
  79
  80       /* Replace the separator with a terminator */
  81       *cp++ = '\0';
  82     }
  83
  84   /* execv requires a null-terminated arg vector */
  85   *argv = NULL;
  86
  87 }
  88
  89
  90 /* Start an inferior Unix child process and sets inferior_pid to its pid.
  91    EXEC_FILE is the file to run.
  92    ALLARGS is a string containing the arguments to the program.
  93    ENV is the environment vector to pass.  SHELL_FILE is the shell file,
  94    or NULL if we should pick one.  Errors reported with error().  */
  95
  96 void
  97 fork_inferior (exec_file, allargs, env, traceme_fun, init_trace_fun,
  98                pre_trace_fun, shell_file)
  99      char *exec_file;
 100      char *allargs;
 101      char **env;
 102      void (*traceme_fun) (void);
 103      void (*init_trace_fun) (int);
 104      void (*pre_trace_fun) (void);
 105      char *shell_file;
 106 {
 107   int pid;
 108   char *shell_command;
 109   static char default_shell_file[] = SHELL_FILE;
 110   int len;
 111   /* Set debug_fork then attach to the child while it sleeps, to debug. */
 112   static int debug_fork = 0;
 113   /* This is set to the result of setpgrp, which if vforked, will be visible
 114      to you in the parent process.  It's only used by humans for debugging.  */
 115   static int debug_setpgrp = 657473;
 116   char **save_our_env;
 117   int shell = 0;
 118   char **argv;
 119
 120   /* If no exec file handed to us, get it from the exec-file command -- with
 121      a good, common error message if none is specified.  */
 122   if (exec_file == 0)
 123     exec_file = get_exec_file (1);
 124
 125   /* STARTUP_WITH_SHELL is defined in inferior.h.
 126    * If 0, we'll just do a fork/exec, no shell, so don't
 127    * bother figuring out what shell.
 128    */
 129   if (STARTUP_WITH_SHELL)
 130     {
 131       /* Figure out what shell to start up the user program under. */
 132       if (shell_file == NULL)
 133         shell_file = getenv ("SHELL");
 134       if (shell_file == NULL)
 135         shell_file = default_shell_file;
 136       shell = 1;
 137     }
 138
 139   /* Multiplying the length of exec_file by 4 is to account for the fact
 140      that it may expand when quoted; it is a worst-case number based on
 141      every character being '.  */
 142   len = 5 + 4 * strlen (exec_file) + 1 + strlen (allargs) + 1 + /*slop */ 12;
 143   /* If desired, concat something onto the front of ALLARGS.
 144      SHELL_COMMAND is the result.  */
 145 #ifdef SHELL_COMMAND_CONCAT
 146   shell_command = (char *) alloca (strlen (SHELL_COMMAND_CONCAT) + len);
 147   strcpy (shell_command, SHELL_COMMAND_CONCAT);
 148 #else
 149   shell_command = (char *) alloca (len);
 150   shell_command[0] = '\0';
 151 #endif
 152
 153   if (!shell)
 154     {
 155       /* We're going to call execvp. Create argv */
 156       /* Largest case: every other character is a separate arg */
 157       argv = (char **) xmalloc (((strlen (allargs) + 1) / (unsigned) 2 + 2) * sizeof (*argv));
 158       argv[0] = exec_file;
 159       breakup_args (allargs, &argv[1]);
 160
 161     }
 162   else
 163     {
 164
 165       /* We're going to call a shell */
 166
 167       /* Now add exec_file, quoting as necessary.  */
 168
 169       char *p;
 170       int need_to_quote;
 171
 172       strcat (shell_command, "exec ");
 173
 174       /* Quoting in this style is said to work with all shells.  But csh
 175          on IRIX 4.0.1 can't deal with it.  So we only quote it if we need
 176          to.  */
 177       p = exec_file;
 178       while (1)
 179         {
 180           switch (*p)
 181             {
 182             case '\'':
 183             case '"':
 184             case '(':
 185             case ')':
 186             case '$':
 187             case '&':
 188             case ';':
 189             case '<':
 190             case '>':
 191             case ' ':
 192             case '\n':
 193             case '\t':
 194               need_to_quote = 1;
 195               goto end_scan;
 196
 197             case '\0':
 198               need_to_quote = 0;
 199               goto end_scan;
 200
 201             default:
 202               break;
 203             }
 204           ++p;
 205         }
 206     end_scan:
 207       if (need_to_quote)
 208         {
 209           strcat (shell_command, "'");
 210           for (p = exec_file; *p != '\0'; ++p)
 211             {
 212               if (*p == '\'')
 213                 strcat (shell_command, "'\\''");
 214               else
 215                 strncat (shell_command, p, 1);
 216             }
 217           strcat (shell_command, "'");
 218         }
 219       else
 220         strcat (shell_command, exec_file);
 221
 222       strcat (shell_command, " ");
 223       strcat (shell_command, allargs);
 224
 225     }
 226
 227   /* exec is said to fail if the executable is open.  */
 228   close_exec_file ();
 229
 230   /* Retain a copy of our environment variables, since the child will
 231      replace the value of  environ  and if we're vforked, we have to
 232      restore it.  */
 233   save_our_env = environ;
 234
 235   /* Tell the terminal handling subsystem what tty we plan to run on;
 236      it will just record the information for later.  */
 237
 238   new_tty_prefork (inferior_io_terminal);
 239
 240   /* It is generally good practice to flush any possible pending stdio
 241      output prior to doing a fork, to avoid the possibility of both the
 242      parent and child flushing the same data after the fork. */
 243
 244   gdb_flush (gdb_stdout);
 245   gdb_flush (gdb_stderr);
 246
 247   /* If there's any initialization of the target layers that must happen
 248      to prepare to handle the child we're about fork, do it now...
 249    */
 250   if (pre_trace_fun != NULL)
 251     (*pre_trace_fun) ();
 252
 253 #if defined(USG) && !defined(HAVE_VFORK)
 254   pid = fork ();
 255 #else
 256   if (debug_fork)
 257     pid = fork ();
 258   else
 259     pid = vfork ();
 260 #endif
 261
 262   if (pid < 0)
 263     perror_with_name ("vfork");
 264
 265   if (pid == 0)
 266     {
 267       if (debug_fork)
 268         sleep (debug_fork);
 269
 270       /* Run inferior in a separate process group.  */
 271       debug_setpgrp = gdb_setpgid ();
 272       if (debug_setpgrp == -1)
 273         perror ("setpgrp failed in child");
 274
 275       /* Ask the tty subsystem to switch to the one we specified earlier
 276          (or to share the current terminal, if none was specified).  */
 277
 278       new_tty ();
 279
 280       /* Changing the signal handlers for the inferior after
 281          a vfork can also change them for the superior, so we don't mess
 282          with signals here.  See comments in
 283          initialize_signals for how we get the right signal handlers
 284          for the inferior.  */
 285
 286       /* "Trace me, Dr. Memory!" */
 287       (*traceme_fun) ();
 288       /* The call above set this process (the "child") as debuggable
 289        * by the original gdb process (the "parent").  Since processes
 290        * (unlike people) can have only one parent, if you are
 291        * debugging gdb itself (and your debugger is thus _already_ the
 292        * controller/parent for this child),  code from here on out
 293        * is undebuggable.  Indeed, you probably got an error message
 294        * saying "not parent".  Sorry--you'll have to use print statements!
 295        */
 296
 297       /* There is no execlpe call, so we have to set the environment
 298          for our child in the global variable.  If we've vforked, this
 299          clobbers the parent, but environ is restored a few lines down
 300          in the parent.  By the way, yes we do need to look down the
 301          path to find $SHELL.  Rich Pixley says so, and I agree.  */
 302       environ = env;
 303
 304       /* If we decided above to start up with a shell,
 305        * we exec the shell,
 306        * "-c" says to interpret the next arg as a shell command
 307        * to execute, and this command is "exec <target-program> <args>".
 308        * "-f" means "fast startup" to the c-shell, which means
 309        * don't do .cshrc file. Doing .cshrc may cause fork/exec
 310        * events which will confuse debugger start-up code.
 311        */
 312       if (shell)
 313         {
 314           execlp (shell_file, shell_file, "-c", shell_command, (char *) 0);
 315
 316           /* If we get here, it's an error */
 317           fprintf_unfiltered (gdb_stderr, "Cannot exec %s: %s.\n", shell_file,
 318                               safe_strerror (errno));
 319           gdb_flush (gdb_stderr);
 320           _exit (0177);
 321         }
 322       else
 323         {
 324           /* Otherwise, we directly exec the target program with execvp. */
 325           int i;
 326           char *errstring;
 327
 328           execvp (exec_file, argv);
 329
 330           /* If we get here, it's an error */
 331           errstring = safe_strerror (errno);
 332           fprintf_unfiltered (gdb_stderr, "Cannot exec %s ", exec_file);
 333
 334           i = 1;
 335           while (argv[i] != NULL)
 336             {
 337               if (i != 1)
 338                 fprintf_unfiltered (gdb_stderr, " ");
 339               fprintf_unfiltered (gdb_stderr, "%s", argv[i]);
 340               i++;
 341             }
 342           fprintf_unfiltered (gdb_stderr, ".\n");
 343           /* This extra info seems to be useless
 344              fprintf_unfiltered (gdb_stderr, "Got error %s.\n", errstring);
 345            */
 346           gdb_flush (gdb_stderr);
 347           _exit (0177);
 348         }
 349     }
 350
 351   /* Restore our environment in case a vforked child clob'd it.  */
 352   environ = save_our_env;
 353
 354   init_thread_list ();
 355
 356   inferior_pid = pid;           /* Needed for wait_for_inferior stuff below */
 357
 358   /* Now that we have a child process, make it our target, and
 359      initialize anything target-vector-specific that needs initializing.  */
 360
 361   (*init_trace_fun) (pid);
 362
 363   /* We are now in the child process of interest, having exec'd the
 364      correct program, and are poised at the first instruction of the
 365      new program.  */
 366
 367   /* Allow target dependant code to play with the new process.  This might be
 368      used to have target-specific code initialize a variable in the new process
 369      prior to executing the first instruction.  */
 370   TARGET_CREATE_INFERIOR_HOOK (pid);
 371
 372 #ifdef SOLIB_CREATE_INFERIOR_HOOK
 373   SOLIB_CREATE_INFERIOR_HOOK (pid);
 374 #endif
 375 }
 376
 377 /* An inferior Unix process CHILD_PID has been created by a call to
 378    fork() (or variants like vfork).  It is presently stopped, and waiting
 379    to be resumed.  clone_and_follow_inferior will fork the debugger,
 380    and that clone will "follow" (attach to) CHILD_PID.  The original copy
 381    of the debugger will not touch CHILD_PID again.
 382
 383    Also, the original debugger will set FOLLOWED_CHILD FALSE, while the
 384    clone will set it TRUE.
 385  */
 386 void
 387 clone_and_follow_inferior (int child_pid, int *followed_child)
 388 {
 389   extern int auto_solib_add;
 390
 391   int debugger_pid;
 392   int status;
 393   char pid_spelling[100];       /* Arbitrary but sufficient length. */
 394
 395   /* This semaphore is used to coordinate the two debuggers' handoff
 396      of CHILD_PID.  The original debugger will detach from CHILD_PID,
 397      and then the clone debugger will attach to it.  (It must be done
 398      this way because on some targets, only one process at a time can
 399      trace another.  Thus, the original debugger must relinquish its
 400      tracing rights before the clone can pick them up.)
 401    */
 402 #define SEM_TALK (1)
 403 #define SEM_LISTEN (0)
 404   int handoff_semaphore[2];     /* Original "talks" to [1], clone "listens" to [0] */
 405   int talk_value = 99;
 406   int listen_value;
 407
 408   /* Set debug_fork then attach to the child while it sleeps, to debug. */
 409   static int debug_fork = 0;
 410
 411   /* It is generally good practice to flush any possible pending stdio
 412      output prior to doing a fork, to avoid the possibility of both the
 413      parent and child flushing the same data after the fork. */
 414
 415   gdb_flush (gdb_stdout);
 416   gdb_flush (gdb_stderr);
 417
 418   /* Open the semaphore pipes.
 419    */
 420   status = pipe (handoff_semaphore);
 421   if (status < 0)
 422     error ("error getting pipe for handoff semaphore");
 423
 424   /* Clone the debugger. */
 425 #if defined(USG) && !defined(HAVE_VFORK)
 426   debugger_pid = fork ();
 427 #else
 428   if (debug_fork)
 429     debugger_pid = fork ();
 430   else
 431     debugger_pid = vfork ();
 432 #endif
 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_pid 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_pid,
 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_pid 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 }