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 ' ':
 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 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   /* Create the child process.  Note that the apparent call to vfork()
 260      below *might* actually be a call to fork() due to the fact that
 261      autoconf will ``#define vfork fork'' on certain platforms.  */
 262   if (debug_fork)
 263     pid = fork ();
 264   else
 265     pid = vfork ();
 266
 267   if (pid < 0)
 268     perror_with_name ("vfork");
 269
 270   if (pid == 0)
 271     {
 272       if (debug_fork)
 273         sleep (debug_fork);
 274
 275       /* Run inferior in a separate process group.  */
 276       debug_setpgrp = gdb_setpgid ();
 277       if (debug_setpgrp == -1)
 278         perror ("setpgrp failed in child");
 279
 280       /* Ask the tty subsystem to switch to the one we specified earlier
 281          (or to share the current terminal, if none was specified).  */
 282
 283       new_tty ();
 284
 285       /* Changing the signal handlers for the inferior after
 286          a vfork can also change them for the superior, so we don't mess
 287          with signals here.  See comments in
 288          initialize_signals for how we get the right signal handlers
 289          for the inferior.  */
 290
 291       /* "Trace me, Dr. Memory!" */
 292       (*traceme_fun) ();
 293       /* The call above set this process (the "child") as debuggable
 294        * by the original gdb process (the "parent").  Since processes
 295        * (unlike people) can have only one parent, if you are
 296        * debugging gdb itself (and your debugger is thus _already_ the
 297        * controller/parent for this child),  code from here on out
 298        * is undebuggable.  Indeed, you probably got an error message
 299        * saying "not parent".  Sorry--you'll have to use print statements!
 300        */
 301
 302       /* There is no execlpe call, so we have to set the environment
 303          for our child in the global variable.  If we've vforked, this
 304          clobbers the parent, but environ is restored a few lines down
 305          in the parent.  By the way, yes we do need to look down the
 306          path to find $SHELL.  Rich Pixley says so, and I agree.  */
 307       environ = env;
 308
 309       /* If we decided above to start up with a shell,
 310        * we exec the shell,
 311        * "-c" says to interpret the next arg as a shell command
 312        * to execute, and this command is "exec <target-program> <args>".
 313        * "-f" means "fast startup" to the c-shell, which means
 314        * don't do .cshrc file. Doing .cshrc may cause fork/exec
 315        * events which will confuse debugger start-up code.
 316        */
 317       if (shell)
 318         {
 319           execlp (shell_file, shell_file, "-c", shell_command, (char *) 0);
 320
 321           /* If we get here, it's an error */
 322           fprintf_unfiltered (gdb_stderr, "Cannot exec %s: %s.\n", shell_file,
 323                               safe_strerror (errno));
 324           gdb_flush (gdb_stderr);
 325           _exit (0177);
 326         }
 327       else
 328         {
 329           /* Otherwise, we directly exec the target program with execvp. */
 330           int i;
 331           char *errstring;
 332
 333           execvp (exec_file, argv);
 334
 335           /* If we get here, it's an error */
 336           errstring = safe_strerror (errno);
 337           fprintf_unfiltered (gdb_stderr, "Cannot exec %s ", exec_file);
 338
 339           i = 1;
 340           while (argv[i] != NULL)
 341             {
 342               if (i != 1)
 343                 fprintf_unfiltered (gdb_stderr, " ");
 344               fprintf_unfiltered (gdb_stderr, "%s", argv[i]);
 345               i++;
 346             }
 347           fprintf_unfiltered (gdb_stderr, ".\n");
 348           /* This extra info seems to be useless
 349              fprintf_unfiltered (gdb_stderr, "Got error %s.\n", errstring);
 350            */
 351           gdb_flush (gdb_stderr);
 352           _exit (0177);
 353         }
 354     }
 355
 356   /* Restore our environment in case a vforked child clob'd it.  */
 357   environ = save_our_env;
 358
 359   init_thread_list ();
 360
 361   inferior_ptid = pid_to_ptid (pid);    /* Needed for wait_for_inferior stuff below */
 362
 363   /* Now that we have a child process, make it our target, and
 364      initialize anything target-vector-specific that needs initializing.  */
 365
 366   (*init_trace_fun) (pid);
 367
 368   /* We are now in the child process of interest, having exec'd the
 369      correct program, and are poised at the first instruction of the
 370      new program.  */
 371
 372   /* Allow target dependent code to play with the new process.  This might be
 373      used to have target-specific code initialize a variable in the new process
 374      prior to executing the first instruction.  */
 375   TARGET_CREATE_INFERIOR_HOOK (pid);
 376
 377 #ifdef SOLIB_CREATE_INFERIOR_HOOK
 378   SOLIB_CREATE_INFERIOR_HOOK (pid);
 379 #endif
 380 }
 381
 382 /* Accept NTRAPS traps from the inferior.  */
 383
 384 void
 385 startup_inferior (int ntraps)
 386 {
 387   int pending_execs = ntraps;
 388   int terminal_initted;
 389
 390   /* The process was started by the fork that created it,
 391      but it will have stopped one instruction after execing the shell.
 392      Here we must get it up to actual execution of the real program.  */
 393
 394   clear_proceed_status ();
 395
 396   init_wait_for_inferior ();
 397
 398   terminal_initted = 0;
 399
 400   if (STARTUP_WITH_SHELL)
 401     inferior_ignoring_startup_exec_events = ntraps;
 402   else
 403     inferior_ignoring_startup_exec_events = 0;
 404   inferior_ignoring_leading_exec_events =
 405     target_reported_exec_events_per_exec_call () - 1;
 406
 407 #ifdef STARTUP_INFERIOR
 408   STARTUP_INFERIOR (pending_execs);
 409 #else
 410   while (1)
 411     {
 412       /* Make wait_for_inferior be quiet */
 413       stop_soon = STOP_QUIETLY;
 414       wait_for_inferior ();
 415       if (stop_signal != TARGET_SIGNAL_TRAP)
 416         {
 417           /* Let shell child handle its own signals in its own way */
 418           /* FIXME, what if child has exit()ed?  Must exit loop somehow */
 419           resume (0, stop_signal);
 420         }
 421       else
 422         {
 423           /* We handle SIGTRAP, however; it means child did an exec.  */
 424           if (!terminal_initted)
 425             {
 426               /* Now that the child has exec'd we know it has already set its
 427                  process group.  On POSIX systems, tcsetpgrp will fail with
 428                  EPERM if we try it before the child's setpgid.  */
 429
 430               /* Set up the "saved terminal modes" of the inferior
 431                  based on what modes we are starting it with.  */
 432               target_terminal_init ();
 433
 434               /* Install inferior's terminal modes.  */
 435               target_terminal_inferior ();
 436
 437               terminal_initted = 1;
 438             }
 439
 440           pending_execs = pending_execs - 1;
 441           if (0 == pending_execs)
 442             break;
 443
 444           resume (0, TARGET_SIGNAL_0);  /* Just make it go on */
 445         }
 446     }
 447 #endif /* STARTUP_INFERIOR */
 448   stop_soon = NO_STOP_QUIETLY;
 449 }