gdb/fork-child.c

   1 /* Fork a Unix child process, and set up to debug it, for GDB.
   2
   3    Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000,
   4    2001, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
   5
   6    Contributed by Cygnus Support.
   7
   8    This file is part of GDB.
   9
  10    This program is free software; you can redistribute it and/or modify
  11    it under the terms of the GNU General Public License as published by
  12    the Free Software Foundation; either version 2 of the License, or
  13    (at your option) any later version.
  14
  15    This program is distributed in the hope that it will be useful,
  16    but WITHOUT ANY WARRANTY; without even the implied warranty of
  17    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18    GNU General Public License for more details.
  19
  20    You should have received a copy of the GNU General Public License
  21    along with this program; if not, write to the Free Software
  22    Foundation, Inc., 51 Franklin Street, Fifth Floor,
  23    Boston, MA 02110-1301, USA.  */
  24
  25 #include "defs.h"
  26 #include "gdb_string.h"
  27 #include "frame.h"              /* required by inferior.h */
  28 #include "inferior.h"
  29 #include "target.h"
  30 #include "gdb_wait.h"
  31 #include "gdb_vfork.h"
  32 #include "gdbcore.h"
  33 #include "terminal.h"
  34 #include "gdbthread.h"
  35 #include "command.h" /* for dont_repeat () */
  36 #include "solib.h"
  37
  38 #include <signal.h>
  39
  40 /* This just gets used as a default if we can't find SHELL.  */
  41 #ifndef SHELL_FILE
  42 #define SHELL_FILE "/bin/sh"
  43 #endif
  44
  45 extern char **environ;
  46
  47 /* Break up SCRATCH into an argument vector suitable for passing to
  48    execvp and store it in ARGV.  E.g., on "run a b c d" this routine
  49    would get as input the string "a b c d", and as output it would
  50    fill in ARGV with the four arguments "a", "b", "c", "d".  */
  51
  52 static void
  53 breakup_args (char *scratch, char **argv)
  54 {
  55   char *cp = scratch;
  56
  57   for (;;)
  58     {
  59       /* Scan past leading separators */
  60       while (*cp == ' ' || *cp == '\t' || *cp == '\n')
  61         cp++;
  62
  63       /* Break if at end of string.  */
  64       if (*cp == '\0')
  65         break;
  66
  67       /* Take an arg.  */
  68       *argv++ = cp;
  69
  70       /* Scan for next arg separator.  */
  71       cp = strchr (cp, ' ');
  72       if (cp == NULL)
  73         cp = strchr (cp, '\t');
  74       if (cp == NULL)
  75         cp = strchr (cp, '\n');
  76
  77       /* No separators => end of string => break.  */
  78       if (cp == NULL)
  79         break;
  80
  81       /* Replace the separator with a terminator.  */
  82       *cp++ = '\0';
  83     }
  84
  85   /* Null-terminate the vector.  */
  86   *argv = NULL;
  87 }
  88
  89 /* When executing a command under the given shell, return non-zero if
  90    the '!' character should be escaped when embedded in a quoted
  91    command-line argument.  */
  92
  93 static int
  94 escape_bang_in_quoted_argument (const char *shell_file)
  95 {
  96   const int shell_file_len = strlen (shell_file);
  97
  98   /* Bang should be escaped only in C Shells.  For now, simply check
  99      that the shell name ends with 'csh', which covers at least csh
 100      and tcsh.  This should be good enough for now.  */
 101
 102   if (shell_file_len < 3)
 103     return 0;
 104
 105   if (shell_file[shell_file_len - 3] == 'c'
 106       && shell_file[shell_file_len - 2] == 's'
 107       && shell_file[shell_file_len - 1] == 'h')
 108     return 1;
 109
 110   return 0;
 111 }
 112
 113 /* Start an inferior Unix child process and sets inferior_ptid to its
 114    pid.  EXEC_FILE is the file to run.  ALLARGS is a string containing
 115    the arguments to the program.  ENV is the environment vector to
 116    pass.  SHELL_FILE is the shell file, or NULL if we should pick
 117    one.  */
 118
 119 /* This function is NOT reentrant.  Some of the variables have been
 120    made static to ensure that they survive the vfork call.  */
 121
 122 void
 123 fork_inferior (char *exec_file_arg, char *allargs, char **env,
 124                void (*traceme_fun) (void), void (*init_trace_fun) (int),
 125                void (*pre_trace_fun) (void), char *shell_file_arg)
 126 {
 127   int pid;
 128   char *shell_command;
 129   static char default_shell_file[] = SHELL_FILE;
 130   int len;
 131   /* Set debug_fork then attach to the child while it sleeps, to debug. */
 132   static int debug_fork = 0;
 133   /* This is set to the result of setpgrp, which if vforked, will be visible
 134      to you in the parent process.  It's only used by humans for debugging.  */
 135   static int debug_setpgrp = 657473;
 136   static char *shell_file;
 137   static char *exec_file;
 138   char **save_our_env;
 139   int shell = 0;
 140   static char **argv;
 141   const char *inferior_io_terminal = get_inferior_io_terminal ();
 142
 143   /* If no exec file handed to us, get it from the exec-file command
 144      -- with a good, common error message if none is specified.  */
 145   exec_file = exec_file_arg;
 146   if (exec_file == 0)
 147     exec_file = get_exec_file (1);
 148
 149   /* STARTUP_WITH_SHELL is defined in inferior.h.  If 0,e we'll just
 150     do a fork/exec, no shell, so don't bother figuring out what
 151     shell.  */
 152   shell_file = shell_file_arg;
 153   if (STARTUP_WITH_SHELL)
 154     {
 155       /* Figure out what shell to start up the user program under.  */
 156       if (shell_file == NULL)
 157         shell_file = getenv ("SHELL");
 158       if (shell_file == NULL)
 159         shell_file = default_shell_file;
 160       shell = 1;
 161     }
 162
 163   /* Multiplying the length of exec_file by 4 is to account for the
 164      fact that it may expand when quoted; it is a worst-case number
 165      based on every character being '.  */
 166   len = 5 + 4 * strlen (exec_file) + 1 + strlen (allargs) + 1 + /*slop */ 12;
 167   /* If desired, concat something onto the front of ALLARGS.
 168      SHELL_COMMAND is the result.  */
 169 #ifdef SHELL_COMMAND_CONCAT
 170   shell_command = (char *) alloca (strlen (SHELL_COMMAND_CONCAT) + len);
 171   strcpy (shell_command, SHELL_COMMAND_CONCAT);
 172 #else
 173   shell_command = (char *) alloca (len);
 174   shell_command[0] = '\0';
 175 #endif
 176
 177   if (!shell)
 178     {
 179       /* We're going to call execvp.  Create argument vector.
 180          Calculate an upper bound on the length of the vector by
 181          assuming that every other character is a separate
 182          argument.  */
 183       int argc = (strlen (allargs) + 1) / 2 + 2;
 184       argv = (char **) xmalloc (argc * sizeof (*argv));
 185       argv[0] = exec_file;
 186       breakup_args (allargs, &argv[1]);
 187     }
 188   else
 189     {
 190       /* We're going to call a shell.  */
 191
 192       /* Now add exec_file, quoting as necessary.  */
 193
 194       char *p;
 195       int need_to_quote;
 196       const int escape_bang = escape_bang_in_quoted_argument (shell_file);
 197
 198       strcat (shell_command, "exec ");
 199
 200       /* Quoting in this style is said to work with all shells.  But
 201          csh on IRIX 4.0.1 can't deal with it.  So we only quote it if
 202          we need to.  */
 203       p = exec_file;
 204       while (1)
 205         {
 206           switch (*p)
 207             {
 208             case '\'':
 209             case '!':
 210             case '"':
 211             case '(':
 212             case ')':
 213             case '$':
 214             case '&':
 215             case ';':
 216             case '<':
 217             case '>':
 218             case ' ':
 219             case '\n':
 220             case '\t':
 221               need_to_quote = 1;
 222               goto end_scan;
 223
 224             case '\0':
 225               need_to_quote = 0;
 226               goto end_scan;
 227
 228             default:
 229               break;
 230             }
 231           ++p;
 232         }
 233     end_scan:
 234       if (need_to_quote)
 235         {
 236           strcat (shell_command, "'");
 237           for (p = exec_file; *p != '\0'; ++p)
 238             {
 239               if (*p == '\'')
 240                 strcat (shell_command, "'\\''");
 241               else if (*p == '!' && escape_bang)
 242                 strcat (shell_command, "\\!");
 243               else
 244                 strncat (shell_command, p, 1);
 245             }
 246           strcat (shell_command, "'");
 247         }
 248       else
 249         strcat (shell_command, exec_file);
 250
 251       strcat (shell_command, " ");
 252       strcat (shell_command, allargs);
 253     }
 254
 255   /* On some systems an exec will fail if the executable is open.  */
 256   close_exec_file ();
 257
 258   /* Retain a copy of our environment variables, since the child will
 259      replace the value of environ and if we're vforked, we have to
 260      restore it.  */
 261   save_our_env = environ;
 262
 263   /* Tell the terminal handling subsystem what tty we plan to run on;
 264      it will just record the information for later.  */
 265   new_tty_prefork (inferior_io_terminal);
 266
 267   /* It is generally good practice to flush any possible pending stdio
 268      output prior to doing a fork, to avoid the possibility of both
 269      the parent and child flushing the same data after the fork. */
 270   gdb_flush (gdb_stdout);
 271   gdb_flush (gdb_stderr);
 272
 273   /* If there's any initialization of the target layers that must
 274      happen to prepare to handle the child we're about fork, do it
 275      now...  */
 276   if (pre_trace_fun != NULL)
 277     (*pre_trace_fun) ();
 278
 279   /* Create the child process.  Since the child process is going to
 280      exec(3) shortly afterwards, try to reduce the overhead by
 281      calling vfork(2).  However, if PRE_TRACE_FUN is non-null, it's
 282      likely that this optimization won't work since there's too much
 283      work to do between the vfork(2) and the exec(3).  This is known
 284      to be the case on ttrace(2)-based HP-UX, where some handshaking
 285      between parent and child needs to happen between fork(2) and
 286      exec(2).  However, since the parent is suspended in the vforked
 287      state, this doesn't work.  Also note that the vfork(2) call might
 288      actually be a call to fork(2) due to the fact that autoconf will
 289      ``#define vfork fork'' on certain platforms.  */
 290   if (pre_trace_fun || debug_fork)
 291     pid = fork ();
 292   else
 293     pid = vfork ();
 294
 295   if (pid < 0)
 296     perror_with_name (("vfork"));
 297
 298   if (pid == 0)
 299     {
 300       if (debug_fork)
 301         sleep (debug_fork);
 302
 303       /* Run inferior in a separate process group.  */
 304       debug_setpgrp = gdb_setpgid ();
 305       if (debug_setpgrp == -1)
 306         perror ("setpgrp failed in child");
 307
 308       /* Ask the tty subsystem to switch to the one we specified
 309          earlier (or to share the current terminal, if none was
 310          specified).  */
 311       new_tty ();
 312
 313       /* Changing the signal handlers for the inferior after
 314          a vfork can also change them for the superior, so we don't mess
 315          with signals here.  See comments in
 316          initialize_signals for how we get the right signal handlers
 317          for the inferior.  */
 318
 319       /* "Trace me, Dr. Memory!" */
 320       (*traceme_fun) ();
 321
 322       /* The call above set this process (the "child") as debuggable
 323         by the original gdb process (the "parent").  Since processes
 324         (unlike people) can have only one parent, if you are debugging
 325         gdb itself (and your debugger is thus _already_ the
 326         controller/parent for this child), code from here on out is
 327         undebuggable.  Indeed, you probably got an error message
 328         saying "not parent".  Sorry; you'll have to use print
 329         statements!  */
 330
 331       /* There is no execlpe call, so we have to set the environment
 332          for our child in the global variable.  If we've vforked, this
 333          clobbers the parent, but environ is restored a few lines down
 334          in the parent.  By the way, yes we do need to look down the
 335          path to find $SHELL.  Rich Pixley says so, and I agree.  */
 336       environ = env;
 337
 338       /* If we decided above to start up with a shell, we exec the
 339          shell, "-c" says to interpret the next arg as a shell command
 340          to execute, and this command is "exec <target-program>
 341          <args>".  */
 342       if (shell)
 343         {
 344           execlp (shell_file, shell_file, "-c", shell_command, (char *) 0);
 345
 346           /* If we get here, it's an error.  */
 347           fprintf_unfiltered (gdb_stderr, "Cannot exec %s: %s.\n", shell_file,
 348                               safe_strerror (errno));
 349           gdb_flush (gdb_stderr);
 350           _exit (0177);
 351         }
 352       else
 353         {
 354           /* Otherwise, we directly exec the target program with
 355              execvp.  */
 356           int i;
 357           char *errstring;
 358
 359           execvp (exec_file, argv);
 360
 361           /* If we get here, it's an error.  */
 362           errstring = safe_strerror (errno);
 363           fprintf_unfiltered (gdb_stderr, "Cannot exec %s ", exec_file);
 364
 365           i = 1;
 366           while (argv[i] != NULL)
 367             {
 368               if (i != 1)
 369                 fprintf_unfiltered (gdb_stderr, " ");
 370               fprintf_unfiltered (gdb_stderr, "%s", argv[i]);
 371               i++;
 372             }
 373           fprintf_unfiltered (gdb_stderr, ".\n");
 374 #if 0
 375           /* This extra info seems to be useless.  */
 376           fprintf_unfiltered (gdb_stderr, "Got error %s.\n", errstring);
 377 #endif
 378           gdb_flush (gdb_stderr);
 379           _exit (0177);
 380         }
 381     }
 382
 383   /* Restore our environment in case a vforked child clob'd it.  */
 384   environ = save_our_env;
 385
 386   init_thread_list ();
 387
 388   /* Needed for wait_for_inferior stuff below.  */
 389   inferior_ptid = pid_to_ptid (pid);
 390
 391   /* Now that we have a child process, make it our target, and
 392      initialize anything target-vector-specific that needs
 393      initializing.  */
 394   (*init_trace_fun) (pid);
 395
 396   /* We are now in the child process of interest, having exec'd the
 397      correct program, and are poised at the first instruction of the
 398      new program.  */
 399 }
 400
 401 /* Accept NTRAPS traps from the inferior.  */
 402
 403 void
 404 startup_inferior (int ntraps)
 405 {
 406   int pending_execs = ntraps;
 407   int terminal_initted = 0;
 408
 409   /* The process was started by the fork that created it, but it will
 410      have stopped one instruction after execing the shell.  Here we
 411      must get it up to actual execution of the real program.  */
 412
 413   clear_proceed_status ();
 414
 415   init_wait_for_inferior ();
 416
 417   inferior_ignoring_leading_exec_events =
 418     target_reported_exec_events_per_exec_call () - 1;
 419
 420   while (1)
 421     {
 422       /* Make wait_for_inferior be quiet. */
 423       stop_soon = STOP_QUIETLY;
 424       wait_for_inferior ();
 425       if (stop_signal != TARGET_SIGNAL_TRAP)
 426         {
 427           /* Let shell child handle its own signals in its own way.
 428              FIXME: what if child has exited?  Must exit loop
 429              somehow.  */
 430           resume (0, stop_signal);
 431         }
 432       else
 433         {
 434           /* We handle SIGTRAP, however; it means child did an exec.  */
 435           if (!terminal_initted)
 436             {
 437               /* Now that the child has exec'd we know it has already
 438                  set its process group.  On POSIX systems, tcsetpgrp
 439                  will fail with EPERM if we try it before the child's
 440                  setpgid.  */
 441
 442               /* Set up the "saved terminal modes" of the inferior
 443                  based on what modes we are starting it with.  */
 444               target_terminal_init ();
 445
 446               /* Install inferior's terminal modes.  */
 447               target_terminal_inferior ();
 448
 449               terminal_initted = 1;
 450             }
 451
 452           if (--pending_execs == 0)
 453             break;
 454
 455           resume (0, TARGET_SIGNAL_0);  /* Just make it go on.  */
 456         }
 457     }
 458   stop_soon = NO_STOP_QUIETLY;
 459 }