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, 1996 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, Boston, MA 02111-1307, USA.  */
  20
  21 #include "defs.h"
  22 #include "gdb_string.h"
  23 #include "frame.h"  /* required by inferior.h */
  24 #include "inferior.h"
  25 #include "target.h"
  26 #include "wait.h"
  27 #include "gdbcore.h"
  28 #include "terminal.h"
  29 #include "gdbthread.h"
  30
  31 #include <signal.h>
  32 #ifdef HAVE_UNISTD_H
  33 #include <unistd.h>
  34 #endif
  35
  36 extern char **environ;
  37
  38 #ifndef SHELL_FILE
  39 #define SHELL_FILE "/bin/sh"
  40 #endif
  41
  42 /* Start an inferior Unix child process and sets inferior_pid to its pid.
  43    EXEC_FILE is the file to run.
  44    ALLARGS is a string containing the arguments to the program.
  45    ENV is the environment vector to pass.  SHELL_FILE is the shell file,
  46    or NULL if we should pick one.  Errors reported with error().  */
  47
  48 void
  49 fork_inferior (exec_file, allargs, env, traceme_fun, init_trace_fun,
  50                shell_file)
  51      char *exec_file;
  52      char *allargs;
  53      char **env;
  54      void (*traceme_fun) PARAMS ((void));
  55      int (*init_trace_fun) PARAMS ((int));
  56      char *shell_file;
  57 {
  58   int pid;
  59   char *shell_command;
  60   static char default_shell_file[] = SHELL_FILE;
  61   int len;
  62   /* Set debug_fork then attach to the child while it sleeps, to debug. */
  63   static int debug_fork = 0;
  64   /* This is set to the result of setpgrp, which if vforked, will be visible
  65      to you in the parent process.  It's only used by humans for debugging.  */
  66   static int debug_setpgrp = 657473;
  67   char **save_our_env;
  68
  69   /* If no exec file handed to us, get it from the exec-file command -- with
  70      a good, common error message if none is specified.  */
  71   if (exec_file == 0)
  72     exec_file = get_exec_file(1);
  73
  74   /* The user might want tilde-expansion, and in general probably wants
  75      the program to behave the same way as if run from
  76      his/her favorite shell.  So we let the shell run it for us.
  77      FIXME-maybe, we might want a "set shell" command so the user can change
  78      the shell from within GDB (if so, change callers which pass in a non-NULL
  79      shell_file too).  */
  80   if (shell_file == NULL)
  81     shell_file = getenv ("SHELL");
  82   if (shell_file == NULL)
  83     shell_file = default_shell_file;
  84
  85   /* Multiplying the length of exec_file by 4 is to account for the fact
  86      that it may expand when quoted; it is a worst-case number based on
  87      every character being '.  */
  88   len = 5 + 4 * strlen (exec_file) + 1 + strlen (allargs) + 1 + /*slop*/ 12;
  89   /* If desired, concat something onto the front of ALLARGS.
  90      SHELL_COMMAND is the result.  */
  91 #ifdef SHELL_COMMAND_CONCAT
  92   shell_command = (char *) alloca (strlen (SHELL_COMMAND_CONCAT) + len);
  93   strcpy (shell_command, SHELL_COMMAND_CONCAT);
  94 #else
  95   shell_command = (char *) alloca (len);
  96   shell_command[0] = '\0';
  97 #endif
  98   strcat (shell_command, "exec ");
  99
 100   /* Now add exec_file, quoting as necessary.  */
 101   {
 102     char *p;
 103     int need_to_quote;
 104
 105     /* Quoting in this style is said to work with all shells.  But csh
 106        on IRIX 4.0.1 can't deal with it.  So we only quote it if we need
 107        to.  */
 108     p = exec_file;
 109     while (1)
 110       {
 111         switch (*p)
 112           {
 113           case '\'':
 114           case '"':
 115           case '(':
 116           case ')':
 117           case '$':
 118           case '&':
 119           case ';':
 120           case '<':
 121           case '>':
 122           case ' ':
 123           case '\n':
 124           case '\t':
 125             need_to_quote = 1;
 126             goto end_scan;
 127
 128           case '\0':
 129             need_to_quote = 0;
 130             goto end_scan;
 131
 132           default:
 133             break;
 134           }
 135         ++p;
 136       }
 137   end_scan:
 138     if (need_to_quote)
 139       {
 140         strcat (shell_command, "'");
 141         for (p = exec_file; *p != '\0'; ++p)
 142           {
 143             if (*p == '\'')
 144               strcat (shell_command, "'\\''");
 145             else
 146               strncat (shell_command, p, 1);
 147           }
 148         strcat (shell_command, "'");
 149       }
 150     else
 151       strcat (shell_command, exec_file);
 152   }
 153
 154   strcat (shell_command, " ");
 155   strcat (shell_command, allargs);
 156
 157   /* exec is said to fail if the executable is open.  */
 158   close_exec_file ();
 159
 160   /* Retain a copy of our environment variables, since the child will
 161      replace the value of  environ  and if we're vforked, we have to
 162      restore it.  */
 163   save_our_env = environ;
 164
 165   /* Tell the terminal handling subsystem what tty we plan to run on;
 166      it will just record the information for later.  */
 167
 168   new_tty_prefork (inferior_io_terminal);
 169
 170   /* It is generally good practice to flush any possible pending stdio
 171      output prior to doing a fork, to avoid the possibility of both the
 172      parent and child flushing the same data after the fork. */
 173
 174   gdb_flush (gdb_stdout);
 175   gdb_flush (gdb_stderr);
 176
 177 #if defined(USG) && !defined(HAVE_VFORK)
 178   pid = fork ();
 179 #else
 180   if (debug_fork)
 181     pid = fork ();
 182   else
 183     pid = vfork ();
 184 #endif
 185
 186   if (pid < 0)
 187     perror_with_name ("vfork");
 188
 189   if (pid == 0)
 190     {
 191       if (debug_fork)
 192         sleep (debug_fork);
 193
 194       /* Run inferior in a separate process group.  */
 195       debug_setpgrp = gdb_setpgid ();
 196       if (debug_setpgrp == -1)
 197          perror("setpgrp failed in child");
 198
 199       /* Ask the tty subsystem to switch to the one we specified earlier
 200          (or to share the current terminal, if none was specified).  */
 201
 202       new_tty ();
 203
 204       /* Changing the signal handlers for the inferior after
 205          a vfork can also change them for the superior, so we don't mess
 206          with signals here.  See comments in
 207          initialize_signals for how we get the right signal handlers
 208          for the inferior.  */
 209
 210       /* "Trace me, Dr. Memory!" */
 211       (*traceme_fun) ();
 212
 213       /* There is no execlpe call, so we have to set the environment
 214          for our child in the global variable.  If we've vforked, this
 215          clobbers the parent, but environ is restored a few lines down
 216          in the parent.  By the way, yes we do need to look down the
 217          path to find $SHELL.  Rich Pixley says so, and I agree.  */
 218       environ = env;
 219       execlp (shell_file, shell_file, "-c", shell_command, (char *)0);
 220
 221       fprintf_unfiltered (gdb_stderr, "Cannot exec %s: %s.\n", shell_file,
 222                safe_strerror (errno));
 223       gdb_flush (gdb_stderr);
 224       _exit (0177);
 225     }
 226
 227   /* Restore our environment in case a vforked child clob'd it.  */
 228   environ = save_our_env;
 229
 230   init_thread_list();
 231
 232   inferior_pid = pid;           /* Needed for wait_for_inferior stuff below */
 233
 234   /* Now that we have a child process, make it our target, and
 235      initialize anything target-vector-specific that needs initializing.  */
 236
 237   /* Note that pid may be modified by this function.  */
 238   inferior_pid = pid = (*init_trace_fun)(pid);
 239
 240   /* We are now in the child process of interest, having exec'd the
 241      correct program, and are poised at the first instruction of the
 242      new program.  */
 243
 244   /* Allow target dependant code to play with the new process.  This might be
 245      used to have target-specific code initialize a variable in the new process
 246      prior to executing the first instruction.  */
 247   TARGET_CREATE_INFERIOR_HOOK (pid);
 248
 249 #ifdef SOLIB_CREATE_INFERIOR_HOOK
 250   SOLIB_CREATE_INFERIOR_HOOK (pid);
 251 #endif
 252 }
 253
 254 /* Accept NTRAPS traps from the inferior.  */
 255
 256 void
 257 startup_inferior (ntraps)
 258      int ntraps;
 259 {
 260   int pending_execs = ntraps;
 261   int terminal_initted;
 262
 263   /* The process was started by the fork that created it,
 264      but it will have stopped one instruction after execing the shell.
 265      Here we must get it up to actual execution of the real program.  */
 266
 267   clear_proceed_status ();
 268
 269   init_wait_for_inferior ();
 270
 271   terminal_initted = 0;
 272
 273 #ifdef STARTUP_INFERIOR
 274   STARTUP_INFERIOR (pending_execs);
 275 #else
 276   while (1)
 277     {
 278       stop_soon_quietly = 1;    /* Make wait_for_inferior be quiet */
 279       wait_for_inferior ();
 280       if (stop_signal != TARGET_SIGNAL_TRAP)
 281         {
 282           /* Let shell child handle its own signals in its own way */
 283           /* FIXME, what if child has exit()ed?  Must exit loop somehow */
 284           resume (0, stop_signal);
 285         }
 286       else
 287         {
 288           /* We handle SIGTRAP, however; it means child did an exec.  */
 289           if (!terminal_initted)
 290             {
 291               /* Now that the child has exec'd we know it has already set its
 292                  process group.  On POSIX systems, tcsetpgrp will fail with
 293                  EPERM if we try it before the child's setpgid.  */
 294
 295               /* Set up the "saved terminal modes" of the inferior
 296                  based on what modes we are starting it with.  */
 297               target_terminal_init ();
 298
 299               /* Install inferior's terminal modes.  */
 300               target_terminal_inferior ();
 301
 302               terminal_initted = 1;
 303             }
 304           if (0 == --pending_execs)
 305             break;
 306           resume (0, TARGET_SIGNAL_0);          /* Just make it go on */
 307         }
 308     }
 309 #endif /* STARTUP_INFERIOR */
 310   stop_soon_quietly = 0;
 311 }