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 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., 675 Mass Ave, Cambridge, MA 02139, USA.  */
  20
  21 #include "defs.h"
  22 #include <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 "thread.h"
  30
  31 #include <signal.h>
  32
  33 extern char **environ;
  34
  35 #ifndef SHELL_FILE
  36 #define SHELL_FILE "/bin/sh"
  37 #endif
  38
  39 /* Start an inferior Unix child process and sets inferior_pid to its pid.
  40    EXEC_FILE is the file to run.
  41    ALLARGS is a string containing the arguments to the program.
  42    ENV is the environment vector to pass.  SHELL_FILE is the shell file,
  43    or NULL if we should pick one.  Errors reported with error().  */
  44
  45 void
  46 fork_inferior (exec_file, allargs, env, traceme_fun, init_trace_fun,
  47                shell_file)
  48      char *exec_file;
  49      char *allargs;
  50      char **env;
  51      void (*traceme_fun) PARAMS ((void));
  52      void (*init_trace_fun) PARAMS ((int));
  53      char *shell_file;
  54 {
  55   int pid;
  56   char *shell_command;
  57   static char default_shell_file[] = SHELL_FILE;
  58   int len;
  59   /* Set debug_fork then attach to the child while it sleeps, to debug. */
  60   static int debug_fork = 0;
  61   /* This is set to the result of setpgrp, which if vforked, will be visible
  62      to you in the parent process.  It's only used by humans for debugging.  */
  63   static int debug_setpgrp = 657473;
  64   char **save_our_env;
  65
  66   /* If no exec file handed to us, get it from the exec-file command -- with
  67      a good, common error message if none is specified.  */
  68   if (exec_file == 0)
  69     exec_file = get_exec_file(1);
  70
  71   /* The user might want tilde-expansion, and in general probably wants
  72      the program to behave the same way as if run from
  73      his/her favorite shell.  So we let the shell run it for us.
  74      FIXME-maybe, we might want a "set shell" command so the user can change
  75      the shell from within GDB (if so, change callers which pass in a non-NULL
  76      shell_file too).  */
  77   if (shell_file == NULL)
  78     shell_file = getenv ("SHELL");
  79   if (shell_file == NULL)
  80     shell_file = default_shell_file;
  81
  82   /* Multiplying the length of exec_file by 4 is to account for the fact
  83      that it may expand when quoted; it is a worst-case number based on
  84      every character being '.  */
  85   len = 5 + 4 * strlen (exec_file) + 1 + strlen (allargs) + 1 + /*slop*/ 12;
  86   /* If desired, concat something onto the front of ALLARGS.
  87      SHELL_COMMAND is the result.  */
  88 #ifdef SHELL_COMMAND_CONCAT
  89   shell_command = (char *) alloca (strlen (SHELL_COMMAND_CONCAT) + len);
  90   strcpy (shell_command, SHELL_COMMAND_CONCAT);
  91 #else
  92   shell_command = (char *) alloca (len);
  93   shell_command[0] = '\0';
  94 #endif
  95   strcat (shell_command, "exec ");
  96
  97   /* Now add exec_file, quoting as necessary.  */
  98   {
  99     char *p;
 100     int need_to_quote;
 101
 102     /* Quoting in this style is said to work with all shells.  But csh
 103        on IRIX 4.0.1 can't deal with it.  So we only quote it if we need
 104        to.  */
 105     p = exec_file;
 106     while (1)
 107       {
 108         switch (*p)
 109           {
 110           case '\'':
 111           case '"':
 112           case '(':
 113           case ')':
 114           case '$':
 115           case '&':
 116           case ';':
 117           case '<':
 118           case '>':
 119           case ' ':
 120           case '\n':
 121           case '\t':
 122             need_to_quote = 1;
 123             goto end_scan;
 124
 125           case '\0':
 126             need_to_quote = 0;
 127             goto end_scan;
 128
 129           default:
 130             break;
 131           }
 132         ++p;
 133       }
 134   end_scan:
 135     if (need_to_quote)
 136       {
 137         strcat (shell_command, "'");
 138         for (p = exec_file; *p != '\0'; ++p)
 139           {
 140             if (*p == '\'')
 141               strcat (shell_command, "'\\''");
 142             else
 143               strncat (shell_command, p, 1);
 144           }
 145         strcat (shell_command, "'");
 146       }
 147     else
 148       strcat (shell_command, exec_file);
 149   }
 150
 151   strcat (shell_command, " ");
 152   strcat (shell_command, allargs);
 153
 154   /* exec is said to fail if the executable is open.  */
 155   close_exec_file ();
 156
 157   /* Retain a copy of our environment variables, since the child will
 158      replace the value of  environ  and if we're vforked, we have to
 159      restore it.  */
 160   save_our_env = environ;
 161
 162   /* Tell the terminal handling subsystem what tty we plan to run on;
 163      it will just record the information for later.  */
 164
 165   new_tty_prefork (inferior_io_terminal);
 166
 167   /* It is generally good practice to flush any possible pending stdio
 168      output prior to doing a fork, to avoid the possibility of both the
 169      parent and child flushing the same data after the fork. */
 170
 171   gdb_flush (gdb_stdout);
 172   gdb_flush (gdb_stderr);
 173
 174 #if defined(USG) && !defined(HAVE_VFORK)
 175   pid = fork ();
 176 #else
 177   if (debug_fork)
 178     pid = fork ();
 179   else
 180     pid = vfork ();
 181 #endif
 182
 183   if (pid < 0)
 184     perror_with_name ("vfork");
 185
 186   if (pid == 0)
 187     {
 188       if (debug_fork)
 189         sleep (debug_fork);
 190
 191       /* Run inferior in a separate process group.  */
 192       debug_setpgrp = gdb_setpgid ();
 193       if (debug_setpgrp == -1)
 194          perror("setpgrp failed in child");
 195
 196       /* Ask the tty subsystem to switch to the one we specified earlier
 197          (or to share the current terminal, if none was specified).  */
 198
 199       new_tty ();
 200
 201       /* Changing the signal handlers for the inferior after
 202          a vfork can also change them for the superior, so we don't mess
 203          with signals here.  See comments in
 204          initialize_signals for how we get the right signal handlers
 205          for the inferior.  */
 206
 207       /* "Trace me, Dr. Memory!" */
 208       (*traceme_fun) ();
 209
 210       /* There is no execlpe call, so we have to set the environment
 211          for our child in the global variable.  If we've vforked, this
 212          clobbers the parent, but environ is restored a few lines down
 213          in the parent.  By the way, yes we do need to look down the
 214          path to find $SHELL.  Rich Pixley says so, and I agree.  */
 215       environ = env;
 216       execlp (shell_file, shell_file, "-c", shell_command, (char *)0);
 217
 218       fprintf_unfiltered (gdb_stderr, "Cannot exec %s: %s.\n", shell_file,
 219                safe_strerror (errno));
 220       gdb_flush (gdb_stderr);
 221       _exit (0177);
 222     }
 223
 224   /* Restore our environment in case a vforked child clob'd it.  */
 225   environ = save_our_env;
 226
 227   init_thread_list();
 228
 229   inferior_pid = pid;           /* Needed for wait_for_inferior stuff below */
 230
 231   /* Now that we have a child process, make it our target, and
 232      initialize anything target-vector-specific that needs initializing.  */
 233   (*init_trace_fun)(pid);
 234
 235   /* We are now in the child process of interest, having exec'd the
 236      correct program, and are poised at the first instruction of the
 237      new program.  */
 238 #ifdef SOLIB_CREATE_INFERIOR_HOOK
 239   SOLIB_CREATE_INFERIOR_HOOK (pid);
 240 #endif
 241 }
 242
 243 /* Accept NTRAPS traps from the inferior.  */
 244
 245 void
 246 startup_inferior (ntraps)
 247      int ntraps;
 248 {
 249   int pending_execs = ntraps;
 250   int terminal_initted;
 251
 252   /* The process was started by the fork that created it,
 253      but it will have stopped one instruction after execing the shell.
 254      Here we must get it up to actual execution of the real program.  */
 255
 256   clear_proceed_status ();
 257
 258   init_wait_for_inferior ();
 259
 260   terminal_initted = 0;
 261
 262 #ifdef STARTUP_INFERIOR
 263   STARTUP_INFERIOR (pending_execs);
 264 #else
 265   while (1)
 266     {
 267       stop_soon_quietly = 1;    /* Make wait_for_inferior be quiet */
 268       wait_for_inferior ();
 269       if (stop_signal != TARGET_SIGNAL_TRAP)
 270         {
 271           /* Let shell child handle its own signals in its own way */
 272           /* FIXME, what if child has exit()ed?  Must exit loop somehow */
 273           resume (0, stop_signal);
 274         }
 275       else
 276         {
 277           /* We handle SIGTRAP, however; it means child did an exec.  */
 278           if (!terminal_initted)
 279             {
 280               /* Now that the child has exec'd we know it has already set its
 281                  process group.  On POSIX systems, tcsetpgrp will fail with
 282                  EPERM if we try it before the child's setpgid.  */
 283
 284               /* Set up the "saved terminal modes" of the inferior
 285                  based on what modes we are starting it with.  */
 286               target_terminal_init ();
 287
 288               /* Install inferior's terminal modes.  */
 289               target_terminal_inferior ();
 290
 291               terminal_initted = 1;
 292             }
 293           if (0 == --pending_execs)
 294             break;
 295           resume (0, TARGET_SIGNAL_0);          /* Just make it go on */
 296         }
 297     }
 298 #endif /* STARTUP_INFERIOR */
 299   stop_soon_quietly = 0;
 300 }