gdb/fork-child.c

   1 /* Fork a Unix child process, and set up to debug it, for GDB.
   2    Copyright 1990, 1991, 1992 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 "frame.h"  /* required by inferior.h */
  23 #include "inferior.h"
  24 #include "target.h"
  25 #include "wait.h"
  26 #include "gdbcore.h"
  27 #include "terminal.h"
  28 #include "thread.h"
  29
  30 #include <signal.h>
  31
  32 #ifdef SET_STACK_LIMIT_HUGE
  33 #include <sys/time.h>
  34 #include <sys/resource.h>
  35
  36 extern int original_stack_limit;
  37 #endif /* SET_STACK_LIMIT_HUGE */
  38
  39 extern char **environ;
  40
  41 #ifndef SHELL_FILE
  42 #define SHELL_FILE "/bin/sh"
  43 #endif
  44
  45 /* Start an inferior Unix child process and sets inferior_pid to its pid.
  46    EXEC_FILE is the file to run.
  47    ALLARGS is a string containing the arguments to the program.
  48    ENV is the environment vector to pass.  SHELL_FILE is the shell file,
  49    or NULL if we should pick one.  Errors reported with error().  */
  50
  51 void
  52 fork_inferior (exec_file, allargs, env, traceme_fun, init_trace_fun,
  53                shell_file)
  54      char *exec_file;
  55      char *allargs;
  56      char **env;
  57      void (*traceme_fun) PARAMS ((void));
  58      void (*init_trace_fun) PARAMS ((int));
  59      char *shell_file;
  60 {
  61   int pid;
  62   char *shell_command;
  63   static char default_shell_file[] = SHELL_FILE;
  64   int len;
  65   /* Set debug_fork then attach to the child while it sleeps, to debug. */
  66   static int debug_fork = 0;
  67   /* This is set to the result of setpgrp, which if vforked, will be visible
  68      to you in the parent process.  It's only used by humans for debugging.  */
  69   static int debug_setpgrp = 657473;
  70   char **save_our_env;
  71
  72   /* If no exec file handed to us, get it from the exec-file command -- with
  73      a good, common error message if none is specified.  */
  74   if (exec_file == 0)
  75     exec_file = get_exec_file(1);
  76
  77   /* The user might want tilde-expansion, and in general probably wants
  78      the program to behave the same way as if run from
  79      his/her favorite shell.  So we let the shell run it for us.
  80      FIXME-maybe, we might want a "set shell" command so the user can change
  81      the shell from within GDB (if so, change callers which pass in a non-NULL
  82      shell_file too).  */
  83   if (shell_file == NULL)
  84     shell_file = getenv ("SHELL");
  85   if (shell_file == NULL)
  86     shell_file = default_shell_file;
  87
  88   /* Multiplying the length of exec_file by 4 is to account for the fact
  89      that it may expand when quoted; it is a worst-case number based on
  90      every character being '.  */
  91   len = 5 + 4 * strlen (exec_file) + 1 + strlen (allargs) + 1 + /*slop*/ 12;
  92   /* If desired, concat something onto the front of ALLARGS.
  93      SHELL_COMMAND is the result.  */
  94 #ifdef SHELL_COMMAND_CONCAT
  95   shell_command = (char *) alloca (strlen (SHELL_COMMAND_CONCAT) + len);
  96   strcpy (shell_command, SHELL_COMMAND_CONCAT);
  97 #else
  98   shell_command = (char *) alloca (len);
  99   shell_command[0] = '\0';
 100 #endif
 101   strcat (shell_command, "exec ");
 102
 103   /* Now add exec_file, quoting as necessary.  */
 104   {
 105     char *p;
 106     int need_to_quote;
 107
 108     /* Quoting in this style is said to work with all shells.  But csh
 109        on IRIX 4.0.1 can't deal with it.  So we only quote it if we need
 110        to.  */
 111     p = exec_file;
 112     while (1)
 113       {
 114         switch (*p)
 115           {
 116           case '\'':
 117           case '"':
 118           case '(':
 119           case ')':
 120           case '$':
 121           case '&':
 122           case ';':
 123           case '<':
 124           case '>':
 125           case ' ':
 126           case '\n':
 127           case '\t':
 128             need_to_quote = 1;
 129             goto end_scan;
 130
 131           case '\0':
 132             need_to_quote = 0;
 133             goto end_scan;
 134
 135           default:
 136             break;
 137           }
 138         ++p;
 139       }
 140   end_scan:
 141     if (need_to_quote)
 142       {
 143         strcat (shell_command, "'");
 144         for (p = exec_file; *p != '\0'; ++p)
 145           {
 146             if (*p == '\'')
 147               strcat (shell_command, "'\\''");
 148             else
 149               strncat (shell_command, p, 1);
 150           }
 151         strcat (shell_command, "'");
 152       }
 153     else
 154       strcat (shell_command, exec_file);
 155   }
 156
 157   strcat (shell_command, " ");
 158   strcat (shell_command, allargs);
 159
 160   /* exec is said to fail if the executable is open.  */
 161   close_exec_file ();
 162
 163   /* Retain a copy of our environment variables, since the child will
 164      replace the value of  environ  and if we're vforked, we have to
 165      restore it.  */
 166   save_our_env = environ;
 167
 168   /* Tell the terminal handling subsystem what tty we plan to run on;
 169      it will just record the information for later.  */
 170
 171   new_tty_prefork (inferior_io_terminal);
 172
 173   /* It is generally good practice to flush any possible pending stdio
 174      output prior to doing a fork, to avoid the possibility of both the
 175      parent and child flushing the same data after the fork. */
 176
 177   gdb_flush (gdb_stdout);
 178   gdb_flush (gdb_stderr);
 179
 180 #if defined(USG) && !defined(HAVE_VFORK)
 181   pid = fork ();
 182 #else
 183   if (debug_fork)
 184     pid = fork ();
 185   else
 186     pid = vfork ();
 187 #endif
 188
 189   if (pid < 0)
 190     perror_with_name ("vfork");
 191
 192   if (pid == 0)
 193     {
 194       if (debug_fork)
 195         sleep (debug_fork);
 196
 197       /* Run inferior in a separate process group.  */
 198       debug_setpgrp = gdb_setpgid ();
 199       if (debug_setpgrp == -1)
 200          perror("setpgrp failed in child");
 201
 202 #ifdef SET_STACK_LIMIT_HUGE
 203       /* Reset the stack limit back to what it was.  */
 204       {
 205         struct rlimit rlim;
 206
 207         getrlimit (RLIMIT_STACK, &rlim);
 208         rlim.rlim_cur = original_stack_limit;
 209         setrlimit (RLIMIT_STACK, &rlim);
 210       }
 211 #endif /* SET_STACK_LIMIT_HUGE */
 212
 213       /* Ask the tty subsystem to switch to the one we specified earlier
 214          (or to share the current terminal, if none was specified).  */
 215
 216       new_tty ();
 217
 218       /* Changing the signal handlers for the inferior after
 219          a vfork can also change them for the superior, so we don't mess
 220          with signals here.  See comments in
 221          initialize_signals for how we get the right signal handlers
 222          for the inferior.  */
 223
 224       /* "Trace me, Dr. Memory!" */
 225       (*traceme_fun) ();
 226
 227       /* There is no execlpe call, so we have to set the environment
 228          for our child in the global variable.  If we've vforked, this
 229          clobbers the parent, but environ is restored a few lines down
 230          in the parent.  By the way, yes we do need to look down the
 231          path to find $SHELL.  Rich Pixley says so, and I agree.  */
 232       environ = env;
 233       execlp (shell_file, shell_file, "-c", shell_command, (char *)0);
 234
 235       fprintf_unfiltered (gdb_stderr, "Cannot exec %s: %s.\n", shell_file,
 236                safe_strerror (errno));
 237       gdb_flush (gdb_stderr);
 238       _exit (0177);
 239     }
 240
 241   /* Restore our environment in case a vforked child clob'd it.  */
 242   environ = save_our_env;
 243
 244   init_thread_list();
 245
 246   inferior_pid = pid;           /* Needed for wait_for_inferior stuff below */
 247
 248   /* Now that we have a child process, make it our target, and
 249      initialize anything target-vector-specific that needs initializing.  */
 250   (*init_trace_fun)(pid);
 251
 252   /* We are now in the child process of interest, having exec'd the
 253      correct program, and are poised at the first instruction of the
 254      new program.  */
 255 #ifdef SOLIB_CREATE_INFERIOR_HOOK
 256   SOLIB_CREATE_INFERIOR_HOOK (pid);
 257 #endif
 258 }
 259
 260 /* Accept NTRAPS traps from the inferior.  */
 261
 262 void
 263 startup_inferior (ntraps)
 264      int ntraps;
 265 {
 266   int pending_execs = ntraps;
 267   int terminal_initted;
 268
 269   /* The process was started by the fork that created it,
 270      but it will have stopped one instruction after execing the shell.
 271      Here we must get it up to actual execution of the real program.  */
 272
 273   clear_proceed_status ();
 274
 275   init_wait_for_inferior ();
 276
 277   terminal_initted = 0;
 278
 279   while (1)
 280     {
 281       stop_soon_quietly = 1;    /* Make wait_for_inferior be quiet */
 282       wait_for_inferior ();
 283       if (stop_signal != TARGET_SIGNAL_TRAP)
 284         {
 285           /* Let shell child handle its own signals in its own way */
 286           /* FIXME, what if child has exit()ed?  Must exit loop somehow */
 287           resume (0, stop_signal);
 288         }
 289       else
 290         {
 291           /* We handle SIGTRAP, however; it means child did an exec.  */
 292           if (!terminal_initted)
 293             {
 294               /* Now that the child has exec'd we know it has already set its
 295                  process group.  On POSIX systems, tcsetpgrp will fail with
 296                  EPERM if we try it before the child's setpgid.  */
 297
 298               /* Set up the "saved terminal modes" of the inferior
 299                  based on what modes we are starting it with.  */
 300               target_terminal_init ();
 301
 302               /* Install inferior's terminal modes.  */
 303               target_terminal_inferior ();
 304
 305               terminal_initted = 1;
 306             }
 307           if (0 == --pending_execs)
 308             break;
 309           resume (0, TARGET_SIGNAL_0);          /* Just make it go on */
 310         }
 311     }
 312   stop_soon_quietly = 0;
 313 }