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/* Fork a Unix child process, and set up to debug it, for GDB.

   Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000,

   2001, 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc.

   Contributed by Cygnus Support.

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify

   it under the terms of the GNU General Public License as published by

   the Free Software Foundation; either version 3 of the License, or

   (at your option) any later version.

   This program is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License

   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include "defs.h"

#include "gdb_string.h"

#include "frame.h"              /* required by inferior.h */

#include "inferior.h"

#include "target.h"

#include "gdb_wait.h"

#include "gdb_vfork.h"

#include "gdbcore.h"

#include "terminal.h"

#include "gdbthread.h"

#include "command.h" /* for dont_repeat () */

#include "solib.h"

#include <signal.h>

/* This just gets used as a default if we can't find SHELL.  */

#define SHELL_FILE "/bin/sh"

extern char **environ;

/* Break up SCRATCH into an argument vector suitable for passing to

   execvp and store it in ARGV.  E.g., on "run a b c d" this routine

   would get as input the string "a b c d", and as output it would

   fill in ARGV with the four arguments "a", "b", "c", "d".  */

static void

breakup_args (char *scratch, char **argv)

{

  char *cp = scratch;

  for (;;)

    {

      /* Scan past leading separators */

      while (*cp == ' ' || *cp == '\t' || *cp == '\n')

        cp++;

      /* Break if at end of string.  */

      if (*cp == '\0')

        break;

      /* Take an arg.  */

      *argv++ = cp;

      /* Scan for next arg separator.  */

      cp = strchr (cp, ' ');

      if (cp == NULL)

        cp = strchr (cp, '\t');

      if (cp == NULL)

        cp = strchr (cp, '\n');

      /* No separators => end of string => break.  */

      if (cp == NULL)

        break;

      /* Replace the separator with a terminator.  */

      *cp++ = '\0';

    }

  /* Null-terminate the vector.  */

  *argv = NULL;

}

/* When executing a command under the given shell, return non-zero if

   the '!' character should be escaped when embedded in a quoted

   command-line argument.  */

static int

escape_bang_in_quoted_argument (const char *shell_file)

{

  const int shell_file_len = strlen (shell_file);

  /* Bang should be escaped only in C Shells.  For now, simply check

     that the shell name ends with 'csh', which covers at least csh

     and tcsh.  This should be good enough for now.  */

  if (shell_file_len < 3)

    return 0;

  if (shell_file[shell_file_len - 3] == 'c'

      && shell_file[shell_file_len - 2] == 's'

      && shell_file[shell_file_len - 1] == 'h')

    return 1;

  return 0;

}

/* Start an inferior Unix child process and sets inferior_ptid to its

   pid.  EXEC_FILE is the file to run.  ALLARGS is a string containing

   the arguments to the program.  ENV is the environment vector to

   pass.  SHELL_FILE is the shell file, or NULL if we should pick

   one.  */

/* This function is NOT reentrant.  Some of the variables have been

   made static to ensure that they survive the vfork call.  */

void

fork_inferior (char *exec_file_arg, char *allargs, char **env,

               void (*traceme_fun) (void), void (*init_trace_fun) (int),

               void (*pre_trace_fun) (void), char *shell_file_arg)

{

  int pid;

  char *shell_command;

  static char default_shell_file[] = SHELL_FILE;

  int len;

  /* Set debug_fork then attach to the child while it sleeps, to debug. */

  static int debug_fork = 0;

  /* This is set to the result of setpgrp, which if vforked, will be visible

     to you in the parent process.  It's only used by humans for debugging.  */

  static int debug_setpgrp = 657473;

  static char *shell_file;

  static char *exec_file;

  char **save_our_env;

  int shell = 0;

  static char **argv;

  const char *inferior_io_terminal = get_inferior_io_terminal ();

  /* If no exec file handed to us, get it from the exec-file command

     -- with a good, common error message if none is specified.  */

  exec_file = exec_file_arg;

  if (exec_file == 0)

    exec_file = get_exec_file (1);

  /* STARTUP_WITH_SHELL is defined in inferior.h.  If 0,e we'll just

    do a fork/exec, no shell, so don't bother figuring out what

    shell.  */

  shell_file = shell_file_arg;

  if (STARTUP_WITH_SHELL)

    {

      /* Figure out what shell to start up the user program under.  */

      if (shell_file == NULL)

        shell_file = getenv ("SHELL");

      if (shell_file == NULL)

        shell_file = default_shell_file;

      shell = 1;

    }

  /* Multiplying the length of exec_file by 4 is to account for the

     fact that it may expand when quoted; it is a worst-case number

     based on every character being '.  */

  len = 5 + 4 * strlen (exec_file) + 1 + strlen (allargs) + 1 + /*slop */ 12;

  shell_command = (char *) alloca (len);

  shell_command[0] = '\0';

  if (!shell)

    {

      /* We're going to call execvp.  Create argument vector.

         Calculate an upper bound on the length of the vector by

         assuming that every other character is a separate

         argument.  */

      int argc = (strlen (allargs) + 1) / 2 + 2;

      argv = (char **) xmalloc (argc * sizeof (*argv));

      argv[0] = exec_file;

      breakup_args (allargs, &argv[1]);

    }

  else

    {

      /* We're going to call a shell.  */

      /* Now add exec_file, quoting as necessary.  */

      char *p;

      int need_to_quote;

      const int escape_bang = escape_bang_in_quoted_argument (shell_file);

      strcat (shell_command, "exec ");

      /* Quoting in this style is said to work with all shells.  But

         csh on IRIX 4.0.1 can't deal with it.  So we only quote it if

         we need to.  */

      p = exec_file;

      while (1)

        {

          switch (*p)

            {

            case '\'':

            case '!':

            case '"':

            case '(':

            case ')':

            case '$':

            case '&':

            case ';':

            case '<':

            case '>':

            case ' ':

            case '\n':

            case '\t':

              need_to_quote = 1;

              goto end_scan;

            case '\0':

              need_to_quote = 0;

              goto end_scan;

            default:

              break;

            }

          ++p;

        }

    end_scan:

      if (need_to_quote)

        {

          strcat (shell_command, "'");

          for (p = exec_file; *p != '\0'; ++p)

            {

              if (*p == '\'')

                strcat (shell_command, "'\\''");

              else if (*p == '!' && escape_bang)

                strcat (shell_command, "\\!");

              else

                strncat (shell_command, p, 1);

            }

          strcat (shell_command, "'");

        }

      else

        strcat (shell_command, exec_file);

      strcat (shell_command, " ");

      strcat (shell_command, allargs);

    }

  /* On some systems an exec will fail if the executable is open.  */

  close_exec_file ();

  /* Retain a copy of our environment variables, since the child will

     replace the value of environ and if we're vforked, we have to

     restore it.  */

  save_our_env = environ;

  /* Tell the terminal handling subsystem what tty we plan to run on;

     it will just record the information for later.  */

  new_tty_prefork (inferior_io_terminal);

  /* It is generally good practice to flush any possible pending stdio

     output prior to doing a fork, to avoid the possibility of both

     the parent and child flushing the same data after the fork. */

  gdb_flush (gdb_stdout);

  gdb_flush (gdb_stderr);

  /* If there's any initialization of the target layers that must

     happen to prepare to handle the child we're about fork, do it

     now...  */

  if (pre_trace_fun != NULL)

    (*pre_trace_fun) ();

  /* Create the child process.  Since the child process is going to

     exec(3) shortly afterwards, try to reduce the overhead by

     calling vfork(2).  However, if PRE_TRACE_FUN is non-null, it's

     likely that this optimization won't work since there's too much

     work to do between the vfork(2) and the exec(3).  This is known

     to be the case on ttrace(2)-based HP-UX, where some handshaking

     between parent and child needs to happen between fork(2) and

     exec(2).  However, since the parent is suspended in the vforked

     state, this doesn't work.  Also note that the vfork(2) call might

     actually be a call to fork(2) due to the fact that autoconf will

     ``#define vfork fork'' on certain platforms.  */

  if (pre_trace_fun || debug_fork)

    pid = fork ();

  else

    pid = vfork ();

  if (pid < 0)

    perror_with_name (("vfork"));

  if (pid == 0)

    {

      if (debug_fork)

        sleep (debug_fork);

      /* Run inferior in a separate process group.  */

      debug_setpgrp = gdb_setpgid ();

      if (debug_setpgrp == -1)

        perror ("setpgrp failed in child");

      /* Ask the tty subsystem to switch to the one we specified

         earlier (or to share the current terminal, if none was

         specified).  */

      new_tty ();

      /* Changing the signal handlers for the inferior after

         a vfork can also change them for the superior, so we don't mess

         with signals here.  See comments in

         initialize_signals for how we get the right signal handlers

         for the inferior.  */

      /* "Trace me, Dr. Memory!" */

      (*traceme_fun) ();

      /* The call above set this process (the "child") as debuggable

        by the original gdb process (the "parent").  Since processes

        (unlike people) can have only one parent, if you are debugging

        gdb itself (and your debugger is thus _already_ the

        controller/parent for this child), code from here on out is

        undebuggable.  Indeed, you probably got an error message

        saying "not parent".  Sorry; you'll have to use print

        statements!  */

      /* There is no execlpe call, so we have to set the environment

         for our child in the global variable.  If we've vforked, this

         clobbers the parent, but environ is restored a few lines down

         in the parent.  By the way, yes we do need to look down the

         path to find $SHELL.  Rich Pixley says so, and I agree.  */

      environ = env;

      /* If we decided above to start up with a shell, we exec the

         shell, "-c" says to interpret the next arg as a shell command

         to execute, and this command is "exec <target-program>

         <args>".  */

      if (shell)

        {

          execlp (shell_file, shell_file, "-c", shell_command, (char *) 0);

          /* If we get here, it's an error.  */

          fprintf_unfiltered (gdb_stderr, "Cannot exec %s: %s.\n", shell_file,

                              safe_strerror (errno));

          gdb_flush (gdb_stderr);

          _exit (0177);

        }

      else

        {

          /* Otherwise, we directly exec the target program with

             execvp.  */

          int i;

          char *errstring;

          execvp (exec_file, argv);

          /* If we get here, it's an error.  */

          errstring = safe_strerror (errno);

          fprintf_unfiltered (gdb_stderr, "Cannot exec %s ", exec_file);

          i = 1;

          while (argv[i] != NULL)

            {

              if (i != 1)

                fprintf_unfiltered (gdb_stderr, " ");

              fprintf_unfiltered (gdb_stderr, "%s", argv[i]);

              i++;

            }

          fprintf_unfiltered (gdb_stderr, ".\n");

#if 0

          /* This extra info seems to be useless.  */

          fprintf_unfiltered (gdb_stderr, "Got error %s.\n", errstring);

#endif

          gdb_flush (gdb_stderr);

          _exit (0177);

        }

    }

  /* Restore our environment in case a vforked child clob'd it.  */

  environ = save_our_env;

  init_thread_list ();

  /* Needed for wait_for_inferior stuff below.  */

  inferior_ptid = pid_to_ptid (pid);

  /* Now that we have a child process, make it our target, and

     initialize anything target-vector-specific that needs

     initializing.  */

  (*init_trace_fun) (pid);

  /* We are now in the child process of interest, having exec'd the

     correct program, and are poised at the first instruction of the

     new program.  */

}

/* Accept NTRAPS traps from the inferior.  */

void

startup_inferior (int ntraps)

{

  int pending_execs = ntraps;

  int terminal_initted = 0;

  /* The process was started by the fork that created it, but it will

     have stopped one instruction after execing the shell.  Here we

     must get it up to actual execution of the real program.  */

  clear_proceed_status ();

  init_wait_for_inferior ();

  inferior_ignoring_leading_exec_events =

    target_reported_exec_events_per_exec_call () - 1;

  while (1)

    {

      /* Make wait_for_inferior be quiet. */

      stop_soon = STOP_QUIETLY;

      wait_for_inferior (1);

      if (stop_signal != TARGET_SIGNAL_TRAP)

        {

          /* Let shell child handle its own signals in its own way.

             FIXME: what if child has exited?  Must exit loop

             somehow.  */

          resume (0, stop_signal);

        }

      else

        {

          /* We handle SIGTRAP, however; it means child did an exec.  */

          if (!terminal_initted)

            {

              /* Now that the child has exec'd we know it has already

                 set its process group.  On POSIX systems, tcsetpgrp

                 will fail with EPERM if we try it before the child's

                 setpgid.  */

              /* Set up the "saved terminal modes" of the inferior

                 based on what modes we are starting it with.  */

              target_terminal_init ();

              /* Install inferior's terminal modes.  */

              target_terminal_inferior ();

              terminal_initted = 1;

            }

          if (--pending_execs == 0)

            break;

          resume (0, TARGET_SIGNAL_0);   /* Just make it go on.  */

        }

    }

  stop_soon = NO_STOP_QUIETLY;

}