gdb/fork-child.c - gdb

Global variables defined

Functions defined

Macros defined

Source code

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

  3.    Copyright (C) 1990-2015 Free Software Foundation, Inc.

  5.    Contributed by Cygnus Support.

  7.    This file is part of GDB.

  9.    This program is free software; you can redistribute it and/or modify
  10.    it under the terms of the GNU General Public License as published by
  11.    the Free Software Foundation; either version 3 of the License, or
  12.    (at your option) any later version.

  14.    This program is distributed in the hope that it will be useful,
  15.    but WITHOUT ANY WARRANTY; without even the implied warranty of
  16.    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17.    GNU General Public License for more details.

  19.    You should have received a copy of the GNU General Public License
  20.    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

  22. #include "defs.h"
  23. #include "inferior.h"
  24. #include "terminal.h"
  25. #include "target.h"
  26. #include "gdb_wait.h"
  27. #include "gdb_vfork.h"
  28. #include "gdbcore.h"
  29. #include "gdbthread.h"
  30. #include "command.h" /* for dont_repeat () */
  31. #include "gdbcmd.h"
  32. #include "solib.h"
  33. #include "filestuff.h"

  35. #include <signal.h>

  37. /* This just gets used as a default if we can't find SHELL.  */
  38. ‌#define SHELL_FILE "/bin/sh"

  40. extern char **environ;

  42. ‌static char *exec_wrapper;

  44. /* Break up SCRATCH into an argument vector suitable for passing to
  45.    execvp and store it in ARGV.  E.g., on "run a b c d" this routine
  46.    would get as input the string "a b c d", and as output it would
  47.    fill in ARGV with the four arguments "a", "b", "c", "d".  */

  49. static void
  50. ‌breakup_args (char *scratch, char **argv)
  51. {
  52.   char *cp = scratch, *tmp;

  54.   for (;;)
  55.     {
  56.       /* Scan past leading separators */
  57.       while (*cp == ' ' || *cp == '\t' || *cp == '\n')
  58.         cp++;

  60.       /* Break if at end of string.  */
  61.       if (*cp == '\0')
  62.         break;

  64.       /* Take an arg.  */
  65.       *argv++ = cp;

  67.       /* Scan for next arg separator.  */
  68.       tmp = strchr (cp, ' ');
  69.       if (tmp == NULL)
  70.         tmp = strchr (cp, '\t');
  71.       if (tmp == NULL)
  72.         tmp = strchr (cp, '\n');

  74.       /* No separators => end of string => break.  */
  75.       if (tmp == NULL)
  76.         break;
  77.       cp = tmp;

  79.       /* Replace the separator with a terminator.  */
  80.       *cp++ = '\0';
  81.     }

  83.   /* Null-terminate the vector.  */
  84.   *argv = NULL;
  85. }

  87. /* When executing a command under the given shell, return non-zero if
  88.    the '!' character should be escaped when embedded in a quoted
  89.    command-line argument.  */

  91. static int
  92. ‌escape_bang_in_quoted_argument (const char *shell_file)
  93. {
  94.   const int shell_file_len = strlen (shell_file);

  96.   /* Bang should be escaped only in C Shells.  For now, simply check
  97.      that the shell name ends with 'csh', which covers at least csh
  98.      and tcsh.  This should be good enough for now.  */

  100.   if (shell_file_len < 3)
  101.     return 0;

  103.   if (shell_file[shell_file_len - 3] == 'c'
  104.       && shell_file[shell_file_len - 2] == 's'
  105.       && shell_file[shell_file_len - 1] == 'h')
  106.     return 1;

  108.   return 0;
  109. }

  111. /* Start an inferior Unix child process and sets inferior_ptid to its
  112.    pid.  EXEC_FILE is the file to run.  ALLARGS is a string containing
  113.    the arguments to the program.  ENV is the environment vector to
  114.    pass.  SHELL_FILE is the shell file, or NULL if we should pick
  115.    one.  EXEC_FUN is the exec(2) function to use, or NULL for the default
  116.    one.  */

  118. /* This function is NOT reentrant.  Some of the variables have been
  119.    made static to ensure that they survive the vfork call.  */

  121. int
  122. ‌fork_inferior (char *exec_file_arg, char *allargs, char **env,
  123.                void (*traceme_fun) (void), void (*init_trace_fun) (int),
  124.                void (*pre_trace_fun) (void), char *shell_file_arg,
  125.                void (*exec_fun)(const char *file, char * const *argv,
  126.                                 char * const *env))
  127. {
  128.   int pid;
  129.   static char default_shell_file[] = SHELL_FILE;
  130.   /* Set debug_fork then attach to the child while it sleeps, to debug.  */
  131.   static int debug_fork = 0;
  132.   /* This is set to the result of setpgrp, which if vforked, will be visible
  133.      to you in the parent process.  It's only used by humans for debugging.  */
  134.   static int debug_setpgrp = 657473;
  135.   static char *shell_file;
  136.   static char *exec_file;
  137.   char **save_our_env;
  138.   int shell = 0;
  139.   static char **argv;
  140.   const char *inferior_io_terminal = get_inferior_io_terminal ();
  141.   struct inferior *inf;
  142.   int i;
  143.   int save_errno;

  145.   /* If no exec file handed to us, get it from the exec-file command
  146.      -- with a good, common error message if none is specified.  */
  147.   exec_file = exec_file_arg;
  148.   if (exec_file == 0)
  149.     exec_file = get_exec_file (1);

  151.   /* 'startup_with_shell' is declared in inferior.h and bound to the
  152.      "set startup-with-shell" option.  If 0, we'll just do a
  153.      fork/exec, no shell, so don't bother figuring out what shell.  */
  154.   shell_file = shell_file_arg;
  155.   if (startup_with_shell)
  156.     {
  157.       /* Figure out what shell to start up the user program under.  */
  158.       if (shell_file == NULL)
  159.         shell_file = getenv ("SHELL");
  160.       if (shell_file == NULL)
  161.         shell_file = default_shell_file;
  162.       shell = 1;
  163.     }

  165.   if (!shell)
  166.     {
  167.       /* We're going to call execvp.  Create argument vector.
  168.          Calculate an upper bound on the length of the vector by
  169.          assuming that every other character is a separate
  170.          argument.  */
  171.       int argc = (strlen (allargs) + 1) / 2 + 2;

  173.       argv = (char **) alloca (argc * sizeof (*argv));
  174.       argv[0] = exec_file;
  175.       breakup_args (allargs, &argv[1]);
  176.     }
  177.   else
  178.     {
  179.       /* We're going to call a shell.  */
  180.       char *shell_command;
  181.       int len;
  182.       char *p;
  183.       int need_to_quote;
  184.       const int escape_bang = escape_bang_in_quoted_argument (shell_file);

  186.       /* Multiplying the length of exec_file by 4 is to account for the
  187.          fact that it may expand when quoted; it is a worst-case number
  188.          based on every character being '.  */
  189.       len = 5 + 4 * strlen (exec_file) + 1 + strlen (allargs) + 1 + /*slop */ 12;
  190.       if (exec_wrapper)
  191.         len += strlen (exec_wrapper) + 1;

  193.       shell_command = (char *) alloca (len);
  194.       shell_command[0] = '\0';

  196.       strcat (shell_command, "exec ");

  198.       /* Add any exec wrapper.  That may be a program name with arguments, so
  199.          the user must handle quoting.  */
  200.       if (exec_wrapper)
  201.         {
  202.           strcat (shell_command, exec_wrapper);
  203.           strcat (shell_command, " ");
  204.         }

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

  208.       /* Quoting in this style is said to work with all shells.  But
  209.          csh on IRIX 4.0.1 can't deal with it.  So we only quote it if
  210.          we need to.  */
  211.       p = exec_file;
  212.       while (1)
  213.         {
  214.           switch (*p)
  215.             {
  216.             case '\'':
  217.             case '!':
  218.             case '"':
  219.             case '(':
  220.             case ')':
  221.             case '$':
  222.             case '&':
  223.             case ';':
  224.             case '<':
  225.             case '>':
  226.             case ' ':
  227.             case '\n':
  228.             case '\t':
  229.               need_to_quote = 1;
  230.               goto end_scan;

  232.             case '\0':
  233.               need_to_quote = 0;
  234.               goto end_scan;

  236.             default:
  237.               break;
  238.             }
  239.           ++p;
  240.         }
  241.     end_scan:
  242.       if (need_to_quote)
  243.         {
  244.           strcat (shell_command, "'");
  245.           for (p = exec_file; *p != '\0'; ++p)
  246.             {
  247.               if (*p == '\'')
  248.                 strcat (shell_command, "'\\''");
  249.               else if (*p == '!' && escape_bang)
  250.                 strcat (shell_command, "\\!");
  251.               else
  252.                 strncat (shell_command, p, 1);
  253.             }
  254.           strcat (shell_command, "'");
  255.         }
  256.       else
  257.         strcat (shell_command, exec_file);

  259.       strcat (shell_command, " ");
  260.       strcat (shell_command, allargs);

  262.       /* If we decided above to start up with a shell, we exec the
  263.          shell, "-c" says to interpret the next arg as a shell command
  264.          to execute, and this command is "exec <target-program>
  265.          <args>".  */
  266.       argv = (char **) alloca (4 * sizeof (char *));
  267.       argv[0] = shell_file;
  268.       argv[1] = "-c";
  269.       argv[2] = shell_command;
  270.       argv[3] = (char *) 0;
  271.     }

  273.   /* Retain a copy of our environment variables, since the child will
  274.      replace the value of environ and if we're vforked, we have to
  275.      restore it.  */
  276.   save_our_env = environ;

  278.   /* Tell the terminal handling subsystem what tty we plan to run on;
  279.      it will just record the information for later.  */
  280.   new_tty_prefork (inferior_io_terminal);

  282.   /* It is generally good practice to flush any possible pending stdio
  283.      output prior to doing a fork, to avoid the possibility of both
  284.      the parent and child flushing the same data after the fork.  */
  285.   gdb_flush (gdb_stdout);
  286.   gdb_flush (gdb_stderr);

  288.   /* If there's any initialization of the target layers that must
  289.      happen to prepare to handle the child we're about fork, do it
  290.      now...  */
  291.   if (pre_trace_fun != NULL)
  292.     (*pre_trace_fun) ();

  294.   /* Create the child process.  Since the child process is going to
  295.      exec(3) shortly afterwards, try to reduce the overhead by
  296.      calling vfork(2).  However, if PRE_TRACE_FUN is non-null, it's
  297.      likely that this optimization won't work since there's too much
  298.      work to do between the vfork(2) and the exec(3).  This is known
  299.      to be the case on ttrace(2)-based HP-UX, where some handshaking
  300.      between parent and child needs to happen between fork(2) and
  301.      exec(2).  However, since the parent is suspended in the vforked
  302.      state, this doesn't work.  Also note that the vfork(2) call might
  303.      actually be a call to fork(2) due to the fact that autoconf will
  304.      ``#define vfork fork'' on certain platforms.  */
  305.   if (pre_trace_fun || debug_fork)
  306.     pid = fork ();
  307.   else
  308.     pid = vfork ();

  310.   if (pid < 0)
  311.     perror_with_name (("vfork"));

  313.   if (pid == 0)
  314.     {
  315.       close_most_fds ();

  317.       if (debug_fork)
  318.         sleep (debug_fork);

  320.       /* Create a new session for the inferior process, if necessary.
  321.          It will also place the inferior in a separate process group.  */
  322.       if (create_tty_session () <= 0)
  323.         {
  324.           /* No session was created, but we still want to run the inferior
  325.              in a separate process group.  */
  326.           debug_setpgrp = gdb_setpgid ();
  327.           if (debug_setpgrp == -1)
  328.             perror (_("setpgrp failed in child"));
  329.         }

  331.       /* Ask the tty subsystem to switch to the one we specified
  332.          earlier (or to share the current terminal, if none was
  333.          specified).  */
  334.       new_tty ();

  336.       /* Changing the signal handlers for the inferior after
  337.          a vfork can also change them for the superior, so we don't mess
  338.          with signals here.  See comments in
  339.          initialize_signals for how we get the right signal handlers
  340.          for the inferior.  */

  342.       /* "Trace me, Dr. Memory!"  */
  343.       (*traceme_fun) ();

  345.       /* The call above set this process (the "child") as debuggable
  346.         by the original gdb process (the "parent").  Since processes
  347.         (unlike people) can have only one parent, if you are debugging
  348.         gdb itself (and your debugger is thus _already_ the
  349.         controller/parent for this child), code from here on out is
  350.         undebuggable.  Indeed, you probably got an error message
  351.         saying "not parent".  Sorry; you'll have to use print
  352.         statements!  */

  354.       /* There is no execlpe call, so we have to set the environment
  355.          for our child in the global variable.  If we've vforked, this
  356.          clobbers the parent, but environ is restored a few lines down
  357.          in the parent.  By the way, yes we do need to look down the
  358.          path to find $SHELL.  Rich Pixley says so, and I agree.  */
  359.       environ = env;

  361.       if (exec_fun != NULL)
  362.         (*exec_fun) (argv[0], argv, env);
  363.       else
  364.         execvp (argv[0], argv);

  366.       /* If we get here, it's an error.  */
  367.       save_errno = errno;
  368.       fprintf_unfiltered (gdb_stderr, "Cannot exec %s", exec_file);
  369.       for (i = 1; argv[i] != NULL; i++)
  370.         fprintf_unfiltered (gdb_stderr, " %s", argv[i]);
  371.       fprintf_unfiltered (gdb_stderr, ".\n");
  372.       fprintf_unfiltered (gdb_stderr, "Error: %s\n",
  373.                           safe_strerror (save_errno));
  374.       gdb_flush (gdb_stderr);
  375.       _exit (0177);
  376.     }

  378.   /* Restore our environment in case a vforked child clob'd it.  */
  379.   environ = save_our_env;

  381.   if (!have_inferiors ())
  382.     init_thread_list ();

  384.   inf = current_inferior ();

  386.   inferior_appeared (inf, pid);

  388.   /* Needed for wait_for_inferior stuff below.  */
  389.   inferior_ptid = pid_to_ptid (pid);

  391.   new_tty_postfork ();

  393.   /* We have something that executes now.  We'll be running through
  394.      the shell at this point, but the pid shouldn't change.  Targets
  395.      supporting MT should fill this task's ptid with more data as soon
  396.      as they can.  */
  397.   add_thread_silent (inferior_ptid);

  399.   /* Now that we have a child process, make it our target, and
  400.      initialize anything target-vector-specific that needs
  401.      initializing.  */
  402.   if (init_trace_fun)
  403.     (*init_trace_fun) (pid);

  405.   /* We are now in the child process of interest, having exec'd the
  406.      correct program, and are poised at the first instruction of the
  407.      new program.  */
  408.   return pid;
  409. }

  411. /* Accept NTRAPS traps from the inferior.  */

  413. void
  414. ‌startup_inferior (int ntraps)
  415. {
  416.   int pending_execs = ntraps;
  417.   int terminal_initted = 0;
  418.   ptid_t resume_ptid;

  420.   if (startup_with_shell)
  421.     {
  422.       /* One trap extra for exec'ing the shell.  */
  423.       pending_execs++;
  424.     }

  426.   if (target_supports_multi_process ())
  427.     resume_ptid = pid_to_ptid (ptid_get_pid (inferior_ptid));
  428.   else
  429.     resume_ptid = minus_one_ptid;

  431.   /* The process was started by the fork that created it, but it will
  432.      have stopped one instruction after execing the shell.  Here we
  433.      must get it up to actual execution of the real program.  */

  435.   if (exec_wrapper)
  436.     pending_execs++;

  438.   while (1)
  439.     {
  440.       enum gdb_signal resume_signal = GDB_SIGNAL_0;
  441.       ptid_t event_ptid;

  443.       struct target_waitstatus ws;
  444.       memset (&ws, 0, sizeof (ws));
  445.       event_ptid = target_wait (resume_ptid, &ws, 0);

  447.       if (ws.kind == TARGET_WAITKIND_IGNORE)
  448.         /* The inferior didn't really stop, keep waiting.  */
  449.         continue;

  451.       switch (ws.kind)
  452.         {
  453.           case TARGET_WAITKIND_SPURIOUS:
  454.           case TARGET_WAITKIND_LOADED:
  455.           case TARGET_WAITKIND_FORKED:
  456.           case TARGET_WAITKIND_VFORKED:
  457.           case TARGET_WAITKIND_SYSCALL_ENTRY:
  458.           case TARGET_WAITKIND_SYSCALL_RETURN:
  459.             /* Ignore gracefully during startup of the inferior.  */
  460.             switch_to_thread (event_ptid);
  461.             break;

  463.           case TARGET_WAITKIND_SIGNALLED:
  464.             target_terminal_ours ();
  465.             target_mourn_inferior ();
  466.             error (_("During startup program terminated with signal %s, %s."),
  467.                    gdb_signal_to_name (ws.value.sig),
  468.                    gdb_signal_to_string (ws.value.sig));
  469.             return;

  471.           case TARGET_WAITKIND_EXITED:
  472.             target_terminal_ours ();
  473.             target_mourn_inferior ();
  474.             if (ws.value.integer)
  475.               error (_("During startup program exited with code %d."),
  476.                      ws.value.integer);
  477.             else
  478.               error (_("During startup program exited normally."));
  479.             return;

  481.           case TARGET_WAITKIND_EXECD:
  482.             /* Handle EXEC signals as if they were SIGTRAP signals.  */
  483.             xfree (ws.value.execd_pathname);
  484.             resume_signal = GDB_SIGNAL_TRAP;
  485.             switch_to_thread (event_ptid);
  486.             break;

  488.           case TARGET_WAITKIND_STOPPED:
  489.             resume_signal = ws.value.sig;
  490.             switch_to_thread (event_ptid);
  491.             break;
  492.         }

  494.       if (resume_signal != GDB_SIGNAL_TRAP)
  495.         {
  496.           /* Let shell child handle its own signals in its own way.  */
  497.           target_resume (resume_ptid, 0, resume_signal);
  498.         }
  499.       else
  500.         {
  501.           /* We handle SIGTRAP, however; it means child did an exec.  */
  502.           if (!terminal_initted)
  503.             {
  504.               /* Now that the child has exec'd we know it has already
  505.                  set its process group.  On POSIX systems, tcsetpgrp
  506.                  will fail with EPERM if we try it before the child's
  507.                  setpgid.  */

  509.               /* Set up the "saved terminal modes" of the inferior
  510.                  based on what modes we are starting it with.  */
  511.               target_terminal_init ();

  513.               /* Install inferior's terminal modes.  */
  514.               target_terminal_inferior ();

  516.               terminal_initted = 1;
  517.             }

  519.           if (--pending_execs == 0)
  520.             break;

  522.           /* Just make it go on.  */
  523.           target_resume (resume_ptid, 0, GDB_SIGNAL_0);
  524.         }
  525.     }

  527.   /* Mark all threads non-executing.  */
  528.   set_executing (resume_ptid, 0);
  529. }

  531. /* Implement the "unset exec-wrapper" command.  */

  533. static void
  534. ‌unset_exec_wrapper_command (char *args, int from_tty)
  535. {
  536.   xfree (exec_wrapper);
  537.   exec_wrapper = NULL;
  538. }

  540. static void
  541. ‌show_startup_with_shell (struct ui_file *file, int from_tty,
  542.                          struct cmd_list_element *c, const char *value)
  543. {
  544.   fprintf_filtered (file,
  545.                     _("Use of shell to start subprocesses is %s.\n"),
  546.                     value);
  547. }

  549. /* Provide a prototype to silence -Wmissing-prototypes.  */
  550. extern initialize_file_ftype _initialize_fork_child;

  552. void
  553. ‌_initialize_fork_child (void)
  554. {
  555.   add_setshow_filename_cmd ("exec-wrapper", class_run, &exec_wrapper, _("\
  556. Set a wrapper for running programs.\n\
  557. The wrapper prepares the system and environment for the new program."),
  558.                             _("\
  559. Show the wrapper for running programs."), NULL,
  560.                             NULL, NULL,
  561.                             &setlist, &showlist);

  563.   add_cmd ("exec-wrapper", class_run, unset_exec_wrapper_command,
  564.            _("Disable use of an execution wrapper."),
  565.            &unsetlist);

  567.   add_setshow_boolean_cmd ("startup-with-shell", class_support,
  568.                            &startup_with_shell, _("\
  569. Set use of shell to start subprocesses.  The default is on."), _("\
  570. Show use of shell to start subprocesses."), NULL,
  571.                            NULL,
  572.                            show_startup_with_shell,
  573.                            &setlist, &showlist);
  574. }