1 /* Fork a Unix child process, and set up to debug it, for GDB.
3 Copyright (C) 1990-2016 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/>. */
27 #include "gdb_vfork.h"
29 #include "gdbthread.h"
30 #include "command.h" /* for dont_repeat () */
33 #include "filestuff.h"
35 #include "signals-state-save-restore.h"
38 /* This just gets used as a default if we can't find SHELL. */
39 #define SHELL_FILE "/bin/sh"
41 extern char **environ;
43 static char *exec_wrapper;
45 /* Break up SCRATCH into an argument vector suitable for passing to
46 execvp and store it in ARGV. E.g., on "run a b c d" this routine
47 would get as input the string "a b c d", and as output it would
48 fill in ARGV with the four arguments "a", "b", "c", "d". */
51 breakup_args (char *scratch, char **argv)
53 char *cp = scratch, *tmp;
57 /* Scan past leading separators */
58 while (*cp == ' ' || *cp == '\t' || *cp == '\n')
61 /* Break if at end of string. */
68 /* Scan for next arg separator. */
69 tmp = strchr (cp, ' ');
71 tmp = strchr (cp, '\t');
73 tmp = strchr (cp, '\n');
75 /* No separators => end of string => break. */
80 /* Replace the separator with a terminator. */
84 /* Null-terminate the vector. */
88 /* When executing a command under the given shell, return non-zero if
89 the '!' character should be escaped when embedded in a quoted
90 command-line argument. */
93 escape_bang_in_quoted_argument (const char *shell_file)
95 const int shell_file_len = strlen (shell_file);
97 /* Bang should be escaped only in C Shells. For now, simply check
98 that the shell name ends with 'csh', which covers at least csh
99 and tcsh. This should be good enough for now. */
101 if (shell_file_len < 3)
104 if (shell_file[shell_file_len - 3] == 'c'
105 && shell_file[shell_file_len - 2] == 's'
106 && shell_file[shell_file_len - 1] == 'h')
112 /* Start an inferior Unix child process and sets inferior_ptid to its
113 pid. EXEC_FILE is the file to run. ALLARGS is a string containing
114 the arguments to the program. ENV is the environment vector to
115 pass. SHELL_FILE is the shell file, or NULL if we should pick
116 one. EXEC_FUN is the exec(2) function to use, or NULL for the default
119 /* This function is NOT reentrant. Some of the variables have been
120 made static to ensure that they survive the vfork call. */
123 fork_inferior (char *exec_file_arg, char *allargs, char **env,
124 void (*traceme_fun) (void), void (*init_trace_fun) (int),
125 void (*pre_trace_fun) (void), char *shell_file_arg,
126 void (*exec_fun)(const char *file, char * const *argv,
130 static char default_shell_file[] = SHELL_FILE;
131 /* Set debug_fork then attach to the child while it sleeps, to debug. */
132 static int debug_fork = 0;
133 /* This is set to the result of setpgrp, which if vforked, will be visible
134 to you in the parent process. It's only used by humans for debugging. */
135 static int debug_setpgrp = 657473;
136 static char *shell_file;
137 static char *exec_file;
141 const char *inferior_io_terminal = get_inferior_io_terminal ();
142 struct inferior *inf;
147 /* If no exec file handed to us, get it from the exec-file command
148 -- with a good, common error message if none is specified. */
149 exec_file = exec_file_arg;
151 exec_file = get_exec_file (1);
153 /* 'startup_with_shell' is declared in inferior.h and bound to the
154 "set startup-with-shell" option. If 0, we'll just do a
155 fork/exec, no shell, so don't bother figuring out what shell. */
156 shell_file = shell_file_arg;
157 if (startup_with_shell)
159 /* Figure out what shell to start up the user program under. */
160 if (shell_file == NULL)
161 shell_file = getenv ("SHELL");
162 if (shell_file == NULL)
163 shell_file = default_shell_file;
169 /* We're going to call execvp. Create argument vector.
170 Calculate an upper bound on the length of the vector by
171 assuming that every other character is a separate
173 int argc = (strlen (allargs) + 1) / 2 + 2;
175 argv = XALLOCAVEC (char *, argc);
177 breakup_args (allargs, &argv[1]);
181 /* We're going to call a shell. */
186 const int escape_bang = escape_bang_in_quoted_argument (shell_file);
188 /* Multiplying the length of exec_file by 4 is to account for the
189 fact that it may expand when quoted; it is a worst-case number
190 based on every character being '. */
191 len = 5 + 4 * strlen (exec_file) + 1 + strlen (allargs) + 1 + /*slop */ 12;
193 len += strlen (exec_wrapper) + 1;
195 shell_command = (char *) alloca (len);
196 shell_command[0] = '\0';
198 strcat (shell_command, "exec ");
200 /* Add any exec wrapper. That may be a program name with arguments, so
201 the user must handle quoting. */
204 strcat (shell_command, exec_wrapper);
205 strcat (shell_command, " ");
208 /* Now add exec_file, quoting as necessary. */
210 /* Quoting in this style is said to work with all shells. But
211 csh on IRIX 4.0.1 can't deal with it. So we only quote it if
246 strcat (shell_command, "'");
247 for (p = exec_file; *p != '\0'; ++p)
250 strcat (shell_command, "'\\''");
251 else if (*p == '!' && escape_bang)
252 strcat (shell_command, "\\!");
254 strncat (shell_command, p, 1);
256 strcat (shell_command, "'");
259 strcat (shell_command, exec_file);
261 strcat (shell_command, " ");
262 strcat (shell_command, allargs);
264 /* If we decided above to start up with a shell, we exec the
265 shell, "-c" says to interpret the next arg as a shell command
266 to execute, and this command is "exec <target-program>
268 argv = (char **) alloca (4 * sizeof (char *));
269 argv[0] = shell_file;
271 argv[2] = shell_command;
272 argv[3] = (char *) 0;
275 /* Retain a copy of our environment variables, since the child will
276 replace the value of environ and if we're vforked, we have to
278 save_our_env = environ;
280 /* Likewise the current UI. */
281 save_ui = current_ui;
283 /* Tell the terminal handling subsystem what tty we plan to run on;
284 it will just record the information for later. */
285 new_tty_prefork (inferior_io_terminal);
287 /* It is generally good practice to flush any possible pending stdio
288 output prior to doing a fork, to avoid the possibility of both
289 the parent and child flushing the same data after the fork. */
290 gdb_flush (main_ui->m_gdb_stdout);
291 gdb_flush (main_ui->m_gdb_stderr);
293 /* If there's any initialization of the target layers that must
294 happen to prepare to handle the child we're about fork, do it
296 if (pre_trace_fun != NULL)
299 /* Create the child process. Since the child process is going to
300 exec(3) shortly afterwards, try to reduce the overhead by
301 calling vfork(2). However, if PRE_TRACE_FUN is non-null, it's
302 likely that this optimization won't work since there's too much
303 work to do between the vfork(2) and the exec(3). This is known
304 to be the case on ttrace(2)-based HP-UX, where some handshaking
305 between parent and child needs to happen between fork(2) and
306 exec(2). However, since the parent is suspended in the vforked
307 state, this doesn't work. Also note that the vfork(2) call might
308 actually be a call to fork(2) due to the fact that autoconf will
309 ``#define vfork fork'' on certain platforms. */
310 if (pre_trace_fun || debug_fork)
316 perror_with_name (("vfork"));
320 /* Switch to the main UI, so that gdb_std{in/out/err} in the
321 child are mapped to std{in/out/err}. This makes it possible
322 to use fprintf_unfiltered/warning/error/etc. in the child
324 current_ui = main_ui;
326 /* Close all file descriptors except those that gdb inherited
327 (usually 0/1/2), so they don't leak to the inferior. Note
328 that this closes the file descriptors of all secondary
335 /* Create a new session for the inferior process, if necessary.
336 It will also place the inferior in a separate process group. */
337 if (create_tty_session () <= 0)
339 /* No session was created, but we still want to run the inferior
340 in a separate process group. */
341 debug_setpgrp = gdb_setpgid ();
342 if (debug_setpgrp == -1)
343 perror (_("setpgrp failed in child"));
346 /* Ask the tty subsystem to switch to the one we specified
347 earlier (or to share the current terminal, if none was
351 /* Changing the signal handlers for the inferior after
352 a vfork can also change them for the superior, so we don't mess
353 with signals here. See comments in
354 initialize_signals for how we get the right signal handlers
357 /* "Trace me, Dr. Memory!" */
360 /* The call above set this process (the "child") as debuggable
361 by the original gdb process (the "parent"). Since processes
362 (unlike people) can have only one parent, if you are debugging
363 gdb itself (and your debugger is thus _already_ the
364 controller/parent for this child), code from here on out is
365 undebuggable. Indeed, you probably got an error message
366 saying "not parent". Sorry; you'll have to use print
369 restore_original_signals_state ();
371 /* There is no execlpe call, so we have to set the environment
372 for our child in the global variable. If we've vforked, this
373 clobbers the parent, but environ is restored a few lines down
374 in the parent. By the way, yes we do need to look down the
375 path to find $SHELL. Rich Pixley says so, and I agree. */
378 if (exec_fun != NULL)
379 (*exec_fun) (argv[0], argv, env);
381 execvp (argv[0], argv);
383 /* If we get here, it's an error. */
385 fprintf_unfiltered (gdb_stderr, "Cannot exec %s", argv[0]);
386 for (i = 1; argv[i] != NULL; i++)
387 fprintf_unfiltered (gdb_stderr, " %s", argv[i]);
388 fprintf_unfiltered (gdb_stderr, ".\n");
389 fprintf_unfiltered (gdb_stderr, "Error: %s\n",
390 safe_strerror (save_errno));
391 gdb_flush (gdb_stderr);
395 /* Restore our environment in case a vforked child clob'd it. */
396 environ = save_our_env;
398 /* Likewise the current UI. */
399 current_ui = save_ui;
401 if (!have_inferiors ())
404 inf = current_inferior ();
406 inferior_appeared (inf, pid);
408 /* Needed for wait_for_inferior stuff below. */
409 inferior_ptid = pid_to_ptid (pid);
413 /* We have something that executes now. We'll be running through
414 the shell at this point, but the pid shouldn't change. Targets
415 supporting MT should fill this task's ptid with more data as soon
417 add_thread_silent (inferior_ptid);
419 /* Now that we have a child process, make it our target, and
420 initialize anything target-vector-specific that needs
423 (*init_trace_fun) (pid);
425 /* We are now in the child process of interest, having exec'd the
426 correct program, and are poised at the first instruction of the
431 /* Accept NTRAPS traps from the inferior. */
434 startup_inferior (int ntraps)
436 int pending_execs = ntraps;
437 int terminal_initted = 0;
440 if (startup_with_shell)
442 /* One trap extra for exec'ing the shell. */
446 if (target_supports_multi_process ())
447 resume_ptid = pid_to_ptid (ptid_get_pid (inferior_ptid));
449 resume_ptid = minus_one_ptid;
451 /* The process was started by the fork that created it, but it will
452 have stopped one instruction after execing the shell. Here we
453 must get it up to actual execution of the real program. */
460 enum gdb_signal resume_signal = GDB_SIGNAL_0;
463 struct target_waitstatus ws;
464 memset (&ws, 0, sizeof (ws));
465 event_ptid = target_wait (resume_ptid, &ws, 0);
467 if (ws.kind == TARGET_WAITKIND_IGNORE)
468 /* The inferior didn't really stop, keep waiting. */
473 case TARGET_WAITKIND_SPURIOUS:
474 case TARGET_WAITKIND_LOADED:
475 case TARGET_WAITKIND_FORKED:
476 case TARGET_WAITKIND_VFORKED:
477 case TARGET_WAITKIND_SYSCALL_ENTRY:
478 case TARGET_WAITKIND_SYSCALL_RETURN:
479 /* Ignore gracefully during startup of the inferior. */
480 switch_to_thread (event_ptid);
483 case TARGET_WAITKIND_SIGNALLED:
484 target_terminal_ours ();
485 target_mourn_inferior ();
486 error (_("During startup program terminated with signal %s, %s."),
487 gdb_signal_to_name (ws.value.sig),
488 gdb_signal_to_string (ws.value.sig));
491 case TARGET_WAITKIND_EXITED:
492 target_terminal_ours ();
493 target_mourn_inferior ();
494 if (ws.value.integer)
495 error (_("During startup program exited with code %d."),
498 error (_("During startup program exited normally."));
501 case TARGET_WAITKIND_EXECD:
502 /* Handle EXEC signals as if they were SIGTRAP signals. */
503 xfree (ws.value.execd_pathname);
504 resume_signal = GDB_SIGNAL_TRAP;
505 switch_to_thread (event_ptid);
508 case TARGET_WAITKIND_STOPPED:
509 resume_signal = ws.value.sig;
510 switch_to_thread (event_ptid);
514 if (resume_signal != GDB_SIGNAL_TRAP)
516 /* Let shell child handle its own signals in its own way. */
517 target_resume (resume_ptid, 0, resume_signal);
521 /* We handle SIGTRAP, however; it means child did an exec. */
522 if (!terminal_initted)
524 /* Now that the child has exec'd we know it has already
525 set its process group. On POSIX systems, tcsetpgrp
526 will fail with EPERM if we try it before the child's
529 /* Set up the "saved terminal modes" of the inferior
530 based on what modes we are starting it with. */
531 target_terminal_init ();
533 /* Install inferior's terminal modes. */
534 target_terminal_inferior ();
536 terminal_initted = 1;
539 if (--pending_execs == 0)
542 /* Just make it go on. */
543 target_resume (resume_ptid, 0, GDB_SIGNAL_0);
547 /* Mark all threads non-executing. */
548 set_executing (resume_ptid, 0);
551 /* Implement the "unset exec-wrapper" command. */
554 unset_exec_wrapper_command (char *args, int from_tty)
556 xfree (exec_wrapper);
561 show_startup_with_shell (struct ui_file *file, int from_tty,
562 struct cmd_list_element *c, const char *value)
564 fprintf_filtered (file,
565 _("Use of shell to start subprocesses is %s.\n"),
569 /* Provide a prototype to silence -Wmissing-prototypes. */
570 extern initialize_file_ftype _initialize_fork_child;
573 _initialize_fork_child (void)
575 add_setshow_filename_cmd ("exec-wrapper", class_run, &exec_wrapper, _("\
576 Set a wrapper for running programs.\n\
577 The wrapper prepares the system and environment for the new program."),
579 Show the wrapper for running programs."), NULL,
581 &setlist, &showlist);
583 add_cmd ("exec-wrapper", class_run, unset_exec_wrapper_command,
584 _("Disable use of an execution wrapper."),
587 add_setshow_boolean_cmd ("startup-with-shell", class_support,
588 &startup_with_shell, _("\
589 Set use of shell to start subprocesses. The default is on."), _("\
590 Show use of shell to start subprocesses."), NULL,
592 show_startup_with_shell,
593 &setlist, &showlist);