1 /* Fork a Unix child process, and set up to debug it, for GDB and GDBserver.
3 Copyright (C) 1990-2018 Free Software Foundation, Inc.
5 This file is part of GDB.
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 3 of the License, or
10 (at your option) any later version.
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.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>. */
20 #include "common-defs.h"
21 #include "fork-inferior.h"
22 #include "target/waitstatus.h"
23 #include "filestuff.h"
24 #include "target/target.h"
25 #include "common-inferior.h"
26 #include "common-gdbthread.h"
27 #include "signals-state-save-restore.h"
28 #include "gdb_tilde_expand.h"
31 extern char **environ
;
33 /* Default shell file to be used if 'startup-with-shell' is set but
35 #define SHELL_FILE "/bin/sh"
37 /* Build the argument vector for execv(3). */
42 /* EXEC_FILE is the file to run. ALLARGS is a string containing the
43 arguments to the program. If starting with a shell, SHELL_FILE
44 is the shell to run. Otherwise, SHELL_FILE is NULL. */
45 execv_argv (const char *exec_file
, const std::string
&allargs
,
46 const char *shell_file
);
48 /* Return a pointer to the built argv, in the type expected by
49 execv. The result is (only) valid for as long as this execv_argv
50 object is live. We return a "char **" because that's the type
51 that the execv functions expect. Note that it is guaranteed that
52 the execv functions do not modify the argv[] array nor the
53 strings to which the array point. */
56 return const_cast<char **> (&m_argv
[0]);
60 DISABLE_COPY_AND_ASSIGN (execv_argv
);
62 /* Helper methods for constructing the argument vector. */
64 /* Used when building an argv for a straight execv call, without
65 going via the shell. */
66 void init_for_no_shell (const char *exec_file
,
67 const std::string
&allargs
);
69 /* Used when building an argv for execing a shell that execs the
71 void init_for_shell (const char *exec_file
,
72 const std::string
&allargs
,
73 const char *shell_file
);
75 /* The argument vector built. Holds non-owning pointers. Elements
76 either point to the strings passed to the execv_argv ctor, or
78 std::vector
<const char *> m_argv
;
80 /* Storage. In the no-shell case, this contains a copy of the
81 arguments passed to the ctor, split by '\0'. In the shell case,
82 this contains the quoted shell command. I.e., SHELL_COMMAND in
83 {"$SHELL" "-c", SHELL_COMMAND, NULL}. */
84 std::string m_storage
;
87 /* Create argument vector for straight call to execvp. Breaks up
88 ALLARGS into an argument vector suitable for passing to execvp and
89 stores it in M_ARGV. E.g., on "run a b c d" this routine would get
90 as input the string "a b c d", and as output it would fill in
91 M_ARGV with the four arguments "a", "b", "c", "d". Each argument
92 in M_ARGV points to a substring of a copy of ALLARGS stored in
96 execv_argv::init_for_no_shell (const char *exec_file
,
97 const std::string
&allargs
)
100 /* Save/work with a copy stored in our storage. The pointers pushed
101 to M_ARGV point directly into M_STORAGE, which is modified in
102 place with the necessary NULL terminators. This avoids N heap
103 allocations and string dups when 1 is sufficient. */
104 std::string
&args_copy
= m_storage
= allargs
;
106 m_argv
.push_back (exec_file
);
108 for (size_t cur_pos
= 0; cur_pos
< args_copy
.size ();)
110 /* Skip whitespace-like chars. */
111 std::size_t pos
= args_copy
.find_first_not_of (" \t\n", cur_pos
);
113 if (pos
!= std::string::npos
)
116 /* Find the position of the next separator. */
117 std::size_t next_sep
= args_copy
.find_first_of (" \t\n", cur_pos
);
119 if (next_sep
== std::string::npos
)
121 /* No separator found, which means this is the last
123 next_sep
= args_copy
.size ();
127 /* Replace the separator with a terminator. */
128 args_copy
[next_sep
++] = '\0';
131 m_argv
.push_back (&args_copy
[cur_pos
]);
136 /* NULL-terminate the vector. */
137 m_argv
.push_back (NULL
);
140 /* When executing a command under the given shell, return true if the
141 '!' character should be escaped when embedded in a quoted
142 command-line argument. */
145 escape_bang_in_quoted_argument (const char *shell_file
)
147 size_t shell_file_len
= strlen (shell_file
);
149 /* Bang should be escaped only in C Shells. For now, simply check
150 that the shell name ends with 'csh', which covers at least csh
151 and tcsh. This should be good enough for now. */
153 if (shell_file_len
< 3)
156 if (shell_file
[shell_file_len
- 3] == 'c'
157 && shell_file
[shell_file_len
- 2] == 's'
158 && shell_file
[shell_file_len
- 1] == 'h')
164 /* See declaration. */
166 execv_argv::execv_argv (const char *exec_file
,
167 const std::string
&allargs
,
168 const char *shell_file
)
170 if (shell_file
== NULL
)
171 init_for_no_shell (exec_file
, allargs
);
173 init_for_shell (exec_file
, allargs
, shell_file
);
176 /* See declaration. */
179 execv_argv::init_for_shell (const char *exec_file
,
180 const std::string
&allargs
,
181 const char *shell_file
)
183 const char *exec_wrapper
= get_exec_wrapper ();
185 /* We're going to call a shell. */
186 bool escape_bang
= escape_bang_in_quoted_argument (shell_file
);
188 /* We need to build a new shell command string, and make argv point
189 to it. So build it in the storage. */
190 std::string
&shell_command
= m_storage
;
192 shell_command
= "exec ";
194 /* Add any exec wrapper. That may be a program name with arguments,
195 so the user must handle quoting. */
196 if (exec_wrapper
!= NULL
)
198 shell_command
+= exec_wrapper
;
199 shell_command
+= ' ';
202 /* Now add exec_file, quoting as necessary. */
204 /* Quoting in this style is said to work with all shells. But csh
205 on IRIX 4.0.1 can't deal with it. So we only quote it if we need
208 const char *p
= exec_file
;
226 need_to_quote
= true;
230 need_to_quote
= false;
241 shell_command
+= '\'';
242 for (p
= exec_file
; *p
!= '\0'; ++p
)
245 shell_command
+= "'\\''";
246 else if (*p
== '!' && escape_bang
)
247 shell_command
+= "\\!";
251 shell_command
+= '\'';
254 shell_command
+= exec_file
;
256 shell_command
+= ' ' + allargs
;
258 /* If we decided above to start up with a shell, we exec the shell.
259 "-c" says to interpret the next arg as a shell command to
260 execute, and this command is "exec <target-program> <args>". */
262 m_argv
.push_back (shell_file
);
263 m_argv
.push_back ("-c");
264 m_argv
.push_back (shell_command
.c_str ());
265 m_argv
.push_back (NULL
);
268 /* Return the shell that must be used to startup the inferior. The
269 first attempt is the environment variable SHELL; if it is not set,
270 then we default to SHELL_FILE. */
275 const char *ret
= getenv ("SHELL");
282 /* See nat/fork-inferior.h. */
285 fork_inferior (const char *exec_file_arg
, const std::string
&allargs
,
286 char **env
, void (*traceme_fun
) (),
287 void (*init_trace_fun
) (int), void (*pre_trace_fun
) (),
288 const char *shell_file_arg
,
289 void (*exec_fun
)(const char *file
, char * const *argv
,
293 /* Set debug_fork then attach to the child while it sleeps, to debug. */
295 const char *shell_file
;
296 const char *exec_file
;
300 const char *inferior_cwd
;
301 std::string expanded_inferior_cwd
;
303 /* If no exec file handed to us, get it from the exec-file command
304 -- with a good, common error message if none is specified. */
305 if (exec_file_arg
== NULL
)
306 exec_file
= get_exec_file (1);
308 exec_file
= exec_file_arg
;
310 /* 'startup_with_shell' is declared in inferior.h and bound to the
311 "set startup-with-shell" option. If 0, we'll just do a
312 fork/exec, no shell, so don't bother figuring out what shell. */
313 if (startup_with_shell
)
315 shell_file
= shell_file_arg
;
317 /* Figure out what shell to start up the user program under. */
318 if (shell_file
== NULL
)
319 shell_file
= get_startup_shell ();
321 gdb_assert (shell_file
!= NULL
);
326 /* Build the argument vector. */
327 execv_argv
child_argv (exec_file
, allargs
, shell_file
);
329 /* Retain a copy of our environment variables, since the child will
330 replace the value of environ and if we're vforked, we have to
332 save_our_env
= environ
;
334 /* Perform any necessary actions regarding to TTY before the
336 prefork_hook (allargs
.c_str ());
338 /* It is generally good practice to flush any possible pending stdio
339 output prior to doing a fork, to avoid the possibility of both
340 the parent and child flushing the same data after the fork. */
341 gdb_flush_out_err ();
343 /* Check if the user wants to set a different working directory for
345 inferior_cwd
= get_inferior_cwd ();
347 if (inferior_cwd
!= NULL
)
349 /* Expand before forking because between fork and exec, the child
350 process may only execute async-signal-safe operations. */
351 expanded_inferior_cwd
= gdb_tilde_expand (inferior_cwd
);
352 inferior_cwd
= expanded_inferior_cwd
.c_str ();
355 /* If there's any initialization of the target layers that must
356 happen to prepare to handle the child we're about fork, do it
358 if (pre_trace_fun
!= NULL
)
361 /* Create the child process. Since the child process is going to
362 exec(3) shortly afterwards, try to reduce the overhead by
363 calling vfork(2). However, if PRE_TRACE_FUN is non-null, it's
364 likely that this optimization won't work since there's too much
365 work to do between the vfork(2) and the exec(3). This is known
366 to be the case on ttrace(2)-based HP-UX, where some handshaking
367 between parent and child needs to happen between fork(2) and
368 exec(2). However, since the parent is suspended in the vforked
369 state, this doesn't work. Also note that the vfork(2) call might
370 actually be a call to fork(2) due to the fact that autoconf will
371 ``#define vfork fork'' on certain platforms. */
372 #if !(defined(__UCLIBC__) && defined(HAS_NOMMU))
373 if (pre_trace_fun
|| debug_fork
)
380 perror_with_name (("vfork"));
384 /* Close all file descriptors except those that gdb inherited
385 (usually 0/1/2), so they don't leak to the inferior. Note
386 that this closes the file descriptors of all secondary
390 /* Change to the requested working directory if the user
392 if (inferior_cwd
!= NULL
)
394 if (chdir (inferior_cwd
) < 0)
395 trace_start_error_with_name (inferior_cwd
);
401 /* Execute any necessary post-fork actions before we exec. */
402 postfork_child_hook ();
404 /* Changing the signal handlers for the inferior after
405 a vfork can also change them for the superior, so we don't mess
406 with signals here. See comments in
407 initialize_signals for how we get the right signal handlers
410 /* "Trace me, Dr. Memory!" */
413 /* The call above set this process (the "child") as debuggable
414 by the original gdb process (the "parent"). Since processes
415 (unlike people) can have only one parent, if you are debugging
416 gdb itself (and your debugger is thus _already_ the
417 controller/parent for this child), code from here on out is
418 undebuggable. Indeed, you probably got an error message
419 saying "not parent". Sorry; you'll have to use print
422 restore_original_signals_state ();
424 /* There is no execlpe call, so we have to set the environment
425 for our child in the global variable. If we've vforked, this
426 clobbers the parent, but environ is restored a few lines down
427 in the parent. By the way, yes we do need to look down the
428 path to find $SHELL. Rich Pixley says so, and I agree. */
431 char **argv
= child_argv
.argv ();
433 if (exec_fun
!= NULL
)
434 (*exec_fun
) (argv
[0], &argv
[0], env
);
436 execvp (argv
[0], &argv
[0]);
438 /* If we get here, it's an error. */
440 warning ("Cannot exec %s", argv
[0]);
442 for (i
= 1; argv
[i
] != NULL
; i
++)
443 warning (" %s", argv
[i
]);
445 warning ("Error: %s\n", safe_strerror (save_errno
));
450 /* Restore our environment in case a vforked child clob'd it. */
451 environ
= save_our_env
;
455 /* Now that we have a child process, make it our target, and
456 initialize anything target-vector-specific that needs
459 (*init_trace_fun
) (pid
);
461 /* We are now in the child process of interest, having exec'd the
462 correct program, and are poised at the first instruction of the
467 /* See nat/fork-inferior.h. */
470 startup_inferior (pid_t pid
, int ntraps
,
471 struct target_waitstatus
*last_waitstatus
,
474 int pending_execs
= ntraps
;
475 int terminal_initted
= 0;
478 if (startup_with_shell
)
480 /* One trap extra for exec'ing the shell. */
484 if (target_supports_multi_process ())
485 resume_ptid
= ptid_t (pid
);
487 resume_ptid
= minus_one_ptid
;
489 /* The process was started by the fork that created it, but it will
490 have stopped one instruction after execing the shell. Here we
491 must get it up to actual execution of the real program. */
492 if (get_exec_wrapper () != NULL
)
497 enum gdb_signal resume_signal
= GDB_SIGNAL_0
;
500 struct target_waitstatus ws
;
501 memset (&ws
, 0, sizeof (ws
));
502 event_ptid
= target_wait (resume_ptid
, &ws
, 0);
504 if (last_waitstatus
!= NULL
)
505 *last_waitstatus
= ws
;
506 if (last_ptid
!= NULL
)
507 *last_ptid
= event_ptid
;
509 if (ws
.kind
== TARGET_WAITKIND_IGNORE
)
510 /* The inferior didn't really stop, keep waiting. */
515 case TARGET_WAITKIND_SPURIOUS
:
516 case TARGET_WAITKIND_LOADED
:
517 case TARGET_WAITKIND_FORKED
:
518 case TARGET_WAITKIND_VFORKED
:
519 case TARGET_WAITKIND_SYSCALL_ENTRY
:
520 case TARGET_WAITKIND_SYSCALL_RETURN
:
521 /* Ignore gracefully during startup of the inferior. */
522 switch_to_thread (event_ptid
);
525 case TARGET_WAITKIND_SIGNALLED
:
526 target_terminal::ours ();
527 target_mourn_inferior (event_ptid
);
528 error (_("During startup program terminated with signal %s, %s."),
529 gdb_signal_to_name (ws
.value
.sig
),
530 gdb_signal_to_string (ws
.value
.sig
));
533 case TARGET_WAITKIND_EXITED
:
534 target_terminal::ours ();
535 target_mourn_inferior (event_ptid
);
536 if (ws
.value
.integer
)
537 error (_("During startup program exited with code %d."),
540 error (_("During startup program exited normally."));
543 case TARGET_WAITKIND_EXECD
:
544 /* Handle EXEC signals as if they were SIGTRAP signals. */
545 xfree (ws
.value
.execd_pathname
);
546 resume_signal
= GDB_SIGNAL_TRAP
;
547 switch_to_thread (event_ptid
);
550 case TARGET_WAITKIND_STOPPED
:
551 resume_signal
= ws
.value
.sig
;
552 switch_to_thread (event_ptid
);
556 if (resume_signal
!= GDB_SIGNAL_TRAP
)
558 /* Let shell child handle its own signals in its own way. */
559 target_continue (resume_ptid
, resume_signal
);
563 /* We handle SIGTRAP, however; it means child did an exec. */
564 if (!terminal_initted
)
566 /* Now that the child has exec'd we know it has already
567 set its process group. On POSIX systems, tcsetpgrp
568 will fail with EPERM if we try it before the child's
571 /* Set up the "saved terminal modes" of the inferior
572 based on what modes we are starting it with. */
573 target_terminal::init ();
575 /* Install inferior's terminal modes. */
576 target_terminal::inferior ();
578 terminal_initted
= 1;
581 if (--pending_execs
== 0)
584 /* Just make it go on. */
585 target_continue_no_signal (resume_ptid
);
592 /* See nat/fork-inferior.h. */
595 trace_start_error (const char *fmt
, ...)
600 warning ("Could not trace the inferior process.\nError: ");
604 gdb_flush_out_err ();
608 /* See nat/fork-inferior.h. */
611 trace_start_error_with_name (const char *string
)
613 trace_start_error ("%s: %s", string
, safe_strerror (errno
));