1 /* Fork a Unix child process, and set up to debug it, for GDB and GDBserver.
3 Copyright (C) 1990-2017 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"
30 extern char **environ
;
32 /* Default shell file to be used if 'startup-with-shell' is set but
34 #define SHELL_FILE "/bin/sh"
36 /* Build the argument vector for execv(3). */
41 /* EXEC_FILE is the file to run. ALLARGS is a string containing the
42 arguments to the program. If starting with a shell, SHELL_FILE
43 is the shell to run. Otherwise, SHELL_FILE is NULL. */
44 execv_argv (const char *exec_file
, const std::string
&allargs
,
45 const char *shell_file
);
47 /* Return a pointer to the built argv, in the type expected by
48 execv. The result is (only) valid for as long as this execv_argv
49 object is live. We return a "char **" because that's the type
50 that the execv functions expect. Note that it is guaranteed that
51 the execv functions do not modify the argv[] array nor the
52 strings to which the array point. */
55 return const_cast<char **> (&m_argv
[0]);
59 DISABLE_COPY_AND_ASSIGN (execv_argv
);
61 /* Helper methods for constructing the argument vector. */
63 /* Used when building an argv for a straight execv call, without
64 going via the shell. */
65 void init_for_no_shell (const char *exec_file
,
66 const std::string
&allargs
);
68 /* Used when building an argv for execing a shell that execs the
70 void init_for_shell (const char *exec_file
,
71 const std::string
&allargs
,
72 const char *shell_file
);
74 /* The argument vector built. Holds non-owning pointers. Elements
75 either point to the strings passed to the execv_argv ctor, or
77 std::vector
<const char *> m_argv
;
79 /* Storage. In the no-shell case, this contains a copy of the
80 arguments passed to the ctor, split by '\0'. In the shell case,
81 this contains the quoted shell command. I.e., SHELL_COMMAND in
82 {"$SHELL" "-c", SHELL_COMMAND, NULL}. */
83 std::string m_storage
;
86 /* Create argument vector for straight call to execvp. Breaks up
87 ALLARGS into an argument vector suitable for passing to execvp and
88 stores it in M_ARGV. E.g., on "run a b c d" this routine would get
89 as input the string "a b c d", and as output it would fill in
90 M_ARGV with the four arguments "a", "b", "c", "d". Each argument
91 in M_ARGV points to a substring of a copy of ALLARGS stored in
95 execv_argv::init_for_no_shell (const char *exec_file
,
96 const std::string
&allargs
)
99 /* Save/work with a copy stored in our storage. The pointers pushed
100 to M_ARGV point directly into M_STORAGE, which is modified in
101 place with the necessary NULL terminators. This avoids N heap
102 allocations and string dups when 1 is sufficient. */
103 std::string
&args_copy
= m_storage
= allargs
;
105 m_argv
.push_back (exec_file
);
107 for (size_t cur_pos
= 0; cur_pos
< args_copy
.size ();)
109 /* Skip whitespace-like chars. */
110 std::size_t pos
= args_copy
.find_first_not_of (" \t\n", cur_pos
);
112 if (pos
!= std::string::npos
)
115 /* Find the position of the next separator. */
116 std::size_t next_sep
= args_copy
.find_first_of (" \t\n", cur_pos
);
118 if (next_sep
== std::string::npos
)
120 /* No separator found, which means this is the last
122 next_sep
= args_copy
.size ();
126 /* Replace the separator with a terminator. */
127 args_copy
[next_sep
++] = '\0';
130 m_argv
.push_back (&args_copy
[cur_pos
]);
135 /* NULL-terminate the vector. */
136 m_argv
.push_back (NULL
);
139 /* When executing a command under the given shell, return true if the
140 '!' character should be escaped when embedded in a quoted
141 command-line argument. */
144 escape_bang_in_quoted_argument (const char *shell_file
)
146 size_t shell_file_len
= strlen (shell_file
);
148 /* Bang should be escaped only in C Shells. For now, simply check
149 that the shell name ends with 'csh', which covers at least csh
150 and tcsh. This should be good enough for now. */
152 if (shell_file_len
< 3)
155 if (shell_file
[shell_file_len
- 3] == 'c'
156 && shell_file
[shell_file_len
- 2] == 's'
157 && shell_file
[shell_file_len
- 1] == 'h')
163 /* See declaration. */
165 execv_argv::execv_argv (const char *exec_file
,
166 const std::string
&allargs
,
167 const char *shell_file
)
169 if (shell_file
== NULL
)
170 init_for_no_shell (exec_file
, allargs
);
172 init_for_shell (exec_file
, allargs
, shell_file
);
175 /* See declaration. */
178 execv_argv::init_for_shell (const char *exec_file
,
179 const std::string
&allargs
,
180 const char *shell_file
)
182 const char *exec_wrapper
= get_exec_wrapper ();
184 /* We're going to call a shell. */
185 bool escape_bang
= escape_bang_in_quoted_argument (shell_file
);
187 /* We need to build a new shell command string, and make argv point
188 to it. So build it in the storage. */
189 std::string
&shell_command
= m_storage
;
191 shell_command
= "exec ";
193 /* Add any exec wrapper. That may be a program name with arguments,
194 so the user must handle quoting. */
195 if (exec_wrapper
!= NULL
)
197 shell_command
+= exec_wrapper
;
198 shell_command
+= ' ';
201 /* Now add exec_file, quoting as necessary. */
203 /* Quoting in this style is said to work with all shells. But csh
204 on IRIX 4.0.1 can't deal with it. So we only quote it if we need
207 const char *p
= exec_file
;
225 need_to_quote
= true;
229 need_to_quote
= false;
240 shell_command
+= '\'';
241 for (p
= exec_file
; *p
!= '\0'; ++p
)
244 shell_command
+= "'\\''";
245 else if (*p
== '!' && escape_bang
)
246 shell_command
+= "\\!";
250 shell_command
+= '\'';
253 shell_command
+= exec_file
;
255 shell_command
+= ' ' + allargs
;
257 /* If we decided above to start up with a shell, we exec the shell.
258 "-c" says to interpret the next arg as a shell command to
259 execute, and this command is "exec <target-program> <args>". */
261 m_argv
.push_back (shell_file
);
262 m_argv
.push_back ("-c");
263 m_argv
.push_back (shell_command
.c_str ());
264 m_argv
.push_back (NULL
);
267 /* Return the shell that must be used to startup the inferior. The
268 first attempt is the environment variable SHELL; if it is not set,
269 then we default to SHELL_FILE. */
274 static const char *ret
;
276 ret
= getenv ("SHELL");
283 /* See nat/fork-inferior.h. */
286 fork_inferior (const char *exec_file_arg
, const std::string
&allargs
,
287 char **env
, void (*traceme_fun
) (),
288 void (*init_trace_fun
) (int), void (*pre_trace_fun
) (),
289 const char *shell_file_arg
,
290 void (*exec_fun
)(const char *file
, char * const *argv
,
294 /* Set debug_fork then attach to the child while it sleeps, to debug. */
296 const char *shell_file
;
297 const char *exec_file
;
302 /* If no exec file handed to us, get it from the exec-file command
303 -- with a good, common error message if none is specified. */
304 if (exec_file_arg
== NULL
)
305 exec_file
= get_exec_file (1);
307 exec_file
= exec_file_arg
;
309 /* 'startup_with_shell' is declared in inferior.h and bound to the
310 "set startup-with-shell" option. If 0, we'll just do a
311 fork/exec, no shell, so don't bother figuring out what shell. */
312 if (startup_with_shell
)
314 shell_file
= shell_file_arg
;
316 /* Figure out what shell to start up the user program under. */
317 if (shell_file
== NULL
)
318 shell_file
= get_startup_shell ();
320 gdb_assert (shell_file
!= NULL
);
325 /* Build the argument vector. */
326 execv_argv
child_argv (exec_file
, allargs
, shell_file
);
328 /* Retain a copy of our environment variables, since the child will
329 replace the value of environ and if we're vforked, we have to
331 save_our_env
= environ
;
333 /* Perform any necessary actions regarding to TTY before the
335 prefork_hook (allargs
.c_str ());
337 /* It is generally good practice to flush any possible pending stdio
338 output prior to doing a fork, to avoid the possibility of both
339 the parent and child flushing the same data after the fork. */
340 gdb_flush_out_err ();
342 /* If there's any initialization of the target layers that must
343 happen to prepare to handle the child we're about fork, do it
345 if (pre_trace_fun
!= NULL
)
348 /* Create the child process. Since the child process is going to
349 exec(3) shortly afterwards, try to reduce the overhead by
350 calling vfork(2). However, if PRE_TRACE_FUN is non-null, it's
351 likely that this optimization won't work since there's too much
352 work to do between the vfork(2) and the exec(3). This is known
353 to be the case on ttrace(2)-based HP-UX, where some handshaking
354 between parent and child needs to happen between fork(2) and
355 exec(2). However, since the parent is suspended in the vforked
356 state, this doesn't work. Also note that the vfork(2) call might
357 actually be a call to fork(2) due to the fact that autoconf will
358 ``#define vfork fork'' on certain platforms. */
359 #if !(defined(__UCLIBC__) && defined(HAS_NOMMU))
360 if (pre_trace_fun
|| debug_fork
)
367 perror_with_name (("vfork"));
371 /* Close all file descriptors except those that gdb inherited
372 (usually 0/1/2), so they don't leak to the inferior. Note
373 that this closes the file descriptors of all secondary
380 /* Execute any necessary post-fork actions before we exec. */
381 postfork_child_hook ();
383 /* Changing the signal handlers for the inferior after
384 a vfork can also change them for the superior, so we don't mess
385 with signals here. See comments in
386 initialize_signals for how we get the right signal handlers
389 /* "Trace me, Dr. Memory!" */
392 /* The call above set this process (the "child") as debuggable
393 by the original gdb process (the "parent"). Since processes
394 (unlike people) can have only one parent, if you are debugging
395 gdb itself (and your debugger is thus _already_ the
396 controller/parent for this child), code from here on out is
397 undebuggable. Indeed, you probably got an error message
398 saying "not parent". Sorry; you'll have to use print
401 restore_original_signals_state ();
403 /* There is no execlpe call, so we have to set the environment
404 for our child in the global variable. If we've vforked, this
405 clobbers the parent, but environ is restored a few lines down
406 in the parent. By the way, yes we do need to look down the
407 path to find $SHELL. Rich Pixley says so, and I agree. */
410 char **argv
= child_argv
.argv ();
412 if (exec_fun
!= NULL
)
413 (*exec_fun
) (argv
[0], &argv
[0], env
);
415 execvp (argv
[0], &argv
[0]);
417 /* If we get here, it's an error. */
419 warning ("Cannot exec %s", argv
[0]);
421 for (i
= 1; argv
[i
] != NULL
; i
++)
422 warning (" %s", argv
[i
]);
424 warning ("Error: %s\n", safe_strerror (save_errno
));
429 /* Restore our environment in case a vforked child clob'd it. */
430 environ
= save_our_env
;
434 /* Now that we have a child process, make it our target, and
435 initialize anything target-vector-specific that needs
438 (*init_trace_fun
) (pid
);
440 /* We are now in the child process of interest, having exec'd the
441 correct program, and are poised at the first instruction of the
446 /* See nat/fork-inferior.h. */
449 startup_inferior (pid_t pid
, int ntraps
,
450 struct target_waitstatus
*last_waitstatus
,
453 int pending_execs
= ntraps
;
454 int terminal_initted
= 0;
457 if (startup_with_shell
)
459 /* One trap extra for exec'ing the shell. */
463 if (target_supports_multi_process ())
464 resume_ptid
= pid_to_ptid (pid
);
466 resume_ptid
= minus_one_ptid
;
468 /* The process was started by the fork that created it, but it will
469 have stopped one instruction after execing the shell. Here we
470 must get it up to actual execution of the real program. */
471 if (get_exec_wrapper () != NULL
)
476 enum gdb_signal resume_signal
= GDB_SIGNAL_0
;
479 struct target_waitstatus ws
;
480 memset (&ws
, 0, sizeof (ws
));
481 event_ptid
= target_wait (resume_ptid
, &ws
, 0);
483 if (last_waitstatus
!= NULL
)
484 *last_waitstatus
= ws
;
485 if (last_ptid
!= NULL
)
486 *last_ptid
= event_ptid
;
488 if (ws
.kind
== TARGET_WAITKIND_IGNORE
)
489 /* The inferior didn't really stop, keep waiting. */
494 case TARGET_WAITKIND_SPURIOUS
:
495 case TARGET_WAITKIND_LOADED
:
496 case TARGET_WAITKIND_FORKED
:
497 case TARGET_WAITKIND_VFORKED
:
498 case TARGET_WAITKIND_SYSCALL_ENTRY
:
499 case TARGET_WAITKIND_SYSCALL_RETURN
:
500 /* Ignore gracefully during startup of the inferior. */
501 switch_to_thread (event_ptid
);
504 case TARGET_WAITKIND_SIGNALLED
:
505 target_terminal::ours ();
506 target_mourn_inferior (event_ptid
);
507 error (_("During startup program terminated with signal %s, %s."),
508 gdb_signal_to_name (ws
.value
.sig
),
509 gdb_signal_to_string (ws
.value
.sig
));
512 case TARGET_WAITKIND_EXITED
:
513 target_terminal::ours ();
514 target_mourn_inferior (event_ptid
);
515 if (ws
.value
.integer
)
516 error (_("During startup program exited with code %d."),
519 error (_("During startup program exited normally."));
522 case TARGET_WAITKIND_EXECD
:
523 /* Handle EXEC signals as if they were SIGTRAP signals. */
524 xfree (ws
.value
.execd_pathname
);
525 resume_signal
= GDB_SIGNAL_TRAP
;
526 switch_to_thread (event_ptid
);
529 case TARGET_WAITKIND_STOPPED
:
530 resume_signal
= ws
.value
.sig
;
531 switch_to_thread (event_ptid
);
535 if (resume_signal
!= GDB_SIGNAL_TRAP
)
537 /* Let shell child handle its own signals in its own way. */
538 target_continue (resume_ptid
, resume_signal
);
542 /* We handle SIGTRAP, however; it means child did an exec. */
543 if (!terminal_initted
)
545 /* Now that the child has exec'd we know it has already
546 set its process group. On POSIX systems, tcsetpgrp
547 will fail with EPERM if we try it before the child's
550 /* Set up the "saved terminal modes" of the inferior
551 based on what modes we are starting it with. */
552 target_terminal::init ();
554 /* Install inferior's terminal modes. */
555 target_terminal::inferior ();
557 terminal_initted
= 1;
560 if (--pending_execs
== 0)
563 /* Just make it go on. */
564 target_continue_no_signal (resume_ptid
);
571 /* See nat/fork-inferior.h. */
574 trace_start_error (const char *fmt
, ...)
579 warning ("Could not trace the inferior process.\nError: ");
583 gdb_flush_out_err ();
587 /* See nat/fork-inferior.h. */
590 trace_start_error_with_name (const char *string
)
592 trace_start_error ("%s: %s", string
, safe_strerror (errno
));