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2090129c SDJ |
1 | /* Fork a Unix child process, and set up to debug it, for GDB and GDBserver. |
2 | ||
3 | Copyright (C) 1990-2017 Free Software Foundation, Inc. | |
4 | ||
5 | This file is part of GDB. | |
6 | ||
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. | |
11 | ||
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. | |
16 | ||
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/>. */ | |
19 | ||
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 <vector> | |
29 | ||
30 | extern char **environ; | |
31 | ||
32 | /* Default shell file to be used if 'startup-with-shell' is set but | |
33 | $SHELL is not. */ | |
34 | #define SHELL_FILE "/bin/sh" | |
35 | ||
36 | /* Build the argument vector for execv(3). */ | |
37 | ||
38 | class execv_argv | |
39 | { | |
40 | public: | |
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); | |
46 | ||
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. */ | |
53 | char **argv () | |
54 | { | |
55 | return const_cast<char **> (&m_argv[0]); | |
56 | } | |
57 | ||
58 | private: | |
59 | /* Disable copying. */ | |
60 | execv_argv (const execv_argv &) = delete; | |
61 | void operator= (const execv_argv &) = delete; | |
62 | ||
63 | /* Helper methods for constructing the argument vector. */ | |
64 | ||
65 | /* Used when building an argv for a straight execv call, without | |
66 | going via the shell. */ | |
67 | void init_for_no_shell (const char *exec_file, | |
68 | const std::string &allargs); | |
69 | ||
70 | /* Used when building an argv for execing a shell that execs the | |
71 | child program. */ | |
72 | void init_for_shell (const char *exec_file, | |
73 | const std::string &allargs, | |
74 | const char *shell_file); | |
75 | ||
76 | /* The argument vector built. Holds non-owning pointers. Elements | |
77 | either point to the strings passed to the execv_argv ctor, or | |
78 | inside M_STORAGE. */ | |
79 | std::vector<const char *> m_argv; | |
80 | ||
81 | /* Storage. In the no-shell case, this contains a copy of the | |
82 | arguments passed to the ctor, split by '\0'. In the shell case, | |
83 | this contains the quoted shell command. I.e., SHELL_COMMAND in | |
84 | {"$SHELL" "-c", SHELL_COMMAND, NULL}. */ | |
85 | std::string m_storage; | |
86 | }; | |
87 | ||
88 | /* Create argument vector for straight call to execvp. Breaks up | |
89 | ALLARGS into an argument vector suitable for passing to execvp and | |
90 | stores it in M_ARGV. E.g., on "run a b c d" this routine would get | |
91 | as input the string "a b c d", and as output it would fill in | |
92 | M_ARGV with the four arguments "a", "b", "c", "d". Each argument | |
93 | in M_ARGV points to a substring of a copy of ALLARGS stored in | |
94 | M_STORAGE. */ | |
95 | ||
96 | void | |
97 | execv_argv::init_for_no_shell (const char *exec_file, | |
98 | const std::string &allargs) | |
99 | { | |
100 | ||
101 | /* Save/work with a copy stored in our storage. The pointers pushed | |
102 | to M_ARGV point directly into M_STORAGE, which is modified in | |
103 | place with the necessary NULL terminators. This avoids N heap | |
104 | allocations and string dups when 1 is sufficient. */ | |
105 | std::string &args_copy = m_storage = allargs; | |
106 | ||
107 | m_argv.push_back (exec_file); | |
108 | ||
109 | for (size_t cur_pos = 0; cur_pos < args_copy.size ();) | |
110 | { | |
111 | /* Skip whitespace-like chars. */ | |
112 | std::size_t pos = args_copy.find_first_not_of (" \t\n", cur_pos); | |
113 | ||
114 | if (pos != std::string::npos) | |
115 | cur_pos = pos; | |
116 | ||
117 | /* Find the position of the next separator. */ | |
118 | std::size_t next_sep = args_copy.find_first_of (" \t\n", cur_pos); | |
119 | ||
120 | if (next_sep == std::string::npos) | |
121 | { | |
122 | /* No separator found, which means this is the last | |
123 | argument. */ | |
124 | next_sep = args_copy.size (); | |
125 | } | |
126 | else | |
127 | { | |
128 | /* Replace the separator with a terminator. */ | |
129 | args_copy[next_sep++] = '\0'; | |
130 | } | |
131 | ||
132 | m_argv.push_back (&args_copy[cur_pos]); | |
133 | ||
134 | cur_pos = next_sep; | |
135 | } | |
136 | ||
137 | /* NULL-terminate the vector. */ | |
138 | m_argv.push_back (NULL); | |
139 | } | |
140 | ||
141 | /* When executing a command under the given shell, return true if the | |
142 | '!' character should be escaped when embedded in a quoted | |
143 | command-line argument. */ | |
144 | ||
145 | static bool | |
146 | escape_bang_in_quoted_argument (const char *shell_file) | |
147 | { | |
148 | size_t shell_file_len = strlen (shell_file); | |
149 | ||
150 | /* Bang should be escaped only in C Shells. For now, simply check | |
151 | that the shell name ends with 'csh', which covers at least csh | |
152 | and tcsh. This should be good enough for now. */ | |
153 | ||
154 | if (shell_file_len < 3) | |
155 | return false; | |
156 | ||
157 | if (shell_file[shell_file_len - 3] == 'c' | |
158 | && shell_file[shell_file_len - 2] == 's' | |
159 | && shell_file[shell_file_len - 1] == 'h') | |
160 | return true; | |
161 | ||
162 | return false; | |
163 | } | |
164 | ||
165 | /* See declaration. */ | |
166 | ||
167 | execv_argv::execv_argv (const char *exec_file, | |
168 | const std::string &allargs, | |
169 | const char *shell_file) | |
170 | { | |
171 | if (shell_file == NULL) | |
172 | init_for_no_shell (exec_file, allargs); | |
173 | else | |
174 | init_for_shell (exec_file, allargs, shell_file); | |
175 | } | |
176 | ||
177 | /* See declaration. */ | |
178 | ||
179 | void | |
180 | execv_argv::init_for_shell (const char *exec_file, | |
181 | const std::string &allargs, | |
182 | const char *shell_file) | |
183 | { | |
184 | const char *exec_wrapper = get_exec_wrapper (); | |
185 | ||
186 | /* We're going to call a shell. */ | |
187 | bool escape_bang = escape_bang_in_quoted_argument (shell_file); | |
188 | ||
189 | /* We need to build a new shell command string, and make argv point | |
190 | to it. So build it in the storage. */ | |
191 | std::string &shell_command = m_storage; | |
192 | ||
193 | shell_command = "exec "; | |
194 | ||
195 | /* Add any exec wrapper. That may be a program name with arguments, | |
196 | so the user must handle quoting. */ | |
197 | if (exec_wrapper != NULL) | |
198 | { | |
199 | shell_command += exec_wrapper; | |
200 | shell_command += ' '; | |
201 | } | |
202 | ||
203 | /* Now add exec_file, quoting as necessary. */ | |
204 | ||
205 | /* Quoting in this style is said to work with all shells. But csh | |
206 | on IRIX 4.0.1 can't deal with it. So we only quote it if we need | |
207 | to. */ | |
208 | bool need_to_quote; | |
209 | const char *p = exec_file; | |
210 | while (1) | |
211 | { | |
212 | switch (*p) | |
213 | { | |
214 | case '\'': | |
215 | case '!': | |
216 | case '"': | |
217 | case '(': | |
218 | case ')': | |
219 | case '$': | |
220 | case '&': | |
221 | case ';': | |
222 | case '<': | |
223 | case '>': | |
224 | case ' ': | |
225 | case '\n': | |
226 | case '\t': | |
227 | need_to_quote = true; | |
228 | goto end_scan; | |
229 | ||
230 | case '\0': | |
231 | need_to_quote = false; | |
232 | goto end_scan; | |
233 | ||
234 | default: | |
235 | break; | |
236 | } | |
237 | ++p; | |
238 | } | |
239 | end_scan: | |
240 | if (need_to_quote) | |
241 | { | |
242 | shell_command += '\''; | |
243 | for (p = exec_file; *p != '\0'; ++p) | |
244 | { | |
245 | if (*p == '\'') | |
246 | shell_command += "'\\''"; | |
247 | else if (*p == '!' && escape_bang) | |
248 | shell_command += "\\!"; | |
249 | else | |
250 | shell_command += *p; | |
251 | } | |
252 | shell_command += '\''; | |
253 | } | |
254 | else | |
255 | shell_command += exec_file; | |
256 | ||
257 | shell_command += ' ' + allargs; | |
258 | ||
259 | /* If we decided above to start up with a shell, we exec the shell. | |
260 | "-c" says to interpret the next arg as a shell command to | |
261 | execute, and this command is "exec <target-program> <args>". */ | |
262 | m_argv.reserve (4); | |
263 | m_argv.push_back (shell_file); | |
264 | m_argv.push_back ("-c"); | |
265 | m_argv.push_back (shell_command.c_str ()); | |
266 | m_argv.push_back (NULL); | |
267 | } | |
268 | ||
269 | /* Return the shell that must be used to startup the inferior. The | |
270 | first attempt is the environment variable SHELL; if it is not set, | |
271 | then we default to SHELL_FILE. */ | |
272 | ||
273 | static const char * | |
274 | get_startup_shell () | |
275 | { | |
276 | static const char *ret; | |
277 | ||
278 | ret = getenv ("SHELL"); | |
279 | if (ret == NULL) | |
280 | ret = SHELL_FILE; | |
281 | ||
282 | return ret; | |
283 | } | |
284 | ||
285 | /* See nat/fork-inferior.h. */ | |
286 | ||
287 | pid_t | |
288 | fork_inferior (const char *exec_file_arg, const std::string &allargs, | |
289 | char **env, void (*traceme_fun) (), | |
290 | void (*init_trace_fun) (int), void (*pre_trace_fun) (), | |
291 | const char *shell_file_arg, | |
292 | void (*exec_fun)(const char *file, char * const *argv, | |
293 | char * const *env)) | |
294 | { | |
295 | pid_t pid; | |
296 | /* Set debug_fork then attach to the child while it sleeps, to debug. */ | |
297 | int debug_fork = 0; | |
298 | const char *shell_file; | |
299 | const char *exec_file; | |
300 | char **save_our_env; | |
301 | int i; | |
302 | int save_errno; | |
303 | ||
304 | /* If no exec file handed to us, get it from the exec-file command | |
305 | -- with a good, common error message if none is specified. */ | |
306 | if (exec_file_arg == NULL) | |
307 | exec_file = get_exec_file (1); | |
308 | else | |
309 | exec_file = exec_file_arg; | |
310 | ||
311 | /* 'startup_with_shell' is declared in inferior.h and bound to the | |
312 | "set startup-with-shell" option. If 0, we'll just do a | |
313 | fork/exec, no shell, so don't bother figuring out what shell. */ | |
314 | if (startup_with_shell) | |
315 | { | |
316 | shell_file = shell_file_arg; | |
317 | ||
318 | /* Figure out what shell to start up the user program under. */ | |
319 | if (shell_file == NULL) | |
320 | shell_file = get_startup_shell (); | |
321 | ||
322 | gdb_assert (shell_file != NULL); | |
323 | } | |
324 | else | |
325 | shell_file = NULL; | |
326 | ||
327 | /* Build the argument vector. */ | |
328 | execv_argv child_argv (exec_file, allargs, shell_file); | |
329 | ||
330 | /* Retain a copy of our environment variables, since the child will | |
331 | replace the value of environ and if we're vforked, we have to | |
332 | restore it. */ | |
333 | save_our_env = environ; | |
334 | ||
335 | /* Perform any necessary actions regarding to TTY before the | |
336 | fork/vfork call. */ | |
337 | prefork_hook (allargs.c_str ()); | |
338 | ||
339 | /* It is generally good practice to flush any possible pending stdio | |
340 | output prior to doing a fork, to avoid the possibility of both | |
341 | the parent and child flushing the same data after the fork. */ | |
342 | gdb_flush_out_err (); | |
343 | ||
344 | /* If there's any initialization of the target layers that must | |
345 | happen to prepare to handle the child we're about fork, do it | |
346 | now... */ | |
347 | if (pre_trace_fun != NULL) | |
348 | (*pre_trace_fun) (); | |
349 | ||
350 | /* Create the child process. Since the child process is going to | |
351 | exec(3) shortly afterwards, try to reduce the overhead by | |
352 | calling vfork(2). However, if PRE_TRACE_FUN is non-null, it's | |
353 | likely that this optimization won't work since there's too much | |
354 | work to do between the vfork(2) and the exec(3). This is known | |
355 | to be the case on ttrace(2)-based HP-UX, where some handshaking | |
356 | between parent and child needs to happen between fork(2) and | |
357 | exec(2). However, since the parent is suspended in the vforked | |
358 | state, this doesn't work. Also note that the vfork(2) call might | |
359 | actually be a call to fork(2) due to the fact that autoconf will | |
360 | ``#define vfork fork'' on certain platforms. */ | |
361 | #if !(defined(__UCLIBC__) && defined(HAS_NOMMU)) | |
362 | if (pre_trace_fun || debug_fork) | |
363 | pid = fork (); | |
364 | else | |
365 | #endif | |
366 | pid = vfork (); | |
367 | ||
368 | if (pid < 0) | |
369 | perror_with_name (("vfork")); | |
370 | ||
371 | if (pid == 0) | |
372 | { | |
373 | /* Close all file descriptors except those that gdb inherited | |
374 | (usually 0/1/2), so they don't leak to the inferior. Note | |
375 | that this closes the file descriptors of all secondary | |
376 | UIs. */ | |
377 | close_most_fds (); | |
378 | ||
379 | if (debug_fork) | |
380 | sleep (debug_fork); | |
381 | ||
382 | /* Execute any necessary post-fork actions before we exec. */ | |
383 | postfork_child_hook (); | |
384 | ||
385 | /* Changing the signal handlers for the inferior after | |
386 | a vfork can also change them for the superior, so we don't mess | |
387 | with signals here. See comments in | |
388 | initialize_signals for how we get the right signal handlers | |
389 | for the inferior. */ | |
390 | ||
391 | /* "Trace me, Dr. Memory!" */ | |
392 | (*traceme_fun) (); | |
393 | ||
394 | /* The call above set this process (the "child") as debuggable | |
395 | by the original gdb process (the "parent"). Since processes | |
396 | (unlike people) can have only one parent, if you are debugging | |
397 | gdb itself (and your debugger is thus _already_ the | |
398 | controller/parent for this child), code from here on out is | |
399 | undebuggable. Indeed, you probably got an error message | |
400 | saying "not parent". Sorry; you'll have to use print | |
401 | statements! */ | |
402 | ||
403 | restore_original_signals_state (); | |
404 | ||
405 | /* There is no execlpe call, so we have to set the environment | |
406 | for our child in the global variable. If we've vforked, this | |
407 | clobbers the parent, but environ is restored a few lines down | |
408 | in the parent. By the way, yes we do need to look down the | |
409 | path to find $SHELL. Rich Pixley says so, and I agree. */ | |
410 | environ = env; | |
411 | ||
412 | char **argv = child_argv.argv (); | |
413 | ||
414 | if (exec_fun != NULL) | |
415 | (*exec_fun) (argv[0], &argv[0], env); | |
416 | else | |
417 | execvp (argv[0], &argv[0]); | |
418 | ||
419 | /* If we get here, it's an error. */ | |
420 | save_errno = errno; | |
421 | warning ("Cannot exec %s", argv[0]); | |
422 | ||
423 | for (i = 1; argv[i] != NULL; i++) | |
424 | warning (" %s", argv[i]); | |
425 | ||
426 | warning ("Error: %s\n", safe_strerror (save_errno)); | |
427 | ||
428 | _exit (0177); | |
429 | } | |
430 | ||
431 | /* Restore our environment in case a vforked child clob'd it. */ | |
432 | environ = save_our_env; | |
433 | ||
434 | postfork_hook (pid); | |
435 | ||
436 | /* Now that we have a child process, make it our target, and | |
437 | initialize anything target-vector-specific that needs | |
438 | initializing. */ | |
439 | if (init_trace_fun) | |
440 | (*init_trace_fun) (pid); | |
441 | ||
442 | /* We are now in the child process of interest, having exec'd the | |
443 | correct program, and are poised at the first instruction of the | |
444 | new program. */ | |
445 | return pid; | |
446 | } | |
447 | ||
448 | /* See nat/fork-inferior.h. */ | |
449 | ||
450 | ptid_t | |
451 | startup_inferior (pid_t pid, int ntraps, | |
452 | struct target_waitstatus *last_waitstatus, | |
453 | ptid_t *last_ptid) | |
454 | { | |
455 | int pending_execs = ntraps; | |
456 | int terminal_initted = 0; | |
457 | ptid_t resume_ptid; | |
458 | ||
459 | if (startup_with_shell) | |
460 | { | |
461 | /* One trap extra for exec'ing the shell. */ | |
462 | pending_execs++; | |
463 | } | |
464 | ||
465 | if (target_supports_multi_process ()) | |
466 | resume_ptid = pid_to_ptid (pid); | |
467 | else | |
468 | resume_ptid = minus_one_ptid; | |
469 | ||
470 | /* The process was started by the fork that created it, but it will | |
471 | have stopped one instruction after execing the shell. Here we | |
472 | must get it up to actual execution of the real program. */ | |
473 | if (get_exec_wrapper () != NULL) | |
474 | pending_execs++; | |
475 | ||
476 | while (1) | |
477 | { | |
478 | enum gdb_signal resume_signal = GDB_SIGNAL_0; | |
479 | ptid_t event_ptid; | |
480 | ||
481 | struct target_waitstatus ws; | |
482 | memset (&ws, 0, sizeof (ws)); | |
483 | event_ptid = target_wait (resume_ptid, &ws, 0); | |
484 | ||
485 | if (last_waitstatus != NULL) | |
486 | *last_waitstatus = ws; | |
487 | if (last_ptid != NULL) | |
488 | *last_ptid = event_ptid; | |
489 | ||
490 | if (ws.kind == TARGET_WAITKIND_IGNORE) | |
491 | /* The inferior didn't really stop, keep waiting. */ | |
492 | continue; | |
493 | ||
494 | switch (ws.kind) | |
495 | { | |
496 | case TARGET_WAITKIND_SPURIOUS: | |
497 | case TARGET_WAITKIND_LOADED: | |
498 | case TARGET_WAITKIND_FORKED: | |
499 | case TARGET_WAITKIND_VFORKED: | |
500 | case TARGET_WAITKIND_SYSCALL_ENTRY: | |
501 | case TARGET_WAITKIND_SYSCALL_RETURN: | |
502 | /* Ignore gracefully during startup of the inferior. */ | |
503 | switch_to_thread (event_ptid); | |
504 | break; | |
505 | ||
506 | case TARGET_WAITKIND_SIGNALLED: | |
507 | target_terminal_ours (); | |
508 | target_mourn_inferior (event_ptid); | |
509 | error (_("During startup program terminated with signal %s, %s."), | |
510 | gdb_signal_to_name (ws.value.sig), | |
511 | gdb_signal_to_string (ws.value.sig)); | |
512 | return resume_ptid; | |
513 | ||
514 | case TARGET_WAITKIND_EXITED: | |
515 | target_terminal_ours (); | |
516 | target_mourn_inferior (event_ptid); | |
517 | if (ws.value.integer) | |
518 | error (_("During startup program exited with code %d."), | |
519 | ws.value.integer); | |
520 | else | |
521 | error (_("During startup program exited normally.")); | |
522 | return resume_ptid; | |
523 | ||
524 | case TARGET_WAITKIND_EXECD: | |
525 | /* Handle EXEC signals as if they were SIGTRAP signals. */ | |
526 | xfree (ws.value.execd_pathname); | |
527 | resume_signal = GDB_SIGNAL_TRAP; | |
528 | switch_to_thread (event_ptid); | |
529 | break; | |
530 | ||
531 | case TARGET_WAITKIND_STOPPED: | |
532 | resume_signal = ws.value.sig; | |
533 | switch_to_thread (event_ptid); | |
534 | break; | |
535 | } | |
536 | ||
537 | if (resume_signal != GDB_SIGNAL_TRAP) | |
538 | { | |
539 | /* Let shell child handle its own signals in its own way. */ | |
540 | target_continue (resume_ptid, resume_signal); | |
541 | } | |
542 | else | |
543 | { | |
544 | /* We handle SIGTRAP, however; it means child did an exec. */ | |
545 | if (!terminal_initted) | |
546 | { | |
547 | /* Now that the child has exec'd we know it has already | |
548 | set its process group. On POSIX systems, tcsetpgrp | |
549 | will fail with EPERM if we try it before the child's | |
550 | setpgid. */ | |
551 | ||
552 | /* Set up the "saved terminal modes" of the inferior | |
553 | based on what modes we are starting it with. */ | |
554 | target_terminal_init (); | |
555 | ||
556 | /* Install inferior's terminal modes. */ | |
557 | target_terminal_inferior (); | |
558 | ||
559 | terminal_initted = 1; | |
560 | } | |
561 | ||
562 | if (--pending_execs == 0) | |
563 | break; | |
564 | ||
565 | /* Just make it go on. */ | |
566 | target_continue_no_signal (resume_ptid); | |
567 | } | |
568 | } | |
569 | ||
570 | return resume_ptid; | |
571 | } | |
572 | ||
573 | /* See nat/fork-inferior.h. */ | |
574 | ||
575 | void | |
576 | trace_start_error (const char *fmt, ...) | |
577 | { | |
578 | va_list ap; | |
579 | ||
580 | va_start (ap, fmt); | |
581 | warning ("Could not trace the inferior process.\nError: "); | |
582 | vwarning (fmt, ap); | |
583 | va_end (ap); | |
584 | ||
585 | gdb_flush_out_err (); | |
586 | _exit (0177); | |
587 | } | |
588 | ||
589 | /* See nat/fork-inferior.h. */ | |
590 | ||
591 | void | |
592 | trace_start_error_with_name (const char *string) | |
593 | { | |
594 | trace_start_error ("%s: %s", string, safe_strerror (errno)); | |
595 | } |