1 /* Linux-specific ptrace manipulation routines.
2 Copyright (C) 2012-2016 Free Software Foundation, Inc.
4 This file is part of GDB.
6 This program is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 3 of the License, or
9 (at your option) any later version.
11 This program is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>. */
19 #include "common-defs.h"
20 #include "linux-ptrace.h"
21 #include "linux-procfs.h"
22 #include "linux-waitpid.h"
25 #include "gdb_ptrace.h"
27 /* Stores the ptrace options supported by the running kernel.
28 A value of -1 means we did not check for features yet. A value
29 of 0 means there are no supported features. */
30 static int supported_ptrace_options
= -1;
32 /* Find all possible reasons we could fail to attach PID and append
33 these as strings to the already initialized BUFFER. '\0'
34 termination of BUFFER must be done by the caller. */
37 linux_ptrace_attach_fail_reason (pid_t pid
, struct buffer
*buffer
)
41 tracerpid
= linux_proc_get_tracerpid_nowarn (pid
);
43 buffer_xml_printf (buffer
, _("process %d is already traced "
45 (int) pid
, (int) tracerpid
);
47 if (linux_proc_pid_is_zombie_nowarn (pid
))
48 buffer_xml_printf (buffer
, _("process %d is a zombie "
49 "- the process has already terminated"),
53 /* See linux-ptrace.h. */
56 linux_ptrace_attach_fail_reason_string (ptid_t ptid
, int err
)
58 static char *reason_string
;
61 long lwpid
= ptid_get_lwp (ptid
);
63 xfree (reason_string
);
65 buffer_init (&buffer
);
66 linux_ptrace_attach_fail_reason (lwpid
, &buffer
);
67 buffer_grow_str0 (&buffer
, "");
68 warnings
= buffer_finish (&buffer
);
69 if (warnings
[0] != '\0')
70 reason_string
= xstrprintf ("%s (%d), %s",
71 safe_strerror (err
), err
, warnings
);
73 reason_string
= xstrprintf ("%s (%d)",
74 safe_strerror (err
), err
);
79 #if defined __i386__ || defined __x86_64__
81 /* Address of the 'ret' instruction in asm code block below. */
82 EXTERN_C
void linux_ptrace_test_ret_to_nx_instr (void);
88 #endif /* defined __i386__ || defined __x86_64__ */
90 /* Test broken off-trunk Linux kernel patchset for NX support on i386. It was
91 removed in Fedora kernel 88fa1f0332d188795ed73d7ac2b1564e11a0b4cd.
93 Test also x86_64 arch for PaX support. */
96 linux_ptrace_test_ret_to_nx (void)
98 #if defined __i386__ || defined __x86_64__
100 gdb_byte
*return_address
, *pc
;
102 int status
, kill_status
;
105 = (gdb_byte
*) mmap (NULL
, 2, PROT_READ
| PROT_WRITE
,
106 MAP_PRIVATE
| MAP_ANONYMOUS
, -1, 0);
107 if (return_address
== MAP_FAILED
)
109 warning (_("linux_ptrace_test_ret_to_nx: Cannot mmap: %s"),
110 safe_strerror (errno
));
114 /* Put there 'int3'. */
115 *return_address
= 0xcc;
121 warning (_("linux_ptrace_test_ret_to_nx: Cannot fork: %s"),
122 safe_strerror (errno
));
126 l
= ptrace (PTRACE_TRACEME
, 0, (PTRACE_TYPE_ARG3
) NULL
,
127 (PTRACE_TYPE_ARG4
) NULL
);
129 warning (_("linux_ptrace_test_ret_to_nx: Cannot PTRACE_TRACEME: %s"),
130 safe_strerror (errno
));
134 asm volatile ("pushl %0;"
135 ".globl linux_ptrace_test_ret_to_nx_instr;"
136 "linux_ptrace_test_ret_to_nx_instr:"
138 : : "r" (return_address
) : "%esp", "memory");
139 #elif defined __x86_64__
140 asm volatile ("pushq %0;"
141 ".globl linux_ptrace_test_ret_to_nx_instr;"
142 "linux_ptrace_test_ret_to_nx_instr:"
144 : : "r" ((uint64_t) (uintptr_t) return_address
)
147 # error "!__i386__ && !__x86_64__"
149 gdb_assert_not_reached ("asm block did not terminate");
156 got_pid
= waitpid (child
, &status
, 0);
157 if (got_pid
!= child
)
159 warning (_("linux_ptrace_test_ret_to_nx: waitpid returned %ld: %s"),
160 (long) got_pid
, safe_strerror (errno
));
164 if (WIFSIGNALED (status
))
166 if (WTERMSIG (status
) != SIGKILL
)
167 warning (_("linux_ptrace_test_ret_to_nx: WTERMSIG %d is not SIGKILL!"),
168 (int) WTERMSIG (status
));
170 warning (_("Cannot call inferior functions, Linux kernel PaX "
171 "protection forbids return to non-executable pages!"));
175 if (!WIFSTOPPED (status
))
177 warning (_("linux_ptrace_test_ret_to_nx: status %d is not WIFSTOPPED!"),
182 /* We may get SIGSEGV due to missing PROT_EXEC of the return_address. */
183 if (WSTOPSIG (status
) != SIGTRAP
&& WSTOPSIG (status
) != SIGSEGV
)
185 warning (_("linux_ptrace_test_ret_to_nx: "
186 "WSTOPSIG %d is neither SIGTRAP nor SIGSEGV!"),
187 (int) WSTOPSIG (status
));
193 l
= ptrace (PTRACE_PEEKUSER
, child
, (PTRACE_TYPE_ARG3
) (uintptr_t) (EIP
* 4),
194 (PTRACE_TYPE_ARG4
) NULL
);
195 #elif defined __x86_64__
196 l
= ptrace (PTRACE_PEEKUSER
, child
, (PTRACE_TYPE_ARG3
) (uintptr_t) (RIP
* 8),
197 (PTRACE_TYPE_ARG4
) NULL
);
199 # error "!__i386__ && !__x86_64__"
203 warning (_("linux_ptrace_test_ret_to_nx: Cannot PTRACE_PEEKUSER: %s"),
204 safe_strerror (errno
));
207 pc
= (gdb_byte
*) (uintptr_t) l
;
209 kill (child
, SIGKILL
);
210 ptrace (PTRACE_KILL
, child
, (PTRACE_TYPE_ARG3
) NULL
,
211 (PTRACE_TYPE_ARG4
) NULL
);
214 got_pid
= waitpid (child
, &kill_status
, 0);
215 if (got_pid
!= child
)
217 warning (_("linux_ptrace_test_ret_to_nx: "
218 "PTRACE_KILL waitpid returned %ld: %s"),
219 (long) got_pid
, safe_strerror (errno
));
222 if (!WIFSIGNALED (kill_status
))
224 warning (_("linux_ptrace_test_ret_to_nx: "
225 "PTRACE_KILL status %d is not WIFSIGNALED!"),
230 /* + 1 is there as x86* stops after the 'int3' instruction. */
231 if (WSTOPSIG (status
) == SIGTRAP
&& pc
== return_address
+ 1)
237 /* We may get SIGSEGV due to missing PROT_EXEC of the RETURN_ADDRESS page. */
238 if (WSTOPSIG (status
) == SIGSEGV
&& pc
== return_address
)
244 if ((void (*) (void)) pc
!= &linux_ptrace_test_ret_to_nx_instr
)
245 warning (_("linux_ptrace_test_ret_to_nx: PC %p is neither near return "
246 "address %p nor is the return instruction %p!"),
247 pc
, return_address
, &linux_ptrace_test_ret_to_nx_instr
);
249 warning (_("Cannot call inferior functions on this system - "
250 "Linux kernel with broken i386 NX (non-executable pages) "
251 "support detected!"));
252 #endif /* defined __i386__ || defined __x86_64__ */
255 /* Helper function to fork a process and make the child process call
256 the function FUNCTION, passing CHILD_STACK as parameter.
258 For MMU-less targets, clone is used instead of fork, and
259 CHILD_STACK is used as stack space for the cloned child. If NULL,
260 stack space is allocated via malloc (and subsequently passed to
261 FUNCTION). For MMU targets, CHILD_STACK is ignored. */
264 linux_fork_to_function (gdb_byte
*child_stack
, int (*function
) (void *))
268 /* Sanity check the function pointer. */
269 gdb_assert (function
!= NULL
);
271 #if defined(__UCLIBC__) && defined(HAS_NOMMU)
272 #define STACK_SIZE 4096
274 if (child_stack
== NULL
)
275 child_stack
= xmalloc (STACK_SIZE
* 4);
277 /* Use CLONE_VM instead of fork, to support uClinux (no MMU). */
279 child_pid
= __clone2 (function
, child_stack
, STACK_SIZE
,
280 CLONE_VM
| SIGCHLD
, child_stack
+ STACK_SIZE
* 2);
281 #else /* !__ia64__ */
282 child_pid
= clone (function
, child_stack
+ STACK_SIZE
,
283 CLONE_VM
| SIGCHLD
, child_stack
+ STACK_SIZE
* 2);
284 #endif /* !__ia64__ */
285 #else /* !defined(__UCLIBC) && defined(HAS_NOMMU) */
290 #endif /* defined(__UCLIBC) && defined(HAS_NOMMU) */
293 perror_with_name (("fork"));
298 /* A helper function for linux_check_ptrace_features, called after
299 the child forks a grandchild. */
302 linux_grandchild_function (void *child_stack
)
304 /* Free any allocated stack. */
307 /* This code is only reacheable by the grandchild (child's child)
312 /* A helper function for linux_check_ptrace_features, called after
313 the parent process forks a child. The child allows itself to
314 be traced by its parent. */
317 linux_child_function (void *child_stack
)
319 ptrace (PTRACE_TRACEME
, 0, (PTRACE_TYPE_ARG3
) 0, (PTRACE_TYPE_ARG4
) 0);
320 kill (getpid (), SIGSTOP
);
322 /* Fork a grandchild. */
323 linux_fork_to_function ((gdb_byte
*) child_stack
, linux_grandchild_function
);
325 /* This code is only reacheable by the child (grandchild's parent)
330 static void linux_test_for_tracesysgood (int child_pid
);
331 static void linux_test_for_tracefork (int child_pid
);
332 static void linux_test_for_exitkill (int child_pid
);
334 /* Determine ptrace features available on this target. */
337 linux_check_ptrace_features (void)
339 int child_pid
, ret
, status
;
341 /* Initialize the options. */
342 supported_ptrace_options
= 0;
344 /* Fork a child so we can do some testing. The child will call
345 linux_child_function and will get traced. The child will
346 eventually fork a grandchild so we can test fork event
348 child_pid
= linux_fork_to_function (NULL
, linux_child_function
);
350 ret
= my_waitpid (child_pid
, &status
, 0);
352 perror_with_name (("waitpid"));
353 else if (ret
!= child_pid
)
354 error (_("linux_check_ptrace_features: waitpid: unexpected result %d."),
356 if (! WIFSTOPPED (status
))
357 error (_("linux_check_ptrace_features: waitpid: unexpected status %d."),
360 linux_test_for_tracesysgood (child_pid
);
362 linux_test_for_tracefork (child_pid
);
364 linux_test_for_exitkill (child_pid
);
366 /* Clean things up and kill any pending children. */
369 ret
= ptrace (PTRACE_KILL
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
370 (PTRACE_TYPE_ARG4
) 0);
372 warning (_("linux_check_ptrace_features: failed to kill child"));
373 my_waitpid (child_pid
, &status
, 0);
375 while (WIFSTOPPED (status
));
378 /* Determine if PTRACE_O_TRACESYSGOOD can be used to catch
382 linux_test_for_tracesysgood (int child_pid
)
386 ret
= ptrace (PTRACE_SETOPTIONS
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
387 (PTRACE_TYPE_ARG4
) PTRACE_O_TRACESYSGOOD
);
390 supported_ptrace_options
|= PTRACE_O_TRACESYSGOOD
;
393 /* Determine if PTRACE_O_TRACEFORK can be used to follow fork
397 linux_test_for_tracefork (int child_pid
)
402 /* First, set the PTRACE_O_TRACEFORK option. If this fails, we
403 know for sure that it is not supported. */
404 ret
= ptrace (PTRACE_SETOPTIONS
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
405 (PTRACE_TYPE_ARG4
) PTRACE_O_TRACEFORK
);
410 /* Check if the target supports PTRACE_O_TRACEVFORKDONE. */
411 ret
= ptrace (PTRACE_SETOPTIONS
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
412 (PTRACE_TYPE_ARG4
) (PTRACE_O_TRACEFORK
413 | PTRACE_O_TRACEVFORKDONE
));
415 supported_ptrace_options
|= PTRACE_O_TRACEVFORKDONE
;
417 /* Setting PTRACE_O_TRACEFORK did not cause an error, however we
418 don't know for sure that the feature is available; old
419 versions of PTRACE_SETOPTIONS ignored unknown options.
420 Therefore, we attach to the child process, use PTRACE_SETOPTIONS
421 to enable fork tracing, and let it fork. If the process exits,
422 we assume that we can't use PTRACE_O_TRACEFORK; if we get the
423 fork notification, and we can extract the new child's PID, then
424 we assume that we can.
426 We do not explicitly check for vfork tracing here. It is
427 assumed that vfork tracing is available whenever fork tracing
429 ret
= ptrace (PTRACE_CONT
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
430 (PTRACE_TYPE_ARG4
) 0);
432 warning (_("linux_test_for_tracefork: failed to resume child"));
434 ret
= my_waitpid (child_pid
, &status
, 0);
436 /* Check if we received a fork event notification. */
437 if (ret
== child_pid
&& WIFSTOPPED (status
)
438 && linux_ptrace_get_extended_event (status
) == PTRACE_EVENT_FORK
)
440 /* We did receive a fork event notification. Make sure its PID
443 ret
= ptrace (PTRACE_GETEVENTMSG
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
444 (PTRACE_TYPE_ARG4
) &second_pid
);
445 if (ret
== 0 && second_pid
!= 0)
449 /* We got the PID from the grandchild, which means fork
450 tracing is supported. */
451 supported_ptrace_options
|= PTRACE_O_TRACECLONE
;
452 supported_ptrace_options
|= (PTRACE_O_TRACEFORK
453 | PTRACE_O_TRACEVFORK
454 | PTRACE_O_TRACEEXEC
);
456 /* Do some cleanup and kill the grandchild. */
457 my_waitpid (second_pid
, &second_status
, 0);
458 ret
= ptrace (PTRACE_KILL
, second_pid
, (PTRACE_TYPE_ARG3
) 0,
459 (PTRACE_TYPE_ARG4
) 0);
461 warning (_("linux_test_for_tracefork: "
462 "failed to kill second child"));
463 my_waitpid (second_pid
, &status
, 0);
467 warning (_("linux_test_for_tracefork: unexpected result from waitpid "
468 "(%d, status 0x%x)"), ret
, status
);
471 /* Determine if PTRACE_O_EXITKILL can be used. */
474 linux_test_for_exitkill (int child_pid
)
478 ret
= ptrace (PTRACE_SETOPTIONS
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
479 (PTRACE_TYPE_ARG4
) PTRACE_O_EXITKILL
);
482 supported_ptrace_options
|= PTRACE_O_EXITKILL
;
485 /* Enable reporting of all currently supported ptrace events.
486 OPTIONS is a bit mask of extended features we want enabled,
487 if supported by the kernel. PTRACE_O_TRACECLONE is always
488 enabled, if supported. */
491 linux_enable_event_reporting (pid_t pid
, int options
)
493 /* Check if we have initialized the ptrace features for this
494 target. If not, do it now. */
495 if (supported_ptrace_options
== -1)
496 linux_check_ptrace_features ();
498 /* We always want clone events. */
499 options
|= PTRACE_O_TRACECLONE
;
501 /* Filter out unsupported options. */
502 options
&= supported_ptrace_options
;
504 /* Set the options. */
505 ptrace (PTRACE_SETOPTIONS
, pid
, (PTRACE_TYPE_ARG3
) 0,
506 (PTRACE_TYPE_ARG4
) (uintptr_t) options
);
509 /* Disable reporting of all currently supported ptrace events. */
512 linux_disable_event_reporting (pid_t pid
)
514 /* Set the options. */
515 ptrace (PTRACE_SETOPTIONS
, pid
, (PTRACE_TYPE_ARG3
) 0, 0);
518 /* Returns non-zero if PTRACE_OPTIONS is contained within
519 SUPPORTED_PTRACE_OPTIONS, therefore supported. Returns 0
523 ptrace_supports_feature (int ptrace_options
)
525 if (supported_ptrace_options
== -1)
526 linux_check_ptrace_features ();
528 return ((supported_ptrace_options
& ptrace_options
) == ptrace_options
);
531 /* Returns non-zero if PTRACE_EVENT_FORK is supported by ptrace,
532 0 otherwise. Note that if PTRACE_EVENT_FORK is supported so is
533 PTRACE_EVENT_CLONE, PTRACE_EVENT_EXEC and PTRACE_EVENT_VFORK,
534 since they were all added to the kernel at the same time. */
537 linux_supports_tracefork (void)
539 return ptrace_supports_feature (PTRACE_O_TRACEFORK
);
542 /* Returns non-zero if PTRACE_EVENT_EXEC is supported by ptrace,
543 0 otherwise. Note that if PTRACE_EVENT_FORK is supported so is
544 PTRACE_EVENT_CLONE, PTRACE_EVENT_FORK and PTRACE_EVENT_VFORK,
545 since they were all added to the kernel at the same time. */
548 linux_supports_traceexec (void)
550 return ptrace_supports_feature (PTRACE_O_TRACEEXEC
);
553 /* Returns non-zero if PTRACE_EVENT_CLONE is supported by ptrace,
554 0 otherwise. Note that if PTRACE_EVENT_CLONE is supported so is
555 PTRACE_EVENT_FORK, PTRACE_EVENT_EXEC and PTRACE_EVENT_VFORK,
556 since they were all added to the kernel at the same time. */
559 linux_supports_traceclone (void)
561 return ptrace_supports_feature (PTRACE_O_TRACECLONE
);
564 /* Returns non-zero if PTRACE_O_TRACEVFORKDONE is supported by
565 ptrace, 0 otherwise. */
568 linux_supports_tracevforkdone (void)
570 return ptrace_supports_feature (PTRACE_O_TRACEVFORKDONE
);
573 /* Returns non-zero if PTRACE_O_TRACESYSGOOD is supported by ptrace,
577 linux_supports_tracesysgood (void)
579 return ptrace_supports_feature (PTRACE_O_TRACESYSGOOD
);
582 /* Display possible problems on this system. Display them only once per GDB
586 linux_ptrace_init_warnings (void)
588 static int warned
= 0;
594 linux_ptrace_test_ret_to_nx ();
597 /* Extract extended ptrace event from wait status. */
600 linux_ptrace_get_extended_event (int wstat
)
602 return (wstat
>> 16);
605 /* Determine whether wait status denotes an extended event. */
608 linux_is_extended_waitstatus (int wstat
)
610 return (linux_ptrace_get_extended_event (wstat
) != 0);
613 /* Return true if the event in LP may be caused by breakpoint. */
616 linux_wstatus_maybe_breakpoint (int wstat
)
618 return (WIFSTOPPED (wstat
)
619 && (WSTOPSIG (wstat
) == SIGTRAP
620 /* SIGILL and SIGSEGV are also treated as traps in case a
621 breakpoint is inserted at the current PC. */
622 || WSTOPSIG (wstat
) == SIGILL
623 || WSTOPSIG (wstat
) == SIGSEGV
));