1 /* Linux-specific ptrace manipulation routines.
2 Copyright (C) 2012-2015 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
;
104 return_address
= mmap (NULL
, 2, PROT_READ
| PROT_WRITE
,
105 MAP_PRIVATE
| MAP_ANONYMOUS
, -1, 0);
106 if (return_address
== MAP_FAILED
)
108 warning (_("linux_ptrace_test_ret_to_nx: Cannot mmap: %s"),
109 safe_strerror (errno
));
113 /* Put there 'int3'. */
114 *return_address
= 0xcc;
120 warning (_("linux_ptrace_test_ret_to_nx: Cannot fork: %s"),
121 safe_strerror (errno
));
125 l
= ptrace (PTRACE_TRACEME
, 0, (PTRACE_TYPE_ARG3
) NULL
,
126 (PTRACE_TYPE_ARG4
) NULL
);
128 warning (_("linux_ptrace_test_ret_to_nx: Cannot PTRACE_TRACEME: %s"),
129 safe_strerror (errno
));
133 asm volatile ("pushl %0;"
134 ".globl linux_ptrace_test_ret_to_nx_instr;"
135 "linux_ptrace_test_ret_to_nx_instr:"
137 : : "r" (return_address
) : "%esp", "memory");
138 #elif defined __x86_64__
139 asm volatile ("pushq %0;"
140 ".globl linux_ptrace_test_ret_to_nx_instr;"
141 "linux_ptrace_test_ret_to_nx_instr:"
143 : : "r" ((uint64_t) (uintptr_t) return_address
)
146 # error "!__i386__ && !__x86_64__"
148 gdb_assert_not_reached ("asm block did not terminate");
155 got_pid
= waitpid (child
, &status
, 0);
156 if (got_pid
!= child
)
158 warning (_("linux_ptrace_test_ret_to_nx: waitpid returned %ld: %s"),
159 (long) got_pid
, safe_strerror (errno
));
163 if (WIFSIGNALED (status
))
165 if (WTERMSIG (status
) != SIGKILL
)
166 warning (_("linux_ptrace_test_ret_to_nx: WTERMSIG %d is not SIGKILL!"),
167 (int) WTERMSIG (status
));
169 warning (_("Cannot call inferior functions, Linux kernel PaX "
170 "protection forbids return to non-executable pages!"));
174 if (!WIFSTOPPED (status
))
176 warning (_("linux_ptrace_test_ret_to_nx: status %d is not WIFSTOPPED!"),
181 /* We may get SIGSEGV due to missing PROT_EXEC of the return_address. */
182 if (WSTOPSIG (status
) != SIGTRAP
&& WSTOPSIG (status
) != SIGSEGV
)
184 warning (_("linux_ptrace_test_ret_to_nx: "
185 "WSTOPSIG %d is neither SIGTRAP nor SIGSEGV!"),
186 (int) WSTOPSIG (status
));
192 l
= ptrace (PTRACE_PEEKUSER
, child
, (PTRACE_TYPE_ARG3
) (uintptr_t) (EIP
* 4),
193 (PTRACE_TYPE_ARG4
) NULL
);
194 #elif defined __x86_64__
195 l
= ptrace (PTRACE_PEEKUSER
, child
, (PTRACE_TYPE_ARG3
) (uintptr_t) (RIP
* 8),
196 (PTRACE_TYPE_ARG4
) NULL
);
198 # error "!__i386__ && !__x86_64__"
202 warning (_("linux_ptrace_test_ret_to_nx: Cannot PTRACE_PEEKUSER: %s"),
203 safe_strerror (errno
));
206 pc
= (void *) (uintptr_t) l
;
208 kill (child
, SIGKILL
);
209 ptrace (PTRACE_KILL
, child
, (PTRACE_TYPE_ARG3
) NULL
,
210 (PTRACE_TYPE_ARG4
) NULL
);
213 got_pid
= waitpid (child
, &kill_status
, 0);
214 if (got_pid
!= child
)
216 warning (_("linux_ptrace_test_ret_to_nx: "
217 "PTRACE_KILL waitpid returned %ld: %s"),
218 (long) got_pid
, safe_strerror (errno
));
221 if (!WIFSIGNALED (kill_status
))
223 warning (_("linux_ptrace_test_ret_to_nx: "
224 "PTRACE_KILL status %d is not WIFSIGNALED!"),
229 /* + 1 is there as x86* stops after the 'int3' instruction. */
230 if (WSTOPSIG (status
) == SIGTRAP
&& pc
== return_address
+ 1)
236 /* We may get SIGSEGV due to missing PROT_EXEC of the RETURN_ADDRESS page. */
237 if (WSTOPSIG (status
) == SIGSEGV
&& pc
== return_address
)
243 if ((void (*) (void)) pc
!= &linux_ptrace_test_ret_to_nx_instr
)
244 warning (_("linux_ptrace_test_ret_to_nx: PC %p is neither near return "
245 "address %p nor is the return instruction %p!"),
246 pc
, return_address
, &linux_ptrace_test_ret_to_nx_instr
);
248 warning (_("Cannot call inferior functions on this system - "
249 "Linux kernel with broken i386 NX (non-executable pages) "
250 "support detected!"));
251 #endif /* defined __i386__ || defined __x86_64__ */
254 /* Helper function to fork a process and make the child process call
255 the function FUNCTION, passing CHILD_STACK as parameter.
257 For MMU-less targets, clone is used instead of fork, and
258 CHILD_STACK is used as stack space for the cloned child. If NULL,
259 stack space is allocated via malloc (and subsequently passed to
260 FUNCTION). For MMU targets, CHILD_STACK is ignored. */
263 linux_fork_to_function (gdb_byte
*child_stack
, void (*function
) (gdb_byte
*))
267 /* Sanity check the function pointer. */
268 gdb_assert (function
!= NULL
);
270 #if defined(__UCLIBC__) && defined(HAS_NOMMU)
271 #define STACK_SIZE 4096
273 if (child_stack
== NULL
)
274 child_stack
= xmalloc (STACK_SIZE
* 4);
276 /* Use CLONE_VM instead of fork, to support uClinux (no MMU). */
278 child_pid
= __clone2 (function
, child_stack
, STACK_SIZE
,
279 CLONE_VM
| SIGCHLD
, child_stack
+ STACK_SIZE
* 2);
280 #else /* !__ia64__ */
281 child_pid
= clone (function
, child_stack
+ STACK_SIZE
,
282 CLONE_VM
| SIGCHLD
, child_stack
+ STACK_SIZE
* 2);
283 #endif /* !__ia64__ */
284 #else /* !defined(__UCLIBC) && defined(HAS_NOMMU) */
289 #endif /* defined(__UCLIBC) && defined(HAS_NOMMU) */
292 perror_with_name (("fork"));
297 /* A helper function for linux_check_ptrace_features, called after
298 the child forks a grandchild. */
301 linux_grandchild_function (gdb_byte
*child_stack
)
303 /* Free any allocated stack. */
306 /* This code is only reacheable by the grandchild (child's child)
311 /* A helper function for linux_check_ptrace_features, called after
312 the parent process forks a child. The child allows itself to
313 be traced by its parent. */
316 linux_child_function (gdb_byte
*child_stack
)
318 ptrace (PTRACE_TRACEME
, 0, (PTRACE_TYPE_ARG3
) 0, (PTRACE_TYPE_ARG4
) 0);
319 kill (getpid (), SIGSTOP
);
321 /* Fork a grandchild. */
322 linux_fork_to_function (child_stack
, linux_grandchild_function
);
324 /* This code is only reacheable by the child (grandchild's parent)
329 static void linux_test_for_tracesysgood (int child_pid
);
330 static void linux_test_for_tracefork (int child_pid
);
331 static void linux_test_for_exitkill (int child_pid
);
333 /* Determine ptrace features available on this target. */
336 linux_check_ptrace_features (void)
338 int child_pid
, ret
, status
;
340 /* Initialize the options. */
341 supported_ptrace_options
= 0;
343 /* Fork a child so we can do some testing. The child will call
344 linux_child_function and will get traced. The child will
345 eventually fork a grandchild so we can test fork event
347 child_pid
= linux_fork_to_function (NULL
, linux_child_function
);
349 ret
= my_waitpid (child_pid
, &status
, 0);
351 perror_with_name (("waitpid"));
352 else if (ret
!= child_pid
)
353 error (_("linux_check_ptrace_features: waitpid: unexpected result %d."),
355 if (! WIFSTOPPED (status
))
356 error (_("linux_check_ptrace_features: waitpid: unexpected status %d."),
359 linux_test_for_tracesysgood (child_pid
);
361 linux_test_for_tracefork (child_pid
);
363 linux_test_for_exitkill (child_pid
);
365 /* Clean things up and kill any pending children. */
368 ret
= ptrace (PTRACE_KILL
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
369 (PTRACE_TYPE_ARG4
) 0);
371 warning (_("linux_check_ptrace_features: failed to kill child"));
372 my_waitpid (child_pid
, &status
, 0);
374 while (WIFSTOPPED (status
));
377 /* Determine if PTRACE_O_TRACESYSGOOD can be used to catch
381 linux_test_for_tracesysgood (int child_pid
)
385 ret
= ptrace (PTRACE_SETOPTIONS
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
386 (PTRACE_TYPE_ARG4
) PTRACE_O_TRACESYSGOOD
);
389 supported_ptrace_options
|= PTRACE_O_TRACESYSGOOD
;
392 /* Determine if PTRACE_O_TRACEFORK can be used to follow fork
396 linux_test_for_tracefork (int child_pid
)
401 /* First, set the PTRACE_O_TRACEFORK option. If this fails, we
402 know for sure that it is not supported. */
403 ret
= ptrace (PTRACE_SETOPTIONS
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
404 (PTRACE_TYPE_ARG4
) PTRACE_O_TRACEFORK
);
409 /* Check if the target supports PTRACE_O_TRACEVFORKDONE. */
410 ret
= ptrace (PTRACE_SETOPTIONS
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
411 (PTRACE_TYPE_ARG4
) (PTRACE_O_TRACEFORK
412 | PTRACE_O_TRACEVFORKDONE
));
414 supported_ptrace_options
|= PTRACE_O_TRACEVFORKDONE
;
416 /* Setting PTRACE_O_TRACEFORK did not cause an error, however we
417 don't know for sure that the feature is available; old
418 versions of PTRACE_SETOPTIONS ignored unknown options.
419 Therefore, we attach to the child process, use PTRACE_SETOPTIONS
420 to enable fork tracing, and let it fork. If the process exits,
421 we assume that we can't use PTRACE_O_TRACEFORK; if we get the
422 fork notification, and we can extract the new child's PID, then
423 we assume that we can.
425 We do not explicitly check for vfork tracing here. It is
426 assumed that vfork tracing is available whenever fork tracing
428 ret
= ptrace (PTRACE_CONT
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
429 (PTRACE_TYPE_ARG4
) 0);
431 warning (_("linux_test_for_tracefork: failed to resume child"));
433 ret
= my_waitpid (child_pid
, &status
, 0);
435 /* Check if we received a fork event notification. */
436 if (ret
== child_pid
&& WIFSTOPPED (status
)
437 && linux_ptrace_get_extended_event (status
) == PTRACE_EVENT_FORK
)
439 /* We did receive a fork event notification. Make sure its PID
442 ret
= ptrace (PTRACE_GETEVENTMSG
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
443 (PTRACE_TYPE_ARG4
) &second_pid
);
444 if (ret
== 0 && second_pid
!= 0)
448 /* We got the PID from the grandchild, which means fork
449 tracing is supported. */
450 supported_ptrace_options
|= PTRACE_O_TRACECLONE
;
451 supported_ptrace_options
|= (PTRACE_O_TRACEFORK
452 | PTRACE_O_TRACEVFORK
453 | PTRACE_O_TRACEEXEC
);
455 /* Do some cleanup and kill the grandchild. */
456 my_waitpid (second_pid
, &second_status
, 0);
457 ret
= ptrace (PTRACE_KILL
, second_pid
, (PTRACE_TYPE_ARG3
) 0,
458 (PTRACE_TYPE_ARG4
) 0);
460 warning (_("linux_test_for_tracefork: "
461 "failed to kill second child"));
462 my_waitpid (second_pid
, &status
, 0);
466 warning (_("linux_test_for_tracefork: unexpected result from waitpid "
467 "(%d, status 0x%x)"), ret
, status
);
470 /* Determine if PTRACE_O_EXITKILL can be used. */
473 linux_test_for_exitkill (int child_pid
)
477 ret
= ptrace (PTRACE_SETOPTIONS
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
478 (PTRACE_TYPE_ARG4
) PTRACE_O_EXITKILL
);
481 supported_ptrace_options
|= PTRACE_O_EXITKILL
;
484 /* Enable reporting of all currently supported ptrace events.
485 OPTIONS is a bit mask of extended features we want enabled,
486 if supported by the kernel. PTRACE_O_TRACECLONE is always
487 enabled, if supported. */
490 linux_enable_event_reporting (pid_t pid
, int options
)
492 /* Check if we have initialized the ptrace features for this
493 target. If not, do it now. */
494 if (supported_ptrace_options
== -1)
495 linux_check_ptrace_features ();
497 /* We always want clone events. */
498 options
|= PTRACE_O_TRACECLONE
;
500 /* Filter out unsupported options. */
501 options
&= supported_ptrace_options
;
503 /* Set the options. */
504 ptrace (PTRACE_SETOPTIONS
, pid
, (PTRACE_TYPE_ARG3
) 0,
505 (PTRACE_TYPE_ARG4
) (uintptr_t) options
);
508 /* Disable reporting of all currently supported ptrace events. */
511 linux_disable_event_reporting (pid_t pid
)
513 /* Set the options. */
514 ptrace (PTRACE_SETOPTIONS
, pid
, (PTRACE_TYPE_ARG3
) 0, 0);
517 /* Returns non-zero if PTRACE_OPTIONS is contained within
518 SUPPORTED_PTRACE_OPTIONS, therefore supported. Returns 0
522 ptrace_supports_feature (int ptrace_options
)
524 if (supported_ptrace_options
== -1)
525 linux_check_ptrace_features ();
527 return ((supported_ptrace_options
& ptrace_options
) == ptrace_options
);
530 /* Returns non-zero if PTRACE_EVENT_FORK is supported by ptrace,
531 0 otherwise. Note that if PTRACE_EVENT_FORK is supported so is
532 PTRACE_EVENT_CLONE, PTRACE_EVENT_EXEC and PTRACE_EVENT_VFORK,
533 since they were all added to the kernel at the same time. */
536 linux_supports_tracefork (void)
538 return ptrace_supports_feature (PTRACE_O_TRACEFORK
);
541 /* Returns non-zero if PTRACE_EVENT_EXEC is supported by ptrace,
542 0 otherwise. Note that if PTRACE_EVENT_FORK is supported so is
543 PTRACE_EVENT_CLONE, PTRACE_EVENT_FORK and PTRACE_EVENT_VFORK,
544 since they were all added to the kernel at the same time. */
547 linux_supports_traceexec (void)
549 return ptrace_supports_feature (PTRACE_O_TRACEEXEC
);
552 /* Returns non-zero if PTRACE_EVENT_CLONE is supported by ptrace,
553 0 otherwise. Note that if PTRACE_EVENT_CLONE is supported so is
554 PTRACE_EVENT_FORK, PTRACE_EVENT_EXEC and PTRACE_EVENT_VFORK,
555 since they were all added to the kernel at the same time. */
558 linux_supports_traceclone (void)
560 return ptrace_supports_feature (PTRACE_O_TRACECLONE
);
563 /* Returns non-zero if PTRACE_O_TRACEVFORKDONE is supported by
564 ptrace, 0 otherwise. */
567 linux_supports_tracevforkdone (void)
569 return ptrace_supports_feature (PTRACE_O_TRACEVFORKDONE
);
572 /* Returns non-zero if PTRACE_O_TRACESYSGOOD is supported by ptrace,
576 linux_supports_tracesysgood (void)
578 return ptrace_supports_feature (PTRACE_O_TRACESYSGOOD
);
581 /* Display possible problems on this system. Display them only once per GDB
585 linux_ptrace_init_warnings (void)
587 static int warned
= 0;
593 linux_ptrace_test_ret_to_nx ();
596 /* Extract extended ptrace event from wait status. */
599 linux_ptrace_get_extended_event (int wstat
)
601 return (wstat
>> 16);
604 /* Determine whether wait status denotes an extended event. */
607 linux_is_extended_waitstatus (int wstat
)
609 return (linux_ptrace_get_extended_event (wstat
) != 0);
612 /* Return true if the event in LP may be caused by breakpoint. */
615 linux_wstatus_maybe_breakpoint (int wstat
)
617 return (WIFSTOPPED (wstat
)
618 && (WSTOPSIG (wstat
) == SIGTRAP
619 /* SIGILL and SIGSEGV are also treated as traps in case a
620 breakpoint is inserted at the current PC. */
621 || WSTOPSIG (wstat
) == SIGILL
622 || WSTOPSIG (wstat
) == SIGSEGV
));