1 /* Linux-specific ptrace manipulation routines.
2 Copyright (C) 2012-2018 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"
24 #ifdef HAVE_SYS_PROCFS_H
25 #include <sys/procfs.h>
28 /* Stores the ptrace options supported by the running kernel.
29 A value of -1 means we did not check for features yet. A value
30 of 0 means there are no supported features. */
31 static int supported_ptrace_options
= -1;
33 /* Find all possible reasons we could fail to attach PID and return these
34 as a string. An empty string is returned if we didn't find any reason. */
37 linux_ptrace_attach_fail_reason (pid_t pid
)
39 pid_t tracerpid
= linux_proc_get_tracerpid_nowarn (pid
);
43 string_appendf (result
,
44 _("process %d is already traced by process %d"),
45 (int) pid
, (int) tracerpid
);
47 if (linux_proc_pid_is_zombie_nowarn (pid
))
48 string_appendf (result
,
49 _("process %d is a zombie - the process has already "
56 /* See linux-ptrace.h. */
59 linux_ptrace_attach_fail_reason_string (ptid_t ptid
, int err
)
61 long lwpid
= ptid
.lwp ();
62 std::string reason
= linux_ptrace_attach_fail_reason (lwpid
);
65 return string_printf ("%s (%d), %s", safe_strerror (err
), err
,
68 return string_printf ("%s (%d)", safe_strerror (err
), err
);
71 #if defined __i386__ || defined __x86_64__
73 /* Address of the 'ret' instruction in asm code block below. */
74 EXTERN_C
void linux_ptrace_test_ret_to_nx_instr (void);
80 #endif /* defined __i386__ || defined __x86_64__ */
82 /* Test broken off-trunk Linux kernel patchset for NX support on i386. It was
83 removed in Fedora kernel 88fa1f0332d188795ed73d7ac2b1564e11a0b4cd.
85 Test also x86_64 arch for PaX support. */
88 linux_ptrace_test_ret_to_nx (void)
90 #if defined __i386__ || defined __x86_64__
92 gdb_byte
*return_address
, *pc
;
94 int status
, kill_status
;
98 = (gdb_byte
*) mmap (NULL
, 2, PROT_READ
| PROT_WRITE
,
99 MAP_PRIVATE
| MAP_ANONYMOUS
, -1, 0);
100 if (return_address
== MAP_FAILED
)
102 warning (_("linux_ptrace_test_ret_to_nx: Cannot mmap: %s"),
103 safe_strerror (errno
));
107 /* Put there 'int3'. */
108 *return_address
= 0xcc;
114 warning (_("linux_ptrace_test_ret_to_nx: Cannot fork: %s"),
115 safe_strerror (errno
));
119 l
= ptrace (PTRACE_TRACEME
, 0, (PTRACE_TYPE_ARG3
) NULL
,
120 (PTRACE_TYPE_ARG4
) NULL
);
122 warning (_("linux_ptrace_test_ret_to_nx: Cannot PTRACE_TRACEME: %s"),
123 safe_strerror (errno
));
127 asm volatile ("pushl %0;"
128 ".globl linux_ptrace_test_ret_to_nx_instr;"
129 "linux_ptrace_test_ret_to_nx_instr:"
131 : : "r" (return_address
) : "%esp", "memory");
132 #elif defined __x86_64__
133 asm volatile ("pushq %0;"
134 ".globl linux_ptrace_test_ret_to_nx_instr;"
135 "linux_ptrace_test_ret_to_nx_instr:"
137 : : "r" ((uint64_t) (uintptr_t) return_address
)
140 # error "!__i386__ && !__x86_64__"
142 gdb_assert_not_reached ("asm block did not terminate");
149 got_pid
= waitpid (child
, &status
, 0);
150 if (got_pid
!= child
)
152 warning (_("linux_ptrace_test_ret_to_nx: waitpid returned %ld: %s"),
153 (long) got_pid
, safe_strerror (errno
));
157 if (WIFSIGNALED (status
))
159 if (WTERMSIG (status
) != SIGKILL
)
160 warning (_("linux_ptrace_test_ret_to_nx: WTERMSIG %d is not SIGKILL!"),
161 (int) WTERMSIG (status
));
163 warning (_("Cannot call inferior functions, Linux kernel PaX "
164 "protection forbids return to non-executable pages!"));
168 if (!WIFSTOPPED (status
))
170 warning (_("linux_ptrace_test_ret_to_nx: status %d is not WIFSTOPPED!"),
175 /* We may get SIGSEGV due to missing PROT_EXEC of the return_address. */
176 if (WSTOPSIG (status
) != SIGTRAP
&& WSTOPSIG (status
) != SIGSEGV
)
178 warning (_("linux_ptrace_test_ret_to_nx: "
179 "WSTOPSIG %d is neither SIGTRAP nor SIGSEGV!"),
180 (int) WSTOPSIG (status
));
184 if (ptrace (PTRACE_GETREGS
, child
, (PTRACE_TYPE_ARG3
) 0,
185 (PTRACE_TYPE_ARG4
) ®s
) < 0)
187 warning (_("linux_ptrace_test_ret_to_nx: Cannot PTRACE_GETREGS: %s"),
188 safe_strerror (errno
));
191 pc
= (gdb_byte
*) (uintptr_t) regs
[EIP
];
192 #elif defined __x86_64__
193 pc
= (gdb_byte
*) (uintptr_t) regs
[RIP
];
195 # error "!__i386__ && !__x86_64__"
198 kill (child
, SIGKILL
);
199 ptrace (PTRACE_KILL
, child
, (PTRACE_TYPE_ARG3
) NULL
,
200 (PTRACE_TYPE_ARG4
) NULL
);
203 got_pid
= waitpid (child
, &kill_status
, 0);
204 if (got_pid
!= child
)
206 warning (_("linux_ptrace_test_ret_to_nx: "
207 "PTRACE_KILL waitpid returned %ld: %s"),
208 (long) got_pid
, safe_strerror (errno
));
211 if (!WIFSIGNALED (kill_status
))
213 warning (_("linux_ptrace_test_ret_to_nx: "
214 "PTRACE_KILL status %d is not WIFSIGNALED!"),
219 /* + 1 is there as x86* stops after the 'int3' instruction. */
220 if (WSTOPSIG (status
) == SIGTRAP
&& pc
== return_address
+ 1)
226 /* We may get SIGSEGV due to missing PROT_EXEC of the RETURN_ADDRESS page. */
227 if (WSTOPSIG (status
) == SIGSEGV
&& pc
== return_address
)
233 if ((void (*) (void)) pc
!= &linux_ptrace_test_ret_to_nx_instr
)
234 warning (_("linux_ptrace_test_ret_to_nx: PC %p is neither near return "
235 "address %p nor is the return instruction %p!"),
236 pc
, return_address
, &linux_ptrace_test_ret_to_nx_instr
);
238 warning (_("Cannot call inferior functions on this system - "
239 "Linux kernel with broken i386 NX (non-executable pages) "
240 "support detected!"));
241 #endif /* defined __i386__ || defined __x86_64__ */
244 /* Helper function to fork a process and make the child process call
245 the function FUNCTION, passing CHILD_STACK as parameter.
247 For MMU-less targets, clone is used instead of fork, and
248 CHILD_STACK is used as stack space for the cloned child. If NULL,
249 stack space is allocated via malloc (and subsequently passed to
250 FUNCTION). For MMU targets, CHILD_STACK is ignored. */
253 linux_fork_to_function (gdb_byte
*child_stack
, int (*function
) (void *))
257 /* Sanity check the function pointer. */
258 gdb_assert (function
!= NULL
);
260 #if defined(__UCLIBC__) && defined(HAS_NOMMU)
261 #define STACK_SIZE 4096
263 if (child_stack
== NULL
)
264 child_stack
= (gdb_byte
*) xmalloc (STACK_SIZE
* 4);
266 /* Use CLONE_VM instead of fork, to support uClinux (no MMU). */
268 child_pid
= __clone2 (function
, child_stack
, STACK_SIZE
,
269 CLONE_VM
| SIGCHLD
, child_stack
+ STACK_SIZE
* 2);
270 #else /* !__ia64__ */
271 child_pid
= clone (function
, child_stack
+ STACK_SIZE
,
272 CLONE_VM
| SIGCHLD
, child_stack
+ STACK_SIZE
* 2);
273 #endif /* !__ia64__ */
274 #else /* !defined(__UCLIBC) && defined(HAS_NOMMU) */
279 #endif /* defined(__UCLIBC) && defined(HAS_NOMMU) */
282 perror_with_name (("fork"));
287 /* A helper function for linux_check_ptrace_features, called after
288 the child forks a grandchild. */
291 linux_grandchild_function (void *child_stack
)
293 /* Free any allocated stack. */
296 /* This code is only reacheable by the grandchild (child's child)
301 /* A helper function for linux_check_ptrace_features, called after
302 the parent process forks a child. The child allows itself to
303 be traced by its parent. */
306 linux_child_function (void *child_stack
)
308 ptrace (PTRACE_TRACEME
, 0, (PTRACE_TYPE_ARG3
) 0, (PTRACE_TYPE_ARG4
) 0);
309 kill (getpid (), SIGSTOP
);
311 /* Fork a grandchild. */
312 linux_fork_to_function ((gdb_byte
*) child_stack
, linux_grandchild_function
);
314 /* This code is only reacheable by the child (grandchild's parent)
319 static void linux_test_for_tracesysgood (int child_pid
);
320 static void linux_test_for_tracefork (int child_pid
);
321 static void linux_test_for_exitkill (int child_pid
);
323 /* Determine ptrace features available on this target. */
326 linux_check_ptrace_features (void)
328 int child_pid
, ret
, status
;
330 /* Initialize the options. */
331 supported_ptrace_options
= 0;
333 /* Fork a child so we can do some testing. The child will call
334 linux_child_function and will get traced. The child will
335 eventually fork a grandchild so we can test fork event
337 child_pid
= linux_fork_to_function (NULL
, linux_child_function
);
339 ret
= my_waitpid (child_pid
, &status
, 0);
341 perror_with_name (("waitpid"));
342 else if (ret
!= child_pid
)
343 error (_("linux_check_ptrace_features: waitpid: unexpected result %d."),
345 if (! WIFSTOPPED (status
))
346 error (_("linux_check_ptrace_features: waitpid: unexpected status %d."),
349 linux_test_for_tracesysgood (child_pid
);
351 linux_test_for_tracefork (child_pid
);
353 linux_test_for_exitkill (child_pid
);
355 /* Clean things up and kill any pending children. */
358 ret
= ptrace (PTRACE_KILL
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
359 (PTRACE_TYPE_ARG4
) 0);
361 warning (_("linux_check_ptrace_features: failed to kill child"));
362 my_waitpid (child_pid
, &status
, 0);
364 while (WIFSTOPPED (status
));
367 /* Determine if PTRACE_O_TRACESYSGOOD can be used to catch
371 linux_test_for_tracesysgood (int child_pid
)
375 ret
= ptrace (PTRACE_SETOPTIONS
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
376 (PTRACE_TYPE_ARG4
) PTRACE_O_TRACESYSGOOD
);
379 supported_ptrace_options
|= PTRACE_O_TRACESYSGOOD
;
382 /* Determine if PTRACE_O_TRACEFORK can be used to follow fork
386 linux_test_for_tracefork (int child_pid
)
391 /* First, set the PTRACE_O_TRACEFORK option. If this fails, we
392 know for sure that it is not supported. */
393 ret
= ptrace (PTRACE_SETOPTIONS
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
394 (PTRACE_TYPE_ARG4
) PTRACE_O_TRACEFORK
);
399 /* Check if the target supports PTRACE_O_TRACEVFORKDONE. */
400 ret
= ptrace (PTRACE_SETOPTIONS
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
401 (PTRACE_TYPE_ARG4
) (PTRACE_O_TRACEFORK
402 | PTRACE_O_TRACEVFORKDONE
));
404 supported_ptrace_options
|= PTRACE_O_TRACEVFORKDONE
;
406 /* Setting PTRACE_O_TRACEFORK did not cause an error, however we
407 don't know for sure that the feature is available; old
408 versions of PTRACE_SETOPTIONS ignored unknown options.
409 Therefore, we attach to the child process, use PTRACE_SETOPTIONS
410 to enable fork tracing, and let it fork. If the process exits,
411 we assume that we can't use PTRACE_O_TRACEFORK; if we get the
412 fork notification, and we can extract the new child's PID, then
413 we assume that we can.
415 We do not explicitly check for vfork tracing here. It is
416 assumed that vfork tracing is available whenever fork tracing
418 ret
= ptrace (PTRACE_CONT
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
419 (PTRACE_TYPE_ARG4
) 0);
421 warning (_("linux_test_for_tracefork: failed to resume child"));
423 ret
= my_waitpid (child_pid
, &status
, 0);
425 /* Check if we received a fork event notification. */
426 if (ret
== child_pid
&& WIFSTOPPED (status
)
427 && linux_ptrace_get_extended_event (status
) == PTRACE_EVENT_FORK
)
429 /* We did receive a fork event notification. Make sure its PID
432 ret
= ptrace (PTRACE_GETEVENTMSG
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
433 (PTRACE_TYPE_ARG4
) &second_pid
);
434 if (ret
== 0 && second_pid
!= 0)
438 /* We got the PID from the grandchild, which means fork
439 tracing is supported. */
440 supported_ptrace_options
|= PTRACE_O_TRACECLONE
;
441 supported_ptrace_options
|= (PTRACE_O_TRACEFORK
442 | PTRACE_O_TRACEVFORK
443 | PTRACE_O_TRACEEXEC
);
445 /* Do some cleanup and kill the grandchild. */
446 my_waitpid (second_pid
, &second_status
, 0);
447 ret
= ptrace (PTRACE_KILL
, second_pid
, (PTRACE_TYPE_ARG3
) 0,
448 (PTRACE_TYPE_ARG4
) 0);
450 warning (_("linux_test_for_tracefork: "
451 "failed to kill second child"));
452 my_waitpid (second_pid
, &status
, 0);
456 warning (_("linux_test_for_tracefork: unexpected result from waitpid "
457 "(%d, status 0x%x)"), ret
, status
);
460 /* Determine if PTRACE_O_EXITKILL can be used. */
463 linux_test_for_exitkill (int child_pid
)
467 ret
= ptrace (PTRACE_SETOPTIONS
, child_pid
, (PTRACE_TYPE_ARG3
) 0,
468 (PTRACE_TYPE_ARG4
) PTRACE_O_EXITKILL
);
471 supported_ptrace_options
|= PTRACE_O_EXITKILL
;
474 /* Enable reporting of all currently supported ptrace events.
475 OPTIONS is a bit mask of extended features we want enabled,
476 if supported by the kernel. PTRACE_O_TRACECLONE is always
477 enabled, if supported. */
480 linux_enable_event_reporting (pid_t pid
, int options
)
482 /* Check if we have initialized the ptrace features for this
483 target. If not, do it now. */
484 if (supported_ptrace_options
== -1)
485 linux_check_ptrace_features ();
487 /* We always want clone events. */
488 options
|= PTRACE_O_TRACECLONE
;
490 /* Filter out unsupported options. */
491 options
&= supported_ptrace_options
;
493 /* Set the options. */
494 ptrace (PTRACE_SETOPTIONS
, pid
, (PTRACE_TYPE_ARG3
) 0,
495 (PTRACE_TYPE_ARG4
) (uintptr_t) options
);
498 /* Disable reporting of all currently supported ptrace events. */
501 linux_disable_event_reporting (pid_t pid
)
503 /* Set the options. */
504 ptrace (PTRACE_SETOPTIONS
, pid
, (PTRACE_TYPE_ARG3
) 0, 0);
507 /* Returns non-zero if PTRACE_OPTIONS is contained within
508 SUPPORTED_PTRACE_OPTIONS, therefore supported. Returns 0
512 ptrace_supports_feature (int ptrace_options
)
514 if (supported_ptrace_options
== -1)
515 linux_check_ptrace_features ();
517 return ((supported_ptrace_options
& ptrace_options
) == ptrace_options
);
520 /* Returns non-zero if PTRACE_EVENT_FORK is supported by ptrace,
521 0 otherwise. Note that if PTRACE_EVENT_FORK is supported so is
522 PTRACE_EVENT_CLONE, PTRACE_EVENT_EXEC and PTRACE_EVENT_VFORK,
523 since they were all added to the kernel at the same time. */
526 linux_supports_tracefork (void)
528 return ptrace_supports_feature (PTRACE_O_TRACEFORK
);
531 /* Returns non-zero if PTRACE_EVENT_EXEC is supported by ptrace,
532 0 otherwise. Note that if PTRACE_EVENT_FORK is supported so is
533 PTRACE_EVENT_CLONE, PTRACE_EVENT_FORK and PTRACE_EVENT_VFORK,
534 since they were all added to the kernel at the same time. */
537 linux_supports_traceexec (void)
539 return ptrace_supports_feature (PTRACE_O_TRACEEXEC
);
542 /* Returns non-zero if PTRACE_EVENT_CLONE is supported by ptrace,
543 0 otherwise. Note that if PTRACE_EVENT_CLONE is supported so is
544 PTRACE_EVENT_FORK, PTRACE_EVENT_EXEC and PTRACE_EVENT_VFORK,
545 since they were all added to the kernel at the same time. */
548 linux_supports_traceclone (void)
550 return ptrace_supports_feature (PTRACE_O_TRACECLONE
);
553 /* Returns non-zero if PTRACE_O_TRACEVFORKDONE is supported by
554 ptrace, 0 otherwise. */
557 linux_supports_tracevforkdone (void)
559 return ptrace_supports_feature (PTRACE_O_TRACEVFORKDONE
);
562 /* Returns non-zero if PTRACE_O_TRACESYSGOOD is supported by ptrace,
566 linux_supports_tracesysgood (void)
568 return ptrace_supports_feature (PTRACE_O_TRACESYSGOOD
);
571 /* Display possible problems on this system. Display them only once per GDB
575 linux_ptrace_init_warnings (void)
577 static int warned
= 0;
583 linux_ptrace_test_ret_to_nx ();
586 /* Extract extended ptrace event from wait status. */
589 linux_ptrace_get_extended_event (int wstat
)
591 return (wstat
>> 16);
594 /* Determine whether wait status denotes an extended event. */
597 linux_is_extended_waitstatus (int wstat
)
599 return (linux_ptrace_get_extended_event (wstat
) != 0);
602 /* Return true if the event in LP may be caused by breakpoint. */
605 linux_wstatus_maybe_breakpoint (int wstat
)
607 return (WIFSTOPPED (wstat
)
608 && (WSTOPSIG (wstat
) == SIGTRAP
609 /* SIGILL and SIGSEGV are also treated as traps in case a
610 breakpoint is inserted at the current PC. */
611 || WSTOPSIG (wstat
) == SIGILL
612 || WSTOPSIG (wstat
) == SIGSEGV
));