1 /* Copyright (C) 2002-2021 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library; if not, see
16 <https://www.gnu.org/licenses/>. */
25 #include <sys/param.h>
26 #include <dl-sysdep.h>
30 #include <lowlevellock.h>
31 #include <futex-internal.h>
32 #include <kernel-features.h>
33 #include <nptl-stack.h>
34 #include <libc-lock.h>
36 /* Default alignment of stack. */
38 # define STACK_ALIGN __alignof__ (long double)
41 /* Default value for minimal stack size after allocating thread
42 descriptor and guard. */
43 #ifndef MINIMAL_REST_STACK
44 # define MINIMAL_REST_STACK 4096
48 /* Newer kernels have the MAP_STACK flag to indicate a mapping is used for
49 a stack. Use it when possible. */
54 /* Get a stack frame from the cache. We have to match by size since
55 some blocks might be too small or far too large. */
56 static struct pthread
*
57 get_cached_stack (size_t *sizep
, void **memp
)
60 struct pthread
*result
= NULL
;
63 lll_lock (GL (dl_stack_cache_lock
), LLL_PRIVATE
);
65 /* Search the cache for a matching entry. We search for the
66 smallest stack which has at least the required size. Note that
67 in normal situations the size of all allocated stacks is the
68 same. As the very least there are only a few different sizes.
69 Therefore this loop will exit early most of the time with an
71 list_for_each (entry
, &GL (dl_stack_cache
))
75 curr
= list_entry (entry
, struct pthread
, list
);
76 if (__nptl_stack_in_use (curr
) && curr
->stackblock_size
>= size
)
78 if (curr
->stackblock_size
== size
)
85 || result
->stackblock_size
> curr
->stackblock_size
)
90 if (__builtin_expect (result
== NULL
, 0)
91 /* Make sure the size difference is not too excessive. In that
92 case we do not use the block. */
93 || __builtin_expect (result
->stackblock_size
> 4 * size
, 0))
95 /* Release the lock. */
96 lll_unlock (GL (dl_stack_cache_lock
), LLL_PRIVATE
);
101 /* Don't allow setxid until cloned. */
102 result
->setxid_futex
= -1;
104 /* Dequeue the entry. */
105 __nptl_stack_list_del (&result
->list
);
107 /* And add to the list of stacks in use. */
108 __nptl_stack_list_add (&result
->list
, &GL (dl_stack_used
));
110 /* And decrease the cache size. */
111 GL (dl_stack_cache_actsize
) -= result
->stackblock_size
;
113 /* Release the lock early. */
114 lll_unlock (GL (dl_stack_cache_lock
), LLL_PRIVATE
);
116 /* Report size and location of the stack to the caller. */
117 *sizep
= result
->stackblock_size
;
118 *memp
= result
->stackblock
;
120 /* Cancellation handling is back to the default. */
121 result
->cancelhandling
= 0;
122 result
->cancelstate
= PTHREAD_CANCEL_ENABLE
;
123 result
->canceltype
= PTHREAD_CANCEL_DEFERRED
;
124 result
->cleanup
= NULL
;
125 result
->setup_failed
= 0;
127 /* No pending event. */
128 result
->nextevent
= NULL
;
130 result
->exiting
= false;
131 __libc_lock_init (result
->exit_lock
);
132 result
->tls_state
= (struct tls_internal_t
) { 0 };
135 dtv_t
*dtv
= GET_DTV (TLS_TPADJ (result
));
136 for (size_t cnt
= 0; cnt
< dtv
[-1].counter
; ++cnt
)
137 free (dtv
[1 + cnt
].pointer
.to_free
);
138 memset (dtv
, '\0', (dtv
[-1].counter
+ 1) * sizeof (dtv_t
));
140 /* Re-initialize the TLS. */
141 _dl_allocate_tls_init (TLS_TPADJ (result
));
146 /* Return the guard page position on allocated stack. */
148 __attribute ((always_inline
))
149 guard_position (void *mem
, size_t size
, size_t guardsize
, struct pthread
*pd
,
152 #ifdef NEED_SEPARATE_REGISTER_STACK
153 return mem
+ (((size
- guardsize
) / 2) & ~pagesize_m1
);
154 #elif _STACK_GROWS_DOWN
156 #elif _STACK_GROWS_UP
157 return (char *) (((uintptr_t) pd
- guardsize
) & ~pagesize_m1
);
161 /* Based on stack allocated with PROT_NONE, setup the required portions with
162 'prot' flags based on the guard page position. */
164 setup_stack_prot (char *mem
, size_t size
, char *guard
, size_t guardsize
,
167 char *guardend
= guard
+ guardsize
;
168 #if _STACK_GROWS_DOWN && !defined(NEED_SEPARATE_REGISTER_STACK)
169 /* As defined at guard_position, for architectures with downward stack
170 the guard page is always at start of the allocated area. */
171 if (__mprotect (guardend
, size
- guardsize
, prot
) != 0)
174 size_t mprots1
= (uintptr_t) guard
- (uintptr_t) mem
;
175 if (__mprotect (mem
, mprots1
, prot
) != 0)
177 size_t mprots2
= ((uintptr_t) mem
+ size
) - (uintptr_t) guardend
;
178 if (__mprotect (guardend
, mprots2
, prot
) != 0)
184 /* Mark the memory of the stack as usable to the kernel. It frees everything
185 except for the space used for the TCB itself. */
186 static __always_inline
void
187 advise_stack_range (void *mem
, size_t size
, uintptr_t pd
, size_t guardsize
)
189 uintptr_t sp
= (uintptr_t) CURRENT_STACK_FRAME
;
190 size_t pagesize_m1
= __getpagesize () - 1;
191 #if _STACK_GROWS_DOWN && !defined(NEED_SEPARATE_REGISTER_STACK)
192 size_t freesize
= (sp
- (uintptr_t) mem
) & ~pagesize_m1
;
193 assert (freesize
< size
);
194 if (freesize
> PTHREAD_STACK_MIN
)
195 __madvise (mem
, freesize
- PTHREAD_STACK_MIN
, MADV_DONTNEED
);
197 /* Page aligned start of memory to free (higher than or equal
198 to current sp plus the minimum stack size). */
199 uintptr_t freeblock
= (sp
+ PTHREAD_STACK_MIN
+ pagesize_m1
) & ~pagesize_m1
;
200 uintptr_t free_end
= (pd
- guardsize
) & ~pagesize_m1
;
201 if (free_end
> freeblock
)
203 size_t freesize
= free_end
- freeblock
;
204 assert (freesize
< size
);
205 __madvise ((void*) freeblock
, freesize
, MADV_DONTNEED
);
210 /* Returns a usable stack for a new thread either by allocating a
211 new stack or reusing a cached stack of sufficient size.
212 ATTR must be non-NULL and point to a valid pthread_attr.
213 PDP must be non-NULL. */
215 allocate_stack (const struct pthread_attr
*attr
, struct pthread
**pdp
,
216 void **stack
, size_t *stacksize
)
220 size_t pagesize_m1
= __getpagesize () - 1;
221 size_t tls_static_size_for_stack
= __nptl_tls_static_size_for_stack ();
222 size_t tls_static_align_m1
= GLRO (dl_tls_static_align
) - 1;
224 assert (powerof2 (pagesize_m1
+ 1));
225 assert (TCB_ALIGNMENT
>= STACK_ALIGN
);
227 /* Get the stack size from the attribute if it is set. Otherwise we
228 use the default we determined at start time. */
229 if (attr
->stacksize
!= 0)
230 size
= attr
->stacksize
;
233 lll_lock (__default_pthread_attr_lock
, LLL_PRIVATE
);
234 size
= __default_pthread_attr
.internal
.stacksize
;
235 lll_unlock (__default_pthread_attr_lock
, LLL_PRIVATE
);
238 /* Get memory for the stack. */
239 if (__glibc_unlikely (attr
->flags
& ATTR_FLAG_STACKADDR
))
242 char *stackaddr
= (char *) attr
->stackaddr
;
244 /* Assume the same layout as the _STACK_GROWS_DOWN case, with struct
245 pthread at the top of the stack block. Later we adjust the guard
246 location and stack address to match the _STACK_GROWS_UP case. */
248 stackaddr
+= attr
->stacksize
;
250 /* If the user also specified the size of the stack make sure it
252 if (attr
->stacksize
!= 0
253 && attr
->stacksize
< (tls_static_size_for_stack
254 + MINIMAL_REST_STACK
))
257 /* Adjust stack size for alignment of the TLS block. */
259 adj
= ((uintptr_t) stackaddr
- TLS_TCB_SIZE
)
260 & tls_static_align_m1
;
261 assert (size
> adj
+ TLS_TCB_SIZE
);
263 adj
= ((uintptr_t) stackaddr
- tls_static_size_for_stack
)
264 & tls_static_align_m1
;
268 /* The user provided some memory. Let's hope it matches the
269 size... We do not allocate guard pages if the user provided
270 the stack. It is the user's responsibility to do this if it
273 pd
= (struct pthread
*) ((uintptr_t) stackaddr
274 - TLS_TCB_SIZE
- adj
);
276 pd
= (struct pthread
*) (((uintptr_t) stackaddr
277 - tls_static_size_for_stack
- adj
)
281 /* The user provided stack memory needs to be cleared. */
282 memset (pd
, '\0', sizeof (struct pthread
));
284 /* The first TSD block is included in the TCB. */
285 pd
->specific
[0] = pd
->specific_1stblock
;
287 /* Remember the stack-related values. */
288 pd
->stackblock
= (char *) stackaddr
- size
;
289 pd
->stackblock_size
= size
;
291 /* This is a user-provided stack. It will not be queued in the
292 stack cache nor will the memory (except the TLS memory) be freed. */
293 pd
->user_stack
= true;
295 /* This is at least the second thread. */
296 pd
->header
.multiple_threads
= 1;
297 #ifndef TLS_MULTIPLE_THREADS_IN_TCB
298 __libc_multiple_threads
= 1;
301 #ifdef NEED_DL_SYSINFO
302 SETUP_THREAD_SYSINFO (pd
);
305 /* Don't allow setxid until cloned. */
306 pd
->setxid_futex
= -1;
308 /* Allocate the DTV for this thread. */
309 if (_dl_allocate_tls (TLS_TPADJ (pd
)) == NULL
)
311 /* Something went wrong. */
312 assert (errno
== ENOMEM
);
317 /* Prepare to modify global data. */
318 lll_lock (GL (dl_stack_cache_lock
), LLL_PRIVATE
);
320 /* And add to the list of stacks in use. */
321 list_add (&pd
->list
, &GL (dl_stack_user
));
323 lll_unlock (GL (dl_stack_cache_lock
), LLL_PRIVATE
);
327 /* Allocate some anonymous memory. If possible use the cache. */
329 size_t reported_guardsize
;
332 const int prot
= (PROT_READ
| PROT_WRITE
333 | ((GL(dl_stack_flags
) & PF_X
) ? PROT_EXEC
: 0));
335 /* Adjust the stack size for alignment. */
336 size
&= ~tls_static_align_m1
;
339 /* Make sure the size of the stack is enough for the guard and
340 eventually the thread descriptor. On some targets there is
341 a minimum guard size requirement, ARCH_MIN_GUARD_SIZE, so
342 internally enforce it (unless the guard was disabled), but
343 report the original guard size for backward compatibility:
344 before POSIX 2008 the guardsize was specified to be one page
345 by default which is observable via pthread_attr_getguardsize
346 and pthread_getattr_np. */
347 guardsize
= (attr
->guardsize
+ pagesize_m1
) & ~pagesize_m1
;
348 reported_guardsize
= guardsize
;
349 if (guardsize
> 0 && guardsize
< ARCH_MIN_GUARD_SIZE
)
350 guardsize
= ARCH_MIN_GUARD_SIZE
;
351 if (guardsize
< attr
->guardsize
|| size
+ guardsize
< guardsize
)
352 /* Arithmetic overflow. */
355 if (__builtin_expect (size
< ((guardsize
+ tls_static_size_for_stack
356 + MINIMAL_REST_STACK
+ pagesize_m1
)
359 /* The stack is too small (or the guard too large). */
362 /* Try to get a stack from the cache. */
364 pd
= get_cached_stack (&size
, &mem
);
367 /* If a guard page is required, avoid committing memory by first
368 allocate with PROT_NONE and then reserve with required permission
369 excluding the guard page. */
370 mem
= __mmap (NULL
, size
, (guardsize
== 0) ? prot
: PROT_NONE
,
371 MAP_PRIVATE
| MAP_ANONYMOUS
| MAP_STACK
, -1, 0);
373 if (__glibc_unlikely (mem
== MAP_FAILED
))
376 /* SIZE is guaranteed to be greater than zero.
377 So we can never get a null pointer back from mmap. */
378 assert (mem
!= NULL
);
380 /* Place the thread descriptor at the end of the stack. */
382 pd
= (struct pthread
*) ((((uintptr_t) mem
+ size
)
384 & ~tls_static_align_m1
);
386 pd
= (struct pthread
*) ((((uintptr_t) mem
+ size
387 - tls_static_size_for_stack
)
388 & ~tls_static_align_m1
)
392 /* Now mprotect the required region excluding the guard area. */
393 if (__glibc_likely (guardsize
> 0))
395 char *guard
= guard_position (mem
, size
, guardsize
, pd
,
397 if (setup_stack_prot (mem
, size
, guard
, guardsize
, prot
) != 0)
399 __munmap (mem
, size
);
404 /* Remember the stack-related values. */
405 pd
->stackblock
= mem
;
406 pd
->stackblock_size
= size
;
407 /* Update guardsize for newly allocated guardsize to avoid
408 an mprotect in guard resize below. */
409 pd
->guardsize
= guardsize
;
411 /* We allocated the first block thread-specific data array.
412 This address will not change for the lifetime of this
414 pd
->specific
[0] = pd
->specific_1stblock
;
416 /* This is at least the second thread. */
417 pd
->header
.multiple_threads
= 1;
418 #ifndef TLS_MULTIPLE_THREADS_IN_TCB
419 __libc_multiple_threads
= 1;
422 #ifdef NEED_DL_SYSINFO
423 SETUP_THREAD_SYSINFO (pd
);
426 /* Don't allow setxid until cloned. */
427 pd
->setxid_futex
= -1;
429 /* Allocate the DTV for this thread. */
430 if (_dl_allocate_tls (TLS_TPADJ (pd
)) == NULL
)
432 /* Something went wrong. */
433 assert (errno
== ENOMEM
);
435 /* Free the stack memory we just allocated. */
436 (void) __munmap (mem
, size
);
442 /* Prepare to modify global data. */
443 lll_lock (GL (dl_stack_cache_lock
), LLL_PRIVATE
);
445 /* And add to the list of stacks in use. */
446 __nptl_stack_list_add (&pd
->list
, &GL (dl_stack_used
));
448 lll_unlock (GL (dl_stack_cache_lock
), LLL_PRIVATE
);
451 /* There might have been a race. Another thread might have
452 caused the stacks to get exec permission while this new
453 stack was prepared. Detect if this was possible and
454 change the permission if necessary. */
455 if (__builtin_expect ((GL(dl_stack_flags
) & PF_X
) != 0
456 && (prot
& PROT_EXEC
) == 0, 0))
458 int err
= __nptl_change_stack_perm (pd
);
461 /* Free the stack memory we just allocated. */
462 (void) __munmap (mem
, size
);
469 /* Note that all of the stack and the thread descriptor is
470 zeroed. This means we do not have to initialize fields
471 with initial value zero. This is specifically true for
472 the 'tid' field which is always set back to zero once the
473 stack is not used anymore and for the 'guardsize' field
474 which will be read next. */
477 /* Create or resize the guard area if necessary. */
478 if (__glibc_unlikely (guardsize
> pd
->guardsize
))
480 char *guard
= guard_position (mem
, size
, guardsize
, pd
,
482 if (__mprotect (guard
, guardsize
, PROT_NONE
) != 0)
485 lll_lock (GL (dl_stack_cache_lock
), LLL_PRIVATE
);
487 /* Remove the thread from the list. */
488 __nptl_stack_list_del (&pd
->list
);
490 lll_unlock (GL (dl_stack_cache_lock
), LLL_PRIVATE
);
492 /* Get rid of the TLS block we allocated. */
493 _dl_deallocate_tls (TLS_TPADJ (pd
), false);
495 /* Free the stack memory regardless of whether the size
496 of the cache is over the limit or not. If this piece
497 of memory caused problems we better do not use it
498 anymore. Uh, and we ignore possible errors. There
499 is nothing we could do. */
500 (void) __munmap (mem
, size
);
505 pd
->guardsize
= guardsize
;
507 else if (__builtin_expect (pd
->guardsize
- guardsize
> size
- reqsize
,
510 /* The old guard area is too large. */
512 #ifdef NEED_SEPARATE_REGISTER_STACK
513 char *guard
= mem
+ (((size
- guardsize
) / 2) & ~pagesize_m1
);
514 char *oldguard
= mem
+ (((size
- pd
->guardsize
) / 2) & ~pagesize_m1
);
517 && __mprotect (oldguard
, guard
- oldguard
, prot
) != 0)
520 if (__mprotect (guard
+ guardsize
,
521 oldguard
+ pd
->guardsize
- guard
- guardsize
,
524 #elif _STACK_GROWS_DOWN
525 if (__mprotect ((char *) mem
+ guardsize
, pd
->guardsize
- guardsize
,
528 #elif _STACK_GROWS_UP
529 char *new_guard
= (char *)(((uintptr_t) pd
- guardsize
)
531 char *old_guard
= (char *)(((uintptr_t) pd
- pd
->guardsize
)
533 /* The guard size difference might be > 0, but once rounded
534 to the nearest page the size difference might be zero. */
535 if (new_guard
> old_guard
536 && __mprotect (old_guard
, new_guard
- old_guard
, prot
) != 0)
540 pd
->guardsize
= guardsize
;
542 /* The pthread_getattr_np() calls need to get passed the size
543 requested in the attribute, regardless of how large the
544 actually used guardsize is. */
545 pd
->reported_guardsize
= reported_guardsize
;
548 /* Initialize the lock. We have to do this unconditionally since the
549 stillborn thread could be canceled while the lock is taken. */
550 pd
->lock
= LLL_LOCK_INITIALIZER
;
552 /* The robust mutex lists also need to be initialized
553 unconditionally because the cleanup for the previous stack owner
554 might have happened in the kernel. */
555 pd
->robust_head
.futex_offset
= (offsetof (pthread_mutex_t
, __data
.__lock
)
556 - offsetof (pthread_mutex_t
,
557 __data
.__list
.__next
));
558 pd
->robust_head
.list_op_pending
= NULL
;
559 #if __PTHREAD_MUTEX_HAVE_PREV
560 pd
->robust_prev
= &pd
->robust_head
;
562 pd
->robust_head
.list
= &pd
->robust_head
;
564 /* We place the thread descriptor at the end of the stack. */
570 /* The stack begins before the TCB and the static TLS block. */
571 stacktop
= ((char *) (pd
+ 1) - tls_static_size_for_stack
);
573 stacktop
= (char *) (pd
- 1);
576 *stacksize
= stacktop
- pd
->stackblock
;
577 *stack
= pd
->stackblock
;