1 /* -----------------------------------------------------------------------------
2 * $Id: Storage.c,v 1.73 2002/12/19 14:33:23 simonmar Exp $
4 * (c) The GHC Team, 1998-1999
6 * Storage manager front end
8 * ---------------------------------------------------------------------------*/
10 #include "PosixSource.h"
16 #include "BlockAlloc.h"
24 #include "OSThreads.h"
25 #include "StoragePriv.h"
27 #include "RetainerProfile.h" // for counting memory blocks (memInventory)
32 StgClosure *caf_list = NULL;
34 bdescr *small_alloc_list; /* allocate()d small objects */
35 bdescr *pinned_object_block; /* allocate pinned objects into this block */
36 nat alloc_blocks; /* number of allocate()d blocks since GC */
37 nat alloc_blocks_lim; /* approximate limit on alloc_blocks */
39 StgPtr alloc_Hp = NULL; /* next free byte in small_alloc_list */
40 StgPtr alloc_HpLim = NULL; /* end of block at small_alloc_list */
42 generation *generations; /* all the generations */
43 generation *g0; /* generation 0, for convenience */
44 generation *oldest_gen; /* oldest generation, for convenience */
45 step *g0s0; /* generation 0, step 0, for convenience */
47 lnat total_allocated = 0; /* total memory allocated during run */
50 * Storage manager mutex: protects all the above state from
51 * simultaneous access by two STG threads.
54 Mutex sm_mutex = INIT_MUTEX_VAR;
60 static void *stgAllocForGMP (size_t size_in_bytes);
61 static void *stgReallocForGMP (void *ptr, size_t old_size, size_t new_size);
62 static void stgDeallocForGMP (void *ptr, size_t size);
71 /* Sanity check to make sure the LOOKS_LIKE_ macros appear to be
72 * doing something reasonable.
74 ASSERT(LOOKS_LIKE_INFO_PTR(&stg_BLACKHOLE_info));
75 ASSERT(LOOKS_LIKE_CLOSURE_PTR(&stg_dummy_ret_closure));
76 ASSERT(!HEAP_ALLOCED(&stg_dummy_ret_closure));
78 if (RtsFlags.GcFlags.maxHeapSize != 0 &&
79 RtsFlags.GcFlags.heapSizeSuggestion >
80 RtsFlags.GcFlags.maxHeapSize) {
81 RtsFlags.GcFlags.maxHeapSize = RtsFlags.GcFlags.heapSizeSuggestion;
84 if (RtsFlags.GcFlags.maxHeapSize != 0 &&
85 RtsFlags.GcFlags.minAllocAreaSize >
86 RtsFlags.GcFlags.maxHeapSize) {
87 prog_belch("maximum heap size (-M) is smaller than minimum alloc area size (-A)");
94 initCondition(&sm_mutex);
97 /* allocate generation info array */
98 generations = (generation *)stgMallocBytes(RtsFlags.GcFlags.generations
99 * sizeof(struct _generation),
100 "initStorage: gens");
102 /* Initialise all generations */
103 for(g = 0; g < RtsFlags.GcFlags.generations; g++) {
104 gen = &generations[g];
106 gen->mut_list = END_MUT_LIST;
107 gen->mut_once_list = END_MUT_LIST;
108 gen->collections = 0;
109 gen->failed_promotions = 0;
113 /* A couple of convenience pointers */
114 g0 = &generations[0];
115 oldest_gen = &generations[RtsFlags.GcFlags.generations-1];
117 /* Allocate step structures in each generation */
118 if (RtsFlags.GcFlags.generations > 1) {
119 /* Only for multiple-generations */
121 /* Oldest generation: one step */
122 oldest_gen->n_steps = 1;
124 stgMallocBytes(1 * sizeof(struct _step), "initStorage: last step");
126 /* set up all except the oldest generation with 2 steps */
127 for(g = 0; g < RtsFlags.GcFlags.generations-1; g++) {
128 generations[g].n_steps = RtsFlags.GcFlags.steps;
129 generations[g].steps =
130 stgMallocBytes (RtsFlags.GcFlags.steps * sizeof(struct _step),
131 "initStorage: steps");
135 /* single generation, i.e. a two-space collector */
137 g0->steps = stgMallocBytes (sizeof(struct _step), "initStorage: steps");
140 /* Initialise all steps */
141 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
142 for (s = 0; s < generations[g].n_steps; s++) {
143 stp = &generations[g].steps[s];
147 stp->gen = &generations[g];
154 stp->large_objects = NULL;
155 stp->n_large_blocks = 0;
156 stp->new_large_objects = NULL;
157 stp->scavenged_large_objects = NULL;
158 stp->n_scavenged_large_blocks = 0;
159 stp->is_compacted = 0;
164 /* Set up the destination pointers in each younger gen. step */
165 for (g = 0; g < RtsFlags.GcFlags.generations-1; g++) {
166 for (s = 0; s < generations[g].n_steps-1; s++) {
167 generations[g].steps[s].to = &generations[g].steps[s+1];
169 generations[g].steps[s].to = &generations[g+1].steps[0];
172 /* The oldest generation has one step and it is compacted. */
173 if (RtsFlags.GcFlags.compact) {
174 if (RtsFlags.GcFlags.generations == 1) {
175 belch("WARNING: compaction is incompatible with -G1; disabled");
177 oldest_gen->steps[0].is_compacted = 1;
180 oldest_gen->steps[0].to = &oldest_gen->steps[0];
182 /* generation 0 is special: that's the nursery */
183 generations[0].max_blocks = 0;
185 /* G0S0: the allocation area. Policy: keep the allocation area
186 * small to begin with, even if we have a large suggested heap
187 * size. Reason: we're going to do a major collection first, and we
188 * don't want it to be a big one. This vague idea is borne out by
189 * rigorous experimental evidence.
191 g0s0 = &generations[0].steps[0];
195 weak_ptr_list = NULL;
198 /* initialise the allocate() interface */
199 small_alloc_list = NULL;
201 alloc_blocks_lim = RtsFlags.GcFlags.minAllocAreaSize;
203 /* Tell GNU multi-precision pkg about our custom alloc functions */
204 mp_set_memory_functions(stgAllocForGMP, stgReallocForGMP, stgDeallocForGMP);
207 initMutex(&sm_mutex);
210 IF_DEBUG(gc, statDescribeGens());
216 stat_exit(calcAllocated());
219 /* -----------------------------------------------------------------------------
222 The entry code for every CAF does the following:
224 - builds a CAF_BLACKHOLE in the heap
225 - pushes an update frame pointing to the CAF_BLACKHOLE
226 - invokes UPD_CAF(), which:
227 - calls newCaf, below
228 - updates the CAF with a static indirection to the CAF_BLACKHOLE
230 Why do we build a BLACKHOLE in the heap rather than just updating
231 the thunk directly? It's so that we only need one kind of update
232 frame - otherwise we'd need a static version of the update frame too.
234 newCaf() does the following:
236 - it puts the CAF on the oldest generation's mut-once list.
237 This is so that we can treat the CAF as a root when collecting
240 For GHCI, we have additional requirements when dealing with CAFs:
242 - we must *retain* all dynamically-loaded CAFs ever entered,
243 just in case we need them again.
244 - we must be able to *revert* CAFs that have been evaluated, to
245 their pre-evaluated form.
247 To do this, we use an additional CAF list. When newCaf() is
248 called on a dynamically-loaded CAF, we add it to the CAF list
249 instead of the old-generation mutable list, and save away its
250 old info pointer (in caf->saved_info) for later reversion.
252 To revert all the CAFs, we traverse the CAF list and reset the
253 info pointer to caf->saved_info, then throw away the CAF list.
254 (see GC.c:revertCAFs()).
258 -------------------------------------------------------------------------- */
261 newCAF(StgClosure* caf)
263 /* Put this CAF on the mutable list for the old generation.
264 * This is a HACK - the IND_STATIC closure doesn't really have
265 * a mut_link field, but we pretend it has - in fact we re-use
266 * the STATIC_LINK field for the time being, because when we
267 * come to do a major GC we won't need the mut_link field
268 * any more and can use it as a STATIC_LINK.
272 ((StgIndStatic *)caf)->saved_info = NULL;
273 ((StgMutClosure *)caf)->mut_link = oldest_gen->mut_once_list;
274 oldest_gen->mut_once_list = (StgMutClosure *)caf;
279 /* If we are PAR or DIST then we never forget a CAF */
281 //belch("<##> Globalising CAF %08x %s",caf,info_type(caf));
282 newGA=makeGlobal(caf,rtsTrue); /*given full weight*/
288 // An alternate version of newCaf which is used for dynamically loaded
289 // object code in GHCi. In this case we want to retain *all* CAFs in
290 // the object code, because they might be demanded at any time from an
291 // expression evaluated on the command line.
293 // The linker hackily arranges that references to newCaf from dynamic
294 // code end up pointing to newDynCAF.
296 newDynCAF(StgClosure *caf)
300 ((StgIndStatic *)caf)->saved_info = (StgInfoTable *)caf->header.info;
301 ((StgIndStatic *)caf)->static_link = caf_list;
307 /* -----------------------------------------------------------------------------
309 -------------------------------------------------------------------------- */
312 allocNurseries( void )
321 for (cap = free_capabilities; cap != NULL; cap = cap->link) {
322 cap->r.rNursery = allocNursery(NULL, RtsFlags.GcFlags.minAllocAreaSize);
323 cap->r.rCurrentNursery = cap->r.rNursery;
324 for (bd = cap->r.rNursery; bd != NULL; bd = bd->link) {
325 bd->u.back = (bdescr *)cap;
328 /* Set the back links to be equal to the Capability,
329 * so we can do slightly better informed locking.
333 g0s0->blocks = allocNursery(NULL, RtsFlags.GcFlags.minAllocAreaSize);
334 g0s0->n_blocks = RtsFlags.GcFlags.minAllocAreaSize;
335 g0s0->to_blocks = NULL;
336 g0s0->n_to_blocks = 0;
337 MainCapability.r.rNursery = g0s0->blocks;
338 MainCapability.r.rCurrentNursery = g0s0->blocks;
339 /* hp, hpLim, hp_bd, to_space etc. aren't used in G0S0 */
344 resetNurseries( void )
350 /* All tasks must be stopped */
351 ASSERT(n_free_capabilities == RtsFlags.ParFlags.nNodes);
353 for (cap = free_capabilities; cap != NULL; cap = cap->link) {
354 for (bd = cap->r.rNursery; bd; bd = bd->link) {
355 bd->free = bd->start;
356 ASSERT(bd->gen_no == 0);
357 ASSERT(bd->step == g0s0);
358 IF_DEBUG(sanity,memset(bd->start, 0xaa, BLOCK_SIZE));
360 cap->r.rCurrentNursery = cap->r.rNursery;
363 for (bd = g0s0->blocks; bd; bd = bd->link) {
364 bd->free = bd->start;
365 ASSERT(bd->gen_no == 0);
366 ASSERT(bd->step == g0s0);
367 IF_DEBUG(sanity,memset(bd->start, 0xaa, BLOCK_SIZE));
369 MainCapability.r.rNursery = g0s0->blocks;
370 MainCapability.r.rCurrentNursery = g0s0->blocks;
375 allocNursery (bdescr *tail, nat blocks)
380 // Allocate a nursery: we allocate fresh blocks one at a time and
381 // cons them on to the front of the list, not forgetting to update
382 // the back pointer on the tail of the list to point to the new block.
383 for (i=0; i < blocks; i++) {
386 processNursery() in LdvProfile.c assumes that every block group in
387 the nursery contains only a single block. So, if a block group is
388 given multiple blocks, change processNursery() accordingly.
392 // double-link the nursery: we might need to insert blocks
399 bd->free = bd->start;
407 resizeNursery ( nat blocks )
413 barf("resizeNursery: can't resize in SMP mode");
416 nursery_blocks = g0s0->n_blocks;
417 if (nursery_blocks == blocks) {
421 else if (nursery_blocks < blocks) {
422 IF_DEBUG(gc, fprintf(stderr, "Increasing size of nursery to %d blocks\n",
424 g0s0->blocks = allocNursery(g0s0->blocks, blocks-nursery_blocks);
430 IF_DEBUG(gc, fprintf(stderr, "Decreasing size of nursery to %d blocks\n",
434 while (nursery_blocks > blocks) {
436 next_bd->u.back = NULL;
437 nursery_blocks -= bd->blocks; // might be a large block
442 // might have gone just under, by freeing a large block, so make
443 // up the difference.
444 if (nursery_blocks < blocks) {
445 g0s0->blocks = allocNursery(g0s0->blocks, blocks-nursery_blocks);
449 g0s0->n_blocks = blocks;
450 ASSERT(countBlocks(g0s0->blocks) == g0s0->n_blocks);
453 /* -----------------------------------------------------------------------------
454 The allocate() interface
456 allocate(n) always succeeds, and returns a chunk of memory n words
457 long. n can be larger than the size of a block if necessary, in
458 which case a contiguous block group will be allocated.
459 -------------------------------------------------------------------------- */
469 TICK_ALLOC_HEAP_NOCTR(n);
472 /* big allocation (>LARGE_OBJECT_THRESHOLD) */
473 /* ToDo: allocate directly into generation 1 */
474 if (n >= LARGE_OBJECT_THRESHOLD/sizeof(W_)) {
475 nat req_blocks = (lnat)BLOCK_ROUND_UP(n*sizeof(W_)) / BLOCK_SIZE;
476 bd = allocGroup(req_blocks);
477 dbl_link_onto(bd, &g0s0->large_objects);
480 bd->flags = BF_LARGE;
481 bd->free = bd->start;
482 /* don't add these blocks to alloc_blocks, since we're assuming
483 * that large objects are likely to remain live for quite a while
484 * (eg. running threads), so garbage collecting early won't make
487 alloc_blocks += req_blocks;
491 /* small allocation (<LARGE_OBJECT_THRESHOLD) */
492 } else if (small_alloc_list == NULL || alloc_Hp + n > alloc_HpLim) {
493 if (small_alloc_list) {
494 small_alloc_list->free = alloc_Hp;
497 bd->link = small_alloc_list;
498 small_alloc_list = bd;
502 alloc_Hp = bd->start;
503 alloc_HpLim = bd->start + BLOCK_SIZE_W;
514 allocated_bytes( void )
518 allocated = alloc_blocks * BLOCK_SIZE_W - (alloc_HpLim - alloc_Hp);
519 if (pinned_object_block != NULL) {
520 allocated -= (pinned_object_block->start + BLOCK_SIZE_W) -
521 pinned_object_block->free;
528 tidyAllocateLists (void)
530 if (small_alloc_list != NULL) {
531 ASSERT(alloc_Hp >= small_alloc_list->start &&
532 alloc_Hp <= small_alloc_list->start + BLOCK_SIZE);
533 small_alloc_list->free = alloc_Hp;
537 /* ---------------------------------------------------------------------------
538 Allocate a fixed/pinned object.
540 We allocate small pinned objects into a single block, allocating a
541 new block when the current one overflows. The block is chained
542 onto the large_object_list of generation 0 step 0.
544 NOTE: The GC can't in general handle pinned objects. This
545 interface is only safe to use for ByteArrays, which have no
546 pointers and don't require scavenging. It works because the
547 block's descriptor has the BF_LARGE flag set, so the block is
548 treated as a large object and chained onto various lists, rather
549 than the individual objects being copied. However, when it comes
550 to scavenge the block, the GC will only scavenge the first object.
551 The reason is that the GC can't linearly scan a block of pinned
552 objects at the moment (doing so would require using the
553 mostly-copying techniques). But since we're restricting ourselves
554 to pinned ByteArrays, not scavenging is ok.
556 This function is called by newPinnedByteArray# which immediately
557 fills the allocated memory with a MutableByteArray#.
558 ------------------------------------------------------------------------- */
561 allocatePinned( nat n )
564 bdescr *bd = pinned_object_block;
568 TICK_ALLOC_HEAP_NOCTR(n);
571 // If the request is for a large object, then allocate()
572 // will give us a pinned object anyway.
573 if (n >= LARGE_OBJECT_THRESHOLD/sizeof(W_)) {
578 // we always return 8-byte aligned memory. bd->free must be
579 // 8-byte aligned to begin with, so we just round up n to
580 // the nearest multiple of 8 bytes.
581 if (sizeof(StgWord) == 4) {
585 // If we don't have a block of pinned objects yet, or the current
586 // one isn't large enough to hold the new object, allocate a new one.
587 if (bd == NULL || (bd->free + n) > (bd->start + BLOCK_SIZE_W)) {
588 pinned_object_block = bd = allocBlock();
589 dbl_link_onto(bd, &g0s0->large_objects);
592 bd->flags = BF_LARGE;
593 bd->free = bd->start;
603 /* -----------------------------------------------------------------------------
604 Allocation functions for GMP.
606 These all use the allocate() interface - we can't have any garbage
607 collection going on during a gmp operation, so we use allocate()
608 which always succeeds. The gmp operations which might need to
609 allocate will ask the storage manager (via doYouWantToGC()) whether
610 a garbage collection is required, in case we get into a loop doing
611 only allocate() style allocation.
612 -------------------------------------------------------------------------- */
615 stgAllocForGMP (size_t size_in_bytes)
618 nat data_size_in_words, total_size_in_words;
620 /* round up to a whole number of words */
621 data_size_in_words = (size_in_bytes + sizeof(W_) + 1) / sizeof(W_);
622 total_size_in_words = sizeofW(StgArrWords) + data_size_in_words;
624 /* allocate and fill it in. */
625 arr = (StgArrWords *)allocate(total_size_in_words);
626 SET_ARR_HDR(arr, &stg_ARR_WORDS_info, CCCS, data_size_in_words);
628 /* and return a ptr to the goods inside the array */
629 return(BYTE_ARR_CTS(arr));
633 stgReallocForGMP (void *ptr, size_t old_size, size_t new_size)
635 void *new_stuff_ptr = stgAllocForGMP(new_size);
637 char *p = (char *) ptr;
638 char *q = (char *) new_stuff_ptr;
640 for (; i < old_size; i++, p++, q++) {
644 return(new_stuff_ptr);
648 stgDeallocForGMP (void *ptr STG_UNUSED,
649 size_t size STG_UNUSED)
651 /* easy for us: the garbage collector does the dealloc'n */
654 /* -----------------------------------------------------------------------------
656 * -------------------------------------------------------------------------- */
658 /* -----------------------------------------------------------------------------
661 * Approximate how much we've allocated: number of blocks in the
662 * nursery + blocks allocated via allocate() - unused nusery blocks.
663 * This leaves a little slop at the end of each block, and doesn't
664 * take into account large objects (ToDo).
665 * -------------------------------------------------------------------------- */
668 calcAllocated( void )
676 /* All tasks must be stopped. Can't assert that all the
677 capabilities are owned by the scheduler, though: one or more
678 tasks might have been stopped while they were running (non-main)
680 /* ASSERT(n_free_capabilities == RtsFlags.ParFlags.nNodes); */
683 n_free_capabilities * RtsFlags.GcFlags.minAllocAreaSize * BLOCK_SIZE_W
686 for (cap = free_capabilities; cap != NULL; cap = cap->link) {
687 for ( bd = cap->r.rCurrentNursery->link; bd != NULL; bd = bd->link ) {
688 allocated -= BLOCK_SIZE_W;
690 if (cap->r.rCurrentNursery->free < cap->r.rCurrentNursery->start
692 allocated -= (cap->r.rCurrentNursery->start + BLOCK_SIZE_W)
693 - cap->r.rCurrentNursery->free;
698 bdescr *current_nursery = MainCapability.r.rCurrentNursery;
700 allocated = (g0s0->n_blocks * BLOCK_SIZE_W) + allocated_bytes();
701 for ( bd = current_nursery->link; bd != NULL; bd = bd->link ) {
702 allocated -= BLOCK_SIZE_W;
704 if (current_nursery->free < current_nursery->start + BLOCK_SIZE_W) {
705 allocated -= (current_nursery->start + BLOCK_SIZE_W)
706 - current_nursery->free;
710 total_allocated += allocated;
714 /* Approximate the amount of live data in the heap. To be called just
715 * after garbage collection (see GarbageCollect()).
724 if (RtsFlags.GcFlags.generations == 1) {
725 live = (g0s0->n_to_blocks - 1) * BLOCK_SIZE_W +
726 ((lnat)g0s0->hp_bd->free - (lnat)g0s0->hp_bd->start) / sizeof(W_);
730 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
731 for (s = 0; s < generations[g].n_steps; s++) {
732 /* approximate amount of live data (doesn't take into account slop
733 * at end of each block).
735 if (g == 0 && s == 0) {
738 stp = &generations[g].steps[s];
739 live += (stp->n_large_blocks + stp->n_blocks - 1) * BLOCK_SIZE_W;
740 if (stp->hp_bd != NULL) {
741 live += ((lnat)stp->hp_bd->free - (lnat)stp->hp_bd->start)
749 /* Approximate the number of blocks that will be needed at the next
750 * garbage collection.
752 * Assume: all data currently live will remain live. Steps that will
753 * be collected next time will therefore need twice as many blocks
754 * since all the data will be copied.
763 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
764 for (s = 0; s < generations[g].n_steps; s++) {
765 if (g == 0 && s == 0) { continue; }
766 stp = &generations[g].steps[s];
767 if (generations[g].steps[0].n_blocks +
768 generations[g].steps[0].n_large_blocks
769 > generations[g].max_blocks
770 && stp->is_compacted == 0) {
771 needed += 2 * stp->n_blocks;
773 needed += stp->n_blocks;
780 /* -----------------------------------------------------------------------------
783 memInventory() checks for memory leaks by counting up all the
784 blocks we know about and comparing that to the number of blocks
785 allegedly floating around in the system.
786 -------------------------------------------------------------------------- */
796 lnat total_blocks = 0, free_blocks = 0;
798 /* count the blocks we current have */
800 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
801 for (s = 0; s < generations[g].n_steps; s++) {
802 stp = &generations[g].steps[s];
803 total_blocks += stp->n_blocks;
804 if (RtsFlags.GcFlags.generations == 1) {
805 /* two-space collector has a to-space too :-) */
806 total_blocks += g0s0->n_to_blocks;
808 for (bd = stp->large_objects; bd; bd = bd->link) {
809 total_blocks += bd->blocks;
810 /* hack for megablock groups: they have an extra block or two in
811 the second and subsequent megablocks where the block
812 descriptors would normally go.
814 if (bd->blocks > BLOCKS_PER_MBLOCK) {
815 total_blocks -= (MBLOCK_SIZE / BLOCK_SIZE - BLOCKS_PER_MBLOCK)
816 * (bd->blocks/(MBLOCK_SIZE/BLOCK_SIZE));
822 /* any blocks held by allocate() */
823 for (bd = small_alloc_list; bd; bd = bd->link) {
824 total_blocks += bd->blocks;
828 if (RtsFlags.ProfFlags.doHeapProfile == HEAP_BY_RETAINER) {
829 for (bd = firstStack; bd != NULL; bd = bd->link)
830 total_blocks += bd->blocks;
834 // count the blocks allocated by the arena allocator
835 total_blocks += arenaBlocks();
837 /* count the blocks on the free list */
838 free_blocks = countFreeList();
840 if (total_blocks + free_blocks != mblocks_allocated *
842 fprintf(stderr, "Blocks: %ld live + %ld free = %ld total (%ld around)\n",
843 total_blocks, free_blocks, total_blocks + free_blocks,
844 mblocks_allocated * BLOCKS_PER_MBLOCK);
847 ASSERT(total_blocks + free_blocks == mblocks_allocated * BLOCKS_PER_MBLOCK);
852 countBlocks(bdescr *bd)
855 for (n=0; bd != NULL; bd=bd->link) {
861 /* Full heap sanity check. */
867 if (RtsFlags.GcFlags.generations == 1) {
868 checkHeap(g0s0->to_blocks);
869 checkChain(g0s0->large_objects);
872 for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
873 for (s = 0; s < generations[g].n_steps; s++) {
874 ASSERT(countBlocks(generations[g].steps[s].blocks)
875 == generations[g].steps[s].n_blocks);
876 ASSERT(countBlocks(generations[g].steps[s].large_objects)
877 == generations[g].steps[s].n_large_blocks);
878 if (g == 0 && s == 0) { continue; }
879 checkHeap(generations[g].steps[s].blocks);
880 checkChain(generations[g].steps[s].large_objects);
882 checkMutableList(generations[g].mut_list, g);
883 checkMutOnceList(generations[g].mut_once_list, g);
887 checkFreeListSanity();
891 // handy function for use in gdb, because Bdescr() is inlined.
892 extern bdescr *_bdescr( StgPtr p );