src/runtime/cheneygc.c

   1 /*
   2  * stop and copy GC based on Cheney's algorithm
   3  */
   4
   5 /*
   6  * This software is part of the SBCL system. See the README file for
   7  * more information.
   8  *
   9  * This software is derived from the CMU CL system, which was
  10  * written at Carnegie Mellon University and released into the
  11  * public domain. The software is in the public domain and is
  12  * provided with absolutely no warranty. See the COPYING and CREDITS
  13  * files for more information.
  14  */
  15
  16 #include <stdio.h>
  17 #include <sys/time.h>
  18 #include <sys/resource.h>
  19 #include <signal.h>
  20 #include "sbcl.h"
  21 #include "runtime.h"
  22 #include "os.h"
  23 #include "gc.h"
  24 #include "gc-internal.h"
  25 #include "globals.h"
  26 #include "interrupt.h"
  27 #include "validate.h"
  28 #include "lispregs.h"
  29 #include "interr.h"
  30 #include "genesis/static-symbols.h"
  31 #include "genesis/primitive-objects.h"
  32 #include "thread.h"
  33 #include "arch.h"
  34
  35 /* So you need to debug? */
  36 #if 0
  37 #define PRINTNOISE
  38 #define DEBUG_SPACE_PREDICATES
  39 #define DEBUG_SCAVENGE_VERBOSE
  40 #define DEBUG_COPY_VERBOSE
  41 #define DEBUG_CODE_GC
  42 #endif
  43
  44 lispobj *from_space;
  45 lispobj *from_space_free_pointer;
  46
  47 lispobj *new_space;
  48 lispobj *new_space_free_pointer;
  49
  50 static void scavenge_newspace(void);
  51
  52 \f
  53 /* collecting garbage */
  54
  55 #ifdef PRINTNOISE
  56 static double
  57 tv_diff(struct timeval *x, struct timeval *y)
  58 {
  59     return (((double) x->tv_sec + (double) x->tv_usec * 1.0e-6) -
  60             ((double) y->tv_sec + (double) y->tv_usec * 1.0e-6));
  61 }
  62 #endif
  63
  64 #define BYTES_ZERO_BEFORE_END (1<<12)
  65
  66 /* FIXME do we need this?  Doesn't it duplicate lisp code in
  67  * scrub-control-stack? */
  68
  69 static void
  70 zero_stack(void)
  71 {
  72     lispobj *ptr = current_control_stack_pointer;
  73  search:
  74     do {
  75         if (*ptr)
  76             goto fill;
  77         ptr++;
  78     } while (((unsigned long)ptr) & (BYTES_ZERO_BEFORE_END-1));
  79     return;
  80  fill:
  81     do {
  82         *ptr++ = 0;
  83     } while (((unsigned long)ptr) & (BYTES_ZERO_BEFORE_END-1));
  84
  85     goto search;
  86 }
  87
  88
  89 void *
  90 gc_general_alloc(long bytes, int page_type_flag, int quick_p) {
  91     lispobj *new=new_space_free_pointer;
  92     new_space_free_pointer+=(bytes/N_WORD_BYTES);
  93     return new;
  94 }
  95
  96 lispobj  copy_large_unboxed_object(lispobj object, long nwords) {
  97     return copy_object(object,nwords);
  98 }
  99 lispobj  copy_unboxed_object(lispobj object, long nwords) {
 100     return copy_object(object,nwords);
 101 }
 102 lispobj  copy_large_object(lispobj object, long nwords) {
 103     return copy_object(object,nwords);
 104 }
 105
 106 /* Note: The generic GC interface we're implementing passes us a
 107  * last_generation argument. That's meaningless for us, since we're
 108  * not a generational GC. So we ignore it. */
 109 void
 110 collect_garbage(generation_index_t ignore)
 111 {
 112 #ifdef PRINTNOISE
 113     struct timeval start_tv, stop_tv;
 114     struct rusage start_rusage, stop_rusage;
 115     double real_time, system_time, user_time;
 116     double percent_retained, gc_rate;
 117     unsigned long size_discarded;
 118 #endif
 119     unsigned long size_retained;
 120     lispobj *current_static_space_free_pointer;
 121     unsigned long static_space_size;
 122     unsigned long control_stack_size, binding_stack_size;
 123     sigset_t tmp, old;
 124     struct thread *th=arch_os_get_current_thread();
 125
 126 #ifdef PRINTNOISE
 127     printf("[Collecting garbage ... \n");
 128
 129     getrusage(RUSAGE_SELF, &start_rusage);
 130     gettimeofday(&start_tv, (struct timezone *) 0);
 131 #endif
 132
 133     /* it's possible that signals are blocked already if this was called
 134      * from a signal handler (e.g. with the sigsegv gc_trigger stuff) */
 135     block_blockable_signals(0, &old);
 136
 137     current_static_space_free_pointer =
 138         (lispobj *) ((unsigned long)
 139                      SymbolValue(STATIC_SPACE_FREE_POINTER,0));
 140
 141
 142     /* Set up from space and new space pointers. */
 143
 144     from_space = current_dynamic_space;
 145     from_space_free_pointer = dynamic_space_free_pointer;
 146
 147 #ifdef PRINTNOISE
 148     fprintf(stderr,"from_space = %lx\n",
 149             (unsigned long) current_dynamic_space);
 150 #endif
 151     if (current_dynamic_space == (lispobj *) DYNAMIC_0_SPACE_START)
 152         new_space = (lispobj *)DYNAMIC_1_SPACE_START;
 153     else if (current_dynamic_space == (lispobj *) DYNAMIC_1_SPACE_START)
 154         new_space = (lispobj *) DYNAMIC_0_SPACE_START;
 155     else {
 156         lose("GC lossage.  Current dynamic space is bogus!\n");
 157     }
 158     new_space_free_pointer = new_space;
 159
 160     /* Initialize the weak pointer list. */
 161     weak_pointers = (struct weak_pointer *) NULL;
 162
 163
 164     /* Scavenge all of the roots. */
 165 #ifdef PRINTNOISE
 166     printf("Scavenging interrupt contexts ...\n");
 167 #endif
 168     scavenge_interrupt_contexts();
 169
 170 #ifdef PRINTNOISE
 171     printf("Scavenging interrupt handlers (%d bytes) ...\n",
 172            (int)sizeof(interrupt_handlers));
 173 #endif
 174     scavenge((lispobj *) interrupt_handlers,
 175              sizeof(interrupt_handlers) / sizeof(lispobj));
 176
 177     /* _size quantities are in units of sizeof(lispobj) - i.e. 4 */
 178     control_stack_size =
 179         current_control_stack_pointer-
 180         (lispobj *)th->control_stack_start;
 181 #ifdef PRINTNOISE
 182     printf("Scavenging the control stack at %p (%ld words) ...\n",
 183            ((lispobj *)th->control_stack_start),
 184            control_stack_size);
 185 #endif
 186     scavenge(((lispobj *)th->control_stack_start), control_stack_size);
 187
 188
 189     binding_stack_size =
 190         current_binding_stack_pointer -
 191         (lispobj *)th->binding_stack_start;
 192 #ifdef PRINTNOISE
 193     printf("Scavenging the binding stack %x - %x (%d words) ...\n",
 194            th->binding_stack_start,current_binding_stack_pointer,
 195            (int)(binding_stack_size));
 196 #endif
 197     scavenge(((lispobj *)th->binding_stack_start), binding_stack_size);
 198
 199     static_space_size =
 200         current_static_space_free_pointer - (lispobj *) STATIC_SPACE_START;
 201 #ifdef PRINTNOISE
 202     printf("Scavenging static space %x - %x (%d words) ...\n",
 203            STATIC_SPACE_START,current_static_space_free_pointer,
 204            (int)(static_space_size));
 205 #endif
 206     scavenge(((lispobj *)STATIC_SPACE_START), static_space_size);
 207
 208     /* Scavenge newspace. */
 209 #ifdef PRINTNOISE
 210     printf("Scavenging new space (%d bytes) ...\n",
 211            (int)((new_space_free_pointer - new_space) * sizeof(lispobj)));
 212 #endif
 213     scavenge_newspace();
 214
 215
 216 #if defined(DEBUG_PRINT_GARBAGE)
 217     print_garbage(from_space, from_space_free_pointer);
 218 #endif
 219
 220     /* Scan the weak pointers. */
 221 #ifdef PRINTNOISE
 222     printf("Scanning weak hash tables ...\n");
 223 #endif
 224     scan_weak_hash_tables();
 225
 226     /* Scan the weak pointers. */
 227 #ifdef PRINTNOISE
 228     printf("Scanning weak pointers ...\n");
 229 #endif
 230     scan_weak_pointers();
 231
 232     /* Flip spaces. */
 233 #ifdef PRINTNOISE
 234     printf("Flipping spaces ...\n");
 235 #endif
 236
 237     /* Maybe FIXME: it's possible that we could significantly reduce
 238      * RSS by zeroing the from_space or madvise(MADV_DONTNEED) or
 239      * similar os-dependent tricks here */
 240 #ifdef LISP_FEATURE_HPUX
 241     /* hpux cant handle unmapping areas that are not 100% mapped */
 242     clear_auto_gc_trigger();
 243 #endif
 244     os_zero((os_vm_address_t) from_space,
 245             (os_vm_size_t) dynamic_space_size);
 246
 247     current_dynamic_space = new_space;
 248     dynamic_space_free_pointer = new_space_free_pointer;
 249
 250 #ifdef PRINTNOISE
 251     size_discarded = (from_space_free_pointer - from_space) * sizeof(lispobj);
 252 #endif
 253     size_retained = (new_space_free_pointer - new_space) * sizeof(lispobj);
 254
 255     os_flush_icache((os_vm_address_t)new_space, size_retained);
 256
 257     /* Zero stack. */
 258 #ifdef PRINTNOISE
 259     printf("Zeroing empty part of control stack ...\n");
 260 #endif
 261     zero_stack();
 262     set_auto_gc_trigger(size_retained+bytes_consed_between_gcs);
 263     thread_sigmask(SIG_SETMASK, &old, 0);
 264
 265
 266 #ifdef PRINTNOISE
 267     gettimeofday(&stop_tv, (struct timezone *) 0);
 268     getrusage(RUSAGE_SELF, &stop_rusage);
 269
 270     printf("done.]\n");
 271
 272     percent_retained = (((float) size_retained) /
 273                         ((float) size_discarded)) * 100.0;
 274
 275     printf("Total of %ld bytes out of %ld bytes retained (%3.2f%%).\n",
 276            size_retained, size_discarded, percent_retained);
 277
 278     real_time = tv_diff(&stop_tv, &start_tv);
 279     user_time = tv_diff(&stop_rusage.ru_utime, &start_rusage.ru_utime);
 280     system_time = tv_diff(&stop_rusage.ru_stime, &start_rusage.ru_stime);
 281
 282     printf("Statistics: %10.2fs real, %10.2fs user, %10.2fs system.\n",
 283            real_time, user_time, system_time);
 284
 285     gc_rate = ((float) size_retained / (float) (1<<20)) / real_time;
 286
 287     printf("%10.2f M bytes/sec collected.\n", gc_rate);
 288 #endif
 289 }
 290
 291 \f
 292 /* scavenging */
 293
 294 static void
 295 scavenge_newspace(void)
 296 {
 297     lispobj *here, *next;
 298
 299     here = new_space;
 300     while (here < new_space_free_pointer) {
 301         /*      printf("here=%lx, new_space_free_pointer=%lx\n",
 302                 here,new_space_free_pointer); */
 303         next = new_space_free_pointer;
 304         scavenge(here, next - here);
 305         scav_weak_hash_tables();
 306         here = next;
 307     }
 308     /* printf("done with newspace\n"); */
 309 }
 310 \f
 311 /* scavenging interrupt contexts */
 312
 313 static int boxed_registers[] = BOXED_REGISTERS;
 314
 315 static void
 316 scavenge_interrupt_context(os_context_t *context)
 317 {
 318     int i;
 319 #ifdef reg_LIP
 320     unsigned long lip;
 321     unsigned long lip_offset;
 322     int lip_register_pair;
 323 #endif
 324     unsigned long pc_code_offset;
 325 #ifdef ARCH_HAS_LINK_REGISTER
 326     unsigned long lr_code_offset;
 327 #endif
 328 #ifdef ARCH_HAS_NPC_REGISTER
 329     unsigned long npc_code_offset;
 330 #endif
 331 #ifdef DEBUG_SCAVENGE_VERBOSE
 332     fprintf(stderr, "Scavenging interrupt context at 0x%x\n",context);
 333 #endif
 334     /* Find the LIP's register pair and calculate its offset */
 335     /* before we scavenge the context. */
 336 #ifdef reg_LIP
 337     lip = *os_context_register_addr(context, reg_LIP);
 338     /* 0x7FFFFFFF on 32-bit platforms;
 339        0x7FFFFFFFFFFFFFFF on 64-bit platforms */
 340     lip_offset = (((unsigned long)1) << (N_WORD_BITS - 1)) - 1;
 341     lip_register_pair = -1;
 342     for (i = 0; i < (int)(sizeof(boxed_registers) / sizeof(int)); i++) {
 343         unsigned long reg;
 344         unsigned long offset;
 345         int index;
 346
 347         index = boxed_registers[i];
 348         reg = *os_context_register_addr(context, index);
 349         /* would be using PTR if not for integer length issues */
 350         if ((reg & ~((1L<<N_LOWTAG_BITS)-1)) <= lip) {
 351             offset = lip - reg;
 352             if (offset < lip_offset) {
 353                 lip_offset = offset;
 354                 lip_register_pair = index;
 355             }
 356         }
 357     }
 358 #endif /* reg_LIP */
 359
 360     /* Compute the PC's offset from the start of the CODE */
 361     /* register. */
 362     pc_code_offset =
 363         *os_context_pc_addr(context) -
 364         *os_context_register_addr(context, reg_CODE);
 365 #ifdef ARCH_HAS_NPC_REGISTER
 366     npc_code_offset =
 367         *os_context_npc_addr(context) -
 368         *os_context_register_addr(context, reg_CODE);
 369 #endif
 370 #ifdef ARCH_HAS_LINK_REGISTER
 371     lr_code_offset =
 372         *os_context_lr_addr(context) -
 373         *os_context_register_addr(context, reg_CODE);
 374 #endif
 375
 376     /* Scavenge all boxed registers in the context. */
 377     for (i = 0; i < (int)(sizeof(boxed_registers) / sizeof(int)); i++) {
 378         int index;
 379         lispobj foo;
 380
 381         index = boxed_registers[i];
 382         foo = *os_context_register_addr(context,index);
 383         scavenge((lispobj *) &foo, 1);
 384         *os_context_register_addr(context,index) = foo;
 385
 386         /* this is unlikely to work as intended on bigendian
 387          * 64 bit platforms */
 388
 389         scavenge((lispobj *)
 390                  os_context_register_addr(context, index), 1);
 391     }
 392
 393 #ifdef reg_LIP
 394     /* Fix the LIP */
 395     *os_context_register_addr(context, reg_LIP) =
 396         *os_context_register_addr(context, lip_register_pair) + lip_offset;
 397 #endif /* reg_LIP */
 398
 399     /* Fix the PC if it was in from space */
 400     if (from_space_p(*os_context_pc_addr(context)))
 401         *os_context_pc_addr(context) =
 402             *os_context_register_addr(context, reg_CODE) + pc_code_offset;
 403 #ifdef ARCH_HAS_LINK_REGISTER
 404     /* Fix the LR ditto; important if we're being called from
 405      * an assembly routine that expects to return using blr, otherwise
 406      * harmless */
 407     if (from_space_p(*os_context_lr_addr(context)))
 408         *os_context_lr_addr(context) =
 409             *os_context_register_addr(context, reg_CODE) + lr_code_offset;
 410 #endif
 411
 412 #ifdef ARCH_HAS_NPC_REGISTER
 413     if (from_space_p(*os_context_npc_addr(context)))
 414         *os_context_npc_addr(context) =
 415             *os_context_register_addr(context, reg_CODE) + npc_code_offset;
 416 #endif
 417 }
 418
 419 void scavenge_interrupt_contexts(void)
 420 {
 421     int i, index;
 422     os_context_t *context;
 423
 424     struct thread *th=arch_os_get_current_thread();
 425
 426     index = fixnum_value(SymbolValue(FREE_INTERRUPT_CONTEXT_INDEX,0));
 427
 428
 429 #ifdef DEBUG_SCAVENGE_VERBOSE
 430     fprintf(stderr, "%d interrupt contexts to scan\n",index);
 431 #endif
 432     for (i = 0; i < index; i++) {
 433         context = th->interrupt_contexts[i];
 434         scavenge_interrupt_context(context);
 435     }
 436 }
 437
 438 \f
 439 /* debugging code */
 440
 441 void
 442 print_garbage(lispobj *from_space, lispobj *from_space_free_pointer)
 443 {
 444     lispobj *start;
 445     int total_words_not_copied;
 446
 447     printf("Scanning from space ...\n");
 448
 449     total_words_not_copied = 0;
 450     start = from_space;
 451     while (start < from_space_free_pointer) {
 452         lispobj object;
 453         int forwardp, type, nwords;
 454         lispobj header;
 455
 456         object = *start;
 457         forwardp = is_lisp_pointer(object) && new_space_p(object);
 458
 459         if (forwardp) {
 460             int tag;
 461             lispobj *pointer;
 462
 463             tag = lowtag_of(object);
 464
 465             switch (tag) {
 466             case LIST_POINTER_LOWTAG:
 467                 nwords = 2;
 468                 break;
 469             case INSTANCE_POINTER_LOWTAG:
 470                 printf("Don't know about instances yet!\n");
 471                 nwords = 1;
 472                 break;
 473             case FUN_POINTER_LOWTAG:
 474                 nwords = 1;
 475                 break;
 476             case OTHER_POINTER_LOWTAG:
 477                 pointer = (lispobj *) native_pointer(object);
 478                 header = *pointer;
 479                 type = widetag_of(header);
 480                 nwords = (sizetab[type])(pointer);
 481                 break;
 482             default: nwords=1;  /* shut yer whinging, gcc */
 483             }
 484         } else {
 485             type = widetag_of(object);
 486             nwords = (sizetab[type])(start);
 487             total_words_not_copied += nwords;
 488             printf("%4d words not copied at 0x%16lx; ",
 489                    nwords, (unsigned long) start);
 490             printf("Header word is 0x%08x\n",
 491                    (unsigned int) object);
 492         }
 493         start += nwords;
 494     }
 495     printf("%d total words not copied.\n", total_words_not_copied);
 496 }
 497
 498 \f
 499 /* weak pointers */
 500
 501 #define WEAK_POINTER_NWORDS \
 502         CEILING((sizeof(struct weak_pointer) / sizeof(lispobj)), 2)
 503
 504 static long
 505 scav_weak_pointer(lispobj *where, lispobj object)
 506 {
 507     /* Do not let GC scavenge the value slot of the weak pointer */
 508     /* (that is why it is a weak pointer).  Note:  we could use */
 509     /* the scav_unboxed method here. */
 510
 511     return WEAK_POINTER_NWORDS;
 512 }
 513 \f
 514 lispobj *
 515 search_read_only_space(void *pointer)
 516 {
 517     lispobj* start = (lispobj*)READ_ONLY_SPACE_START;
 518     lispobj* end = (lispobj*)SymbolValue(READ_ONLY_SPACE_FREE_POINTER,0);
 519     if ((pointer < (void *)start) || (pointer >= (void *)end))
 520         return NULL;
 521     return (gc_search_space(start,
 522                             (((lispobj *)pointer)+2)-start,
 523                             (lispobj *)pointer));
 524 }
 525
 526 lispobj *
 527 search_static_space(void *pointer)
 528 {
 529     lispobj* start = (lispobj*)STATIC_SPACE_START;
 530     lispobj* end = (lispobj*)SymbolValue(STATIC_SPACE_FREE_POINTER,0);
 531     if ((pointer < (void *)start) || (pointer >= (void *)end))
 532         return NULL;
 533     return (gc_search_space(start,
 534                             (((lispobj *)pointer)+2)-start,
 535                             (lispobj *)pointer));
 536 }
 537
 538 lispobj *
 539 search_dynamic_space(void *pointer)
 540 {
 541     lispobj *start = (lispobj *) current_dynamic_space;
 542     lispobj *end = (lispobj *) dynamic_space_free_pointer;
 543     if ((pointer < (void *)start) || (pointer >= (void *)end))
 544         return NULL;
 545     return (gc_search_space(start,
 546                             (((lispobj *)pointer)+2)-start,
 547                             (lispobj *)pointer));
 548 }
 549 \f
 550 /* initialization.  if gc_init can be moved to after core load, we could
 551  * combine these two functions */
 552
 553 void
 554 gc_init(void)
 555 {
 556     gc_init_tables();
 557     scavtab[WEAK_POINTER_WIDETAG] = scav_weak_pointer;
 558 }
 559
 560 void
 561 gc_initialize_pointers(void)
 562 {
 563     /* FIXME: We do nothing here.  We (briefly) misguidedly attempted
 564        to set current_dynamic_space to DYNAMIC_0_SPACE_START here,
 565        forgetting that (a) actually it could be the other and (b) it's
 566        set in coreparse.c anyway.  There's a FIXME note left here to
 567        note that current_dynamic_space is a violation of OAOO: we can
 568        tell which dynamic space we're currently in by looking at
 569        dynamic_space_free_pointer.  -- CSR, 2002-08-09 */
 570 }
 571
 572
 573
 574 \f
 575 /* noise to manipulate the gc trigger stuff */
 576
 577 /* Functions that substantially change the dynamic space free pointer
 578  * (collect_garbage, purify) are responsible also for resetting the
 579  * auto_gc_trigger */
 580 void set_auto_gc_trigger(os_vm_size_t dynamic_usage)
 581 {
 582     os_vm_address_t addr;
 583     os_vm_size_t length;
 584
 585     addr = os_round_up_to_page((os_vm_address_t)current_dynamic_space
 586                                + dynamic_usage);
 587     if (addr < (os_vm_address_t)dynamic_space_free_pointer)
 588         lose("set_auto_gc_trigger: tried to set gc trigger too low! (%ld < 0x%08lx)\n",
 589              (unsigned long)dynamic_usage,
 590              (unsigned long)((os_vm_address_t)dynamic_space_free_pointer
 591                              - (os_vm_address_t)current_dynamic_space));
 592
 593     length = os_trunc_size_to_page(dynamic_space_size - dynamic_usage);
 594     if (length < 0)
 595         lose("set_auto_gc_trigger: tried to set gc trigger too high! (0x%08lx)\n",
 596              (unsigned long)dynamic_usage);
 597
 598 #if defined(SUNOS) || defined(SOLARIS) || defined(LISP_FEATURE_HPUX)
 599     os_invalidate(addr, length);
 600 #else
 601     os_protect(addr, length, 0);
 602 #endif
 603
 604     current_auto_gc_trigger = (lispobj *)addr;
 605 }
 606
 607 void clear_auto_gc_trigger(void)
 608 {
 609     os_vm_address_t addr;
 610     os_vm_size_t length;
 611
 612     if (current_auto_gc_trigger == NULL)
 613         return;
 614
 615     addr = (os_vm_address_t)current_auto_gc_trigger;
 616     length = dynamic_space_size + (os_vm_address_t)current_dynamic_space - addr;
 617
 618 #if defined(SUNOS) || defined(SOLARIS) || defined(LISP_FEATURE_HPUX)
 619     /* don't want to force whole space into swapping mode... */
 620     os_validate(addr, length);
 621 #else
 622     os_protect(addr, length, OS_VM_PROT_ALL);
 623 #endif
 624
 625     current_auto_gc_trigger = NULL;
 626 }
 627
 628 static boolean
 629 gc_trigger_hit(void *addr)
 630 {
 631     if (current_auto_gc_trigger == NULL)
 632         return 0;
 633     else{
 634         return (addr >= (void *)current_auto_gc_trigger &&
 635                 addr <((void *)current_dynamic_space + dynamic_space_size));
 636     }
 637 }
 638
 639 boolean
 640 cheneygc_handle_wp_violation(os_context_t *context, void *addr)
 641 {
 642     if(!foreign_function_call_active && gc_trigger_hit(addr)){
 643         struct thread *thread=arch_os_get_current_thread();
 644         clear_auto_gc_trigger();
 645         /* Don't flood the system with interrupts if the need to gc is
 646          * already noted. This can happen for example when SUB-GC
 647          * allocates or after a gc triggered in a WITHOUT-GCING. */
 648         if (SymbolValue(GC_PENDING,thread) == NIL) {
 649             if (SymbolValue(GC_INHIBIT,thread) == NIL) {
 650                 if (arch_pseudo_atomic_atomic(context)) {
 651                     /* set things up so that GC happens when we finish
 652                      * the PA section */
 653                     SetSymbolValue(GC_PENDING,T,thread);
 654                     arch_set_pseudo_atomic_interrupted(context);
 655                     maybe_save_gc_mask_and_block_deferrables
 656                         (os_context_sigmask_addr(context));
 657                 } else {
 658                     maybe_gc(context);
 659                 }
 660             } else {
 661                 SetSymbolValue(GC_PENDING,T,thread);
 662             }
 663         }
 664         return 1;
 665     }
 666     return 0;
 667 }