racket/c/gcwrapper.c

/* gcwrapper.c
 * Copyright 1984-2017 Cisco Systems, Inc.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "system.h"

/* locally defined functions */
static IBOOL memqp PROTO((ptr x, ptr ls));
static IBOOL remove_first_nomorep PROTO((ptr x, ptr *pls, IBOOL look));
static void segment_tell PROTO((uptr seg));
static void check_heap_dirty_msg PROTO((char *msg, ptr *x));
static IBOOL dirty_listedp PROTO((seginfo *x, IGEN from_g, IGEN to_g));
static void check_dirty_space PROTO((ISPC s));
static void check_dirty PROTO((void));

static IBOOL checkheap_noisy;

void S_gc_init() {
  IGEN g; INT i;

  S_checkheap = 0; /* 0 for disabled, 1 for enabled */
  S_checkheap_errors = 0; /* count of errors detected by checkheap */
  checkheap_noisy = 0; /* 0 for error output only; 1 for more noisy output */
  S_G.prcgeneration = static_generation;

  if (S_checkheap) {
    printf(checkheap_noisy ? "NB: check_heap is enabled and noisy\n" : "NB: check_heap_is_enabled\n");
    fflush(stdout);
  }

#ifndef WIN32
  for (g = 0; g <= static_generation; g++) {
    S_child_processes[g] = Snil;
  }
#endif /* WIN32 */

  if (!S_boot_time) return;

  for (g = 0; g <= static_generation; g++) {
    S_G.guardians[g] = Snil;
    S_G.locked_objects[g] = Snil;
    S_G.unlocked_objects[g] = Snil;
  }
  S_G.max_nonstatic_generation = 
    S_G.new_max_nonstatic_generation = 
      S_G.min_free_gen = 
        S_G.new_min_free_gen = default_max_nonstatic_generation;

  for (g = 0; g <= static_generation; g += 1) {
    for (i = 0; i < countof_types; i += 1) {
      S_G.countof[g][i] = 0;
      S_G.bytesof[g][i] = 0;
    }
    S_G.gctimestamp[g] = 0;
    S_G.rtds_with_counts[g] = Snil;
  }

  S_G.countof[static_generation][countof_oblist] += 1;
  S_G.bytesof[static_generation][countof_oblist] += S_G.oblist_length * sizeof(bucket *);

  S_protect(&S_G.static_id);
  S_G.static_id = S_intern((const unsigned char *)"static");

  S_protect(&S_G.countof_names);
  S_G.countof_names = S_vector(countof_types);
  for (i = 0; i < countof_types; i += 1) {
    INITVECTIT(S_G.countof_names, i) = FIX(0);
    S_G.countof_size[i] = 0;
  }
  INITVECTIT(S_G.countof_names, countof_pair) = S_intern((const unsigned char *)"pair");
    S_G.countof_size[countof_pair] = size_pair;
  INITVECTIT(S_G.countof_names, countof_symbol) = S_intern((const unsigned char *)"symbol");
    S_G.countof_size[countof_symbol] = size_symbol;
  INITVECTIT(S_G.countof_names, countof_flonum) = S_intern((const unsigned char *)"flonum");
    S_G.countof_size[countof_flonum] = size_flonum;
  INITVECTIT(S_G.countof_names, countof_closure) = S_intern((const unsigned char *)"procedure");
    S_G.countof_size[countof_closure] = 0;
  INITVECTIT(S_G.countof_names, countof_continuation) = S_intern((const unsigned char *)"continuation");
    S_G.countof_size[countof_continuation] = size_continuation;
  INITVECTIT(S_G.countof_names, countof_bignum) = S_intern((const unsigned char *)"bignum");
    S_G.countof_size[countof_bignum] = 0;
  INITVECTIT(S_G.countof_names, countof_ratnum) = S_intern((const unsigned char *)"ratnum");
    S_G.countof_size[countof_ratnum] = size_ratnum;
  INITVECTIT(S_G.countof_names, countof_inexactnum) = S_intern((const unsigned char *)"inexactnum");
    S_G.countof_size[countof_inexactnum] = size_inexactnum;
  INITVECTIT(S_G.countof_names, countof_exactnum) = S_intern((const unsigned char *)"exactnum");
    S_G.countof_size[countof_exactnum] = size_exactnum;
  INITVECTIT(S_G.countof_names, countof_box) = S_intern((const unsigned char *)"box");
    S_G.countof_size[countof_box] = size_box;
  INITVECTIT(S_G.countof_names, countof_port) = S_intern((const unsigned char *)"port");
    S_G.countof_size[countof_port] = size_port;
  INITVECTIT(S_G.countof_names, countof_code) = S_intern((const unsigned char *)"code");
    S_G.countof_size[countof_code] = 0;
  INITVECTIT(S_G.countof_names, countof_thread) = S_intern((const unsigned char *)"thread");
    S_G.countof_size[countof_thread] = size_thread;
  INITVECTIT(S_G.countof_names, countof_tlc) = S_intern((const unsigned char *)"tlc");
    S_G.countof_size[countof_tlc] = size_tlc;
  INITVECTIT(S_G.countof_names, countof_rtd_counts) = S_intern((const unsigned char *)"rtd-counts");
    S_G.countof_size[countof_rtd_counts] = size_rtd_counts;
  INITVECTIT(S_G.countof_names, countof_stack) = S_intern((const unsigned char *)"stack");
    S_G.countof_size[countof_stack] = 0;
  INITVECTIT(S_G.countof_names, countof_relocation_table) = S_intern((const unsigned char *)"reloc-table");
    S_G.countof_size[countof_relocation_table] = 0;
  INITVECTIT(S_G.countof_names, countof_weakpair) = S_intern((const unsigned char *)"weakpair");
    S_G.countof_size[countof_weakpair] = size_pair;
  INITVECTIT(S_G.countof_names, countof_vector) = S_intern((const unsigned char *)"vector");
    S_G.countof_size[countof_vector] = 0;
  INITVECTIT(S_G.countof_names, countof_string) = S_intern((const unsigned char *)"string");
    S_G.countof_size[countof_string] = 0;
  INITVECTIT(S_G.countof_names, countof_fxvector) = S_intern((const unsigned char *)"fxvector");
    S_G.countof_size[countof_fxvector] = 0;
  INITVECTIT(S_G.countof_names, countof_bytevector) = S_intern((const unsigned char *)"bytevector");
    S_G.countof_size[countof_bytevector] = 0;
  INITVECTIT(S_G.countof_names, countof_locked) = S_intern((const unsigned char *)"locked");
    S_G.countof_size[countof_locked] = 0;
  INITVECTIT(S_G.countof_names, countof_guardian) = S_intern((const unsigned char *)"guardian");
    S_G.countof_size[countof_guardian] = size_guardian_entry;
  INITVECTIT(S_G.countof_names, countof_oblist) = S_intern((const unsigned char *)"oblist");
    S_G.countof_size[countof_guardian] = 0;
  INITVECTIT(S_G.countof_names, countof_ephemeron) = S_intern((const unsigned char *)"ephemron");
    S_G.countof_size[countof_ephemeron] = 0;
  for (i = 0; i < countof_types; i += 1) {
    if (Svector_ref(S_G.countof_names, i) == FIX(0)) {
      fprintf(stderr, "uninitialized countof_name at index %d\n", i);
      S_abnormal_exit();
    }
  }
}

IGEN S_maxgen(void) {
  return S_G.new_max_nonstatic_generation;
}

void S_set_maxgen(IGEN g) {
  if (g < 0 || g >= static_generation) {
    fprintf(stderr, "invalid maxgen %d\n", g);
    S_abnormal_exit();
  }
  if (S_G.new_min_free_gen == S_G.new_max_nonstatic_generation || S_G.new_min_free_gen > g) {
    S_G.new_min_free_gen = g;
  }
  S_G.new_max_nonstatic_generation = g;
}

IGEN S_minfreegen(void) {
  return S_G.new_min_free_gen;
}

void S_set_minfreegen(IGEN g) {
  S_G.new_min_free_gen = g;
  if (S_G.new_max_nonstatic_generation == S_G.max_nonstatic_generation) {
    S_G.min_free_gen = g;
  }
}

static IBOOL memqp(x, ls) ptr x, ls; {
  for (;;) {
    if (ls == Snil) return 0;
    if (Scar(ls) == x) return 1;
    ls = Scdr(ls);
  }
}

static IBOOL remove_first_nomorep(x, pls, look) ptr x, *pls; IBOOL look; {
  ptr ls;

  for (;;) {
    ls = *pls;
    if (ls == Snil) break;
    if (Scar(ls) == x) {
      ls = Scdr(ls);
      *pls = ls;
      if (look) return !memqp(x, ls);
      break;
    }
    pls = &Scdr(ls);
  }

 /* must return 0 if we don't look for more */
  return 0;
}

IBOOL Slocked_objectp(x) ptr x; {
  seginfo *si; IGEN g; IBOOL ans; ptr ls;

  if (IMMEDIATE(x) || (si = MaybeSegInfo(ptr_get_segment(x))) == NULL || (g = si->generation) == static_generation) return 1;

  tc_mutex_acquire()

  ans = 0;
  for (ls = S_G.locked_objects[g]; ls != Snil; ls = Scdr(ls)) {
    if (x == Scar(ls)) {
      ans = 1;
      break;
    }
  }

  tc_mutex_release()

  return ans;
}

ptr S_locked_objects(void) {
  IGEN g; ptr ans; ptr ls;

  tc_mutex_acquire()

  ans = Snil;
  for (g = 0; g <= static_generation; INCRGEN(g)) {
    for (ls = S_G.locked_objects[g]; ls != Snil; ls = Scdr(ls)) {
      ans = Scons(Scar(ls), ans);
    }
  }

  tc_mutex_release()

  return ans;
}

void Slock_object(x) ptr x; {
  seginfo *si; IGEN g;

  tc_mutex_acquire()

 /* weed out pointers that won't be relocated */
  if (!IMMEDIATE(x) && (si = MaybeSegInfo(ptr_get_segment(x))) != NULL && (g = si->generation) != static_generation) {
    S_pants_down += 1;
   /* add x to locked list. remove from unlocked list */
    S_G.locked_objects[g] = S_cons_in((g == 0 ? space_new : space_impure), g, x, S_G.locked_objects[g]);
    if (S_G.enable_object_counts) {
      if (g != 0) S_G.countof[g][countof_pair] += 1;
    }
    if (si->space & space_locked)
      (void)remove_first_nomorep(x, &S_G.unlocked_objects[g], 0);
    S_pants_down -= 1;
  }

  tc_mutex_release()
}

void Sunlock_object(x) ptr x; {
  seginfo *si; IGEN g;

  tc_mutex_acquire()

  if (!IMMEDIATE(x) && (si = MaybeSegInfo(ptr_get_segment(x))) != NULL && (g = si->generation) != static_generation) {
    S_pants_down += 1;
   /* remove first occurrence of x from locked list. if there are no
      others, add x to unlocked list */
    if (remove_first_nomorep(x, &S_G.locked_objects[g], si->space & space_locked)) {
      S_G.unlocked_objects[g] = S_cons_in((g == 0 ? space_new : space_impure), g, x, S_G.unlocked_objects[g]);
      if (S_G.enable_object_counts) {
        if (g != 0) S_G.countof[g][countof_pair] += 1;
      }
    }
    S_pants_down -= 1;
  }

  tc_mutex_release()
}

ptr s_help_unregister_guardian(ptr *pls, ptr tconc, ptr result) {
  ptr rep, ls;
  while ((ls = *pls) != Snil) {
    if (GUARDIANTCONC(ls) == tconc) {
      result = Scons(((rep = GUARDIANREP(ls)) == ftype_guardian_rep ? GUARDIANOBJ(ls) : rep), result);
      *pls = ls = GUARDIANNEXT(ls);
    } else {
      ls = *(pls = &GUARDIANNEXT(ls));
    }
  }
  return result;
}

ptr S_unregister_guardian(ptr tconc) {
  ptr result, tc; IGEN g;
  tc_mutex_acquire()
  tc = get_thread_context();
  /* in the interest of thread safety, gather entries only in the current thread, ignoring any others */
  result = s_help_unregister_guardian(&GUARDIANENTRIES(tc), tconc, Snil);
  /* plus, of course, any already known to the storage-management system */
  for (g = 0; g <= static_generation; INCRGEN(g)) {
    result = s_help_unregister_guardian(&S_G.guardians[g], tconc, result);
  }
  tc_mutex_release()
  return result;
}

#ifndef WIN32
void S_register_child_process(INT child) {
  tc_mutex_acquire()
  S_child_processes[0] = Scons(FIX(child), S_child_processes[0]);
  tc_mutex_release()
}
#endif /* WIN32 */

IBOOL S_enable_object_counts(void) {
  return S_G.enable_object_counts;
}

void S_set_enable_object_counts(IBOOL eoc) {
  S_G.enable_object_counts = eoc;
}

ptr S_object_counts(void) {
  IGEN grtd, g; ptr ls; iptr i; ptr outer_alist;

  tc_mutex_acquire()

  outer_alist = Snil;

 /* add rtds w/nonozero counts to the alist */
  for (grtd = 0; grtd <= static_generation; INCRGEN(grtd)) {
    for (ls = S_G.rtds_with_counts[grtd]; ls != Snil; ls = Scdr(ls)) {
      ptr rtd = Scar(ls);
      ptr counts = RECORDDESCCOUNTS(rtd);
      IGEN g;
      uptr size = size_record_inst(UNFIX(RECORDDESCSIZE(rtd)));
      ptr inner_alist = Snil;

      S_fixup_counts(counts);
      for (g = 0; g <= static_generation; INCRGEN(g)) {
        uptr count = RTDCOUNTSIT(counts, g); IGEN gcurrent = g;
        if (g == S_G.new_max_nonstatic_generation) {
          while (g < S_G.max_nonstatic_generation) {
            g += 1;
            count += RTDCOUNTSIT(counts, g);
          }
        }
        if (count != 0) inner_alist = Scons(Scons((gcurrent == static_generation ? S_G.static_id : FIX(gcurrent)), Scons(Sunsigned(count), Sunsigned(count * size))), inner_alist);
      }
      if (inner_alist != Snil) outer_alist = Scons(Scons(rtd, inner_alist), outer_alist);
    }
  }

 /* add primary types w/nonozero counts to the alist */
  for (i = 0 ; i < countof_types; i += 1) {
    ptr inner_alist = Snil;
    for (g = 0; g <= static_generation; INCRGEN(g)) {
      IGEN gcurrent = g;
      uptr count = S_G.countof[g][i];
      uptr bytes = S_G.bytesof[g][i];

      if (g == S_G.new_max_nonstatic_generation) {
        while (g < S_G.max_nonstatic_generation) {
          g += 1;
          /* NB: S_G.max_nonstatic_generation + 1 <= static_generation, but coverity complains about overrun */
          /* coverity[overrun-buffer-val] */
          count += S_G.countof[g][i];
          /* coverity[overrun-buffer-val] */
          bytes += S_G.bytesof[g][i];
        }
      }

      if (count != 0) {
        if (bytes == 0) bytes = count * S_G.countof_size[i];
        inner_alist = Scons(Scons((gcurrent == static_generation ? S_G.static_id : FIX(gcurrent)), Scons(Sunsigned(count), Sunsigned(bytes))), inner_alist);
      }
    }
    if (inner_alist != Snil) outer_alist = Scons(Scons(Svector_ref(S_G.countof_names, i), inner_alist), outer_alist);
  }

  tc_mutex_release()

  return outer_alist;
}

/* Scompact_heap().  Compact into as few O/S chunks as possible and
 * move objects into static generation
 */
void Scompact_heap() {
  ptr tc = get_thread_context();
  S_pants_down += 1;
  S_gc_oce(tc, S_G.max_nonstatic_generation, static_generation);
  S_pants_down -= 1;
}

/* S_check_heap checks for various kinds of heap consistency
   It currently checks for:
       dangling references in space_impure (generation > 0) and space_pure
       extra dirty bits
       missing dirty bits

   Some additional things it should check for but doesn't:
       correct dirty bytes, following sweep_dirty conventions
       dangling references in in space_code and space_continuation
       dirty bits set for non-impure segments outside of generation zero
       proper chaining of segments of a space and generation:
          chains contain all and only the appropriate segments

   If noisy is nonzero, additional comments may be included in the output
*/

static void segment_tell(seg) uptr seg; {
  seginfo *si;
  ISPC s, s1;
  static char *spacename[max_space+1] = { alloc_space_names };

  printf("segment %#tx", (ptrdiff_t)seg);
  if ((si = MaybeSegInfo(seg)) == NULL) {
    printf(" out of heap bounds\n");
  } else {
    printf(" generation=%d", si->generation);
    s = si->space;
    s1 = si->space & ~(space_old|space_locked);
    if (s1 < 0 || s1 > max_space)
      printf(" space-bogus (%d)", s);
    else {
      printf(" space-%s", spacename[s1]);
      if (s & space_old) printf(" oldspace");
      if (s & space_locked) printf(" locked");
    }
    printf("\n");
  }
  fflush(stdout);
}

void S_ptr_tell(ptr p) {
  segment_tell(ptr_get_segment(p));
}

void S_addr_tell(ptr p) {
  segment_tell(addr_get_segment(p));
}

static void check_heap_dirty_msg(msg, x) char *msg; ptr *x; {
    INT d; seginfo *si;

    si = SegInfo(addr_get_segment(x));
    d = (INT)(((uptr)x >> card_offset_bits) & ((1 << segment_card_offset_bits) - 1));
    printf("%s dirty byte %d found in segment %#tx, card %d at %#tx\n", msg, si->dirty_bytes[d], (ptrdiff_t)(si->number), d, (ptrdiff_t)x);
    printf("from "); segment_tell(addr_get_segment(x));
    printf("to   "); segment_tell(addr_get_segment(*x));
}

void S_check_heap(aftergc) IBOOL aftergc; {
  uptr seg; INT d; ISPC s; IGEN g; IDIRTYBYTE dirty; IBOOL found_eos; IGEN pg;
  ptr p, *pp1, *pp2, *nl;
  iptr i;
  uptr empty_segments = 0;
  uptr used_segments = 0;
  uptr static_segments = 0;
  uptr nonstatic_segments = 0;

  check_dirty();

  for (i = PARTIAL_CHUNK_POOLS; i >= -1; i -= 1) {
    chunkinfo *chunk = i == -1 ? S_chunks_full : S_chunks[i];
    while (chunk != NULL) {
      seginfo *si = chunk->unused_segs;
      iptr count = 0;
      while(si) {
        count += 1;
        if (si->space != space_empty) {
          S_checkheap_errors += 1;
          printf("!!! unused segment has unexpected space\n");
        }
        si = si->next;
      }
      if ((chunk->segs - count) != chunk->nused_segs) {
        S_checkheap_errors += 1;
        printf("!!! unexpected used segs count %td with %td total segs and %td segs on the unused list\n",
            (ptrdiff_t)chunk->nused_segs, (ptrdiff_t)chunk->segs, (ptrdiff_t)count);
      }
      used_segments += chunk->nused_segs;
      empty_segments += count;
      chunk = chunk->next;
    }
  }

  for (s = 0; s <= max_real_space; s += 1) {
    seginfo *si;
    for (g = 0; g <= S_G.max_nonstatic_generation; INCRGEN(g)) {
      for (si = S_G.occupied_segments[s][g]; si != NULL; si = si->next) {
        nonstatic_segments += 1;
      }
    }
    for (si = S_G.occupied_segments[s][static_generation]; si != NULL; si = si->next) {
      static_segments += 1;
    }
  }

  if (used_segments != nonstatic_segments + static_segments) {
    S_checkheap_errors += 1;
    printf("!!! found %#tx used segments and %#tx occupied segments\n",
        (ptrdiff_t)used_segments,
        (ptrdiff_t)(nonstatic_segments + static_segments));
  }

  if (S_G.number_of_nonstatic_segments != nonstatic_segments) {
    S_checkheap_errors += 1;
    printf("!!! S_G.number_of_nonstatic_segments %#tx is different from occupied number %#tx\n",
        (ptrdiff_t)S_G.number_of_nonstatic_segments,
        (ptrdiff_t)nonstatic_segments);
  }

  if (S_G.number_of_empty_segments != empty_segments) {
    S_checkheap_errors += 1;
    printf("!!! S_G.number_of_empty_segments %#tx is different from unused number %#tx\n",
        (ptrdiff_t)S_G.number_of_empty_segments,
        (ptrdiff_t)empty_segments);
  }

  for (i = PARTIAL_CHUNK_POOLS; i >= -1; i -= 1) {
    chunkinfo *chunk = i == -1 ? S_chunks_full : S_chunks[i];
    while (chunk != NULL) {
      uptr nsegs; seginfo *si;
      for (si = &chunk->sis[0], nsegs = chunk->segs; nsegs != 0; nsegs -= 1, si += 1) {
        seginfo *recorded_si; uptr recorded_seg;
        if ((seg = si->number) != (recorded_seg = (chunk->base + chunk->segs - nsegs))) {
          S_checkheap_errors += 1;
          printf("!!! recorded segment number %#tx differs from actual segment number %#tx", (ptrdiff_t)seg, (ptrdiff_t)recorded_seg);
        }
        if ((recorded_si = SegInfo(seg)) != si) {
          S_checkheap_errors += 1;
          printf("!!! recorded segment %#tx seginfo %#tx differs from actual seginfo %#tx", (ptrdiff_t)seg, (ptrdiff_t)recorded_si, (ptrdiff_t)si);
        }
        s = si->space;
        g = si->generation;

        if (s == space_new) {
          if (g != 0) {
            S_checkheap_errors += 1;
            printf("!!! unexpected generation %d segment %#tx in space_new\n", g, (ptrdiff_t)seg);
          }
        } else if (s == space_impure || s == space_symbol || s == space_pure || s == space_weakpair /* || s == space_ephemeron */) {
          /* out of date: doesn't handle space_port, space_continuation, space_code, space_pure_typed_object, space_impure_record */
          nl = (ptr *)S_G.next_loc[s][g];

          /* check for dangling references */
          pp1 = (ptr *)build_ptr(seg, 0);
          pp2 = (ptr *)build_ptr(seg + 1, 0);
          if (pp1 <= nl && nl < pp2) pp2 = nl;

          while (pp1 != pp2) {
            seginfo *psi; ISPC ps;
            p = *pp1;
            if (p == forward_marker) break;
            if (!IMMEDIATE(p) && (psi = MaybeSegInfo(ptr_get_segment(p))) != NULL && ((ps = psi->space) & space_old || ps == space_empty)) {
              S_checkheap_errors += 1;
              printf("!!! dangling reference at %#tx to %#tx\n", (ptrdiff_t)pp1, (ptrdiff_t)p);
              printf("from: "); segment_tell(seg);
              printf("to:   "); segment_tell(ptr_get_segment(p));
            }
            pp1 += 1;
          }

          /* verify that dirty bits are set appropriately */
          /* out of date: doesn't handle space_impure_record, space_port, and maybe others */
          /* also doesn't check the SYMCODE for symbols */
          if (s == space_impure || s == space_symbol || s == space_weakpair /* || s == space_ephemeron */) {
            found_eos = 0;
            pp2 = pp1 = build_ptr(seg, 0);
            for (d = 0; d < cards_per_segment; d += 1) {
              if (found_eos) {
                if (si->dirty_bytes[d] != 0xff) {
                  S_checkheap_errors += 1;
                  printf("!!! Dirty byte set past end-of-segment for segment %#tx, card %d\n", (ptrdiff_t)seg, d);
                  segment_tell(seg);
                }
                continue;
              }

              pp2 += bytes_per_card / sizeof(ptr);
              if (pp1 <= nl && nl < pp2) {
                found_eos = 1;
                pp2 = nl;
              }

#ifdef DEBUG
              printf("pp1 = %#tx, pp2 = %#tx, nl = %#tx\n", (ptrdiff_t)pp1, (ptrdiff_t)pp2, (ptrdiff_t)nl);
              fflush(stdout);
#endif

              dirty = 0xff;
              while (pp1 != pp2) {
                seginfo *psi;
                p = *pp1;

                if (p == forward_marker) {
                  found_eos = 1;
                  break;
                }
                if (!IMMEDIATE(p) && (psi = MaybeSegInfo(ptr_get_segment(p))) != NULL && (pg = psi->generation) < g) {
                  if (pg < dirty) dirty = pg;
                  if (si->dirty_bytes[d] > pg) {
                    S_checkheap_errors += 1;
                    check_heap_dirty_msg("!!! INVALID", pp1);
                  }
                  else if (checkheap_noisy)
                    check_heap_dirty_msg("... ", pp1);
                }
                pp1 += 1;
              }
              if (checkheap_noisy && si->dirty_bytes[d] < dirty) {
                /* sweep_dirty won't sweep, and update dirty byte, for
                   cards with dirty pointers to segments older than the
                   maximum copyied generation, so we can get legitimate
                   conservative dirty bytes even after gc */
                printf("... Conservative dirty byte %x (%x) %sfor segment %#tx card %d ",
                    si->dirty_bytes[d], dirty,
                    (aftergc ? "after gc " : ""),
                    (ptrdiff_t)seg, d);
                segment_tell(seg);
              }
            }
          }
        }
        if (aftergc && s != space_empty && !(s & space_locked) && (g == 0 || (s != space_impure && s != space_symbol && s != space_port && s != space_weakpair && s != space_ephemeron && s != space_impure_record))) {
          for (d = 0; d < cards_per_segment; d += 1) {
            if (si->dirty_bytes[d] != 0xff) {
              S_checkheap_errors += 1;
              printf("!!! Unnecessary dirty byte %x (%x) after gc for segment %#tx card %d ",
                  si->dirty_bytes[d], 0xff, (ptrdiff_t)(si->number), d);
              segment_tell(seg);
            }
          }
        }
      }
      chunk = chunk->next;
    }
  }
}

static IBOOL dirty_listedp(seginfo *x, IGEN from_g, IGEN to_g) {
  seginfo *si = DirtySegments(from_g, to_g);
  while (si != NULL) {
    if (si == x) return 1;
    si = si->dirty_next;
  }
  return 0;
}

static void check_dirty_space(ISPC s) {
  IGEN from_g, to_g, min_to_g; INT d; seginfo *si;

  for (from_g = 0; from_g <= static_generation; from_g += 1) {
    for (si = S_G.occupied_segments[s][from_g]; si != NULL; si = si->next) {
      if (si->space & space_locked) continue;
      min_to_g = 0xff;
      for (d = 0; d < cards_per_segment; d += 1) {
        to_g = si->dirty_bytes[d];
        if (to_g != 0xff) {
          if (to_g < min_to_g) min_to_g = to_g;
          if (from_g == 0) {
            S_checkheap_errors += 1;
            printf("!!! (check_dirty): space %d, generation %d segment %#tx card %d is marked dirty\n", s, from_g, (ptrdiff_t)(si->number), d);
          }
        }
      }
      if (min_to_g != si->min_dirty_byte) {
        S_checkheap_errors += 1;
        printf("!!! (check_dirty): space %d, generation %d segment %#tx min_dirty_byte is %d while actual min is %d\n",  s, from_g, (ptrdiff_t)(si->number), si->min_dirty_byte, min_to_g);
        segment_tell(si->number);
      } else if (min_to_g != 0xff) {
        if (!dirty_listedp(si, from_g, min_to_g)) {
          S_checkheap_errors += 1;
          printf("!!! (check_dirty): space %d, generation %d segment %#tx is marked dirty but not in dirty-segment list\n", s, from_g, (ptrdiff_t)(si->number));
          segment_tell(si->number);
        }
      }
    }
  }
}

static void check_dirty() {
  IGEN from_g, to_g; seginfo *si;

  for (from_g = 1; from_g <= static_generation; from_g = from_g == S_G.max_nonstatic_generation ? static_generation : from_g + 1) {
    for (to_g = 0; (from_g == static_generation) ? (to_g <= S_G.max_nonstatic_generation) : (to_g < from_g); to_g += 1) {
      si = DirtySegments(from_g, to_g);
      if (from_g > S_G.max_nonstatic_generation && from_g != static_generation) {
        if (si != NULL) {
          S_checkheap_errors += 1;
          printf("!!! (check_dirty): unexpected nonempty from-generation %d, to-generation %d dirty segment list\n", from_g, to_g);
        }
      } else {
        while (si != NULL) {
          ISPC s = si->space & ~space_locked;
          IGEN g = si->generation;
          IGEN mingval = si->min_dirty_byte;
          if (g != from_g) {
            S_checkheap_errors += 1;
            printf("!!! (check_dirty): generation %d segment %#tx in %d -> %d dirty list\n", g, (ptrdiff_t)(si->number), from_g, to_g);
          }
          if (mingval != to_g) {
            S_checkheap_errors += 1;
            printf("!!! (check_dirty): dirty byte = %d for segment %#tx in %d -> %d dirty list\n", mingval, (ptrdiff_t)(si->number), from_g, to_g);
          }
          if (s != space_new && s != space_impure && s != space_symbol && s != space_port && s != space_impure_record && s != space_weakpair && s != space_ephemeron) {
            S_checkheap_errors += 1;
            printf("!!! (check_dirty): unexpected space %d for dirty segment %#tx\n", s, (ptrdiff_t)(si->number));
          }
          si = si->dirty_next;
        }
      }
    }
  }

  check_dirty_space(space_impure);
  check_dirty_space(space_symbol);
  check_dirty_space(space_port);
  check_dirty_space(space_impure_record);
  check_dirty_space(space_weakpair);
  check_dirty_space(space_ephemeron);

  fflush(stdout);
}

void S_fixup_counts(ptr counts) {
  IGEN g; U64 timestamp;

  timestamp = RTDCOUNTSTIMESTAMP(counts);
  for (g = 0; g <= static_generation; INCRGEN(g)) {
    if (timestamp >= S_G.gctimestamp[g]) break;
    RTDCOUNTSIT(counts, g) = 0;
  }
  RTDCOUNTSTIMESTAMP(counts) = S_G.gctimestamp[0];
}

void S_do_gc(IGEN mcg, IGEN tg) {
  ptr tc = get_thread_context();
  ptr code;

  code = CP(tc);
  if (Sprocedurep(code)) code = CLOSCODE(code);
  Slock_object(code);

 /* Scheme side grabs mutex before calling S_do_gc */
  S_pants_down += 1;

  if (S_G.new_max_nonstatic_generation > S_G.max_nonstatic_generation) {
    S_G.min_free_gen = S_G.new_min_free_gen;
    S_G.max_nonstatic_generation = S_G.new_max_nonstatic_generation;
  }

  if (tg == mcg && mcg == S_G.new_max_nonstatic_generation && mcg < S_G.max_nonstatic_generation) {
    IGEN new_g, old_g, from_g, to_g; ISPC s; seginfo *si, *nextsi, *tail;
   /* reducing max_nonstatic_generation */
    new_g = S_G.new_max_nonstatic_generation;
    old_g = S_G.max_nonstatic_generation;
   /* first, collect everything to old_g */
    S_gc(tc, old_g, old_g);
   /* now transfer old_g info to new_g, and clear old_g info */
    for (s = 0; s <= max_real_space; s += 1) {
      S_G.first_loc[s][new_g] = S_G.first_loc[s][old_g]; S_G.first_loc[s][old_g] = FIX(0);
      S_G.base_loc[s][new_g] = S_G.base_loc[s][old_g]; S_G.base_loc[s][old_g] = FIX(0);
      S_G.next_loc[s][new_g] = S_G.next_loc[s][old_g]; S_G.next_loc[s][old_g] = FIX(0);
      S_G.bytes_left[s][new_g] = S_G.bytes_left[s][old_g]; S_G.bytes_left[s][old_g] = 0;
      S_G.bytes_of_space[s][new_g] = S_G.bytes_of_space[s][old_g]; S_G.bytes_of_space[s][old_g] = 0;
      S_G.occupied_segments[s][new_g] = S_G.occupied_segments[s][old_g]; S_G.occupied_segments[s][old_g] = NULL;
      for (si = S_G.occupied_segments[s][new_g]; si != NULL; si = si->next) {
        si->generation = new_g;
      }
    }
    S_G.guardians[new_g] = S_G.guardians[old_g]; S_G.guardians[old_g] = Snil;
    S_G.locked_objects[new_g] = S_G.locked_objects[old_g]; S_G.locked_objects[old_g] = Snil;
    S_G.unlocked_objects[new_g] = S_G.unlocked_objects[old_g]; S_G.unlocked_objects[old_g] = Snil;
    S_G.buckets_of_generation[new_g] = S_G.buckets_of_generation[old_g]; S_G.buckets_of_generation[old_g] = NULL;
    if (S_G.enable_object_counts) {
      INT i; ptr ls;
      for (i = 0; i < countof_types; i += 1) {
        S_G.countof[new_g][i] = S_G.countof[old_g][i]; S_G.countof[old_g][i] = 0;
        S_G.bytesof[new_g][i] = S_G.bytesof[old_g][i]; S_G.bytesof[old_g][i] = 0;
      }
      S_G.rtds_with_counts[new_g] = S_G.rtds_with_counts[old_g]; S_G.rtds_with_counts[old_g] = Snil;
      for (ls = S_G.rtds_with_counts[new_g]; ls != Snil; ls = Scdr(ls)) {
        ptr counts = RECORDDESCCOUNTS(Scar(ls));
        RTDCOUNTSIT(counts, new_g) = RTDCOUNTSIT(counts, old_g); RTDCOUNTSIT(counts, old_g) = 0;
      }
      for (ls = S_G.rtds_with_counts[static_generation]; ls != Snil; ls = Scdr(ls)) {
        ptr counts = RECORDDESCCOUNTS(Scar(ls));
        RTDCOUNTSIT(counts, new_g) = RTDCOUNTSIT(counts, old_g); RTDCOUNTSIT(counts, old_g) = 0;
      }
    }

    /* change old_g dirty bytes in static generation to new_g; splice list of old_g
       seginfos onto front of new_g seginfos */
    for (from_g = 1; from_g <= static_generation; INCRGEN(from_g)) {
      for (to_g = 0; (from_g == static_generation) ? (to_g <= S_G.max_nonstatic_generation) : (to_g < from_g); to_g += 1) {
        if ((si = DirtySegments(from_g, to_g)) != NULL) {
          if (from_g == old_g) {
            DirtySegments(from_g, to_g) = NULL;
            DirtySegments(new_g, to_g) = si;
            si->dirty_prev = &DirtySegments(new_g, to_g);
          } else if (from_g == static_generation) {
            if (to_g == old_g) {
              DirtySegments(from_g, to_g) = NULL;
              tail = DirtySegments(from_g, new_g);
              DirtySegments(from_g, new_g) = si;
              si->dirty_prev = &DirtySegments(from_g, new_g);
              for (;;) {
                INT d;
                si->min_dirty_byte = new_g;
                for (d = 0; d < cards_per_segment; d += 1) {
                  if (si->dirty_bytes[d] == old_g) si->dirty_bytes[d] = new_g;
                }
                nextsi = si->dirty_next;
                if (nextsi == NULL) break;
                si = nextsi;
              }
              if (tail != NULL) tail->dirty_prev = &si->dirty_next;
              si->dirty_next = tail;
            } else {
              do {
                INT d;
                for (d = 0; d < cards_per_segment; d += 1) {
                  if (si->dirty_bytes[d] == old_g) si->dirty_bytes[d] = new_g;
                }
                si = si->dirty_next;
              } while (si != NULL);
            }
          } else {
            S_error_abort("S_do_gc(gc): unexpected nonempty dirty segment list");
          }
        }
      }
    }

   /* tell profile_release_counters to scan only through new_g */
    if (S_G.prcgeneration == old_g) S_G.prcgeneration = new_g;

   /* finally reset max_nonstatic_generation */
    S_G.min_free_gen = S_G.new_min_free_gen;
    S_G.max_nonstatic_generation = new_g;
  } else {
    S_gc(tc, mcg, tg);
  }
  S_pants_down -= 1;

 /* eagerly give collecting thread, the only one guaranteed to be
    active, a fresh allocation area.  the other threads have to trap
    to get_more_room if and when they awake and try to allocate */
  S_reset_allocation_pointer(tc);

  Sunlock_object(code);
}


void S_gc(ptr tc, IGEN mcg, IGEN tg) {
  if (tg == static_generation || S_G.enable_object_counts)
    S_gc_oce(tc, mcg, tg);
  else
    S_gc_ocd(tc, mcg, tg);
}