checksums.c

/*
 * Copyright (c) 1992-1994 by Xerox Corporation.  All rights reserved.
 *
 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
 * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
 *
 * Permission is hereby granted to use or copy this program
 * for any purpose, provided the above notices are retained on all copies.
 * Permission to modify the code and to distribute modified code is granted,
 * provided the above notices are retained, and a notice that the code was
 * modified is included with the above copyright notice.
 */

#include "private/gc_priv.h"

#ifdef CHECKSUMS

/* This is debugging code intended to verify the results of dirty bit   */
/* computations.  Works only in a single threaded environment.          */
# define NSUMS 10000
# define OFFSET 0x10000

typedef struct {
        GC_bool new_valid;
        word old_sum;
        word new_sum;
        struct hblk * block;    /* Block to which this refers + OFFSET  */
                                /* to hide it from collector.           */
} page_entry;

page_entry GC_sums[NSUMS];

STATIC word GC_faulted[NSUMS] = { 0 };
                /* Record of pages on which we saw a write fault.       */

STATIC size_t GC_n_faulted = 0;

#ifdef MPROTECT_VDB
  void GC_record_fault(struct hblk * h)
  {
    GC_ASSERT(GC_page_size != 0);
    if (GC_n_faulted >= NSUMS) ABORT("write fault log overflowed");
    GC_faulted[GC_n_faulted++] = ADDR(HBLK_PAGE_ALIGNED(h));
  }
#endif

STATIC GC_bool GC_was_faulted(struct hblk *h)
{
    size_t i;
    word page = ADDR(HBLK_PAGE_ALIGNED(h));

    for (i = 0; i < GC_n_faulted; ++i) {
        if (GC_faulted[i] == page) return TRUE;
    }
    return FALSE;
}

STATIC word GC_checksum(struct hblk *h)
{
    word *p;
    word *lim = (word *)(h + 1);
    word result = 0;

    for (p = (word *)h; ADDR_LT((ptr_t)p, (ptr_t)lim); p++) {
        result += *p;
    }
    return result | SIGNB; /* does not look like pointer */
}

int GC_n_dirty_errors = 0;
int GC_n_faulted_dirty_errors = 0;
unsigned long GC_n_clean = 0;
unsigned long GC_n_dirty = 0;

STATIC void GC_update_check_page(struct hblk *h, int index)
{
    page_entry *pe = GC_sums + index;
    hdr * hhdr = HDR(h);

    if (pe -> block != 0 && pe -> block != h + OFFSET) ABORT("goofed");
    pe -> old_sum = pe -> new_sum;
    pe -> new_sum = GC_checksum(h);
#   if !defined(MSWIN32) && !defined(MSWINCE)
        if (pe -> new_sum != SIGNB && !GC_page_was_ever_dirty(h)) {
            GC_err_printf("GC_page_was_ever_dirty(%p) is wrong\n", (void *)h);
        }
#   endif
    if (GC_page_was_dirty(h)) {
        GC_n_dirty++;
    } else {
        GC_n_clean++;
    }
    if (hhdr != NULL) {
        (void)GC_find_starting_hblk(h, &hhdr);
        if (pe -> new_valid
#           ifdef SOFT_VDB
              && !HBLK_IS_FREE(hhdr)
#           endif
            && !IS_PTRFREE(hhdr) && pe -> old_sum != pe -> new_sum) {
            if (!GC_page_was_dirty(h) || !GC_page_was_ever_dirty(h)) {
                GC_bool was_faulted = GC_was_faulted(h);
                /* Set breakpoint here */GC_n_dirty_errors++;
                if (was_faulted) GC_n_faulted_dirty_errors++;
            }
        }
    }
    pe -> new_valid = TRUE;
    pe -> block = h + OFFSET;
}

word GC_bytes_in_used_blocks = 0;

STATIC void GC_CALLBACK GC_add_block(struct hblk *h, void *dummy)
{
   const hdr *hhdr = HDR(h);

   UNUSED_ARG(dummy);
   GC_bytes_in_used_blocks += (hhdr -> hb_sz + HBLKSIZE-1) & ~(HBLKSIZE-1);
}

STATIC void GC_check_blocks(void)
{
    word bytes_in_free_blocks = GC_large_free_bytes;

    GC_bytes_in_used_blocks = 0;
    GC_apply_to_all_blocks(GC_add_block, NULL);
    GC_COND_LOG_PRINTF("GC_bytes_in_used_blocks= %lu,"
                       " bytes_in_free_blocks= %lu, heapsize= %lu\n",
                       (unsigned long)GC_bytes_in_used_blocks,
                       (unsigned long)bytes_in_free_blocks,
                       (unsigned long)GC_heapsize);
    if (GC_bytes_in_used_blocks + bytes_in_free_blocks != GC_heapsize) {
        GC_err_printf("LOST SOME BLOCKS!!\n");
    }
}

/* Should be called immediately after GC_read_dirty.    */
void GC_check_dirty(void)
{
    int index;
    size_t i;

    GC_check_blocks();
    GC_n_dirty_errors = 0;
    GC_n_faulted_dirty_errors = 0;
    GC_n_clean = 0;
    GC_n_dirty = 0;

    index = 0;
    for (i = 0; i < GC_n_heap_sects; i++) {
        ptr_t start = GC_heap_sects[i].hs_start;
        struct hblk *h;

        for (h = (struct hblk *)start;
             ADDR_LT((ptr_t)h, start + GC_heap_sects[i].hs_bytes); h++) {
            GC_update_check_page(h, index);
            index++;
            if (index >= NSUMS) {
                i = GC_n_heap_sects;
                break;
            }
        }
    }

    GC_COND_LOG_PRINTF("Checked %lu clean and %lu dirty pages\n",
                       GC_n_clean, GC_n_dirty);
    if (GC_n_dirty_errors > 0) {
        GC_err_printf("Found %d dirty bit errors (%d were faulted)\n",
                      GC_n_dirty_errors, GC_n_faulted_dirty_errors);
    }
    for (i = 0; i < GC_n_faulted; ++i) {
        GC_faulted[i] = 0; /* Don't expose block pointers to GC */
    }
    GC_n_faulted = 0;
}

#endif /* CHECKSUMS */