-/*
- * Minefield - a Windows equivalent for Electric Fence
- */
-
-#define PAGESIZE 4096
-
-/*
- * Design:
- *
- * We start by reserving as much virtual address space as Windows
- * will sensibly (or not sensibly) let us have. We flag it all as
- * invalid memory.
- *
- * Any allocation attempt is satisfied by committing one or more
- * pages, with an uncommitted page on either side. The returned
- * memory region is jammed up against the _end_ of the pages.
- *
- * Freeing anything causes instantaneous decommitment of the pages
- * involved, so stale pointers are caught as soon as possible.
- */
-
-static int minefield_initialised = 0;
-static void *minefield_region = NULL;
-static long minefield_size = 0;
-static long minefield_npages = 0;
-static long minefield_curpos = 0;
-static unsigned short *minefield_admin = NULL;
-static void *minefield_pages = NULL;
-
-static void minefield_admin_hide(int hide)
-{
- int access = hide ? PAGE_NOACCESS : PAGE_READWRITE;
- VirtualProtect(minefield_admin, minefield_npages * 2, access, NULL);
-}
-
-static void minefield_init(void)
-{
- int size;
- int admin_size;
- int i;
-
- for (size = 0x40000000; size > 0; size = ((size >> 3) * 7) & ~0xFFF) {
- minefield_region = VirtualAlloc(NULL, size,
- MEM_RESERVE, PAGE_NOACCESS);
- if (minefield_region)
- break;
- }
- minefield_size = size;
-
- /*
- * Firstly, allocate a section of that to be the admin block.
- * We'll need a two-byte field for each page.
- */
- minefield_admin = minefield_region;
- minefield_npages = minefield_size / PAGESIZE;
- admin_size = (minefield_npages * 2 + PAGESIZE - 1) & ~(PAGESIZE - 1);
- minefield_npages = (minefield_size - admin_size) / PAGESIZE;
- minefield_pages = (char *) minefield_region + admin_size;
-
- /*
- * Commit the admin region.
- */
- VirtualAlloc(minefield_admin, minefield_npages * 2,
- MEM_COMMIT, PAGE_READWRITE);
-
- /*
- * Mark all pages as unused (0xFFFF).
- */
- for (i = 0; i < minefield_npages; i++)
- minefield_admin[i] = 0xFFFF;
-
- /*
- * Hide the admin region.
- */
- minefield_admin_hide(1);
-
- minefield_initialised = 1;
-}
-
-static void minefield_bomb(void)
-{
- div(1, *(int *) minefield_pages);
-}
-
-static void *minefield_alloc(int size)
-{
- int npages;
- int pos, lim, region_end, region_start;
- int start;
- int i;
-
- npages = (size + PAGESIZE - 1) / PAGESIZE;
-
- minefield_admin_hide(0);
-
- /*
- * Search from current position until we find a contiguous
- * bunch of npages+2 unused pages.
- */
- pos = minefield_curpos;
- lim = minefield_npages;
- while (1) {
- /* Skip over used pages. */
- while (pos < lim && minefield_admin[pos] != 0xFFFF)
- pos++;
- /* Count unused pages. */
- start = pos;
- while (pos < lim && pos - start < npages + 2 &&
- minefield_admin[pos] == 0xFFFF)
- pos++;
- if (pos - start == npages + 2)
- break;
- /* If we've reached the limit, reset the limit or stop. */
- if (pos >= lim) {
- if (lim == minefield_npages) {
- /* go round and start again at zero */
- lim = minefield_curpos;
- pos = 0;
- } else {
- minefield_admin_hide(1);
- return NULL;
- }
- }
- }
-
- minefield_curpos = pos - 1;
-
- /*
- * We have npages+2 unused pages starting at start. We leave
- * the first and last of these alone and use the rest.
- */
- region_end = (start + npages + 1) * PAGESIZE;
- region_start = region_end - size;
- /* FIXME: could align here if we wanted */
-
- /*
- * Update the admin region.
- */
- for (i = start + 2; i < start + npages - 1; i++)
- minefield_admin[i] = 0xFFFE; /* used but no region starts here */
- minefield_admin[start + 1] = region_start % PAGESIZE;
-
- minefield_admin_hide(1);
-
- VirtualAlloc((char *) minefield_pages + region_start, size,
- MEM_COMMIT, PAGE_READWRITE);
- return (char *) minefield_pages + region_start;
-}
-
-static void minefield_free(void *ptr)
-{
- int region_start, i, j;
-
- minefield_admin_hide(0);
-
- region_start = (char *) ptr - (char *) minefield_pages;
- i = region_start / PAGESIZE;
- if (i < 0 || i >= minefield_npages ||
- minefield_admin[i] != region_start % PAGESIZE)
- minefield_bomb();
- for (j = i; j < minefield_npages && minefield_admin[j] != 0xFFFF; j++) {
- minefield_admin[j] = 0xFFFF;
- }
-
- VirtualFree(ptr, j * PAGESIZE - region_start, MEM_DECOMMIT);
-
- minefield_admin_hide(1);
-}
-
-static int minefield_get_size(void *ptr)
-{
- int region_start, i, j;
-
- minefield_admin_hide(0);
-
- region_start = (char *) ptr - (char *) minefield_pages;
- i = region_start / PAGESIZE;
- if (i < 0 || i >= minefield_npages ||
- minefield_admin[i] != region_start % PAGESIZE)
- minefield_bomb();
- for (j = i; j < minefield_npages && minefield_admin[j] != 0xFFFF; j++);
-
- minefield_admin_hide(1);
-
- return j * PAGESIZE - region_start;
-}
-
-static void *minefield_c_malloc(size_t size)
-{
- if (!minefield_initialised)
- minefield_init();
- return minefield_alloc(size);
-}
-
-static void minefield_c_free(void *p)
-{
- if (!minefield_initialised)
- minefield_init();
- minefield_free(p);
-}
-
-/*
- * realloc _always_ moves the chunk, for rapid detection of code
- * that assumes it won't.
- */
-static void *minefield_c_realloc(void *p, size_t size)
-{
- size_t oldsize;
- void *q;
- if (!minefield_initialised)
- minefield_init();
- q = minefield_alloc(size);
- oldsize = minefield_get_size(p);
- memcpy(q, p, (oldsize < size ? oldsize : size));
- minefield_free(p);
- return q;
-}
-
-#endif /* MINEFIELD */