malloc.c

   1 #include <stdlib.h>
   2 #include <string.h>
   3 #include <sys/mman.h>
   4
   5 #define PGSIZE          4096
   6 #define PGMASK          (PGSIZE - 1)
   7 #define MSETMAX         4096
   8 #define MSETLEN         (1 << 15)
   9
  10 struct mset {
  11         int refs;
  12         int size;
  13 };
  14
  15 static struct mset *pool;
  16
  17 static int mk_pool(void)
  18 {
  19         if (pool && !pool->refs) {
  20                 pool->size = sizeof(*pool);
  21                 return 0;
  22         }
  23         pool = mmap(NULL, MSETLEN, PROT_READ | PROT_WRITE,
  24                                 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
  25         if (pool == MAP_FAILED) {
  26                 pool = NULL;
  27                 return 1;
  28         }
  29         pool->size = sizeof(*pool);
  30         pool->refs = 0;
  31         return 0;
  32 }
  33
  34 void *malloc(long n)
  35 {
  36         void *m;
  37         if (n >= MSETMAX) {
  38                 m = mmap(NULL, n + PGSIZE, PROT_READ | PROT_WRITE,
  39                                 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
  40                 if (m == MAP_FAILED)
  41                         return NULL;
  42                 *(long *) m = n + PGSIZE;       /* store length in the first page */
  43                 return m + PGSIZE;
  44         }
  45         if (!pool || MSETLEN - pool->size < n + sizeof(void *))
  46                 if (mk_pool())
  47                         return NULL;
  48         m = (void *) pool + pool->size;
  49         *(void **) m = pool;                    /* the address of the owning mset */
  50         pool->refs++;
  51         pool->size += (n + sizeof(void *) + 7) & ~7;
  52         if (!((unsigned long) (pool + pool->size + sizeof(void *)) & PGMASK))
  53                 pool->size += sizeof(long);
  54         return m + sizeof(void *);
  55 }
  56
  57 void *calloc(long n, long sz)
  58 {
  59         void *r = malloc(n * sz);
  60         if (r)
  61                 memset(r, 0, n * sz);
  62         return r;
  63 }
  64
  65 void free(void *v)
  66 {
  67         if (!v)
  68                 return;
  69         if ((unsigned long) v & PGMASK) {
  70                 struct mset *mset = *(void **) (v - sizeof(void *));
  71                 mset->refs--;
  72                 if (!mset->refs && mset != pool)
  73                         munmap(mset, mset->size);
  74         } else {
  75                 munmap(v - PGSIZE, *(long *) (v - PGSIZE));
  76         }
  77 }