src/http/ngx_http_file_cache.c:998: error: Integer Overflow L2
  ([0, +oo] - [0, 15]):unsigned64 by call to `ngx_slab_free_locked`.

src/http/ngx_http_file_cache.c:998:5: Call
 996.     ngx_rbtree_delete(cache->rbtree, &fcn->node);
 997. 
 998.     ngx_slab_free_locked(cache->shpool, fcn);
          ^
 999. 
1000.     ngx_shmtx_unlock(&cache->shpool->mutex);

src/core/ngx_slab.c:412:1: <LHS trace>
410. 
411. 
412. void
     ^
413. ngx_slab_free_locked(ngx_slab_pool_t *pool, void *p)
414. {

src/core/ngx_slab.c:412:1: Global `ngx_pagesize_shift`
  410. 
  411. 
  412. void
       ^
  413. ngx_slab_free_locked(ngx_slab_pool_t *pool, void *p)
  414. {

src/core/ngx_slab.c:412:1: <RHS trace>
410. 
411. 
412. void
     ^
413. ngx_slab_free_locked(ngx_slab_pool_t *pool, void *p)
414. {

src/core/ngx_slab.c:412:1: Parameter `pool->pages->slab`
  410. 
  411. 
  412. void
       ^
  413. ngx_slab_free_locked(ngx_slab_pool_t *pool, void *p)
  414. {

src/core/ngx_slab.c:429:5: Assignment
  427.     n = ((u_char *) p - pool->start) >> ngx_pagesize_shift;
  428.     page = &pool->pages[n];
  429.     slab = page->slab;
           ^
  430.     type = page->prev & NGX_SLAB_PAGE_MASK;
  431. 

src/core/ngx_slab.c:436:9: Assignment
  434.     case NGX_SLAB_SMALL:
  435. 
  436.         shift = slab & NGX_SLAB_SHIFT_MASK;
               ^
  437.         size = 1 << shift;
  438. 

src/core/ngx_slab.c:464:13: Binary operation: ([0, +oo] - [0, 15]):unsigned64 by call to `ngx_slab_free_locked` 
  462.             bitmap[n] &= ~m;
  463. 
  464.             n = (1 << (ngx_pagesize_shift - shift)) / 8 / (1 << shift);
                   ^
  465. 
  466.             if (n == 0) {
