Function fallback_malloc

system/lib/libcxxabi/src/fallback_malloc.cpp:132–185

}

void* fallback_malloc(size_t len) {
  heap_node *p, *prev;
  const size_t nelems = alloc_size(len);
  mutexor mtx(&heap_mutex);

  if (NULL == freelist)
    init_heap();

  //  Walk the free list, looking for a "big enough" chunk
  for (p = freelist, prev = 0; p && p != list_end;
       prev = p, p = node_from_offset(p->next_node)) {

    // Check the invariant that all heap_nodes pointers 'p' are aligned
    // so that 'p + 1' has an alignment of at least RequiredAlignment
    _LIBCXXABI_ASSERT(reinterpret_cast<size_t>(p + 1) % RequiredAlignment == 0, "");

    // Calculate the number of extra padding elements needed in order
    // to split 'p' and create a properly aligned heap_node from the tail
    // of 'p'. We calculate aligned_nelems such that 'p->len - aligned_nelems'
    // will be a multiple of NodesPerAlignment.
    size_t aligned_nelems = nelems;
    if (p->len > nelems) {
      heap_size remaining_len = static_cast<heap_size>(p->len - nelems);
      aligned_nelems += remaining_len % NodesPerAlignment;
    }

    // chunk is larger and we can create a properly aligned heap_node
    // from the tail. In this case we shorten 'p' and return the tail.
    if (p->len > aligned_nelems) {
      heap_node* q;
      p->len = static_cast<heap_size>(p->len - aligned_nelems);
      q = p + p->len;
      q->next_node = 0;
      q->len = static_cast<heap_size>(aligned_nelems);
      void* ptr = q + 1;
      _LIBCXXABI_ASSERT(reinterpret_cast<size_t>(ptr) % RequiredAlignment == 0, "");
      return ptr;
    }

    // The chunk is the exact size or the chunk is larger but not large
    // enough to split due to alignment constraints.
    if (p->len >= nelems) {
      if (prev == 0)
        freelist = node_from_offset(p->next_node);
      else
        prev->next_node = p->next_node;
      p->next_node = 0;
      void* ptr = p + 1;
      _LIBCXXABI_ASSERT(reinterpret_cast<size_t>(ptr) % RequiredAlignment == 0, "");
      return ptr;
    }
  }
  return NULL; // couldn't find a spot big enough
}

//  Return the start of the next block
heap_node* after(struct heap_node* p) { return p + p->len; }