.

wcfs/client/wcfs.cpp

@@ -1072,6 +1072,8 @@ pair<Mapping, error> _FileH::mmap(int64_t blk_start, int64_t blk_len, VMA *vma)
             mm::unmap(mem_start, mem_stop - mem_start); // ignore error
     });
 
+    // part of mmapped region is beyond file size - mmap that with zeros - else
+    // access to memory after file.size will raise SIGBUS. (assumes head/f size ↑=)
     if (stop > f._headfsize) {
         uint8_t *zmem_start = mem_start + (max(f._headfsize, start) - start);
         err = mmap_zero_into_ro(zmem_start, mem_stop - zmem_start);