fix overflow of slice count, PR #877

src/segment.c

@@ -820,6 +820,7 @@ static mi_segment_t* mi_segment_os_alloc( size_t required, size_t page_alignment
     const size_t extra = align_offset - info_size;
     // recalculate due to potential guard pages
     *psegment_slices = mi_segment_calculate_slices(required + extra, ppre_size, pinfo_slices);
+    mi_assert_internal(*psegment_slices > 0 && *psegment_slices <= UINT32_MAX);
   }
 
   const size_t segment_size = (*psegment_slices) * MI_SEGMENT_SLICE_SIZE;
@@ -869,6 +870,7 @@ static mi_segment_t* mi_segment_alloc(size_t required, size_t page_alignment, mi
   size_t info_slices;
   size_t pre_size;
   size_t segment_slices = mi_segment_calculate_slices(required, &pre_size, &info_slices);
+  mi_assert_internal(segment_slices > 0 && segment_slices <= UINT32_MAX);
 
   // Commit eagerly only if not the first N lazy segments (to reduce impact of many threads that allocate just a little)
   const bool eager_delay = (// !_mi_os_has_overcommit() &&             // never delay on overcommit systems