Properly handle fencepost with MALLOC_ALIGN_MASK

1 files changed, 7 insertions, 3 deletions

diff --git a/malloc/arena.c b/malloc/arena.c
index 97c0b909cc..f24e76c4f6 100644
--- a/malloc/arena.c
+++ b/malloc/arena.c
@@ -655,15 +655,19 @@ heap_trim(heap_info *heap, size_t pad)
   unsigned long pagesz = GLRO(dl_pagesize);
   mchunkptr top_chunk = top(ar_ptr), p, bck, fwd;
   heap_info *prev_heap;
-  long new_size, top_size, extra;
+  long new_size, top_size, extra, prev_size, misalign;
 
   /* Can this heap go away completely? */
   while(top_chunk == chunk_at_offset(heap, sizeof(*heap))) {
     prev_heap = heap->prev;
-    p = chunk_at_offset(prev_heap, prev_heap->size - (MINSIZE-2*SIZE_SZ));
+    prev_size = prev_heap->size - (MINSIZE-2*SIZE_SZ);
+    p = chunk_at_offset(prev_heap, prev_size);
+    /* fencepost must be properly aligned.  */
+    misalign = ((long) p) & MALLOC_ALIGN_MASK;
+    p = chunk_at_offset(prev_heap, prev_size - misalign);
     assert(p->size == (0|PREV_INUSE)); /* must be fencepost */
     p = prev_chunk(p);
-    new_size = chunksize(p) + (MINSIZE-2*SIZE_SZ);
+    new_size = chunksize(p) + (MINSIZE-2*SIZE_SZ) + misalign;
     assert(new_size>0 && new_size<(long)(2*MINSIZE));
     if(!prev_inuse(p))
       new_size += p->prev_size;