PING: PATCH: [BZ #14562] Properly handle fencepost with MALLOC_ALIGN_MASK

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Mon, Sep 10, 2012 at 4:58 AM, H.J. Lu <hongjiu.lu@intel.com> wrote:
> Hi,
>
> fencepost is aligned at MALLOC_ALIGNMENT:
>
>      /* Setup fencepost and free the old top chunk with a multiple of
>          MALLOC_ALIGNMENT in size. */
>       /* The fencepost takes at least MINSIZE bytes, because it might
>          become the top chunk again later.  Note that a footer is set
>          up, too, although the chunk is marked in use. */
>       old_size = (old_size - MINSIZE) & ~MALLOC_ALIGN_MASK;
>       set_head(chunk_at_offset(old_top, old_size + 2*SIZE_SZ), 0|PREV_INUSE);
>
> We need to align fencepost to MALLOC_ALIGNMENT in heap_trim and count
> the misaligned extra bytes in new size.  Tested on ia32, x86-64 and
> x32.  It fixes all issues on x32.  OK to install?
>
> Thanks.
>
> H.J.
> ---
> 2012-09-08  H.J. Lu  <hongjiu.lu@intel.com>
>
>         [BZ #14562]
>         * malloc/arena.c (heap_trim): Properly get fencepost and adjust
>         new chunk size with MALLOC_ALIGN_MASK.
>
> diff --git a/malloc/arena.c b/malloc/arena.c
> index 97c0b90..dd4f3e3 100644
> --- a/malloc/arena.c
> +++ b/malloc/arena.c
> @@ -655,15 +655,18 @@ 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, 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));
> +    /* fencepost must be properly aligned.  */
> +    misalign = ((long) p) & MALLOC_ALIGN_MASK;
> +    p = (mchunkptr)(((unsigned long) p) & ~MALLOC_ALIGN_MASK);
>      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;

PING.

-- 
H.J.