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


On Wed, Sep 12, 2012 at 8:37 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> 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.
>

PING.

-- 
H.J.


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