This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
PATCH: [BZ #14562] Properly handle fencepost with MALLOC_ALIGN_MASK
- From: "H.J. Lu" <hongjiu dot lu at intel dot com>
- To: GNU C Library <libc-alpha at sourceware dot org>
- Date: Mon, 10 Sep 2012 04:58:28 -0700
- Subject: PATCH: [BZ #14562] Properly handle fencepost with MALLOC_ALIGN_MASK
- Reply-to: "H.J. Lu" <hjl dot tools at gmail dot com>
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;