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malloc: Correct size computation in realloc for dumped fake mmapped chunks 

For regular mmapped chunks there are two size fields (hence a reduction
by 2 * SIZE_SZ bytes), but for fake chunks, we only have one size field,
so we need to subtract SIZE_SZ bytes.

This was initially reported as Emacs bug 23726.
This commit is contained in:
Florian Weimer 2016-06-08 20:50:21 +02:00
parent 8fa8a330f9
commit 1e8a8875d6
2 changed files with 15 additions and 4 deletions
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7
ChangeLog
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@ -1,3 +1,10 @@
2016-06-08 Florian Weimer <fweimer@redhat.com>
Emacs bug 23726.
* malloc/malloc.c (dumped_main_arena_start): Update comment.
(__libc_realloc): Correct size computation for dumped fake mmapped
chunks.
2016-06-07 Joseph Myers <joseph@codesourcery.com>
[BZ #20219]

12
malloc/malloc.c
View File

@ -1748,7 +1748,9 @@ static struct malloc_state main_arena =
/* These variables are used for undumping support. Chunked are marked
as using mmap, but we leave them alone if they fall into this
range. */
range. NB: The chunk size for these chunks only includes the
initial size field (of SIZE_SZ bytes), there is no trailing size
field (unlike with regular mmapped chunks). */
static mchunkptr dumped_main_arena_start; /* Inclusive. */
static mchunkptr dumped_main_arena_end; /* Exclusive. */
@ -3029,9 +3031,11 @@ __libc_realloc (void *oldmem, size_t bytes)
if (newmem == 0)
return NULL;
/* Copy as many bytes as are available from the old chunk
and fit into the new size. */
if (bytes > oldsize - 2 * SIZE_SZ)
bytes = oldsize - 2 * SIZE_SZ;
and fit into the new size. NB: The overhead for faked
mmapped chunks is only SIZE_SZ, not 2 * SIZE_SZ as for
regular mmapped chunks. */
if (bytes > oldsize - SIZE_SZ)
bytes = oldsize - SIZE_SZ;
memcpy (newmem, oldmem, bytes);
return newmem;
}