| Message ID | 20160608185123.BB0D84012CF92@oldenburg.str.redhat.com |
|---|---|
| State | New |
| Headers | show |
Thanks for the quick work! This patch looks good to me.
On 06/08/2016 02:51 PM, Florian Weimer wrote: > 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. > > 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. Reviewed the existing mmapped chunk code, and this fix looks good to me.
On 08 Jun 2016 20:51, Florian Weimer wrote: > 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. is it normally user visible ? if so, i think we'd want a bug on our side too for it. -mike
On 06/09/2016 09:22 PM, Mike Frysinger wrote: > On 08 Jun 2016 20:51, Florian Weimer wrote: >> 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. > > is it normally user visible ? if so, i think we'd want a bug on our side > too for it. Well, it was, unless you were a vi user. But the bug was never part of a released version, and the patch isn't exactly backporting material. So it doesn't really matter from a release documentation and tracking perspective. I can file a bug and put it into the appropriate state. I normally file such bugs only if there's a risk I get side-tracked and fail to fix the bug. Thanks, Florian
On 09 Jun 2016 21:45, Florian Weimer wrote: > On 06/09/2016 09:22 PM, Mike Frysinger wrote: > > On 08 Jun 2016 20:51, Florian Weimer wrote: > >> 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. > > > > is it normally user visible ? if so, i think we'd want a bug on our side > > too for it. > > Well, it was, unless you were a vi user. > > But the bug was never part of a released version, and the patch isn't > exactly backporting material. So it doesn't really matter from a > release documentation and tracking perspective. np then -mike
diff --git a/malloc/malloc.c b/malloc/malloc.c index ead9a21..6f77d37 100644 --- a/malloc/malloc.c +++ b/malloc/malloc.c @@ -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; }