expand NEED_ALIGN for chunked items

some whackarse ARM platforms on specific glibc/gcc (new?) versions trip
SIGBUS while reading the header chunk for a split item.

the header chunk is unfortunate magic: It lives in ITEM_data() at a random
offset, is zero sized, and only exists to simplify code around finding the
orignial slab class, and linking/relinking subchunks to an item.

there's no fix to this which isn't a lot of code. I need to refactor chunked
items, and attempted to do so, but couldn't come up with something I liked
quickly enough.

This change pads the first chunk if alignment is necessary, which wastes
bytes and a little CPU, but I'm not going to worry a ton for these obscure
platforms.

this works with rebalancing because in the case of ITEM_CHUNKED header, it
treats the item size as the size of the class it resides in, and memcpy's the
item during recovery.

all other cases were changes from ITEM_data to a new ITEM_schunk() inline
function that is created when NEED_ALIGN is set, else it's equal to ITEM_data
still.

1 files changed, 8 insertions, 1 deletions

diff --git a/items.c b/items.c
index 01ce2a4..d4ce5a1 100644
--- a/items.c
+++ b/items.c
@@ -285,6 +285,13 @@ item *do_item_alloc(char *key, const size_t nkey, const unsigned int flags,
         if (settings.use_cas) {
             htotal += sizeof(uint64_t);
         }
+#ifdef NEED_ALIGN
+        // header chunk needs to be padded on some systems
+        int remain = htotal % 8;
+        if (remain != 0) {
+            htotal += 8 - remain;
+        }
+#endif
         hdr_id = slabs_clsid(htotal);
         it = do_item_alloc_pull(htotal, hdr_id);
         /* setting ITEM_CHUNKED is fine here because we aren't LINKED yet. */
@@ -336,7 +343,7 @@ item *do_item_alloc(char *key, const size_t nkey, const unsigned int flags,
 
     /* Initialize internal chunk. */
     if (it->it_flags & ITEM_CHUNKED) {
-        item_chunk *chunk = (item_chunk *) ITEM_data(it);
+        item_chunk *chunk = (item_chunk *) ITEM_schunk(it);
 
         chunk->next = 0;
         chunk->prev = 0;