Make slab allocator work on platforms with MAXIMUM_ALIGNOF < sizeof(int).

Notably, m68k only needs 2-byte alignment. Per report from Christoph Berg.

Discussion: https://www.postgresql.org/message-id/20170517193957.fwntkgi6epuso5l2@msg.df7cb.de

diff --git a/src/backend/utils/mmgr/slab.c b/src/backend/utils/mmgr/slab.c
index 0fcfcb4c786e2b2f1046258470fbf0479f004ed5..e59154ddda4bd113e056463740c07a200cbef80a 100644 (file)
--- a/src/backend/utils/mmgr/slab.c
+++ b/src/backend/utils/mmgr/slab.c
@@ -194,9 +194,9 @@ SlabContextCreate(MemoryContext parent,
                                         MAXALIGN(sizeof(SlabChunk)),
                                         "padding calculation in SlabChunk is wrong");
 
-       /* otherwise the linked list inside freed chunk isn't guaranteed to fit */
-       StaticAssertStmt(MAXIMUM_ALIGNOF >= sizeof(int),
-                                        "MAXALIGN too small to fit int32");
+       /* Make sure the linked list node fits inside a freed chunk */
+       if (chunkSize < sizeof(int))
+               chunkSize = sizeof(int);
 
        /* chunk, including SLAB header (both addresses nicely aligned) */
        fullChunkSize = MAXALIGN(sizeof(SlabChunk) + MAXALIGN(chunkSize));