BUILD: ebtree: improve architecture-specific alignment

Commit 2c315ee75e ("BUG/MEDIUM: ebtree: don't set attribute packed
without unaligned access support") addressed alignment issues in
ebtrees in a way that is not really optimal since it will leave holes
in eb32trees for example.

This fix is better in that it restores the packed attribute on ebnode
but enforces proper alignment on the carrying nodes where necessary.
This also has the benefit of closing holes wherever possible and to
align data to the minimally required size.

The only thing it cannot close is the 32-bit hole at the end of ebmbnode
due to the required 64-bit on certain archs but at least it guarantees
that the key correctly points to the end of the node and that there is
never a hole after it.

This is a better fix than the one above and should be backported to
branches where the one above will be backported.

ebtree/eb32sctree.h

@@ -38,13 +38,18 @@ typedef   signed int s32;
  * have put some sort of transparent union here to reduce the indirection
  * level, but the fact is, the end user is not meant to manipulate internals,
  * so this is pointless.
+ * In case sizeof(void*)>=sizeof(long), we know there will be some padding after
+ * the leaf if it's unaligned. In this case we force the alignment on void* so
+ * that we prefer to have the padding before for more efficient accesses.
  */
 struct eb32sc_node {
 	struct eb_node node; /* the tree node, must be at the beginning */
+	MAYBE_ALIGN(sizeof(u32));
 	u32 key;
+	ALWAYS_ALIGN(sizeof(void*));
 	unsigned long node_s; /* visibility of this node's branches */
 	unsigned long leaf_s; /* visibility of this node's leaf */
-};
+} ALIGNED(sizeof(void*));
 
 /*
  * Exported functions and macros.

ebtree/eb32tree.h

@@ -41,8 +41,9 @@ typedef   signed int s32;
  */
 struct eb32_node {
 	struct eb_node node; /* the tree node, must be at the beginning */
+	MAYBE_ALIGN(sizeof(u32));
 	u32 key;
-};
+} ALIGNED(sizeof(void*));
 
 /*
  * Exported functions and macros.

ebtree/eb64tree.h

@@ -38,11 +38,16 @@ typedef   signed long long s64;
  * eb_node so that it can be cast into an eb_node. We could also have put some
  * sort of transparent union here to reduce the indirection level, but the fact
  * is, the end user is not meant to manipulate internals, so this is pointless.
+ * In case sizeof(void*)>=sizeof(u64), we know there will be some padding after
+ * the key if it's unaligned. In this case we force the alignment on void* so
+ * that we prefer to have the padding before for more efficient accesses.
  */
 struct eb64_node {
 	struct eb_node node; /* the tree node, must be at the beginning */
+	MAYBE_ALIGN(sizeof(u64));
+	ALWAYS_ALIGN(sizeof(void*));
 	u64 key;
-};
+} ALIGNED(sizeof(void*));
 
 /*
  * Exported functions and macros.

ebtree/ebmbtree.h

@@ -36,11 +36,16 @@
  * is, the end user is not meant to manipulate internals, so this is pointless.
  * The 'node.bit' value here works differently from scalar types, as it contains
  * the number of identical bits between the two branches.
+ * Note that we take a great care of making sure the key is located exactly at
+ * the end of the struct even if that involves holes before it, so that it
+ * always aliases any external key a user would append after. This is why the
+ * key uses the same alignment as the struct.
  */
 struct ebmb_node {
 	struct eb_node node; /* the tree node, must be at the beginning */
+	ALWAYS_ALIGN(sizeof(void*));
 	unsigned char key[0]; /* the key, its size depends on the application */
-};
+} ALIGNED(sizeof(void*));
 
 /*
  * Exported functions and macros.

ebtree/ebpttree.h

@@ -44,11 +44,14 @@ typedef PTR_INT_TYPE ptr_t;
  * sort of transparent union here to reduce the indirection level, but the fact
  * is, the end user is not meant to manipulate internals, so this is pointless.
  * Internally, it is automatically cast as an eb32_node or eb64_node.
+ * We always align the key since the struct itself will be padded to the same
+ * size anyway.
  */
 struct ebpt_node {
 	struct eb_node node; /* the tree node, must be at the beginning */
+	ALWAYS_ALIGN(sizeof(void*));
 	void *key;
-};
+} ALIGNED(sizeof(void*));
 
 /*
  * Exported functions and macros.

ebtree/ebtree.h

@@ -379,11 +379,7 @@ struct eb_node {
 	eb_troot_t    *leaf_p;  /* leaf node's parent */
 	short int      bit;     /* link's bit position. */
 	short unsigned int pfx; /* data prefix length, always related to leaf */
-}
-#ifdef HA_UNALIGNED
-   __attribute__((packed))
-#endif
-   ;
+} __attribute__((packed));
 
 /* Return the structure of type <type> whose member <member> points to <ptr> */
 #define eb_entry(ptr, type, member) container_of(ptr, type, member)