Re: [PATCH] netlink: align attributes on 64-bits

Le 14/12/2012 16:49, Ben Hutchings a écrit :

On Fri, 2012-12-14 at 14:16 +0100, Nicolas Dichtel wrote:

quoted

On 64 bits arch, we must ensure that attributes are always aligned on 64-bits
boundary. We do that by adding attributes of type 0, size 4 (alignment on
32-bits is already done) when needed. Attribute type 0 should be available and
unused in all netlink families.

[...]

quoted

--- a/lib/nlattr.c
+++ b/lib/nlattr.c

@@ -450,9 +450,18 @@ EXPORT_SYMBOL(__nla_put_nohdr);
   */
  int nla_put(struct sk_buff *skb, int attrtype, int attrlen, const void *data)
  {
-	if (unlikely(skb_tailroom(skb) < nla_total_size(attrlen)))
+	int align = IS_ALIGNED((unsigned long)skb_tail_pointer(skb), sizeof(void *)) ? 0 : 4;

The assumption here is that nothing needs to be aligned to a greater
width than that of a pointer.  However, for most 32-bit architectures
(i386 being an exception) the C ABI requires 64-bit alignment for 64-bit
types.  There may be cases where a mostly 32-bit processor really
requires 64-bit alignment, e.g. to load or save a pair of registers.

Ok, I will wait other comments to send a v2 (which will align these attributes 
for all arch).

Nicolas