Re: [RFC v2 1/7] hashtable: introduce a small and naive hashtable

On 08/03/2012 11:48 PM, Tejun Heo wrote:

Hello,

On Fri, Aug 03, 2012 at 11:41:34PM +0200, Sasha Levin wrote:

quoted

I forgot to comment on that one, sorry.

If we put hash entries after struct hash_table we don't take the
bits field size into account, or did I miss something?

So, if you do the following,

	struct {
		struct {
			int i;
			long ar[];
		} B;
		long __ar_storage[32];
	} A;

struct A should have been an union, right?

It should always be safe to dereference A.B.ar[31].  I'm not sure
whether this is something guaranteed by C tho.  Maybe compilers are
allowed to put members in reverse order but I think we already depend
on the above.

why is accessing A.B.ar[31] safe?

__ar_storage is only 32*sizeof(long) bytes long, while struct B would need to be 32*sizeof(long) + sizeof(int) bytes long so that A.B.ar[31] access would be safe.

Thanks.

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