Got it. You did mention about typedef in email chain, but I understood as different way to achieve same.

I reviewed my code and found that most of the fields between driver-adapter doesn't need attribute.
So far (a) removing packed and (b) BUILD_BUG_ON looks sufficient for current set of structures. Initial test suffice the need.

Thanks.
Parav

-----Original Message-----
From: Jason Gunthorpe [mailto:jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org]
Sent: Friday, March 23, 2012 10:24 PM
To: Pandit, Parav
Cc: David.Laight-ZS65k/vG3HxXrIkS9f7CXA@public.gmane.org; roland-BHEL68pLQRGGvPXPguhicg@public.gmane.org; linux-
rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH 2/9] ocrdma: Driver for Emulex OneConnect RDMA
adapter

On Fri, Mar 23, 2012 at 07:03:37AM -0700, Parav.Pandit-iH1Dq9VlAzfQT0dZR+AlfA@public.gmane.org wrote:

quoted

quoted

David is saying you will get a 12 byte struct and fieldb will be
unaligned. Since
12 is aligned to 4 no padding is added.

So I decided to experiment above example before implementing in
driver. However I find structure of 16 bytes (instead of 12) with
padding after fielda in below example.  Am I missing some compiler
option or syntax error in attribute? Sorry to ask this silly question.
I tried __attribute__((__aligned__(4))); too based on usage in other
kernel code.

I got the syntax wrong for that specific case (it is a little unintuitive.. IMHO,
capping the alignment of a container should cap the alignment of all
members, otherwise it is nonsense!):

typedef uint64_t u64_unaligned_8 __attribute__((__aligned__(4)));

struct foo {
        uint32_t fielda;
        u64_unaligned_8 fieldb;
};

struct foo2 {
        uint32_t fielda;
        uint64_t fieldb;
};

int main(int argc,const char *argv[])
{
	printf("sizeof(foo) = %zu, fieldb = %zu\n",sizeof(struct foo),
	       offsetof(struct foo,fieldb));
	printf("sizeof(foo2) = %zu, fieldb = %zu\n",sizeof(struct foo2),
	       offsetof(struct foo2,fieldb));
	return 0;
}

sizeof(foo) = 12, fieldb = 4
sizeof(foo2) = 16, fieldb = 8

gcc version 4.6.1 (Ubuntu/Linaro 4.6.1-9ubuntu3)

Jason

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