[net-next,2/2] net: sctp: add build check for sctp_sf_eat_sack_6_2/jsctp_sf_eat_sack

In order to avoid any future surprises of kernel panics due to jprobes
function mismatches (as e.g. fixed in 4cb9d6eaf85ecd: sctp: jsctp_sf_eat_sack:
fix jprobes function signature mismatch), we should check both function
types during build and scream loudly if they do not match. __same_type
resolves to __builtin_types_compatible_p, which is 1 in case both types
are the same and 0 otherwise, qualifiers are ignored. Tested by myself.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
---
 net/sctp/probe.c | 7 +++++++
 1 file changed, 7 insertions(+)

On Wed, Feb 13, 2013 at 12:03:50PM +0100, Daniel Borkmann wrote:
> In order to avoid any future surprises of kernel panics due to jprobes
> function mismatches (as e.g. fixed in 4cb9d6eaf85ecd: sctp: jsctp_sf_eat_sack:
> fix jprobes function signature mismatch), we should check both function
> types during build and scream loudly if they do not match. __same_type
> resolves to __builtin_types_compatible_p, which is 1 in case both types
> are the same and 0 otherwise, qualifiers are ignored. Tested by myself.
> 
> Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
> ---
>  net/sctp/probe.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/net/sctp/probe.c b/net/sctp/probe.c
> index 4eaaaf6..261b7b9 100644
> --- a/net/sctp/probe.c
> +++ b/net/sctp/probe.c
> @@ -183,6 +183,13 @@ static __init int sctpprobe_init(void)
>  {
>  	int ret = -ENOMEM;
>  
> +	/* Warning: if the function signature of sctp_sf_eat_sack_6_2,
> +	 * has been changed, you also have to change the signature of
> +	 * jsctp_sf_eat_sack, otherwise you end up right here!
> +	 */
> +	BUILD_BUG_ON(__same_type(sctp_sf_eat_sack_6_2,
> +				 jsctp_sf_eat_sack) == 0);
> +
>  	init_waitqueue_head(&sctpw.wait);
>  	spin_lock_init(&sctpw.lock);
>  	if (kfifo_alloc(&sctpw.fifo, bufsize, GFP_KERNEL))
> -- 
> 1.7.11.7
Acked-by: Neil Horman <nhorman@tuxdriver.com>

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