Re: [PATCH] tcp: fix tcp_fastopen unaligned access complaints on sparc

[Rob Gardner]

On 01/12/2017 01:13 PM, Eric Dumazet wrote:
> On Thu, 2017-01-12 at 11:59 -0800, Shannon Nelson wrote:
> > Fix up a data alignment issue on sparc by swapping the order
> > of the cookie byte array field with the length field in
> > struct tcp_fastopen_cookie
> >
> > This addresses log complaints like these:
> >      log_unaligned: 113 callbacks suppressed
> >      Kernel unaligned access at TPC[976490] tcp_try_fastopen+0x2d0/0x360
> >      Kernel unaligned access at TPC[9764ac] tcp_try_fastopen+0x2ec/0x360
> >      Kernel unaligned access at TPC[9764c8] tcp_try_fastopen+0x308/0x360
> >      Kernel unaligned access at TPC[9764e4] tcp_try_fastopen+0x324/0x360
> >      Kernel unaligned access at TPC[976490] tcp_try_fastopen+0x2d0/0x360
> >
> > Signed-off-by: Shannon Nelson <shannon.nelson@xxxxxxxxxx>
> > ---
> >   include/linux/tcp.h |    2 +-
> >   1 files changed, 1 insertions(+), 1 deletions(-)
> >
> > diff --git a/include/linux/tcp.h b/include/linux/tcp.h
> > index fc5848d..95cda75 100644
> > --- a/include/linux/tcp.h
> > +++ b/include/linux/tcp.h
> > @@ -62,8 +62,8 @@ static inline unsigned int tcp_optlen(const struct sk_buff *skb)
> >   
> >   /* TCP Fast Open Cookie as stored in memory */
> >   struct tcp_fastopen_cookie {
> > -	s8	len;
> >   	u8	val[TCP_FASTOPEN_COOKIE_MAX];
> > +	s8	len;
> >   	bool	exp;	/* In RFC6994 experimental option format */
> >   };
> >   
> Strange... Do you have an explanation of why this patch would be
> needed ? A compiler issue ?
>
>
> s8 and u8 are bytes after all.


I suspect that someplace, somebody is casting val to an int * or 
something like that.