Re: [PATCH] Fix an inproper alignment accessing in irda protocol stack

[Andrew Morton <akpm@osdl.org>]

On Thu, 8 Jun 2006 15:15:11 +0800
"Luke Yang" <luke.adi@gmail.com> wrote:

> Hi all,
> 
>  For "struct irda_device_info" in irda.h:
> struct irda_device_info {
> 	__u32       saddr;    /* Address of local interface */
> 	__u32       daddr;    /* Address of remote device */
> 	char        info[22]; /* Description */
> 	__u8        charset;  /* Charset used for description */
> 	__u8        hints[2]; /* Hint bits */
> };
>    The "hints" member aligns at the third byte of a word, an odd
> address. So if we visit "hints" as a short in irlmp.c:
> 
>     u16ho(irlmp->discovery_cmd.data.hints) = irlmp->hints.word;
> 
>   will cause alignment problem on some machines. Architectures with
> strict alignment rules do not allow 16-bit read on an odd address.
> 
> Signed-off-by: Luke Yang <luke.adi@gmail.com>
> 
>  irlmp.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletion(-)
> 
> --- net/irda/irlmp.c.old        2006-06-08 14:49:20.000000000 +0800
> +++ net/irda/irlmp.c    2006-06-08 14:54:29.000000000 +0800
> @@ -849,7 +849,8 @@
>         }
> 
>         /* Construct new discovery info to be used by IrLAP, */
> -       u16ho(irlmp->discovery_cmd.data.hints) = irlmp->hints.word;
> +       irlmp->discovery_cmd.data.hints[0] = irlmp->hints.word & 0xff;
> +       irlmp->discovery_cmd.data.hints[1] = (irlmp->hints.word & 0xff00) >> 8;

This change will have the effect of swapping those two bytes on big-endian
machines.