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

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Hi Andrew,

  Thanks. I modified the patch (don't know if there is any way better
to solve this).

Signed-off-by: Luke Yang <[email protected]>

irlmp.c |    8 +++++++-
1 files changed, 7 insertions(+), 1 deletion(-)

--- net/irda/irlmp.c.old        2006-06-08 14:49:20.000000000 +0800
+++ net/irda/irlmp.c    2006-06-09 19:43:58.000000000 +0800
@@ -849,7 +849,13 @@
       }

       /* Construct new discovery info to be used by IrLAP, */
-       u16ho(irlmp->discovery_cmd.data.hints) = irlmp->hints.word;
+#ifdef __LITTLE_ENDIAN
+       irlmp->discovery_cmd.data.hints[0] = irlmp->hints.word & 0xff;
+       irlmp->discovery_cmd.data.hints[1] = (irlmp->hints.word & 0xff00) >> 8;
+#else /* ifdef __BIG_ENDIAN */
+       irlmp->discovery_cmd.data.hints[0] = (irlmp->hints.word & 0xff00) >> 8;
+       irlmp->discovery_cmd.data.hints[1] = irlmp->hints.word & 0xff;
+#endif

       /*
        *  Set character set for device name (we use ASCII), and

On 6/8/06, Andrew Morton <[email protected]> wrote:
On Thu, 8 Jun 2006 15:15:11 +0800
"Luke Yang" <[email protected]> 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 <[email protected]>
>
>  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.




--
Best regards,
Luke Yang
[email protected]
--- net/irda/irlmp.c.old	2006-06-08 14:49:20.000000000 +0800
+++ net/irda/irlmp.c	2006-06-09 19:43:58.000000000 +0800
@@ -849,7 +849,13 @@
 	}
 
 	/* Construct new discovery info to be used by IrLAP, */
-	u16ho(irlmp->discovery_cmd.data.hints) = irlmp->hints.word;
+#ifdef __LITTLE_ENDIAN
+	irlmp->discovery_cmd.data.hints[0] = irlmp->hints.word & 0xff;
+	irlmp->discovery_cmd.data.hints[1] = (irlmp->hints.word & 0xff00) >> 8;
+#else /* ifdef __BIG_ENDIAN */
+	irlmp->discovery_cmd.data.hints[0] = (irlmp->hints.word & 0xff00) >> 8;
+	irlmp->discovery_cmd.data.hints[1] = irlmp->hints.word & 0xff;
+#endif
 
 	/*
 	 *  Set character set for device name (we use ASCII), and

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