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

[Luke Yang]

Hi Andrew,

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

Signed-off-by: Luke Yang <luke.adi@xxxxxxxxx>

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 <akpm@xxxxxxxx> wrote:
> On Thu, 8 Jun 2006 15:15:11 +0800
> "Luke Yang" <luke.adi@xxxxxxxxx> 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@xxxxxxxxx>
> >
> >  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
luke.adi@xxxxxxxxx
--- 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