[mc1322x] Non-aligned structure copies

[Ian Martin]

Hi Jon,

I had a similar issue in either Contiki or uIP and inevitably had to
redefine the uip_ipaddr_copy macro with a call to the ANSI memcpy
function. It was something along the lines of:

#define uip_ipaddr_copy(dest, src) memcpy((void*)(dest), (void*)(src),
sizeof(uip_ipaddr_t))

...which shouldn't have any trouble with unaligned addressing.  I see
that you have created the equivalent using inline code.  I think uIP
even defines the macro differently for IPv4 vs IPv6 (besides for the
obvious reason).  IIRC, the only other occasion where I ran into
trouble with unaligned access was in the DHCP client code.

I don't know of a compiler switch offhand.

-Ian

On Tue, Nov 3, 2009 at 10:48 PM, Jon Smirl <jonsmirl at gmail.com> wrote:
> My TTL field was getting stomped in the packets so I added some debug
>
> uip_nd6_io_rs_output(void) {
>  UIP_IP_BUF->vtc = 0x60;
>  UIP_IP_BUF->tcflow = 0;
>  UIP_IP_BUF->flow = 0;
>  UIP_IP_BUF->proto = UIP_PROTO_ICMP6;
>  UIP_IP_BUF->ttl = UIP_ND6_HOP_LIMIT;
> printf("ttl 1 %d\n", UIP_IP_BUF->ttl);
>  uip_create_linklocal_allrouters_mcast(&UIP_IP_BUF->destipaddr);
> printf("ttl 2 %d %p %p\n", UIP_IP_BUF->ttl, &UIP_IP_BUF->ttl,
> &UIP_IP_BUF->srcipaddr);
>  uip_netif_select_src(&UIP_IP_BUF->srcipaddr, &UIP_IP_BUF->destipaddr);
> printf("ttl 3 %d\n", UIP_IP_BUF->ttl);
>
> The select_src(... was stomping TTL
>
> More debug and I track it down to ipaddr_copy...
>
> printf("uip_netif_select_src %d %d\n", best, index);
>
>  uip_ipaddr_copy(src, &(uip_netif_physical_if.addresses[index].ipaddr));
>  return;
>
> --- It's doing a struct copy. I'm suspicious about non-aligned access on ARM
>
> #ifndef uip_ipaddr_copy
> #define uip_ipaddr_copy(dest, src) (*(dest) = *(src))
> #endif
>
> I change it to:
>
> #ifndef uip_ipaddr_copy
> //#define uip_ipaddr_copy(dest, src) (*(dest) = *(src))
> #define uip_ipaddr_copy(dest, src) \
> { \
> int i; \
> for (i = 0; i < sizeof *(dest); i++) { \
>        *(((char *)(dest)) + i) = *(( (char *)(src)) + i); \
> } \
> }
> #endif
>
> --- TTL doesn't get stomped any more
>
> Sending NS to ff00:0000:0000:0000:0000:0001:ffff:ee00 from
> 0000:0000:0000:0000:0000:0000:0000:0000 with target address
> fe80:0000:0000:0000:dfcc:bbaa:aa99:ffee
> output;
> Sending RS 0
> ttl 1 255
> ttl 2 255 40e59a 40e59b
> uip_netif_select_src
> uip_netif_select_src 0 0
> ttl 3 255
> ttl 4 255
>
> The code still doesn't work because there are more of these floating around.
>
> Is there some compiler switch to tell it to do the right thing with an
> unaligned struct copy?
>
> --
> Jon Smirl
> jonsmirl at gmail.com
>
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