[U-Boot] [PATCH] net: Mark the ip_udp_hdr struct as packed

[Joe Hershberger]

Hi Maxime,

On Wed, Jul 12, 2017 at 9:34 AM, Maxime Ripard
<maxime.ripard at free-electrons.com> wrote:
> The -mno-unaligned-access flag used on ARM to prevent GCC from generating
> unaligned accesses (obviously) will only do so on packed structures.
>
> It seems like gcc 7.1 is a bit stricter than previous gcc versions on this,
> and using it lead to data abort for unaligned accesses when generating
> network traffic.
>
> Fix this by adding the packed attribute to the ip_udp_hdr structure in
> order to let GCC do its job.
>
> Signed-off-by: Maxime Ripard <maxime.ripard at free-electrons.com>
> ---
>  include/net.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/net.h b/include/net.h
> index 997db9210a8f..7b815afffafa 100644
> --- a/include/net.h
> +++ b/include/net.h
> @@ -390,7 +390,7 @@ struct ip_udp_hdr {
>         u16             udp_dst;        /* UDP destination port         */
>         u16             udp_len;        /* Length of UDP packet         */
>         u16             udp_xsum;       /* Checksum                     */
> -};
> +} __attribute__ ((packed));

Do you have an example of why this is unaligned? It seems that the
structure itself is naturally packed (each element is aligned to its
access size). It seems the only time this would hit a dabort is if the
head of the buffer is not 32-bit aligned. Maybe we should address the
place where that is the case instead of forcing byte-wise accesses in
general for this structure?

Thanks,
-Joe

>  #define IP_UDP_HDR_SIZE                (sizeof(struct ip_udp_hdr))
>  #define UDP_HDR_SIZE           (IP_UDP_HDR_SIZE - IP_HDR_SIZE)
> --
> 2.13.0
>
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