From: Arnd Bergmann <[email protected]>
Three of the sfc drivers define a packed loopback_payload structure with an
ethernet header followed by an IP header. However, the kernel definition
of iphdr specifies that this is 4-byte aligned, causing a W=1 warning:
net/ethernet/sfc/siena/selftest.c:46:15: error: field ip within 'struct efx_loopback_payload' is less aligned than 'struct iphdr' and is usually due to 'struct efx_loopback_payload' being packed, which can lead to unaligned accesses [-Werror,-Wunaligned-access]
struct iphdr ip;
As the iphdr packing is not easily changed without breaking other code,
change the three structures to use a local definition instead.
Signed-off-by: Arnd Bergmann <[email protected]>
---
drivers/net/ethernet/sfc/falcon/selftest.c | 21 ++++++++++++++++++++-
drivers/net/ethernet/sfc/selftest.c | 21 ++++++++++++++++++++-
drivers/net/ethernet/sfc/siena/selftest.c | 21 ++++++++++++++++++++-
3 files changed, 60 insertions(+), 3 deletions(-)
diff --git a/drivers/net/ethernet/sfc/falcon/selftest.c b/drivers/net/ethernet/sfc/falcon/selftest.c
index 6a454ac6f8763..fb7fcd27a33a5 100644
--- a/drivers/net/ethernet/sfc/falcon/selftest.c
+++ b/drivers/net/ethernet/sfc/falcon/selftest.c
@@ -40,7 +40,26 @@
*/
struct ef4_loopback_payload {
struct ethhdr header;
- struct iphdr ip;
+ struct {
+#if defined(__LITTLE_ENDIAN_BITFIELD)
+ __u8 ihl:4,
+ version:4;
+#elif defined (__BIG_ENDIAN_BITFIELD)
+ __u8 version:4,
+ ihl:4;
+#else
+#error "Please fix <asm/byteorder.h>"
+#endif
+ __u8 tos;
+ __be16 tot_len;
+ __be16 id;
+ __be16 frag_off;
+ __u8 ttl;
+ __u8 protocol;
+ __sum16 check;
+ __be32 saddr;
+ __be32 daddr;
+ } __packed ip; /* unaligned struct iphdr */
struct udphdr udp;
__be16 iteration;
char msg[64];
diff --git a/drivers/net/ethernet/sfc/selftest.c b/drivers/net/ethernet/sfc/selftest.c
index 3c5227afd4977..440a57953779c 100644
--- a/drivers/net/ethernet/sfc/selftest.c
+++ b/drivers/net/ethernet/sfc/selftest.c
@@ -43,7 +43,26 @@
*/
struct efx_loopback_payload {
struct ethhdr header;
- struct iphdr ip;
+ struct {
+#if defined(__LITTLE_ENDIAN_BITFIELD)
+ __u8 ihl:4,
+ version:4;
+#elif defined (__BIG_ENDIAN_BITFIELD)
+ __u8 version:4,
+ ihl:4;
+#else
+#error "Please fix <asm/byteorder.h>"
+#endif
+ __u8 tos;
+ __be16 tot_len;
+ __be16 id;
+ __be16 frag_off;
+ __u8 ttl;
+ __u8 protocol;
+ __sum16 check;
+ __be32 saddr;
+ __be32 daddr;
+ } __packed ip; /* unaligned struct iphdr */
struct udphdr udp;
__be16 iteration;
char msg[64];
diff --git a/drivers/net/ethernet/sfc/siena/selftest.c b/drivers/net/ethernet/sfc/siena/selftest.c
index 07715a3d6beab..b8a8b0495f661 100644
--- a/drivers/net/ethernet/sfc/siena/selftest.c
+++ b/drivers/net/ethernet/sfc/siena/selftest.c
@@ -43,7 +43,26 @@
*/
struct efx_loopback_payload {
struct ethhdr header;
- struct iphdr ip;
+ struct {
+#if defined(__LITTLE_ENDIAN_BITFIELD)
+ __u8 ihl:4,
+ version:4;
+#elif defined (__BIG_ENDIAN_BITFIELD)
+ __u8 version:4,
+ ihl:4;
+#else
+#error "Please fix <asm/byteorder.h>"
+#endif
+ __u8 tos;
+ __be16 tot_len;
+ __be16 id;
+ __be16 frag_off;
+ __u8 ttl;
+ __u8 protocol;
+ __sum16 check;
+ __be32 saddr;
+ __be32 daddr;
+ } __packed ip; /* unaligned struct iphdr */
struct udphdr udp;
__be16 iteration;
char msg[64];
--
2.39.2
On 19/06/2023 10:12, Arnd Bergmann wrote:
> From: Arnd Bergmann <[email protected]>
>
> Three of the sfc drivers define a packed loopback_payload structure with an
> ethernet header followed by an IP header. However, the kernel definition
> of iphdr specifies that this is 4-byte aligned, causing a W=1 warning:
>
> net/ethernet/sfc/siena/selftest.c:46:15: error: field ip within 'struct efx_loopback_payload' is less aligned than 'struct iphdr' and is usually due to 'struct efx_loopback_payload' being packed, which can lead to unaligned accesses [-Werror,-Wunaligned-access]
> struct iphdr ip;
>
> As the iphdr packing is not easily changed without breaking other code,
> change the three structures to use a local definition instead.
>
> Signed-off-by: Arnd Bergmann <[email protected]>
Duplicating the definition isn't the prettiest thing in the world; it'd
do for a quick fix if needed but I assume W=1 warnings aren't blocking
anyone, so maybe defer this one for now and I'll follow up soon with a
rewrite that fixes this more cleanly? My idea is to drop the __packed
from the containing struct, make efx_begin_loopback() copy the layers
separately, and efx_loopback_rx_packet() similarly do something less
direct than casting the packet data to the struct.
But I don't insist on it; if you want this fix in immediately then I'm
okay with that too.
> ---
> drivers/net/ethernet/sfc/falcon/selftest.c | 21 ++++++++++++++++++++-
> drivers/net/ethernet/sfc/selftest.c | 21 ++++++++++++++++++++-
> drivers/net/ethernet/sfc/siena/selftest.c | 21 ++++++++++++++++++++-
> 3 files changed, 60 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/ethernet/sfc/falcon/selftest.c b/drivers/net/ethernet/sfc/falcon/selftest.c
> index 6a454ac6f8763..fb7fcd27a33a5 100644
> --- a/drivers/net/ethernet/sfc/falcon/selftest.c
> +++ b/drivers/net/ethernet/sfc/falcon/selftest.c
> @@ -40,7 +40,26 @@
> */
> struct ef4_loopback_payload {
> struct ethhdr header;
> - struct iphdr ip;
> + struct {
> +#if defined(__LITTLE_ENDIAN_BITFIELD)
> + __u8 ihl:4,
> + version:4;
> +#elif defined (__BIG_ENDIAN_BITFIELD)
> + __u8 version:4,
> + ihl:4;
> +#else
> +#error "Please fix <asm/byteorder.h>"
> +#endif
> + __u8 tos;
> + __be16 tot_len;
> + __be16 id;
> + __be16 frag_off;
> + __u8 ttl;
> + __u8 protocol;
> + __sum16 check;
> + __be32 saddr;
> + __be32 daddr;
> + } __packed ip; /* unaligned struct iphdr */
> struct udphdr udp;
> __be16 iteration;
> char msg[64];
> diff --git a/drivers/net/ethernet/sfc/selftest.c b/drivers/net/ethernet/sfc/selftest.c
> index 3c5227afd4977..440a57953779c 100644
> --- a/drivers/net/ethernet/sfc/selftest.c
> +++ b/drivers/net/ethernet/sfc/selftest.c
> @@ -43,7 +43,26 @@
> */
> struct efx_loopback_payload {
> struct ethhdr header;
> - struct iphdr ip;
> + struct {
> +#if defined(__LITTLE_ENDIAN_BITFIELD)
> + __u8 ihl:4,
> + version:4;
> +#elif defined (__BIG_ENDIAN_BITFIELD)
> + __u8 version:4,
> + ihl:4;
> +#else
> +#error "Please fix <asm/byteorder.h>"
> +#endif
> + __u8 tos;
> + __be16 tot_len;
> + __be16 id;
> + __be16 frag_off;
> + __u8 ttl;
> + __u8 protocol;
> + __sum16 check;
> + __be32 saddr;
> + __be32 daddr;
> + } __packed ip; /* unaligned struct iphdr */
> struct udphdr udp;
> __be16 iteration;
> char msg[64];
> diff --git a/drivers/net/ethernet/sfc/siena/selftest.c b/drivers/net/ethernet/sfc/siena/selftest.c
> index 07715a3d6beab..b8a8b0495f661 100644
> --- a/drivers/net/ethernet/sfc/siena/selftest.c
> +++ b/drivers/net/ethernet/sfc/siena/selftest.c
> @@ -43,7 +43,26 @@
> */
> struct efx_loopback_payload {
> struct ethhdr header;
> - struct iphdr ip;
> + struct {
> +#if defined(__LITTLE_ENDIAN_BITFIELD)
> + __u8 ihl:4,
> + version:4;
> +#elif defined (__BIG_ENDIAN_BITFIELD)
> + __u8 version:4,
> + ihl:4;
> +#else
> +#error "Please fix <asm/byteorder.h>"
> +#endif
> + __u8 tos;
> + __be16 tot_len;
> + __be16 id;
> + __be16 frag_off;
> + __u8 ttl;
> + __u8 protocol;
> + __sum16 check;
> + __be32 saddr;
> + __be32 daddr;
> + } __packed ip; /* unaligned struct iphdr */
> struct udphdr udp;
> __be16 iteration;
> char msg[64];
>
On Mon, Jun 19, 2023, at 12:25, Edward Cree wrote:
> On 19/06/2023 10:12, Arnd Bergmann wrote:
>> From: Arnd Bergmann <[email protected]>
>>
>> Three of the sfc drivers define a packed loopback_payload structure with an
>> ethernet header followed by an IP header. However, the kernel definition
>> of iphdr specifies that this is 4-byte aligned, causing a W=1 warning:
>>
>> net/ethernet/sfc/siena/selftest.c:46:15: error: field ip within 'struct efx_loopback_payload' is less aligned than 'struct iphdr' and is usually due to 'struct efx_loopback_payload' being packed, which can lead to unaligned accesses [-Werror,-Wunaligned-access]
>> struct iphdr ip;
>>
>> As the iphdr packing is not easily changed without breaking other code,
>> change the three structures to use a local definition instead.
>>
>> Signed-off-by: Arnd Bergmann <[email protected]>
>
> Duplicating the definition isn't the prettiest thing in the world; it'd
> do for a quick fix if needed but I assume W=1 warnings aren't blocking
> anyone, so maybe defer this one for now and I'll follow up soon with a
> rewrite that fixes this more cleanly? My idea is to drop the __packed
> from the containing struct, make efx_begin_loopback() copy the layers
> separately, and efx_loopback_rx_packet() similarly do something less
> direct than casting the packet data to the struct.
>
> But I don't insist on it; if you want this fix in immediately then I'm
> okay with that too.
>
>> ---
>> drivers/net/ethernet/sfc/falcon/selftest.c | 21 ++++++++++++++++++++-
>> drivers/net/ethernet/sfc/selftest.c | 21 ++++++++++++++++++++-
>> drivers/net/ethernet/sfc/siena/selftest.c | 21 ++++++++++++++++++++-
>> 3 files changed, 60 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/sfc/falcon/selftest.c b/drivers/net/ethernet/sfc/falcon/selftest.c
>> index 6a454ac6f8763..fb7fcd27a33a5 100644
>> --- a/drivers/net/ethernet/sfc/falcon/selftest.c
>> +++ b/drivers/net/ethernet/sfc/falcon/selftest.c
>> @@ -40,7 +40,26 @@
>> */
>> struct ef4_loopback_payload {
>> struct ethhdr header;
>> - struct iphdr ip;
>> + struct {
>> +#if defined(__LITTLE_ENDIAN_BITFIELD)
>> + __u8 ihl:4,
>> + version:4;
>> +#elif defined (__BIG_ENDIAN_BITFIELD)
>> + __u8 version:4,
>> + ihl:4;
>> +#else
>> +#error "Please fix <asm/byteorder.h>"
>> +#endif
>> + __u8 tos;
>> + __be16 tot_len;
>> + __be16 id;
>> + __be16 frag_off;
>> + __u8 ttl;
>> + __u8 protocol;
>> + __sum16 check;
>> + __be32 saddr;
>> + __be32 daddr;
>> + } __packed ip; /* unaligned struct iphdr */
>> struct udphdr udp;
>> __be16 iteration;
>> char msg[64];
>> diff --git a/drivers/net/ethernet/sfc/selftest.c b/drivers/net/ethernet/sfc/selftest.c
>> index 3c5227afd4977..440a57953779c 100644
>> --- a/drivers/net/ethernet/sfc/selftest.c
>> +++ b/drivers/net/ethernet/sfc/selftest.c
>> @@ -43,7 +43,26 @@
>> */
>> struct efx_loopback_payload {
>> struct ethhdr header;
>> - struct iphdr ip;
>> + struct {
>> +#if defined(__LITTLE_ENDIAN_BITFIELD)
>> + __u8 ihl:4,
>> + version:4;
>> +#elif defined (__BIG_ENDIAN_BITFIELD)
>> + __u8 version:4,
>> + ihl:4;
>> +#else
>> +#error "Please fix <asm/byteorder.h>"
>> +#endif
>> + __u8 tos;
>> + __be16 tot_len;
>> + __be16 id;
>> + __be16 frag_off;
>> + __u8 ttl;
>> + __u8 protocol;
>> + __sum16 check;
>> + __be32 saddr;
>> + __be32 daddr;
>> + } __packed ip; /* unaligned struct iphdr */
>> struct udphdr udp;
>> __be16 iteration;
>> char msg[64];
>> diff --git a/drivers/net/ethernet/sfc/siena/selftest.c b/drivers/net/ethernet/sfc/siena/selftest.c
>> index 07715a3d6beab..b8a8b0495f661 100644
>> --- a/drivers/net/ethernet/sfc/siena/selftest.c
>> +++ b/drivers/net/ethernet/sfc/siena/selftest.c
>> @@ -43,7 +43,26 @@
>> */
>> struct efx_loopback_payload {
>> struct ethhdr header;
>> - struct iphdr ip;
>> + struct {
>> +#if defined(__LITTLE_ENDIAN_BITFIELD)
>> + __u8 ihl:4,
>> + version:4;
>> +#elif defined (__BIG_ENDIAN_BITFIELD)
>> + __u8 version:4,
>> + ihl:4;
>> +#else
>> +#error "Please fix <asm/byteorder.h>"
>> +#endif
>> + __u8 tos;
>> + __be16 tot_len;
>> + __be16 id;
>> + __be16 frag_off;
>> + __u8 ttl;
>> + __u8 protocol;
>> + __sum16 check;
>> + __be32 saddr;
>> + __be32 daddr;
>> + } __packed ip; /* unaligned struct iphdr */
>> struct udphdr udp;
>> __be16 iteration;
>> char msg[64];
>>
On Mon, Jun 19, 2023, at 12:25, Edward Cree wrote:
> On 19/06/2023 10:12, Arnd Bergmann wrote:
>> From: Arnd Bergmann <[email protected]>
>>
>> Three of the sfc drivers define a packed loopback_payload structure with an
>> ethernet header followed by an IP header. However, the kernel definition
>> of iphdr specifies that this is 4-byte aligned, causing a W=1 warning:
>>
>> net/ethernet/sfc/siena/selftest.c:46:15: error: field ip within 'struct efx_loopback_payload' is less aligned than 'struct iphdr' and is usually due to 'struct efx_loopback_payload' being packed, which can lead to unaligned accesses [-Werror,-Wunaligned-access]
>> struct iphdr ip;
>>
>> As the iphdr packing is not easily changed without breaking other code,
>> change the three structures to use a local definition instead.
>>
>> Signed-off-by: Arnd Bergmann <[email protected]>
>
> Duplicating the definition isn't the prettiest thing in the world; it'd
> do for a quick fix if needed but I assume W=1 warnings aren't blocking
> anyone, so maybe defer this one for now and I'll follow up soon with a
> rewrite that fixes this more cleanly? My idea is to drop the __packed
> from the containing struct, make efx_begin_loopback() copy the layers
> separately, and efx_loopback_rx_packet() similarly do something less
> direct than casting the packet data to the struct.
>
> But I don't insist on it; if you want this fix in immediately then I'm
> okay with that too.
It's not urgent, if you can come up with a nicer solution, that is
probably better than applying my patch now. I have a patch [1] that
addresses -Wunaligned-access for all x86 and arm randconfig builds,
and this currently affects 23 drivers. Most of the changes don't
have changelog texts yet, and some need a more detailed analysis to
come up with a correct patch. I'd probably aim for linux-6.6 or
later to get them all done, at which point we could move the warning
from W=1 to the default set.
Arnd
[1] https://pastebin.com/g6D9NTS4
...
> Duplicating the definition isn't the prettiest thing in the world; it'd
> do for a quick fix if needed but I assume W=1 warnings aren't blocking
> anyone, so maybe defer this one for now and I'll follow up soon with a
> rewrite that fixes this more cleanly? My idea is to drop the __packed
> from the containing struct, make efx_begin_loopback() copy the layers
> separately, and efx_loopback_rx_packet() similarly do something less
> direct than casting the packet data to the struct.
Maybe you can get away with adding a 16bit pad before the ethernet
header so that the IP header is actually aligned.
(Then fight all the stuff that stops you doing a memcpy()
that runs into a second field of a structure.)
Failing that maybe a single shared copy of the misaligned
IP header.
I also suspect you could just add __packed to the two 32bit
address fields.
That would generate better code on systems that care.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
On 23/06/2023 11:52, David Laight wrote:
> Maybe you can get away with adding a 16bit pad before the ethernet
> header so that the IP header is actually aligned.
That's what I ended up doing, because my original idea was
overcomplicated and turned out super ugly.
See https://lore.kernel.org/netdev/[email protected]/T/
> (Then fight all the stuff that stops you doing a memcpy()
> that runs into a second field of a structure.)
Yeah, I don't know how you're meant to annotate that stuff.
I guess I'll have to wait until Kees shouts at me and tells
me what to do :S
-ed