In commit ea7800565a ("can: add optional DLC element to Classical
CAN frame structure") the struct can_frame::can_dlc was put into an
anonymous union with another u8 variable.
For various reasons some members in struct can_frame and canfd_frame
including the first 8 byes of data are expected to have the same
memory layout. This is enforced by a BUILD_BUG_ON check in af_can.c.
Since the above mentioned commit this check fails on ARM kernels
compiled with the ARM OABI (which means CONFIG_AEABI not set). In this
case -mabi=apcs-gnu is passed to the compiler, which leads to a
structure size boundary of 32, instead of 8 compared to CONFIG_AEABI
enabled. This means the the union in struct can_frame takes 4 bytes
instead of the expected 1.
Rong Chen illustrates the problem with pahole in the ARM OABI case:
| struct can_frame {
| canid_t can_id; /* 0 4 */
| union {
| __u8 len; /* 4 1 */
| __u8 can_dlc; /* 4 1 */
| }; /* 4 4 */
| __u8 __pad; /* 8 1 */
| __u8 __res0; /* 9 1 */
| __u8 len8_dlc; /* 10 1 */
|
| /* XXX 5 bytes hole, try to pack */
|
| __u8 data[8]
| __attribute__((__aligned__(8))); /* 16 8 */
|
| /* size: 24, cachelines: 1, members: 6 */
| /* sum members: 19, holes: 1, sum holes: 5 */
| /* forced alignments: 1, forced holes: 1, sum forced holes: 5 */
| /* last cacheline: 24 bytes */
| } __attribute__((__aligned__(8)));
Marking the anonymous union as __attribute__((packed)) fixes the
BUILD_BUG_ON problem on these compilers.
Fixes: ea7800565a ("can: add optional DLC element to Classical CAN frame structure")
Reported-by: kernel test robot <lkp@intel.com>
Suggested-by: Rong Chen <rong.a.chen@intel.com>
Link: https://lore.kernel.org/linux-can/2c82ec23-3551-61b5-1bd8-178c3407ee83@hartkopp.net/
Link: https://lore.kernel.org/r/20210325125850.1620-3-socketcan@hartkopp.net
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
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