| Message ID | 20210329085355.921447-4-mkl@pengutronix.de (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | f5076c6ba02e8e24c61c40bbf48078929bc0fc79 |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | pull-request: can 2021-03-29 | expand |
| Context | Check | Description |
|---|---|---|
| netdev/tree_selection | success | Series ignored based on subject |
diff --git a/include/uapi/linux/can.h b/include/uapi/linux/can.h index f75238ac6dce..c7535352fef6 100644 --- a/include/uapi/linux/can.h +++ b/include/uapi/linux/can.h @@ -113,7 +113,7 @@ struct can_frame { */ __u8 len; __u8 can_dlc; /* deprecated */ - }; + } __attribute__((packed)); /* disable padding added in some ABIs */ __u8 __pad; /* padding */ __u8 __res0; /* reserved / padding */ __u8 len8_dlc; /* optional DLC for 8 byte payload length (9 .. 15) */
In commit ea7800565a12 ("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: ea7800565a12 ("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> --- include/uapi/linux/can.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)