| From 0084115277906a63aa1a04266be996b4fcd78c91 Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Mon, 22 Mar 2021 10:44:54 +0100 |
| Subject: can: uapi: can.h: mark union inside struct can_frame packed |
| |
| From: Marc Kleine-Budde <mkl@pengutronix.de> |
| |
| [ Upstream commit f5076c6ba02e8e24c61c40bbf48078929bc0fc79 ] |
| |
| 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> |
| Signed-off-by: Sasha Levin <sashal@kernel.org> |
| --- |
| include/uapi/linux/can.h | 2 +- |
| 1 file changed, 1 insertion(+), 1 deletion(-) |
| |
| 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) */ |
| -- |
| 2.30.2 |
| |