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Marc Kleine-Budde f5076c6ba0 can: uapi: can.h: mark union inside struct can_frame packed 
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>
2021-03-29 09:51:49 +02:00
arch Merge branch 'akpm' (patches from Andrew) 2021-03-25 11:43:43 -07:00
block block: Discard page cache of zone reset target range 2021-03-11 11:49:25 -07:00
certs certs: Replace K{U,G}IDT_INIT() with GLOBAL_ROOT_{U,G}ID 2021-01-21 16:16:10 +00:00
crypto crypto: mips/poly1305 - enable for all MIPS processors 2021-03-08 11:52:17 +01:00
Documentation dt-bindings: net: micrel-ksz90x1.txt: correct documentation 2021-03-25 16:51:53 -07:00
drivers drivers/net/wan/hdlc_fr: Fix a double free in pvc_xmit 2021-03-28 18:08:43 -07:00
fs Merge branch 'akpm' (patches from Andrew) 2021-03-25 11:43:43 -07:00
include can: uapi: can.h: mark union inside struct can_frame packed 2021-03-29 09:51:49 +02:00
init Merge branch 'akpm' (patches from Andrew) 2021-03-14 12:23:34 -07:00
ipc fs: make helpers idmap mount aware 2021-01-24 14:27:20 +01:00
kernel Merge branch 'akpm' (patches from Andrew) 2021-03-25 11:43:43 -07:00
lib Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2021-03-24 18:16:04 -07:00
LICENSES LICENSES: Add the CC-BY-4.0 license 2020-12-08 10:33:27 -07:00
mm Merge branch 'akpm' (patches from Andrew) 2021-03-25 11:43:43 -07:00
net can: isotp: fix msg_namelen values depending on CAN_REQUIRED_SIZE 2021-03-29 09:51:43 +02:00
samples Merge git://git.kernel.org:/pub/scm/linux/kernel/git/netdev/net 2021-03-09 17:15:56 -08:00
scripts kbuild: fix ld-version.sh to not be affected by locale 2021-03-13 11:12:13 +09:00
security selinux/stable-5.12 PR 20210322 2021-03-22 11:34:31 -07:00
sound sound fixes for 5.12-rc4 2021-03-19 09:53:32 -07:00
tools Merge branch 'akpm' (patches from Andrew) 2021-03-25 11:43:43 -07:00
usr Kbuild updates for v5.12 2021-02-25 10:17:31 -08:00
virt KVM: x86/mmu: Consider the hva in mmu_notifier retry 2021-02-22 13:16:53 -05:00
.clang-format cxl for 5.12 2021-02-24 09:38:36 -08:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore clang-lto series for v5.12-rc1 2021-02-23 09:28:51 -08:00
.mailmap Merge branch 'akpm' (patches from Andrew) 2021-03-25 11:43:43 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS treewide: Miguel has moved 2021-02-26 09:41:03 -08:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2021-03-24 18:16:04 -07:00
Makefile Linux 5.12-rc4 2021-03-21 14:56:43 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.