Hi Rong,
On 22.03.21 09:52, Rong Chen wrote:
On 3/21/21 10:19 PM, Oliver Hartkopp wrote:
Two reminders in two days? ;-)
Did you check my answer here?
https://lore.kernel.org/lkml/afffeb73-ba4c-ca2c-75d0-9e7899e5cbe1@xxxxxxxxxxxx/
And did you try the partly revert?
Hi Oliver,
Sorry for the delay, we tried the revert patch and the problem still
exists,
we also found that commit c7b74967 changed the error message which
triggered
the report.
The problem is that offsetof(struct can_frame, data) != offsetof(struct
canfd_frame, data)
the following struct layout shows that the offset has been changed by
union:
struct can_frame {
canid_t can_id; /* 0 4 */
union {
__u8 len; /* 4 1 */
__u8 can_dlc; /* 4 1 */
}; /* 4 4 */
Ugh! Why did the compiler extend the space for the union to 4 bytes?!?
__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)));
struct canfd_frame {
canid_t can_id; /* 0 4 */
__u8 len; /* 4 1 */
__u8 flags; /* 5 1 */
__u8 __res0; /* 6 1 */
__u8 __res1; /* 7 1 */
__u8 data[64]
__attribute__((__aligned__(8))); /* 8 64 */
/* size: 72, cachelines: 2, members: 6 */
/* forced alignments: 1 */
/* last cacheline: 8 bytes */
} __attribute__((__aligned__(8)))
and I tried to add "__attribute__((packed))" to the union, the issue is
gone:
diff --git a/include/uapi/linux/can.h b/include/uapi/linux/can.h
index f75238ac6dce..9842bb55ffd9 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));
__u8 __pad; /* padding */
__u8 __res0; /* reserved / padding */
__u8 len8_dlc; /* optional DLC for 8 byte payload length (9 ..
15) */
This is pretty strange!
pahole on my x86_64 machine shows the correct data structure layout:
struct can_frame {
canid_t can_id; /* 0 4 */
union {
__u8 len; /* 4 1 */
__u8 can_dlc; /* 4 1 */
}; /* 4 1 */
__u8 __pad; /* 5 1 */
__u8 __res0; /* 6 1 */
__u8 len8_dlc; /* 7 1 */
__u8 data[8]
__attribute__((__aligned__(8))); /* 8 8 */
/* size: 16, cachelines: 1, members: 6 */
/* forced alignments: 1 */
/* last cacheline: 16 bytes */
} __attribute__((__aligned__(8)));
Target: x86_64-linux-gnu
gcc version 10.2.1 20210110 (Debian 10.2.1-6)
Linux 5.12.0-rc3-00070-g8b12a62a4e3e x86_64 GNU/Linux
So it looks like your compiler does not behave correctly - and I wonder
if it would be the correct approach to add the __packed() attribute or
better fix/change the (ARM) compiler.
At least I'm very happy that the BUILD_BUG_ON() triggered correctly - so
it was worth to have it ;-)
Best regards,
Oliver
Maybe there's a mismatch in include files - or BUILD_BUG_ON()
generally does not work with unions on ARM as assumed here:
https://lore.kernel.org/lkml/6e57d5d2-9b88-aee6-fb7a-82e24144d179@xxxxxxxxxxxx/
In both cases I can not really fix the issue.
When the partly revert (suggested above) works, this would be a hack too.
Best,
Oliver
On 20.03.21 21:43, kernel test robot wrote:
Hi Oliver,
FYI, the error/warning still remains.
tree:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
master
head: 812da4d39463a060738008a46cfc9f775e4bfcf6
commit: c7b74967799b1af52b3045d69d4c26836b2d41de can: replace can_dlc
as variable/element for payload length
date: 4 months ago
config: arm-randconfig-r016-20210321 (attached as .config)
compiler: arm-linux-gnueabi-gcc (GCC) 9.3.0
reproduce (this is a W=1 build):
wget
https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross
-O ~/bin/make.cross
chmod +x ~/bin/make.cross
#
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c7b74967799b1af52b3045d69d4c26836b2d41de
git remote add linus
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
git fetch --no-tags linus master
git checkout c7b74967799b1af52b3045d69d4c26836b2d41de
# save the attached .config to linux build tree
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0
make.cross ARCH=arm
If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@xxxxxxxxx>
All errors (new ones prefixed by >>):
In file included from <command-line>:
net/can/af_can.c: In function 'can_init':
include/linux/compiler_types.h:315:38: error: call to
'__compiletime_assert_536' declared with attribute error:
BUILD_BUG_ON failed: offsetof(struct can_frame, len) !=
offsetof(struct canfd_frame, len) || offsetof(struct can_frame,
data) != offsetof(struct canfd_frame, data)
315 | _compiletime_assert(condition, msg,
__compiletime_assert_, __COUNTER__)
| ^
include/linux/compiler_types.h:296:4: note: in definition of
macro '__compiletime_assert'
296 | prefix ## suffix(); \
| ^~~~~~
include/linux/compiler_types.h:315:2: note: in expansion of macro
'_compiletime_assert'
315 | _compiletime_assert(condition, msg,
__compiletime_assert_, __COUNTER__)
| ^~~~~~~~~~~~~~~~~~~
include/linux/build_bug.h:39:37: note: in expansion of macro
'compiletime_assert'
39 | #define BUILD_BUG_ON_MSG(cond, msg)
compiletime_assert(!(cond), msg)
| ^~~~~~~~~~~~~~~~~~
include/linux/build_bug.h:50:2: note: in expansion of macro
'BUILD_BUG_ON_MSG'
50 | BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: "
#condition)
| ^~~~~~~~~~~~~~~~
net/can/af_can.c:891:2: note: in expansion of macro 'BUILD_BUG_ON'
891 | BUILD_BUG_ON(offsetof(struct can_frame, len) !=
| ^~~~~~~~~~~~
vim +/__compiletime_assert_536 +315 include/linux/compiler_types.h
eb5c2d4b45e3d2 Will Deacon 2020-07-21 301
eb5c2d4b45e3d2 Will Deacon 2020-07-21 302 #define
_compiletime_assert(condition, msg, prefix, suffix) \
eb5c2d4b45e3d2 Will Deacon 2020-07-21 303
__compiletime_assert(condition, msg, prefix, suffix)
eb5c2d4b45e3d2 Will Deacon 2020-07-21 304
eb5c2d4b45e3d2 Will Deacon 2020-07-21 305 /**
eb5c2d4b45e3d2 Will Deacon 2020-07-21 306 * compiletime_assert -
break build and emit msg if condition is false
eb5c2d4b45e3d2 Will Deacon 2020-07-21 307 * @condition: a
compile-time constant condition to check
eb5c2d4b45e3d2 Will Deacon 2020-07-21 308 * @msg: a message
to emit if condition is false
eb5c2d4b45e3d2 Will Deacon 2020-07-21 309 *
eb5c2d4b45e3d2 Will Deacon 2020-07-21 310 * In tradition of POSIX
assert, this macro will break the build if the
eb5c2d4b45e3d2 Will Deacon 2020-07-21 311 * supplied condition is
*false*, emitting the supplied error message if the
eb5c2d4b45e3d2 Will Deacon 2020-07-21 312 * compiler has support
to do so.
eb5c2d4b45e3d2 Will Deacon 2020-07-21 313 */
eb5c2d4b45e3d2 Will Deacon 2020-07-21 314 #define
compiletime_assert(condition, msg) \
eb5c2d4b45e3d2 Will Deacon 2020-07-21 @315
_compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
eb5c2d4b45e3d2 Will Deacon 2020-07-21 316
:::::: The code at line 315 was first introduced by commit
:::::: eb5c2d4b45e3d2d5d052ea6b8f1463976b1020d5 compiler.h: Move
compiletime_assert() macros into compiler_types.h
:::::: TO: Will Deacon <will@xxxxxxxxxx>
:::::: CC: Will Deacon <will@xxxxxxxxxx>
---
0-DAY CI Kernel Test Service, Intel Corporation
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