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Date: Mon, 22 Mar 2021 17:24:37 +0100
From: Oliver Hartkopp <socketcan@...tkopp.net>
To: Rong Chen <rong.a.chen@...el.com>,
kernel test robot <lkp@...el.com>
Cc: kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org,
Marc Kleine-Budde <mkl@...gutronix.de>,
linux-can <linux-can@...r.kernel.org>
Subject: Re: [kbuild-all] Re: 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(struc...
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@hartkopp.net/
>>
>>
>> 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@hartkopp.net/
>>
>>
>> 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@...el.com>
>>>
>>> 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@...nel.org>
>>> :::::: CC: Will Deacon <will@...nel.org>
>>>
>>> ---
>>> 0-DAY CI Kernel Test Service, Intel Corporation
>>> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
>>>
>> _______________________________________________
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