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Date: Tue, 23 Mar 2021 10:54:40 +0800
From: Rong Chen <rong.a.chen@...el.com>
To: Oliver Hartkopp <socketcan@...tkopp.net>,
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...
On 3/23/21 12:24 AM, Oliver Hartkopp wrote:
> 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.
Hi Oliver,
I tried arm-linux-gnueabi (gcc version 10.2.0) and the problem still exists,
btw we prefer to not use the latest gcc compiler to avoid false positives.
Best Regards,
Rong Chen
>
> 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
>>>>
>>> _______________________________________________
>>> kbuild-all mailing list -- kbuild-all@...ts.01.org
>>> To unsubscribe send an email to kbuild-all-leave@...ts.01.org
>>
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