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Date: Tue, 23 Mar 2021 14:06:21 +0800
From: Rong Chen <rong.a.chen@...el.com>
To: Vincent MAILHOL <mailhol.vincent@...adoo.fr>
Cc: Oliver Hartkopp <socketcan@...tkopp.net>,
kernel test robot <lkp@...el.com>, kbuild-all@...ts.01.org,
open list <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 Vincent,
On 3/23/21 1:46 PM, Vincent MAILHOL wrote:
> Hi Oliver and Rong,
>
> This is an interesting and quite surprising issue!
>
> On Tue. 23 mars 2021 at 11:54, Rong Chen <rong.a.chen@...el.com> wrote:
>> 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?!?
> Just a random idea but maybe the added padding is due to some
> kind of odd intrication with the __attribute__((__aligned__(8)))
> just below? Does this reproduce if we remove the
> __attribute__((__aligned__(8)))?
Here is the layout without __attribute__((__aligned__(8))),
the union is still extended to 4 bytes:
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 */
__u8 data[8]; /* 11 8 */
/* size: 20, cachelines: 1, members: 6 */
/* padding: 1 */
/* last cacheline: 20 bytes */
};
Best Regards,
Rong Chen
>
> (I am not saying that we should permanently remove it, this is
> only a suggestion for troubleshooting).
>
>>>> __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.
> I had a look at the ISO/IEC 9899-1999 (aka C99 standard). In
> section 6.7.2.1 "Structure and union specifiers", there are no
> clauses to forbid this behavior...
> Here are the relevant clauses of that section:
> * 12 Each non-bit-field member of a structure or union object
> is aligned in an implementation-defined appropriate to its
> type.
> * 13 [...] There may be unnamed padding within a structure
> object, but not at its beginning.
> * 14 The size of a union is sufficient to contain the largest
> of its members. [...]
> * 15 There may be unnamed padding at the end of a structure or
> union.
>
> So while I am really curious to understand why the compiler
> behaves like that, technically speaking, it does not violate the
> standard. As such, I think that Mark's patch (which negates
> clause 15) makes sense.
>
>> 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
>>>>>>
>>>>> _______________________________________________
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