Re: include/linux/compiler_types.h:699:45: error: call to '__compiletime_assert_881' declared with attribute error: BUILD_BUG_ON failed: sizeof_field(struct mptcp_ext, flags) != sizeof(u16)

[David Laight <david.laight.linux@gmail.com>]

On Fri, 03 Jul 2026 11:51:39 +0800
kernel test robot <lkp@intel.com> wrote:

> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   51512e22efe813d8223de27f6fd02a8a48ea2323
> commit: 5e939544f9d2b4d5c052a07cfcde97de44263946 mptcp: fix uninit-value in mptcp_established_options
> date:   4 weeks ago
> config: arm-randconfig-r051-20260702 (https://download.01.org/0day-ci/archive/20260703/202607031100.upQfRZTM-lkp@intel.com/config)
> compiler: arm-linux-gnueabi-gcc (GCC) 16.1.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260703/202607031100.upQfRZTM-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Fixes: 5e939544f9d2 ("mptcp: fix uninit-value in mptcp_established_options")
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202607031100.upQfRZTM-lkp@intel.com/
> 
> All errors (new ones prefixed by >>):
> 
>    In file included from <command-line>:
>    In function 'mptcp_established_options_dss',
>        inlined from 'mptcp_established_options' at net/mptcp/options.c:881:11:
> >> include/linux/compiler_types.h:699:45: error: call to '__compiletime_assert_881' declared with attribute error: BUILD_BUG_ON failed: sizeof_field(struct mptcp_ext, flags) != sizeof(u16)  
>      699 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>          |                                             ^
>    include/linux/compiler_types.h:680:25: note: in definition of macro '__compiletime_assert'
>      680 |                         prefix ## suffix();                             \
>          |                         ^~~~~~
>    include/linux/compiler_types.h:699:9: note: in expansion of macro '_compiletime_assert'
>      699 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>          |         ^~~~~~~~~~~~~~~~~~~
>    include/linux/build_bug.h:40:37: note: in expansion of macro 'compiletime_assert'
>       40 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
>          |                                     ^~~~~~~~~~~~~~~~~~
>    include/linux/build_bug.h:51:9: note: in expansion of macro 'BUILD_BUG_ON_MSG'
>       51 |         BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
>          |         ^~~~~~~~~~~~~~~~
>    net/mptcp/options.c:576:9: note: in expansion of macro 'BUILD_BUG_ON'
>      576 |         BUILD_BUG_ON(sizeof_field(struct mptcp_ext, flags) != sizeof(u16));
>          |         ^~~~~~~~~~~~

This is probably the old 32bit arm abi that aligns all structures to 32 bits.

	David

> 
> 
> vim +/__compiletime_assert_881 +699 include/linux/compiler_types.h
> 
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  685  
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  686  #define _compiletime_assert(condition, msg, prefix, suffix) \
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  687  	__compiletime_assert(condition, msg, prefix, suffix)
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  688  
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  689  /**
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  690   * compiletime_assert - break build and emit msg if condition is false
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  691   * @condition: a compile-time constant condition to check
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  692   * @msg:       a message to emit if condition is false
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  693   *
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  694   * In tradition of POSIX assert, this macro will break the build if the
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  695   * supplied condition is *false*, emitting the supplied error message if the
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  696   * compiler has support to do so.
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  697   */
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  698  #define compiletime_assert(condition, msg) \
> eb5c2d4b45e3d2 Will Deacon 2020-07-21 @699  	_compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  700  
> 
> :::::: The code at line 699 was first introduced by commit
> :::::: eb5c2d4b45e3d2d5d052ea6b8f1463976b1020d5 compiler.h: Move compiletime_assert() macros into compiler_types.h
> 
> :::::: TO: Will Deacon <will@kernel.org>
> :::::: CC: Will Deacon <will@kernel.org>
> 
> --
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