[PATCH v5 3/3] xtensa: Emulate two-byte cmpxchg

[Paul E. McKenney]

On Tue, Oct 06, 2026 at 05:54:53PM +0800, kernel test robot wrote:
> Hi Bradley,
> 
> kernel test robot noticed the following build errors:
> 
> [auto build test ERROR on akpm-mm/mm-everything]
> [also build test ERROR on vgupta-arc/for-curr jcmvbkbc-xtensa/xtensa-for-next linus/master v7.3-rc6 next-20261005]
> [cannot apply to vgupta-arc/for-next]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch#_base_tree_information]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Bradley-Morgan/ARC-Emulate-two-byte-cmpxchg/20261005-120658
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
> patch link:    https://lore.kernel.org/r/20261005120700.383058-4-brads%40mainlining.org
> patch subject: [PATCH v5 3/3] xtensa: Emulate two-byte cmpxchg
> config: xtensa-allyesconfig (https://download.01.org/0day-ci/archive/20261006/202610061704.rvbolgPy-lkp@intel.com/config)
> compiler: xtensa-linux-gcc (GCC) 16.1.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20261006/202610061704.rvbolgPy-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
> | Reported-by: kernel test robot <lkp at intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202610061704.rvbolgPy-lkp@intel.com/
> 
> All errors (new ones prefixed by >>):

These patches need to be applied on top of my -rcu tree's "dev" branch,
which supplies cmpxchg_emu_u16().

Nevertheless, thank you for your testing efforts!

							Thanx, Paul

>    In file included from arch/xtensa/include/asm/atomic.h:19,
>                     from include/linux/atomic.h:7,
>                     from include/asm-generic/bitops/atomic.h:5,
>                     from arch/xtensa/include/asm/bitops.h:192,
>                     from include/linux/bitops.h:67,
>                     from include/linux/log2.h:12,
>                     from kernel/bounds.c:14:
>    arch/xtensa/include/asm/cmpxchg.h: In function '__cmpxchg':
> >> arch/xtensa/include/asm/cmpxchg.h:79:25: error: implicit declaration of function 'cmpxchg_emu_u16'; did you mean 'cmpxchg_emu_u8'? [-Wimplicit-function-declaration]
>       79 |         case 2:  return cmpxchg_emu_u16(ptr, old, new);
>          |                         ^~~~~~~~~~~~~~~
>          |                         cmpxchg_emu_u8
>    make[3]: *** [scripts/Makefile.build:185: kernel/bounds.s] Error 1
>    make[3]: Target 'prepare' not remade because of errors.
>    make[2]: *** [Makefile:1405: prepare0] Error 2
>    make[2]: Target 'prepare' not remade because of errors.
>    make[1]: *** [Makefile:248: __sub-make] Error 2
>    make[1]: Target 'prepare' not remade because of errors.
>    make: *** [Makefile:248: __sub-make] Error 2
>    make: Target 'prepare' not remade because of errors.
> 
> 
> vim +79 arch/xtensa/include/asm/cmpxchg.h
> 
>     73	
>     74	static __inline__ unsigned long
>     75	__cmpxchg(volatile void *ptr, unsigned long old, unsigned long new, int size)
>     76	{
>     77		switch (size) {
>     78		case 1:  return cmpxchg_emu_u8(ptr, old, new);
>   > 79		case 2:  return cmpxchg_emu_u16(ptr, old, new);
>     80		case 4:  return __cmpxchg_u32(ptr, old, new);
>     81		default: __cmpxchg_called_with_bad_pointer();
>     82			 return old;
>     83		}
>     84	}
>     85	
> 
> --
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