arch/arm/include/asm/memory.h:298:23: warning: array subscript -1 is outside array bounds of 'const void[2147483647]'

arch/arm/include/asm/memory.h:298:23: warning: array subscript -1 is outside array bounds of 'const void[2147483647]'

[kernel test robot]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   dd72f9c7e512da377074d47d990564959b772643
commit: a9ff6961601d9aa0c42b6eb7d850371f31b1f5e6 ARM: mm: Make virt_to_pfn() a static inline
date:   5 months ago
config: arm-randconfig-r022-20230725 (https://download.01.org/0day-ci/archive/20231019/202310190854.yTRUMqLL-lkp@intel.com/config)
compiler: arm-linux-gnueabi-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231019/202310190854.yTRUMqLL-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@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202310190854.yTRUMqLL-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from arch/arm/include/asm/page.h:166,
                    from arch/arm/include/asm/thread_info.h:14,
                    from include/linux/thread_info.h:60,
                    from include/asm-generic/preempt.h:5,
                    from ./arch/arm/include/generated/asm/preempt.h:1,
                    from include/linux/preempt.h:78,
                    from include/linux/spinlock.h:56,
                    from include/linux/mmzone.h:8,
                    from include/linux/gfp.h:7,
                    from include/linux/mm.h:7,
                    from arch/arm/kernel/hibernate.c:17:
   In function 'virt_to_pfn',
       inlined from 'pfn_is_nosave' at arch/arm/kernel/hibernate.c:29:33:
>> arch/arm/include/asm/memory.h:298:23: warning: array subscript -1 is outside array bounds of 'const void[2147483647]' [-Warray-bounds=]
     298 |         unsigned long kaddr = (unsigned long)p;
         |                       ^~~~~
   In file included from arch/arm/include/asm/sections.h:5,
                    from include/linux/interrupt.h:21,
                    from include/linux/kernel_stat.h:9,
                    from include/linux/cgroup.h:26,
                    from include/linux/memcontrol.h:13,
                    from include/linux/swap.h:9,
                    from include/linux/suspend.h:5,
                    from arch/arm/kernel/hibernate.c:18:
   include/asm-generic/sections.h: In function 'pfn_is_nosave':
   include/asm-generic/sections.h:59:45: note: at offset -1 into object '__nosave_end' of size [0, 2147483647]
      59 | extern __visible const void __nosave_begin, __nosave_end;
         |                                             ^~~~~~~~~~~~


vim +298 arch/arm/include/asm/memory.h

   295	
   296	static inline unsigned long virt_to_pfn(const void *p)
   297	{
 > 298		unsigned long kaddr = (unsigned long)p;
   299		return (((kaddr - PAGE_OFFSET) >> PAGE_SHIFT) +
   300			PHYS_PFN_OFFSET);
   301	}
   302	#define __pa_symbol_nodebug(x)	__virt_to_phys_nodebug((x))
   303	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: arch/arm/include/asm/memory.h:298:23: warning: array subscript -1 is outside array bounds of 'const void[2147483647]'

[Linus Walleij]

Hi Robot,

On Thu, Oct 19, 2023 at 2:22 AM kernel test robot <lkp@intel.com> wrote:

>    In function 'virt_to_pfn',
>        inlined from 'pfn_is_nosave' at arch/arm/kernel/hibernate.c:29:33:
> >> arch/arm/include/asm/memory.h:298:23: warning: array subscript -1 is outside array bounds of 'const void[2147483647]' [-Warray-bounds=]
>      298 |         unsigned long kaddr = (unsigned long)p;

What does this even mean?

>    296  static inline unsigned long virt_to_pfn(const void *p)
>    297  {
>  > 298          unsigned long kaddr = (unsigned long)p;
>    299          return (((kaddr - PAGE_OFFSET) >> PAGE_SHIFT) +
>    300                  PHYS_PFN_OFFSET);
>    301  }

Array out of bounds? It's not even an array! What's up with this warning?

Yours,
Linus Walleij