linux-kernel - include/asm-generic/unaligned.h:14:15: warning: array subscript -1 is outside array bounds of 'char[]'

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Date:   Tue, 19 Sep 2023 23:29:21 +0800
From:   kernel test robot <lkp@...el.com>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: include/asm-generic/unaligned.h:14:15: warning: array subscript -1
 is outside array bounds of 'char[]'

Hi Ard,

FYI, the error/warning still remains.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   2cf0f715623872823a72e451243bbf555d10d032
commit: a050910972bb25152b42ad2e544652117c5ad915 efi/libstub: implement generic EFI zboot
date:   12 months ago
config: loongarch-defconfig (https://download.01.org/0day-ci/archive/20230919/202309192322.kHMCRGo5-lkp@intel.com/config)
compiler: loongarch64-linux-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20230919/202309192322.kHMCRGo5-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@...el.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202309192322.kHMCRGo5-lkp@intel.com/

All warnings (new ones prefixed by >>):

   drivers/firmware/efi/libstub/zboot.c:163:1: warning: no previous prototype for 'efi_zboot_entry' [-Wmissing-prototypes]
     163 | efi_zboot_entry(efi_handle_t handle, efi_system_table_t *systab)
         | ^~~~~~~~~~~~~~~
   In file included from include/linux/byteorder/little_endian.h:5,
                    from arch/loongarch/include/uapi/asm/byteorder.h:11,
                    from include/asm-generic/qrwlock_types.h:6,
                    from ./arch/loongarch/include/generated/asm/qrwlock_types.h:1,
                    from include/asm-generic/spinlock_types.h:13,
                    from ./arch/loongarch/include/generated/asm/spinlock_types.h:1,
                    from include/linux/spinlock_types_raw.h:7,
                    from include/linux/ratelimit_types.h:7,
                    from include/linux/printk.h:9,
                    from include/asm-generic/bug.h:22,
                    from arch/loongarch/include/asm/bug.h:21,
                    from include/linux/bug.h:5,
                    from include/linux/thread_info.h:13,
                    from include/asm-generic/preempt.h:5,
                    from ./arch/loongarch/include/generated/asm/preempt.h:1,
                    from include/linux/preempt.h:78,
                    from include/linux/spinlock.h:55,
                    from include/linux/wait.h:9,
                    from include/linux/wait_bit.h:8,
                    from include/linux/fs.h:6,
                    from include/linux/proc_fs.h:10,
                    from include/linux/efi.h:19,
                    from drivers/firmware/efi/libstub/zboot.c:3:
   In function 'get_unaligned_le32',
       inlined from 'load_file' at drivers/firmware/efi/libstub/zboot.c:92:22:
>> include/asm-generic/unaligned.h:14:15: warning: array subscript -1 is outside array bounds of 'char[]' [-Warray-bounds=]
      14 |         __pptr->x;                                                              \
         |         ~~~~~~^~~
   include/uapi/linux/byteorder/little_endian.h:35:51: note: in definition of macro '__le32_to_cpu'
      35 | #define __le32_to_cpu(x) ((__force __u32)(__le32)(x))
         |                                                   ^
   include/asm-generic/unaligned.h:32:28: note: in expansion of macro '__get_unaligned_t'
      32 |         return le32_to_cpu(__get_unaligned_t(__le32, p));
         |                            ^~~~~~~~~~~~~~~~~
   drivers/firmware/efi/libstub/zboot.c: In function 'load_file':
   drivers/firmware/efi/libstub/zboot.c:33:30: note: at offset -4 into object '_gzdata_end' of size [0, 9223372036854775807]
      33 | extern char _gzdata_start[], _gzdata_end[];
         |                              ^~~~~~~~~~~


vim +14 include/asm-generic/unaligned.h

aafe4dbed0bf6c Arnd Bergmann 2009-05-13  11  
803f4e1eab7a89 Arnd Bergmann 2021-05-08  12  #define __get_unaligned_t(type, ptr) ({						\
803f4e1eab7a89 Arnd Bergmann 2021-05-08  13  	const struct { type x; } __packed *__pptr = (typeof(__pptr))(ptr);	\
803f4e1eab7a89 Arnd Bergmann 2021-05-08 @14  	__pptr->x;								\
803f4e1eab7a89 Arnd Bergmann 2021-05-08  15  })
803f4e1eab7a89 Arnd Bergmann 2021-05-08  16  

:::::: The code at line 14 was first introduced by commit
:::::: 803f4e1eab7a8938ba3a3c30dd4eb5e9eeef5e63 asm-generic: simplify asm/unaligned.h

:::::: TO: Arnd Bergmann <arnd@...db.de>
:::::: CC: Arnd Bergmann <arnd@...db.de>

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