partly outside array bounds warning on fs/jffs2/summary.c, GCC 12.1.0

[Bagas Sanjaya]

Hi everyone,

When I build arm64 kernel with GCC 12.1.0 (bcm2711_defconfig), I get
partly outside array bounds warning on fs/jffs2/summary.c:

  CC [M]  fs/jffs2/summary.o
In file included from fs/jffs2/summary.c:23:
In function 'jffs2_sum_add_mem',
    inlined from 'jffs2_sum_add_inode_mem' at fs/jffs2/summary.c:130:9:
fs/jffs2/nodelist.h:43:28: warning: array subscript 'union jffs2_sum_mem[0]' is partly outside array bounds of 'unsigned char[26]' [-Warray-bounds]
   43 | #define je16_to_cpu(x) ((x).v16)
      |                        ~~~~^~~~~
fs/jffs2/summary.c:71:17: note: in expansion of macro 'je16_to_cpu'
   71 |         switch (je16_to_cpu(item->u.nodetype)) {
      |                 ^~~~~~~~~~~
In file included from fs/jffs2/summary.c:17:
In function 'kmalloc',
    inlined from 'jffs2_sum_add_inode_mem' at fs/jffs2/summary.c:118:37:
./include/linux/slab.h:600:24: note: object of size 26 allocated by 'kmem_cache_alloc_trace'
  600 |                 return kmem_cache_alloc_trace(
      |                        ^~~~~~~~~~~~~~~~~~~~~~~
  601 |                                 kmalloc_caches[kmalloc_type(flags)][index],
      |                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  602 |                                 flags, size);
      |                                 ~~~~~~~~~~~~
In file included from fs/jffs2/nodelist.h:22:
In function 'jffs2_sum_add_mem',
    inlined from 'jffs2_sum_add_inode_mem' at fs/jffs2/summary.c:130:9:
fs/jffs2/summary.c:79:73: warning: array subscript 'union jffs2_sum_mem[0]' is partly outside array bounds of 'unsigned char[26]' [-Warray-bounds]
   79 |                         s->sum_size += JFFS2_SUMMARY_DIRENT_SIZE(item->d.nsize);
fs/jffs2/summary.h:34:80: note: in definition of macro 'JFFS2_SUMMARY_DIRENT_SIZE'
   34 | #define JFFS2_SUMMARY_DIRENT_SIZE(x) (sizeof(struct jffs2_sum_dirent_flash) + (x))
      |                                                                                ^
In function 'kmalloc',
    inlined from 'jffs2_sum_add_inode_mem' at fs/jffs2/summary.c:118:37:
./include/linux/slab.h:600:24: note: object of size 26 allocated by 'kmem_cache_alloc_trace'
  600 |                 return kmem_cache_alloc_trace(
      |                        ^~~~~~~~~~~~~~~~~~~~~~~
  601 |                                 kmalloc_caches[kmalloc_type(flags)][index],
      |                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  602 |                                 flags, size);
      |                                 ~~~~~~~~~~~~

I first found these warnings when reviewing linux-5.18.y stable rc [1],
for which Greg recommends me to contact JFFS subsystem developers.

Thanks.

[1]: https://lore.kernel.org/stable/YpxU%2FbVogip64iQF@debian.me/ 

-- 
An old man doll... just what I always wanted! - Clara