disk/mdraid1x_linux.c:181:15: warning: array subscript <unknown> is outside array bounds of ‘grub_uint16_t[0]’ {aka ‘short unsigned int[0]’} [-Warray-bounds]

[Paul Menzel]

Dear GRUB folks,


Using Debian Sid/unstable with

    gcc (Debian 10-20200312-2) 10.0.1 20200312 (experimental) [master 
revision c56871dd15a:7ba6e7f0f21:daf2852b883762d921361462dad1f99320faca2a]

building GRUB fails with the error below due to treating warnings as errors.

> gcc -DHAVE_CONFIG_H -I. -I..  -Wall -W  -DGRUB_MACHINE_EFI=1 -DGRUB_MACHINE=X86_64_EFI 
> -m64 -nostdinc -isystem /usr/lib/gcc/x86_64-linux-gnu/10/include -I../include 
> -I../include -DGRUB_FILE=\"disk/mdraid1x_linux.c\" -I. -I. -I.. -I.. 
> -I../include -I../include -I../grub-core/lib/libgcrypt-grub/src/    
> -D_FILE_OFFSET_BITS=64 -Os -m64 -Wall -W -Wshadow -Wpointer-arith -Wundef 
> -Wchar-subscripts -Wcomment -Wdeprecated-declarations -Wdisabled-optimization 
> -Wdiv-by-zero -Wfloat-equal -Wformat-extra-args -Wformat-security -Wformat-y2k -Wimplicit 
> -Wimplicit-function-declaration -Wimplicit-int -Wmain -Wmissing-braces 
> -Wmissing-format-attribute -Wmultichar -Wparentheses -Wreturn-type -Wsequence-point 
> -Wshadow -Wsign-compare -Wswitch -Wtrigraphs -Wunknown-pragmas -Wunused -Wunused-function 
> -Wunused-label -Wunused-parameter -Wunused-value  -Wunused-variable -Wwrite-strings 
> -Wnested-externs -Wstrict-prototypes -g -Wredundant-decls -Wmissing-prototypes 
> -Wmissing-declarations  -Wextra -Wattributes -Wendif-labels -Winit-self 
> -Wint-to-pointer-cast -Winvalid-pch -Wmissing-field-initializers -Wnonnull -Woverflow 
> -Wvla -Wpointer-to-int-cast -Wstrict-aliasing -Wvariadic-macros -Wvolatile-register-var 
> -Wpointer-sign -Wmissing-include-dirs -Wmissing-prototypes -Wmissing-declarations 
> -Wformat=2 -freg-struct-return -mno-mmx -mno-sse -mno-sse2 -mno-sse3 -mno-3dnow 
> -msoft-float -fno-dwarf2-cfi-asm -mno-stack-arg-probe -fno-asynchronous-unwind-tables 
> -fno-unwind-tables -fno-ident -mcmodel=large -mno-red-zone -fno-PIE -fno-pie 
> -fno-stack-protector -Wtrampolines   -ffreestanding   -MT 
> disk/mdraid1x_module-mdraid1x_linux.o -MD -MP -MF 
> disk/.deps-core/mdraid1x_module-mdraid1x_linux.Tpo -c -o 
> disk/mdraid1x_module-mdraid1x_linux.o `test -f 'disk/mdraid1x_linux.c' || echo 
> './'`disk/mdraid1x_linux.c
> disk/mdraid1x_linux.c: In function ‘grub_mdraid_detect’:
> disk/mdraid1x_linux.c:181:15: warning: array subscript <unknown> is outside 
> array bounds of ‘grub_uint16_t[0]’ {aka ‘short unsigned int[0]’} [-Warray-bounds]
>   181 |      (char *) &sb.dev_roles[grub_le_to_cpu32 (sb.dev_number)]
>       |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> disk/mdraid1x_linux.c:98:17: note: while referencing ‘dev_roles’
>    98 |   grub_uint16_t dev_roles[]; /* Role in array, or 0xffff for a spare, 
> or 0xfffe for faulty.  */
>       |                 ^~~~~~~~~
> disk/mdraid1x_linux.c:127:33: note: defined here ‘sb’
>   127 |       struct grub_raid_super_1x sb;
>       |

Code in question seems to be:

      if (grub_disk_read (disk, sector,
                          (char *) &sb.dev_roles[grub_le_to_cpu32 
(sb.dev_number)]
                          - (char *) &sb,
                          sizeof (role), &role))
        return NULL;

Normally, it should be fixed by using `grub_uint16_t[]` instead of 
`grub_uint16_t[0]`, but I haven’t found out where yet.


Kind regards,

Paul