Unidefined symbols when building modules

[Lucas Pires Camargo]

Hello,

I am making modifications to the luks module to enable it to use a
personal security device. If the initialization fails, I want the
bootloader to reboot the computer and try again, so (amongst other
things) I added the following function call to grub-core/disk/luks.c :

    if(!env_board_material)
    {
        grub_reboot();
    }

However the compilation fails with the following error:

    [...]
    Makefile:4159: recipe for target 'grub-fstest' failed
    libgrubkern.a(libgrubkern_a-luks.o): In function `luks_recover_key':
    luks.c:(.text+0xea2): undefined reference to `grub_reboot'
    collect2: error: ld returned 1 exit status
    make[2]: *** [grub-fstest] Error 1
    make[2]: Leaving directory '/home/camargo/bluechip/dev/distro-grub'
    Makefile:10904: recipe for target 'all-recursive' failed
    [...]

I don't get it. Isn't grub_reboot supposed to be a kernel symbol? Do I
have to add any dependencies to the module, somewhere? Or could I get
the symbol location dynamically? Any help would be appreciated.

Thanks in advance,
Lucas Camargo