Linking trouble with Grubs' example kernel

[gablooky]

I've been experimenting with using the example multiboot 'kernel' that comes with Grub (the files are boot.S, kernel.c and multiboot.h, available here: http://savannah.gnu.org/cgi-bin/viewcvs/grub/grub/docs/) as a basis for my own developments, but I've snagged on a fairly simple thing. I've moved the printf, putchar, atoi and cls functions in the kernel.c file to a stdio.c file and written a header to accompany it. I include the header in the kernel.c file to access the functions, compile the lot with these:

   gcc -I. -c boot.S
   gcc -I. -fno-builtin -c stdio.c
   gcc -I. -fno-builtin -c kernel.c
   ld boot.o stdio.o kernel.o -o kernel -nostdlib -N -Ttext 0x100000

But I get this when compiling and ld executes:
   [stdio.c]
   stdio.c:11: warning: `cls' defined but not used

   [kernel.c]
   stdio.h:33: warning: `cls' used but never defined
   stdio.h:34: warning: `itoa' declared `static' but never defined
   stdio.h:35: warning: `putchar' declared `static' but never defined

   kernel.o(.text+0x7): In function 'cmain':
   : undefined reference to 'cls'

Any ideas what this is?

[Moose]

function cls is now referenced
you need to have something like global cls in the file holding it, and another one, extern cls maybe, in the file referencing it.

Moose.