Each code module in your shared library should define the GOT as an external symbol:

extern _GLOBAL_OFFSETTABLE ; in ELF
extern __GLOBAL_OFFSETTABLE ; in BSD a.out

At the beginning of any function in your shared library which plans to access your data or BSS sections, you must first calculate the address of the GOT. This is typically done by writing the function in this form:

func: push ebp
mov ebp,esp
push ebx
call .get_GOT
.get_GOT:
pop ebx
add ebx,_GLOBAL_OFFSETTABLE+$$-.get_GOT wrt ..gotpc

    ; the function body comes here 

    mov     ebx,[ebp-4] 
    mov     esp,ebp 
    pop     ebp 
    ret

Quick how to on nasm