data starts at 00404000h
     bVal BYTE ?
     wVal WORD ?
     dVal DWORD ?
     dVal2 DWORD ?


00404000h   _     bVal
00404001    _     wVal
00404002    _     wVal
00404003    _     dVal
00404004    _     dVal
00404005    _     dVal
00404006    _     dVal
00404007    _     dVAl2
00404008    _     dVAl2
00404009    _     dVAl2
0040400A    _     dVAl2


[mweeks@gsuad.gsu.edu@snowball ~]$ cat offset.asm
; Assemble:	  nasm -f elf64 offset.asm
; Link:		  gcc offset.o -o offset

; This is adapted for NASM.

    extern  printf      ; We will use this external function

    section .data       ; Data section, initialized variables

mystr:    db "%x", 10, 0   ; String format to use (decimal), followed by NL

bVal:     db 0
wVal:     dw 0
dVal:     dd 0
dVal2:    dd 0

    section .text
    global main
main:
   xor rax, rax          ; A = 0

     mov rsi,bVal
   mov   rax, 0
   mov   rdi, mystr   ; 
   call  printf

     mov rsi,wVal
   mov   rax, 0
   mov   rdi, mystr   ; 
   call  printf

     mov rsi,dVal
   mov   rax, 0
   mov   rdi, mystr   ; 
   call  printf

     mov rsi,dVal2
   mov   rax, 0
   mov   rdi, mystr   ; 
   call  printf

   mov  rax, 0
   ret
[mweeks@gsuad.gsu.edu@snowball ~]$ nasm -f elf64 offset.asm
[mweeks@gsuad.gsu.edu@snowball ~]$ gcc offset.o -o offset
[mweeks@gsuad.gsu.edu@snowball ~]$ ./offset
601038
601039
60103b
60103f
[mweeks@gsuad.gsu.edu@snowball ~]$ 




unsigned int myDouble = 0x12345678;

myDouble + 1

can access a byte instead of the whole 32 bits