nasm calling subroutine from another file

Question

I'm doing a project that attaches a subroutine that I wrote to a main file included by the teacher. He gave us the instructions for making our subroutine global but apparently I'm an idiot. The two asm files are in the same folder, I'm using nasm -f elf -g prt_dec.asm and ld prt_dec and then doing the same for main.asm. Here's the relevant code in the main.asm:

    SECTION .text                   ; Code section.
global  _start                  ; let loader see entry point
extern  prt_dec

_start:
mov     ebx, 17
mov     edx, 214123
mov     edi, 2223187809
mov     ebp, 1555544444


mov     eax, dword 0x0
call    prt_dec
call    prt_lf

The line call prt_dec throws "undefined reference to prt_dec" when i use ld main.o

Here's the a code segment from my prt_dec.asm:

    Section .text
    global prt_dec
    global _start

start:
prt_dec:
      (pushing some stuff)
L1_top:
(code continues)

Answer 1

You want to call a routine in another asm file or object file? if you are Assembling prt_dec.asm and are linking multiple asm files to use in your main program, here is a sample, 2 asm files Assembled and linked together... * NOTE * hello.asm *DOES NOT * have a start label!

Main asm file: hellothere.asm

sys_exit    equ 1

extern Hello 
global _start 

section .text
_start:
    call    Hello

    mov     eax, sys_exit
    xor     ebx, ebx
    int     80H

Second asm file: hello.asm

sys_write   equ 4
stdout      equ 1

global Hello

section .data
szHello     db  "Hello", 10
Hello_Len   equ ($ - szHello)

section .text
Hello:
        mov     edx, Hello_Len
        mov     ecx, szHello
        mov     eax, sys_write
        mov     ebx, stdout
        int     80H   
    ret

makefile:

APP = hellothere

$(APP): $(APP).o hello.o
    ld -o $(APP) $(APP).o hello.o

$(APP).o: $(APP).asm 
    nasm -f elf $(APP).asm 

hello.o: hello.asm
    nasm -f elf hello.asm

Now, if you just want to separate your code into multiple asm files, you can include them into your main source: with %include "asmfile.asm" at the beginning of your main source file and just assemble and link your main file.