NASM Program error

Question

Created Jan ’23

Replies 1

Boosts 0

Participants 2

Hi I tried to create a asm code which will just print "My name" and "id".

; To assemble and run:
; nasm -f bin -o boot.bin boot.asm
; dd if=boot.bin of=/dev/sdb bs=512 count=1
; (replace /dev/sdb with the appropriate device file for your USB drive)

section .text
    global _start

_start:
    ; Print "Hello, my name is "
    mov rax, 0x1301
    mov rbx, 0x0003
    mov rcx, 22
    mov rdx, msg ;
    int 0x10    ;call the kernel

    ; Print " and my roll number is "
    mov rax, 0x1301
    mov rbx, 0x0003
    mov rcx, 23
    mov rdx, msg2 
    int 0x10

    ; Print "123456"
    mov rax, 0x1301
    mov rbx, 0x0003
    mov rcx, 6
    mov rdx, msg3
    int 0x10

    ; Wait for a key press
    mov rax, 0x16
    int 0x10

    ; Return to boot loader
    mov rax, 0x0000
    int 0x18

section .data
    msg db "Hello, my name is ManuJain " ;message is kind of a variable, db - define bits
    msg2 db " My College number is  "
    msg3 db "1234567"

this is command

ld test.o -o test -demangle -dynamic -macosx_version_min 11.0 -L/usr/local/lib -syslibroot /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk -lSystem -no_pie

When I running this on terminal I am getting this message

Undefined symbols for architecture x86_64:
  "_main", referenced from:
     implicit entry/start for main executable
ld: symbol(s) not found for architecture x86_64

Boost

Answer 1

DTS Engineer OP

Apple

Jan ’23

When I running this on terminal I am getting this message

That isn’t going to work. The assembly language code you posted looks like it was written to run in the MS-DOS environment. Specifically:

Its entry point is the first instruction.
It uses int instructions to call the OS.

macOS command-line tools don’t work that way. Specifically:

Their entry point is defined by a Mach-O load command (LC_MAIN) which usually points to start which then bounces through to main.
They call the OS by calling functions in libSystem, accessed using the dynamic linker (dyld).

You need to decide on your path forward here:

If you want to run your command from Terminal, you’ll have to write code for that environment.
If you want to run your code in the MS-DOS environment, you’ll need to actually do that, but also adjust your build system to not create a Mach-O.

I should stress that both of these are hard. I don’t have any useful info to share about MS-DOS programming but, with regards that first option, writing a useful macOS command-line tool using only assembly language is a serious challenge. If you want to play around with assembly language, it’s much easier to write your main function in C and then have it call your assembly language function. That allows you to focus on the assembly language rather than get distracted by packaging.

For example:

% cat main.c
#include <stdio.h>

extern void test();

int main(int argc, char ** argv) {
    printf("will call `test`\n");
    test();
    printf("did call `test`\n");
    return 0;
}
% cat test.s
.text

    .globl _test

_test:
    ret
% clang main.c test.s
% ./a.out            
will call `test`
did call `test`

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