Unable to compile program：CMach-O 64-bit format does not support 32-bit absolute addresses-CodePudding

I want to study NASM x86 assembly language on my macOS Monterey 12.1.

MY code is as below:

SECTION .data
msg     db      'Hello World!', 0Ah     ; assign msg variable with your message string
 
SECTION .text
global  _start
 
_start:
 
    mov     edx, 13     ; number of bytes to write - one for each letter plus 0Ah (line feed character)
    mov     ecx, msg    ; move the memory address of our message string into ecx
    mov     ebx, 1      ; write to the STDOUT file
    mov     eax, 4      ; invoke SYS_WRITE (kernel opcode 4)
    int     80h

After I input the command:

nasm -f macho64 -o helloworld.o helloworld.asm

I will get:

helloworld.asm:15: error: Mach-O 64-bit format does not support 32-bit absolute addresses

Is there any solutions to solve it?

CodePudding user response：

The addressing space used for macho64 is x86-64, so the registers are a different size which can handle 64-bit addressing. ECX for example is 32 bits, and you try to load it with a 64 bit address, causing the error.

This is what the Hello World code looks like for x86-64:

global _main

SECTION .data
msg     db      'Hello World!', 0x0A ; assign msg variable
 
SECTION .text
 
_main:
 
    mov     rdx, 13          ; number of bytes to write - one for each letter plus LF char.
    lea     rsi, [rel msg]   ; move the memory address of our message string into rsi
    mov     rdi, 1           ; write to the STDOUT file
    mov     rax, 0x2000004   ; invoke SYS_WRITE (kernel opcode 4)
    syscall
    
    mov     rax, 0x2000001   ; exit
    mov     rdi, 0
    syscall

Compiled, linked, executed:

% nasm -f macho64 -o helloworld.o helloworld.asm
% ld helloworld.o -o hello -lSystem -L/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/lib
% ./hello
Hello World!