CODEWITHSUNDEEP
assemblyx86x86-64nasmmacos-big-sur
not_here_to_play
not_here_to_play

Reputation: 158

compiling assembly code on mac os big sur (x8664)

Hello I would like to begin coding a little in assembly.

I have installed the latest nasm version (2.15). I followed all the steps and I set up nasm correctly.

Now I wanted to run my first hello world program using:

nasm -f macho64 hello.asm

or also

nasm -fmacho64 hello.asm && ld hello.o && ./a.out

or also

nasm -f macho64 hello.asm -o hell.o  && ld -e _main -macosx_version_min 10.8 -arch x86_64 hello.o -lSystem

and none of these work. Actually nasm -f macho64 hello.asm does not throw errors but does not print to the screen either. This is the code I copied and pasted to see if everything worked:

; Writes "Hello, World" to the console using only system calls. Runs on 64-b
; To assemble and run:
;
;     nasm -fmacho64 hello.asm && ld hello.o && ./a.out
; --------------------------------------------------------------------------

          global    start

          section   .text
start:    mov       rax, 0x02000004         ; system call for write
          mov       rdi, 1                  ; file handle 1 is stdout
          mov       rsi, message            ; address of string to output
          mov       rdx, 13                 ; number of bytes
          syscall                           ; invoke operating system to do 
          mov       rax, 0x02000001         ; system call for exit
          xor       rdi, rdi                ; exit code 0
          syscall                           ; invoke operating system to exi

          section   .data
message:  db        "Hello, World", 10      ; note the newline at the end

and this is the error that I get from running the other two commands:

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

Could someone help me and tell me how to set up everything correctly. As I said the command nasm -f macho64 hello.asm does not give any error but it does not print anything out but it should, so either it is a problem with the actual code or it is a problem with nasm itself. Could you also give me a brief explanation of why the other two commands fail. Thanks in advance :)

Upvotes: 0

Views: 507

Answers (1)

AKX
AKX

Reputation: 168967

You'll just need to adjust your code a little and link it with the correct switches (see _main instead of start):

          global    _main

          section   .text
_main:    mov       rax, 0x02000004         ; system call for write
          mov       rdi, 1                  ; file handle 1 is stdout
          mov       rsi, message            ; address of string to output
          mov       rdx, 13                 ; number of bytes
          syscall                           ; invoke operating system to do 
          mov       rax, 0x02000001         ; system call for exit
          xor       rdi, rdi                ; exit code 0
          syscall                           ; invoke operating system to exi

          section   .data
message:  db        "Hello, World", 10      ; note the newline at the end

$ nasm -fmacho64 hello.asm && ld -e _main hello.o -lSystem && ./a.out
Hello, World
$

Upvotes: 1

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