Differences of Mac and Linux Assembly Language

This example demo the differences of Assembly Language in Mac and Linux for x86_64 architecture. For arm64 assembly language differences, see these 2 codes in github. https://github.com/below/HelloSilicon and https://github.com/Apress/programming-with-64-bit-ARM-assembly-language

The assembly code has read and write functions. The differences of Linux and macOS are using the %ifdef MACHO64 which is the code for macOS %else is for Linux. For example the system call numbers are different and macho64 cannot use absolute addressing.

01_05-solution1.asm   Select all

; solution - answer to Chapter 1 challenge ; Read decimal input, add 10, generate output section .data prompt db "How old are you? ",0 result db "In 10 years, you will be ",0 newline db 10 ; newline, \n ten dq 10 ; used for multiplication size equ 4 ; buffer size azero equ 0x30 ; ASCII zero, '0' anine equ 0x39 ; ASCII nine, '9' nullchar equ 0x0 ; null terminator, \0 STDIN equ 0 ; standard input device STDOUT equ 1 ; standard output device %ifdef MACHO64 SYS_read equ 0x2000003 ; system call to read input macOS SYS_write equ 0x2000004 ; system call to write message macOS SYS_exit equ 0x2000001 ; system call to terminate program macOS %else SYS_read equ 0 ; system call to read input SYS_write equ 1 ; system call to write message SYS_exit equ 60 ; system call to terminate program %endif EXIT_OK equ 0 ; OK exit status TENS dq 10000 ; tens table dq 1000 dq 100 dq 10 dq 1 ; uninitialized data section .bss input_buf resb size ; age input buffer age resq 1 ; binary age value output_buf resb size ; modified age string ; code section .text global _start _start: ; output the prompt mov rsi, prompt ; prompt string output call print_string ; read input mov rbx, input_buf ; age string storage call input ; translate decimal string to binary mov rsi, input_buf ; where string value is stored call decimal2binary cmp al, 0 ; check for bogus input jz start_exit ; bail if so add rax, 10 ; add 10 to the value %ifdef MACHO64 mov [rel age], rax ; store result %else mov [age], rax ; store result %endif ; output the final prompt mov rsi, result ; First part of the string call print_string ; convert the value in 'age' to a string %ifdef MACHO64 mov rbx, [rel age] ; value %else mov rbx, [age] ; value %endif mov rsi, output_buf ; modified string call binary2decimal ; output the age-value string mov rsi, output_buf call print_value ; use this function to strip leading ; zeros ; exit program start_exit: mov rax, SYS_exit ; system exit call mov rdi, EXIT_OK syscall ; end of _start ; functions ;--------; ; output a null terminated string in rsi print_string: cmp byte [rsi], nullchar ; end-of-string test je print_string_exit ; bail on null char mov rdx, 1 ; number of characters to write mov rdi, STDOUT ; to standard output mov rax, SYS_write ; Write characters(s) syscall inc rsi ; next character jmp print_string ; keep looping print_string_exit: ret ;--------; ; grab standard input in the buffer in rbx input: mov r12, 1 ; buffer position read_char: mov rsi, rbx ; input char storage mov rdx, 1 ; character count mov rdi, STDIN ; from standard input mov rax, SYS_read ; read into rsi (rbx) syscall cmp byte [rbx], 10 ; is character read newline? je input_exit ; finish, don't store newline inc rbx ; next byte in the buffer inc r12 ; up the character count cmp r12, size ; check buffer size jl read_char ; keep looping if room ; otherwise, fall through: input_exit: mov byte [rbx], 0 ; cap the string ret ;--------; ; translate string input at rsi into binary value in rax ; if garbage input, returned value is zero decimal2binary: mov rax, 0 ; initial value d2b0: mov rbx, 0 ; initialize bax mov bl, byte [rsi] ; character, digit ; filter out non-digit values cmp bl, azero jl d2b_exit ; exit on character < '0' cmp bl, anine jg d2b_exit ; exit on character > '9' sub bl, azero ; convert from ASCII to binary %ifdef MACHO64 mul qword [rel ten] ; multiply rax by 10 %else mul qword [ten] ; multiply rax by 10 %endif add rax, rbx ; add new value inc rsi ; next char cmp byte [rsi], nullchar ; end of string? jnz d2b0 ; if not, keep looping d2b_exit: ret ;--------; ; generate a string at rsi representing the value in rbx binary2decimal: mov rdi, TENS ; reference comparision table ; values here are subtracted from ; rbx to calculate base 10 digits b2d0: xor al, al ; zero out al; al stores the character mov rcx, [rdi] ; get power of ten b2d1: or al, al ; clear carry bit (for jb) sub rbx, rcx ; subtract power of ten jb b2d2 ; if <0, the count in al is the value inc al ; decimal value++ jmp b2d1 ; keep subtracting b2d2: add al, azero ; make al ASCII add rbx, rcx ; recover from last subtraction mov byte [rsi], al ; add character to the string inc rsi ; next string position add rdi, 8 ; next value in TENS table cmp rcx, 1 ; end of table? jnz b2d0 ; loop again if not mov byte [rsi], nullchar ; terminate string ret ;--------; ; output a null-terminated string in rsi ; strip any leading zero characters print_value: cmp byte [rsi], nullchar ; always check for null char je print_value_exit ; and exit; string empty cmp byte [rsi], azero ; ASCII zero jne pv1 ; if the char isnt zero, continue inc rsi ; otherwise, check next character jmp print_value ; keep looping pv1: ; process the remaining non-zero digits cmp byte [rsi], nullchar ; null char terminator je print_value_exit ; if true, exit mov rdx, 1 ; chars to write mov rdi, STDOUT ; standard output mov rax, SYS_write ; write characters syscall inc rsi ; next char jmp pv1 ; loop until null char print_value_exit: mov rsi, newline ; newline defined as \n mov rdx, 1 ; write 1 char mov rax, SYS_write ; write character mov rdi, STDOUT ; to standard output syscall ret ; end

makefile for Linux

makefile   Select all

#makefile for Linux filename_prefix := 01_05- src_files := $(wildcard *.asm) obj_files := $(src_files:.asm=.o) prog_files := $(subst $(filename_prefix), ,$(basename $(src_files))) all: $(prog_files) $(prog_files): % : $(filename_prefix)%.o ld -o $@ $< -arch x86_64 $(filter %.o,$(obj_files)): %.o : %.asm nasm -g -f elf64 $< -o $@ .PHONY: clean clean: rm -f $(obj_files) $(prog_files)

makefile for macOS

makefile    Select all

#makefile for macOS filename_prefix := 01_05- src_files := $(wildcard *.asm) obj_files := $(src_files:.asm=.o) prog_files := $(subst $(filename_prefix), ,$(basename $(src_files))) all: $(prog_files) $(prog_files): % : $(filename_prefix)%.o ld -no_pie -macosx_version_min 11.0.0 -o $@ $< -lSystem -syslibroot `xcrun -sdk macosx --show-sdk-path` -e _start -arch x86_64 codesign --entitlement entitlements --force -s - $@ $(filter %.o,$(obj_files)): %.o : %.asm nasm -g -f macho64 -dMACHO64 $< -o $@ .PHONY: clean clean: rm -f $(obj_files) $(prog_files)

In order to debug in macOS, codesign entitlement file is needed.

entitlements   Select all

<?xml version="1.0" encoding="UTF-8"> <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"> <plist version="1.0"> <dict> <key>com.apple.security.get-task-allow</key> <true/> </dict> </plist>

For linux, it is required to install these packages "sudo apt install build-essentials nasm gdb lldb"

For macOS, it is required to install Xcode and Command Line Tools and Homebrew package "brew install nasm"
It is possible to build, run and debug x86_64 program on M1 Macs, if Rosetta is installed.