41 lines
2.1 KiB
NASM
41 lines
2.1 KiB
NASM
; nah it's pretty easy.
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; take a look in this hello world i made with assembly x86_64 on linux, i recommend to copy and paste
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; it in vscode or other code editor to better understand it, use the .asm
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; extension and compile it using NASM and GCC using the following commands:
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; nasm -f elf64 hello.asm -o hello.o
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; gcc hello.o -o hello -no-pie
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; to run:
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; ./hello
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; i highly recommend the "ASM Code Lens" if you're using vscode.
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; now here's the code with explanations:
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global _start ; declaring the "main function"
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section .rodata ; when "variables" is, rodata means that the variables will NOT change
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msg: db "hello, assembly", 0xA ; msg is the variable name, "db" is define byte, which in our case is that string,
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; 0xA is a hex representation for newline character (/n)
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msglen: equ $ - msg ; here we calculate the string "msg" length, as equ being "equate" - that defines a constant,
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;'$' being the location counter - is our current address, basically it means "how many bytes have pass since here"
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section .text ; this basically says that the code the cpu will execute is above, .text means executable code (instructions)
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_start: ; now this is the main function, here we want to make some syscalls to the OS, for print the message,
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;in our case is for Linux, that follows the following parameter structure: syscall number (RAX),
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;and take up to 6 arguments (RDI, RSI, RDX, R10, R8, R9 - yeah, the register R8 comes before R9),
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;it's cool to know, but most of the time you'll only need the arguments required by the syscall
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mov rax, 1 ; moving constant 1 to register RAX, it means the sys_write linux's syscall
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mov rdi, 1 ; moving 1 to RDI, means that the file descriptor is stdout (default linux output)
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;others include stdin (0, input) and stderr (2, error output) - this is the first argument
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mov rsi, msg ; moving the string address (buffer) to rsi, second argument
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mov rdx, msglen ; moving the string size to rdx, it says how many bytes msg will use
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syscall ; finally, we call system.
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; here has another syscall to exit program
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mov rax, 60 ; 60th syscall: sys_exit
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mov rdi, 0 ; exit status, 0 means "no errors"
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syscall ; calling again |