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Rooted by: Netwide Assembler Hello World
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  • Description

    The original code used 32-bit system call. I refactored the code to use 64-bit system call.

     Code 
    global say_hello
section .text
say_hello:
  mov rax, 1 ; system call for write (for Linux 64)
  mov rdi, 1 ; file handle 1 is STDOUT
  lea rsi, [rel message] ; memory address of output buffer
  mov rdx, msgLen ; size of output buffer in bytes
  syscall ; invoke OS to do the write
  ret ; Return to the caller

section .data ; Read-only data
message db "Hello World!", 10 ; message = "Hello World!\n"
msgLen equ $-message ; msgLen = strlen(message)
     Test Cases 
    #include <criterion/criterion.h>

void say_hello();

Test(say_hello, should_print_hello_world) {
  say_hello();
  cr_assert(1);
}
    View Run Output
  • Code
    • global say_hello
    • section .text
    • say_hello:
    • mov eax, 4 ; system call for write (for Linux)
    • mov ebx, 1 ; file handle 1 is STDOUT
    • mov ecx, message ; memory address of output buffer
    • mov edx, msgLen ; size of output buffer in bytes
    • int 0x80 ; invoke OS to do the write
    • mov rax, 1 ; system call for write (for Linux 64)
    • mov rdi, 1 ; file handle 1 is STDOUT
    • lea rsi, [rel message] ; memory address of output buffer
    • mov rdx, msgLen ; size of output buffer in bytes
    • syscall ; invoke OS to do the write
    • ret ; Return to the caller
    • section .data ; Read-only data
    • message db "Hello World!", 10 ; message = "Hello World!\n"
    • msgLen equ $-message ; msgLen = strlen(message)