basic asm learning
Well, I have to say learn some ASM is mandatory while inspecting linux kernel code, hence I give a sample of simply write an asm code.
There are six registers that are used for the arguments that the system call takes.
The first argument goes in EBX, the second in ECX, then EDX, ESI, EDI, and finally EBP.
mov eax,1 ; The exit syscall number
mov ebx,0 ; Have an exit code of 0
int 80h ; Interrupt 80h, the thing that pokes the kernel and says, "Yo, do this"Hello world sample
section .data
hello: db 'Hello world!',10 ; 'Hello world!' plus a linefeed character
helloLen: equ $-hello ; Length of the 'Hello world!' string
; (I'll explain soon)
section .text
global _start
_start:
mov eax,4 ; The system call for write (sys_write)
mov ebx,1 ; File descriptor 1 - standard output
mov ecx,hello ; Put the offset of hello in ecx
mov edx,helloLen ; helloLen is a constant, so we don't need to say
; mov edx,[helloLen] to get it's actual value
int 80h ; Call the kernel
mov eax,1 ; The system call for exit (sys_exit)
mov ebx,0 ; Exit with return code of 0 (no error)
int 80h