calls.asm

global sys_read
global sys_write
global sys_errno
section .text

generic_syscall_3:
        push ebp
        mov ebp, esp
        push ebx
        mov ebx, [ebp + 8]
        mov ecx, [ebp + 12]
        mov edx, [ebp + 16]
        int 80h
        mov edx, eax
        and edx, 0fffff000h
        cmp edx, 0fffff000h
        jnz .okay
        mov [sys_errno], eax
        mov eax, -1

.okay:
        pop ebx
        mov esp, ebp
        pop ebp
        ret

sys_read:
        mov eax, 3
        jmp generic_syscall_3

sys_write:
        mov eax, 4
        jmp generic_syscall_3

section .bss
sys_errno resd 1

greet3.c

int sys_write (int fd, const void *buf, int size);
static const char dunno[] = "I don't know how to greet you\n";
static const char hello[] = "Hello, dear ";
static int
string_length (const char *s)
{
  int i = 0;
  while (s[i])
    i++;
  return i;
}

int
main (int argc, char **argv)
{
  if (argc < 2)
    {
      sys_write (1, dunno, sizeof (dunno) - 1);
      return 1;
    }
  sys_write (1, hello, sizeof (hello) - 1);
  char *argv0 = argv[0];
  int length = string_length (argv0);
  sys_write (1, argv0, length);
  sys_write (1, "\n", 1);
  return 0;
}
/*
...
Program received signal SIGSEGV, Segmentation fault.
0x080490e8 in main (argc=2, argv=0x6) at greet3.c:22
22	 char *argv0 = argv[0];
*/

start.asm

global _start
extern main
section .text
_start:
        mov ecx, [esp]  ; argc in ecx
        mov eax, [esp]  ;
        add eax, 4  ; argv in eax
        push eax
        push ecx
        call main
        add esp, 8
        mov ebx, eax
        mov eax, 1
        int 80h