macOS aarch64 syscall

macos_aarch64_syscalls.c

i64 syscall1(i64 sys_num, i64 a0) {
  i64 ret;
  __asm__ volatile (
    "mov x16, %[sys_num]\n"
    "mov x0, %[a0]\n"
    "svc 0x80\n"
    "mov %0, x0\n"
    : "=r" (ret)
    : [sys_num] "r" (sys_num), [a0] "r" (a0)
    : "x16", "x0"
  );
  return ret;
}

i64 syscall2(i64 sys_num, i64 a0, i64 a1) {
  i64 ret;
  __asm__ volatile (
    "mov x16, %[sys_num]\n"
    "mov x0, %[a0]\n"
    "mov x1, %[a1]\n"
    "svc 0x80\n"
    "mov %0, x0\n"
    : "=r" (ret)
    : [sys_num] "r" (sys_num), [a0] "r" (a0), [a1] "r" (a1)
    : "x16", "x0", "x1"
  );
  return ret;
}

i64 syscall3(i64 sys_num, i64 a0, i64 a1, i64 a2) {
  i64 ret;
  __asm__ volatile (
    "mov x16, %[sys_num]\n"
    "mov x0, %[a0]\n"
    "mov x1, %[a1]\n"
    "mov x2, %[a2]\n"
    "svc 0x80\n"
    "mov %0, x0\n"
    : "=r" (ret)
    : [sys_num] "r" (sys_num), [a0] "r" (a0), [a1] "r" (a1), [a2] "r" (a2)
    : "x16", "x0", "x1", "x2"
  );
  return ret;
}

#define STDIN_FILENO    0
#define STDOUT_FILENO   1
#define STDERR_FILENO   2

#define SYS_exit        1
#define SYS_write       4

void start(void) {
  const char *msg = "Hello, World!\n";
  syscall3(SYS_write, STDOUT_FILENO, (i64)msg, 14);
  syscall1(SYS_exit, 0);
}