Shutdown the computer using assembly

Question

How can I shutdown the computer using only assembly code?

Answer 1

take a look here and here

Answer 2

Call the ExitWindowsEx API function in kernel32.dll

Answer 3

You need to say what processor family it is and which OS you're using. Also what privileges your code is running under - if it's kernel code then it has more privileges than user code.

Assuming you're using some member of the Windows NT family (including XP or Vista) on an Intel x86 family CPU, and your code is normal (userspace) code, then... you need to call the Windows built-in function to do this. You can't just execute some magic sequence of assembly.

Even if you could just execute some magic sequence of assembly, you wouldn't want to - you almost certainly want to give the OS chance to write data from the disk cache to disk, and do other graceful-shutdown stuff.

If you're writing your own OS for x86, then you need to look at the ACPI (or APM) specs. If GPL code is OK, then the relevent Linux kernel routines are here (ACPI) and here (APM).

Answer 4

In Linux read reboot(2).

sources files of interest:

kernel/sys.c kernel/exit.c and arch/x86/kernel/apm.c

not a complete answer but i think it's a good start. I'll have to read my BIOS machine code to see what they do. but this part is machine specific. maby if you know wich IC contol power on your motherboard you can figure out wich IO port, register and command you need. then setup proper board/devices states and then issue command to turn the power off.

BIOS manage power via INT 15h ah=53h ( so called Advanced Power Management aka APM ) function al=07 used in Linux is the set power state cmd. parameters bx=0001h mean all devices and cx=0003k mean stop.

Answer 5

From arch/x86/kernel/amp.c

/**
 * apm_power_off - ask the BIOS to power off
 *
 * Handle the power off sequence. This is the one piece of code we
 * will execute even on SMP machines. In order to deal with BIOS
 * bugs we support real mode APM BIOS power off calls. We also make
 * the SMP call on CPU0 as some systems will only honour this call
 * on their first cpu.
 */

static void apm_power_off(void)
{
 unsigned char po_bios_call[] = {
  0xb8, 0x00, 0x10, /* movw  $0x1000,ax  */
  0x8e, 0xd0,  /* movw  ax,ss       */
  0xbc, 0x00, 0xf0, /* movw  $0xf000,sp  */
  0xb8, 0x07, 0x53, /* movw  $0x5307,ax  */
  0xbb, 0x01, 0x00, /* movw  $0x0001,bx  */
  0xb9, 0x03, 0x00, /* movw  $0x0003,cx  */
  0xcd, 0x15  /* int   $0x15       */
 };

 /* Some bioses don't like being called from CPU != 0 */
 if (apm_info.realmode_power_off) {
  set_cpus_allowed_ptr(current, cpumask_of(0));
  machine_real_restart(po_bios_call, sizeof(po_bios_call));
 } else {
  (void)set_system_power_state(APM_STATE_OFF);
 }
}