Question

The following application generates a Segmentation Fault when executed:

.set __NR_reboot, 169
.set LINUX_REBOOT_CMD_POWER_OFF, 0x4321FEDC

.section .text
.globl _start
_start:
   movl $LINUX_REBOOT_CMD_POWER_OFF, %ebx
   movl $__NR_reboot, %eax
   int $0x80

It’s a quite simple application and I must be missing something really obvious. Can someone help me?

It was compiled with:

as shutdown.s -o shutdown.o
ld shutdown.o -o shutdown

EDIT:

Even a simple application that just calls syscall sync() generates a Segmentation Fault:

.set __NR_sync, 36

.section .text
.globl _start
_start:
   movl $__NR_sync, %eax
   int $0x80

   movl $1, %eax         #syscall exit
   movl $0, %eax
   int $0x80

Answer 1

WARNING: remember to sync(2) before calling reboot(2).

The reboot(2) system call takes 4 parameters.You are confusing it with the libc
wrapper.

WARNING: remember to sync(2) before calling reboot(2).

(It actually takes the magic* parameters so that people have to reread the documentation and don’t forget calling sync(2).)

WARNING: Did I say that you have to sync(2) before calling reboot(2)?