nasm assembly linux timer or sleep - linux

Question

I'm trying to find a way to make my code wait for two seconds before proceeding. I'm using nasm for Linux in protected mode, so I can only use int 80h. I found a syscall called "alarm" (27) and another called "pause" (29). However, when I try to use those, the program waits and finishes instead of continuing execution. I've also found another syscall, sigaction, which changes the behavior of a signal (so I think it can be used to make the program ignore the signal generated by alarm instead of exiting) but I didn't quite understand how sigaction works. Thanks for any help.
Useful links:http://man7.org/linux/man-pages/man2/alarm.2.html
http://man7.org/linux/man-pages/man2/sigaction.2.html

Answer 1

There is a system call for sleeping the program, sys_nanosleep:
sys_nanosleep : eax = 162, ebx = struct timespec *, ecx = struct timespec *
this struct timespec structure has two members:
;; This is for 32-bit. Note that x86-64 uses 2x 64-bit members
tv_sec ; 32 bit seconds
tv_nsec ; 32 bit nanoseconds
this structure can be declared in nasm as:
section .data
timeval:
tv_sec dd 0
tv_usec dd 0
and then you sets the values and call it as:
mov dword [tv_sec], 5
mov dword [tv_usec], 0
mov eax, 162
mov ebx, timeval
mov ecx, 0
int 0x80
the program then will sleep for 5 seconds. A complete example:
global _start
section .text
_start:
; print "Sleep"
mov eax, 4
mov ebx, 1
mov ecx, bmessage
mov edx, bmessagel
int 0x80
; Sleep for 5 seconds and 0 nanoseconds
mov dword [tv_sec], 5
mov dword [tv_usec], 0
mov eax, 162
mov ebx, timeval
mov ecx, 0
int 0x80
; print "Continue"
mov eax, 4
mov ebx, 1
mov ecx, emessage
mov edx, emessagel
int 0x80
; exit
mov eax, 1
mov ebx, 0
int 0x80
section .data
timeval:
tv_sec dd 0
tv_usec dd 0
bmessage db "Sleep", 10, 0
bmessagel equ $ - bmessage
emessage db "Continue", 10, 0
emessagel equ $ - emessage

Answer 2

With NASM, if you are targeting Linux x86-64, you can simply do something similar to the following:
global _start
section .data
timespec:
tv_sec dq 1
tv_nsec dq 200000000
section .text
_start:
mov rax, 35
mov rdi, timespec
xor rsi, rsi
syscall
...
35 corresponds to the 64-bit system call number for sys_nanosleep (as listed here). If the call is interrupted, the remaining sleep time is written to the memory location pointed by register rsi; in this example rsi is set to 0 to ignore the value if it happens. This call will sleep for tv_sec seconds + tv_nsec nanoseconds, 1.2 seconds in the above code snippet.
More information about this system call can be found in the nanosleep man page.