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Author: XlogicX

ASM_x86/LinuxAPI_13_setitimer.asm

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+;Example of setting interrupt timers with the setitimer API. API calls found in this example program:
+; 	setitimer, signal, write, exit
+; High level description of what theis example program does:
+;	set up an initial signal handler for our alarm signal
+;	initialize the timer values to 0
+;	Set up timer with 5 second delay with setitimer
+;	Go to infinite loop and wait for signals
+; First handler
+;	prints message
+;	sets up a new handler (second handler)
+;	sets a re-occuring timer for every 2 seconds
+;	returns to infinite loop
+; Second handler
+;	writes a new message
+;	refreshes the signal handler for itself for persistence
+
+section .text
+global _start
+
+_start:
+
+; Set up signal handler to intercept SIGINT (CTRL+C)
+;------------------------------------------------------------------------------
+	mov 	eax, 48			; signal
+    mov 	ebx, 14			; SIGALRM
+    mov		ecx, handle_it	; Address to signal handler when catching sigint
+    int    	0x80
+
+
+; Setup timing values
+;------------------------------------------------------------------------------
+mov word [timeval_interval_s], 0
+mov word [timeval_interval_su], 0
+mov word [timeval_stop_s], 0
+mov word [timeval_stop_su], 0
+
+; Set Timer
+;------------------------------------------------------------------------------
+	mov		word [timeval_stop_s], 5	;Set one-time delay of 5 seconds
+	mov		eax, 104					; setitimer
+	mov		ebx, 0						; type 0, REAL
+	mov		ecx, timeval_interval_s		; stop interval
+	mov		edx, 0
+	int		0x80
+
+; Infinit Loop
+;------------------------------------------------------------------------------
+iloop:
+	jmp iloop
+
+; Handler for Interupt Signal
+;------------------------------------------------------------------------------
+handle_it:
+	mov		eax, 4				; write
+	mov		ebx, 1				; stdout
+	mov		ecx, message
+	mov		edx, 5				; how many bytes to print
+	int		0x80
+	; Set up signal handler to intercept SIGINT (CTRL+C)
+	;------------------------------------------------------------------------------
+		mov 	eax, 48				; signal
+		mov 	ebx, 14				; SIGALRM
+	    mov		ecx, annoying_you	; Address to signal handler when catching sigint
+	    int    	0x80	
+	; Set New Timer (interval of every 2 seconds)
+	;------------------------------------------------------------------------------
+		mov word [timeval_stop_s], 2
+		mov word [timeval_interval_s], 2		
+		mov		eax, 104			; setitimer
+		mov		ebx, 0				; type 0, REAL
+		mov		ecx, timeval_interval_s	; stop interval
+		int		0x80
+	ret								; but for now, go back to our infinite loop
+
+; Handler for Interupt Signal
+;------------------------------------------------------------------------------
+annoying_you:
+	mov		eax, 4				; write
+	mov		ebx, 1				; stdout
+	mov		ecx, message2
+	mov		edx, 14				; how many bytes to print
+	int		0x80
+	; Persist signal handler to intercept SIGINT (CTRL+C)
+	;------------------------------------------------------------------------------
+		mov 	eax, 48				; signal
+		mov 	ebx, 14				; SIGALRM
+	    mov		ecx, annoying_you	; Address to signal handler when catching sigint
+	    int    	0x80		
+	ret								; but for now, go back to our infinite loop
+
+section .data
+	message db 'Ohai', 0x0a
+	message2 db 'Annoying You!', 0x0a
+
+section .bss
+	timeval_interval_s resb 4
+	timeval_interval_su resb 4
+	timeval_stop_s resb 4
+	timeval_stop_su resb 4
+
+; itimerval structure - Each value can be null
+;------------------------------------------------------------------------------
+; timeval interval		- if null, interupt once based on timeval current time
+; timeval current time	- if null, interupt at interval specified by the interval
+
+; timeval structure
+;------------------------------------------------------------------------------
+; sec
+; usec