Create LinuxAPI_18_fork.asm

Author: XlogicX

ASM_x86/LinuxAPI_18_fork.asm

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+; Mostly an example of the fork API, also uses waitpid and execve for better illustration
+; API calls found in this example program:
+; 	fork, waitpid, execve, write, exit
+; High level description of what theis example program does:
+;	Forks
+;	The parent waits for the child and prints a message when done
+;	prints a message and then executes /bin/ps before returning to parent
+
+
+section .text
+global _start
+
+_start:
+
+; Fork
+;------------------------------------------------------------------------------
+	mov 	eax, 2			; fork()
+    int    	0x80
+	    ; Return on failure is -1
+	    ; Return is 0 if child
+	    ; Return is the pid of child if parent
+    cmp		eax, 0			; Compare to child value
+    jz		child			; Go to child process if so
+
+parent:						; otherwise your the parent with pid of child in eax
+	; Wait for child
+	mov		ebx, eax		; Get that pid into ebx, we need it
+	mov		eax, 7			; waitpid()
+	int		0x80
+
+	; Let STDOUT know you're the parent
+	mov		eax, 4			; write()
+	mov		ebx, 1			; STDOUT
+	mov		ecx, parent_msg	; Message for parent
+	mov		edx, 11			; Message length
+	int		0x80 
+
+	; Bail
+	jmp		exit
+
+child:
+	; Let STDOUT know you're the child
+	mov		eax, 4			; write()
+	mov		ebx, 1			; STDOUT
+	mov		ecx, child_msg	; Message for child
+	mov		edx, 10			; Message length
+	int		0x80
+
+	; Execute a shell command
+	mov		eax, 11			; execve()
+	mov		ebx, command	; command to execute
+	mov		ecx, args		; arguments (none)
+	mov		edx, env		; enviornment (none)
+	int 	0x80
+
+	; Bail (but parent waiting on this)
+	jmp		exit
+
+
+; Exit
+;------------------------------------------------------------------------------
+	exit:
+	mov 	eax, 1				; exit
+	mov		ebx, 0				; null argument to exit
+	int 	0x80
+
+section .data
+	child_msg db 'Ima Child', 0x0a
+	parent_msg db 'Ima Parent', 0x0a
+	command	db '/bin/ps', 0x00
+	args dd command
+	env db 0x00,0x00,0x00,0x00