#
# Code to detect an easter-egg with AMD64 processors
# 
#  assemble/link with "as -o hammer.o hammer.s ; ld -o hammer hammer.o"
#
#  by Vince Weaver <vince@deater.net>
#  Easter egg pointed out by Adam Sulmicki <adam@CFAR.UMD.EDU>
#
# Writing 64-bit assembly is amazingly easy [as in similar to x86]
# for the amd64, which is comforting and also somehow perversely 
# evil at the same time.
#


# Sycscalls
.equ SYSCALL_EXIT,     1
.equ SYSCALL_WRITE,    4

.equ STDOUT,1

	.globl _start	
_start:	

	mov	$0x8fffffff,%eax	# Load magic value into ax
	cpuid				# call cpuid
	
	push 	%edx			# store the result
	push	%ecx			# to memory
	push	%ebx
	push	%eax
	
	mov	$string, %rbx		# point to a string
	
	push	$4	     		# cycle 4 times writing to string
	pop	%rcx
move_to_mem:	
	pop	%eax
	mov	%eax,(%rbx)
	add	$4,%ebx
	loop	move_to_mem
		
	movb	$'\n',(%rbx)	        # Tack a linefeed onto the end
	
	mov	$string, %rcx
	call	write_stdout
	

	#================================
	# Exit
	#================================
exit:
        xor     %ebx,%ebx
	xor	%eax,%eax
	inc	%eax	 		# put exit syscall number (1) in eax
        int     $0x80             	# and exit


	#================================
	# WRITE_STDOUT
	#================================
	# ecx has string
	# eax,ebx,ecx,edx trashed
write_stdout:
	push    %rdx
	push	$SYSCALL_WRITE		# put 4 in eax (write syscall)
	pop     %rax     		# in 3 bytes of code
	
	cdq   	      			# clear edx
	
	xor	%ebx,%ebx		# put 1 in ebx (stdout)
	inc	%ebx			# in 3 bytes of code
	
                       # another way of doing this:    lea 1(%edx), %ebx

str_loop1:
	inc	%edx
	cmpb	$0,(%rcx,%rdx)		# repeat till zero
	jne	str_loop1

	int	$0x80  			# run the syscall
	pop	%edx
	ret


#============================================================================
#	section .bss
#============================================================================
.bss

.lcomm  string, 18