[syslinux] isolinux source, detecting 8086 cpu

[Michael K Ter Louw]

Hi, I was looking through isolinux and noticed you had trouble detecting
8086 cpu's.  I have some experience with this so I thought you might
like some different info.  The behavior of the "push sp" instruction
changed after the 8086 to pushing sp before updating it.  I've included
a snippet of one of my bootstraps in case you want to use it (or just
want to understand better).  I also use a different method for detecting
the 386.  Basically I just attempt a 32-bit instruction and hook the
invalid opcode exception.  Hope this helps. :)

Mike


	push	sp
; save sp
	pop		ax
; ax = saved sp
	cmp		ax, sp
; 8086 modifies sp before pushing
	je 		.not_8086
; processor is not an 8086
	
;
.invalid_cpu:							;
	mov		si, .err_cpu				; si
points to error message
	jmp		.error_handler				;
display message and reboot
	
;
.not_8086:
;
	mov W	[6 << 2], .invalid_cpu		; store offset of
invalid opcode handler
	mov		[(6 << 2) + 2], cs			; store
segment of handler
	xor		eax, eax
; test a 32-bit instruction