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Subject: PERFORCE change 27475 for review
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http://perforce.freebsd.org/chv.cgi?CH=27475

Change 27475 by jhb@jhb_laptop on 2003/03/27 11:56:17

	First pass at letting BIOS programs read both %CR0 and %CR4
	into any register rather than just %eax.  Unfortunately, boot2
	now overflows by 29 bytes.  Also, this isn't tested.  I'm not
	quite sure how I will test it either. :-(

Affected files ...

.. //depot/projects/smpng/sys/boot/i386/btx/btx/btx.s#4 edit

Differences ...

==== //depot/projects/smpng/sys/boot/i386/btx/btx/btx.s#4 (text+ko) ====

@@ -494,9 +494,9 @@
 		cmpb $0x32,(%esi)		# Is it a RDMSR?
 		je v86rdmsr			# Yes
 		cmpb $0x20,(%esi)		# Is this a
-		jne v86mon.4			#  MOV EAX,CR0
-		cmpb $0xc0,0x1(%esi)		#  instruction?
-		je v86mov			# Yes
+		jne v86mon.4			#  MOV reg,CR[04]
+		testb $0x18,0x1(%esi)		#  instruction?
+		jz v86mov			# Yes
 v86mon.4:	cmpb $0xfa,%al			# CLI?
 		je v86cli			# Yes
 		cmpb $0xfb,%al			# STI?
@@ -527,10 +527,17 @@
 		leal 0x8(%esp,1),%esp		# Discard int no, error
 		iret				# To V86 mode
 #
-# Emulate MOV EAX,CR0.
+# Emulate MOV reg,CR[04].
 #
-v86mov: 	movl %cr0,%eax			# CR0 to
-		movl %eax,0x1c(%ebp)		#  saved EAX
+v86mov: 	movb 0x1(%esi),%bl		# Fetch Mod R/M byte
+		movl %cr0,%eax			# Read CR0
+		testb $0x20,%bl			# Read CR4 instead?
+		jz v86mov.1			# No
+		movl %cr4,%eax			# Read CR4
+v86mov.1:	andl $0x7,%ebx			# Compute offset in
+		shl $2,%ebx			#  frame of destination
+		neg %ebx			#  register
+		movl %eax,0x1c(%ebp,%ebx,1)	# Store CR to reg
 		incl %esi			# Adjust IP
 #
 # Return from emulating a 0x0f prefixed instruction