BTX halted trying to boot X4100 from disk

[Michiel Boland]

Ok here is a patch for /sys/boot/i386/btx/btx/btx.S that will get X4100s
to boot.

It extends the v86 monitor in the BTX so that it catches INT3 and treats
it like any other interrupt. Not sure if it's a great idea, but it's
better than nothing at this point.

You will need to update the bootblock and /boot/loader since they both
appear to be linking in their own copy of BTX.

--- btx.S.orig	Thu Oct  5 17:30:51 2006
+++ btx.S	Sun Nov 26 16:26:12 2006
@@ -510,6 +510,8 @@
 		je v86popf			# Yes
 		cmpb $0xcd,%al			# INT imm8?
 		je v86intn			# Yes
+		cmpb $0xcc,%al			# INT3?
+		je v86int3			# Yes
 		cmpb $0xcf,%al			# IRET/IRETD?
 		je v86iret			# Yes
 		popl %ebx			# Restore
@@ -651,6 +653,11 @@
 reboot:		orb $0x1,btx_hdr+0x7		# Set the reboot flag
 		jmp exit			# Terminate BTX and reboot

+/*
+ * Emulate INT3
+ */
+v86int3:	movb $3,%al
+		jmp v86intn.1
 /*
  * Emulate INT imm8... also make sure to check if it's int 15/87
  */