;
;	File:		PatchProtector.a
;
;	Contains:	a patch to SetTrapAddress and GetTrapAddress that “protects” come-from patches
;
;	Written by:	Darin Adler
;
;	Copyright:	© 1990-1991 by Apple Computer, Inc., all rights reserved.
;
;	Change History (most recent first):
;
;		<11>	 8/28/91	JSM		Cleanup header.
;		<10>	  4/5/91	gbm		dba: Exit via jCacheFlush when setting the trap address. This
;									makes it possible to use copy-back mode on '040's
;		 <9>	  4/3/91	dba		kill the fun
;		 <8>	 3/25/91	dba		VL: get rid of that stupid StripAddress
;		 <7>	  3/4/91	dba		gbm: do a StripAddress for all the 24-bit slobs out there
;		 <6>	12/18/90	gbm		(dba) Use the noPatchProtector conditional to prevent two patch
;									protectors from getting upset at each other.
;		 <5>	 12/5/90	dba		<gbm> disallow come-from patch headers except from people who
;									use the $CXXX form of SetTrapAddress; also check the address
;									passed to SetTrapAddress for validity, by reading the first long
;									word and looking for the come-from header
;		 <4>	  8/2/90	dba		get rid of the MemTop and odd checks
;		 <3>	 5/30/90	dba		add validation for the old address in GetTrapAddress
;		 <2>	  5/1/90	dba		do nothing to this file, just touch it so that people will get
;									the LinkedPatchLib rebuilt
;		 <1>	 3/21/90	dba		fixed some more bugs and checked in for general use
;				  2/1/90	dba		fixed the bug that Ed found
;				 1/30/90	dba		revamped, added [GS]etTrapWordAddress
;				 1/25/90	dba		added a header
;
;	To Do:
;		take into account the number of toolbox traps on each machine in [GS]etTrapWordAddress
;
;	This is a patch to Get/SetTrapAddress that respects come-from patches with a special format.
;
;		bra.s	*+6
;		jmp		OldTrapAddress
;
;	Get and SetTrapAddress will notice patches that begin with this sequence and treat them as
;	“come-from” patches. Instead of changing the address of the trap in the trap table, instead
;	they will change the “old” address in the last come-from patch in the chain.
;
;	This patch needs to be installed before any come-from patches are installed. This can be done
;	by linking it first in the first 'lpch' to be loaded.
;
;	This patch also implements a new variant of [GS]etTrapAddress called [GS]etTrapWordAddress.
;	It takes a whole trap word, and does the right thing, removing the need for N[GS]etTrapAddress.
;

		print push,off
		load 'StandardEqu.d'
		include 'LinkedPatchMacros.a'
		print pop

; opcodes

kBranchOverJMPLOpcode	equ		$6006
kJMPLOpcode				equ		$4EF9

kComeFromHeader			equ		(kBranchOverJMPLOpcode << 16) + kJMPLOpcode

; bits in trap numbers and Set/GetTrapAddress opcodes

TrapNumber				record	0
toolboxBit				equ		11
						endr

TrapAddressOpcode		record	0
newBit					equ		9
toolboxBit				equ		10
						endr

; The following patch has to use $A046 as the trap number instead of _GetTrapAddress.
; This is because it is installed before these patches modify the behavior of [GS]etTrapAddress
; to work properly for full trap words. The trap number is thus used as an “old-style” trap number.
; $A046 is GetTrapAddress, but $A146 (the value of _GetTrapAddress) is interpreted as $A946.

ProtectGetTrap	patchproc $A046,(Plus,SE,II,Portable,IIci,noPatchProtector)
				import TrapAddressBits
				export OldGetTrapAddress

		jsr		TrapAddressBits				; set bits in the trap word
		move	sr,-(sp)					; would do a MOVE CCR, but it is not available on 68000
		bsr.s	OldGetTrapAddress			; call the old GetTrapAddress
		move	(sp)+,ccr					; get condition codes back
		bcs.s	@done						; come-from patches bypass our trickery
@next
		cmp.l	#kComeFromHeader,(a0)		; does this have the come-from header?
		bne.s	@done						; no we are done
		move.l	4(a0),a0					; go on to the next
		bra.s	@next
@done
		moveq	#0,d0						; must zero the result code again
		rts

OldGetTrapAddress
		jmpOld

				endproc

; Since SetTrapAddress looks at the first long word of the previous value of the trap’s address,
; it can be dangerous to call SetTrapAddress on some random value. Later, a correct SetTrapAddress
; might encounter a bus error or address error or some other problem. To avoid this, SetTrapAddress
; looks at the first long word of the new trap address *before* setting the address in the trap table
; or come-from chain. This ensures that the bus error will happen right away.

ProtectSetTrap	patchproc _SetTrapAddress,(Plus,SE,II,Portable,IIci,noPatchProtector)
				import TrapAddressBits
				import OldGetTrapAddress

		move.l	(a0),d2						; get header of trap, and check for bus errors		<5>

		jsr		TrapAddressBits				; set bits in the trap word
		bcs.s	OldSetTrapAddress			; come-from patches bypass our trickery

		cmp.l	#kComeFromHeader,d2			; headers can only be used on come-from patches		<5>
		beq.s	@illegalHeader				; saw a header, so I must system error				<5>

		movem.l	d0-d1/a0,-(sp)				; save trap address, number, and bits
		jsr		OldGetTrapAddress			; call the old GetTrapAddress
		move.l	#0,a1						; no come-froms found yet
@next
		cmp.l	#kComeFromHeader,(a0)+		; does this have the come-from header?
		bne.s	@done						; no we are done
		move.l	a0,a1						; remember this address
		move.l	(a0),a0						; go on to the next
		bra.s	@next
@done
		movem.l	(sp)+,d0-d1/a0				; restore trap address, number, and bits

		cmp.l	#0,a1						; any come-froms found?
		beq.s	OldSetTrapAddress			; no, go do the real SetTrapAddress
		move.l	a0,(a1)						; set the trap address
		move.l	jCacheFlush,-(sp)			; get the cache flush vector						<9>
		rts									; call it, and then return to the trap dispatcher	<9>

@illegalHeader
		move.w	#dsBadPatchHeader,d0		; get error code									<5>
		_SysError							; report it to the unsuspecting user				<5>

OldSetTrapAddress
		jsrOld								; call so we can flush the cache when we return		<9>
		move.l	jCacheFlush,-(sp)			; get the cache flush vector						<9>
		rts									; call it, and then return to the trap dispatcher	<9>

				endproc

TrapAddressBits	proc

; TrapAddressBits
;
;	In:
;		d0.w	trap number
;		d1.w	[GS]etTrapAddress trap word
;
;	Out:
;		d1.w	(modified) [GS]etTrapAddress trap word
;		ccr		CC if it is not a come-from, CS if it is a come-from

		btst	#TrapAddressOpcode.newBit,d1		; is this N[GS]etTrapAddress?
		bnz.s	@notFullWord						; yes, don’t handle it
		btst	#TrapAddressOpcode.toolboxBit,d1	; is this normal [GS]etTrapAddress?
		bz.s	@notFullWord						; yes, don’t handle it

@fullWord
		; adjust the trap bits

		bset	#TrapAddressOpcode.newBit,d1		; is this NGetTrapAddress?
		btst	#TrapNumber.toolboxBit,d0			; is the trap a Toolbox trap?
		bnz.s	@toolbox							; yes, leave the bit set
		bclr	#TrapAddressOpcode.toolboxBit,d1	; clear bit for OS
@toolbox

		cmp.w	#$C000,d0					; is this a come-from trap word?
		blo.s	@notComeFrom				; no, it is not
		cmp.w	#$D000,d0					; is it a come-from trap word?
		bhs.s	@notComeFrom				; no, it is not
@comeFrom
		; oooh... carry is set for us, we can return
		rts

@notFullWord
@notComeFrom
		and		#$FE,ccr					; clear the carry bit
		rts

				endproc

				end