bryce@cbmvax.commodore.com (Bryce Nesbitt) (06/08/90)
**
**
** Decigel020 - The functionality of the famous "decigel" program, but
** working on the 68020/68030 processors.
**
** The old Decigel would correctly patch the instruction on the 68020,
** but chances are the old (bad) instruction was still in the instruction
** cache. This code flushes the cache after modifying memory.
**
** This code may not function under future revisions of the operating
** system. This code is safe on the 68000/68010/68020 and 68030.
** This code is not expected to function on the 68040. This code may be
** called from CLI only.
**
**
** Written Tuesday 03-Apr-90 21:21:47 -Bryce Nesbitt
**
**
INCLUDE "exec/types.i"
INCLUDE "exec/memory.i"
INCLUDE "exec/ables.i"
INCLUDE "exec/execbase.i"
INCLUDE "libraries/dosextens.i"
INT_ABLES
XREF _LVOFindTask
XREF _LVOSupervisor
ABSEXECBASE EQU 4
PrivTrapVector EQU $20
;-------------- install patch then detach -----------------------------------
move.l ABSEXECBASE,a6
;
; Contents of the old vector are used to self-modify our
; code. The new vector replaces the old.
;
DISABLE
move.l PrivTrapVector,ModifyCode+2
bsr.s FlushCache
move.l #NewPrivTrap,PrivTrapVector
ENABLE
;
; Detach our code from the CLI
;
suba.l a1,a1
jsr _LVOFindTask(a6)
move.l d0,a0
move.l pr_CLI(a0),a0
add.l a0,a0
add.l a0,a0
move.l a0,d0
beq.s not_cli
clr.l cli_Module(a0)
not_cli: moveq #0,d0
rts
*
* Flush the instruction cache
*
FlushCache: movem.l a5/a6,-(sp)
move.l ABSEXECBASE,a6
btst.b #AFB_68020,AttnFlags+1(a6) ;>=68020 includes cache
beq.s fc_nocache
lea.l FlushTrap(pc),a5
jsr _LVOSupervisor(a6)
fc_nocache: movem.l (sp)+,a5/a6
rts
;
;
FlushTrap: dc.w $4e7a,$0002 ;movec.l CACR,d0
bset #3,d0 ;Set "Clear instruction cache" bit
dc.w $4e7b,$0002 ;movec.l d0,CACR
rte
*****************************************************************************
** **
** **
** The trap handler wedged into the privilege violation vector. **
** **
** If the instruction was MOVE SR,<ea> it is converted to MOVE CCR,<ea>. **
** The instruction cache is flushed, then the instruction is re-executed. **
** **
** **
*****************************************************************************
STKOFFSET EQU 4*3
;
; New privilege violation vector
;
NewPrivTrap: movem.l d0/a0/a6,-(sp)
move.l STKOFFSET+2(sp),a0
move.w (a0),d0 ; Examine opcode
andi.w #~%111111,d0 ; Mask out EA field
cmpi.w #$40C0,d0 ; A MOVE SR,<ea>?
beq.s GotOne
movem.l (sp)+,d0/a0/a6
ModifyCode: jmp $01234567 ; To previous handler... (exit)
;
; Code executed if the instruction was MOVE SR,<ea>
;
GotOne: move.l ABSEXECBASE,a6
DISABLE
bset #1,(a0) ; Convert to MOVE CCR,<ea>
btst.b #AFB_68020,AttnFlags+1(a6) ;>=68020 includes cache
beq.s no_cache
dc.w $4e7b,$8802 ; movec.l a0,CAAR
dc.w $4e7a,$0002 ; movec.l CACR,d0
bset #2,d0 ; Set "Clear entry in instruction cache"
dc.w $4e7b,$0002 ; movec.l d0,CACR
no_cache: ENABLE
movem.l (sp)+,d0/a0/a6
rte ; Rerun new opcode... (exit)
END
begin 644 decigel020
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end
size 504
--
|\_/| . "ACK!, NAK!, EOT!, SOH!" "Lawyers: America's untapped export market."
{X o} . Bryce Nesbitt, Commodore-Amiga, Inc.
(") BIX: bnesbitt
U USENET: bryce@commodore.COM -or- uunet!cbmvax!bryce