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The outline of a solution

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But it doesn't actually work yet.
This commit is contained in:
Elliot Nunn 2021-02-22 08:37:43 +08:00
parent c898af28d3
commit 3cbc61b625
1 changed files with 172 additions and 313 deletions
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485
ChainLoader.a
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@ -1,19 +1,173 @@
myUnitNum equ 52
myDRefNum equ ~myUnitNum
serverBufSize equ 32
Code Code
; This is the entry point, which the ROM jumps to with one of three ; The ROM issued a _Read call that eventually reached here.
; selectors. This whole block of code lives inside the system heap, in a ; We need to handle this _Read trap directly, without the intervening .netBOOT and .ATBOOT drivers.
; block that the ROM code forgets ever to free. So we simply drop our ; We do this by rewinding the Device Manager's return address by 2 bytes.
; driver here, and relegate the one-time init code to the end of the
; block.
bra OneTimeInitCode ; Why?
dc.l 'NtBt' ; The ROM network boot mechanism is complicated and buggy.
; The workarounds are difficult.
; Therefore this big hack obviates many little hacks.
; First problem: this is not a safe place to keep code. Jump away.
; (Using the heap while all the netBOOT junk is there would cause fragmentation.)
lea ResumeAfterCopy,A0
move.l #CodeEnd-ResumeAfterCopy,D0
lea 4096(A5),A1
dc.w $A02E ; _BlockMove
jmp 4096(A5)
ResumeAfterCopy
; Salvage some possibly useful information from ATBOOT, while it is still running:
; Server address
move.l 8(SP),A0 ; global pointer
move.l 24(A0),D0 ; AddrBlock
lea gSaveAddr,A0
move.b #10,15(A0) ; hardcode DDP protocol ID
move.b D0,13(A0) ; socket
lsr.w #4,D0
lsr.w #4,D0
move.b D0,11(A0) ; node
swap D0
move.w D0,7(A0) ; network
; User record
lea gUserRec,A1
move.l 8(SP),A0 ; global pointer
move.l 40(A0),A0
move.l #574,D0
dc.w $A02E ; _BlockMove
; Currently the call stack looks like this:
; ROM _Read to get boot blocks
; .netBOOT Read routine
; .ATBOOT Control routine
; direct call to this block of code
; But we want to close and remove .netBOOT & .ATBOOT, so we need to return
; from their Device Manager calls, and steal control from the ROM.
; We do this by scanning the stack for the return address of the original _Read.
move.l $2AE,A0 ; A0 = ROMBase (lower limit)
lea $4000(A0),A1 ; A1 = ROMBase + a bit (upper limit)
lea -2(SP),A2
.loop subq.l #2,A2 ; A2 = where we search the stack
move.l (A2),A3 ; A3 = potential return address
cmp.l A0,A3 ; lower limit check
bls.s .loop
cmp.l A1,A3 ; upper limit check
bhi.s .loop
cmp.w #$A002,-2(A3) ; _Read trap check
bne.s .loop
pea GoHereFromReadTrap ; take over
move.l (SP)+,(A2)
lea ROMAfterReadTrap,A2 ; save original for later
move.l A3,(A2)
moveq.l #-1,D0 ; .netBOOT/.ATBOOT don't do any more damage if an error is returned
rts
ROMAfterReadTrap
dc.l 0
GoHereFromReadTrap
; Now we are outside .netBOOT/.ATBOOT. We can shut them down, and set up our driver in a clean environment.
move.l ROMAfterReadTrap,-(SP) ; our return address is to ROM
sub.l #2,-(SP) ; repeating the _Read trap
movem.l A0-A6/D0-D7,-(SP) ; save registers conservatively (especially A0)
; A4 = param block to the .netBOOT _Read call, because we will use it a lot
move.l A0,A4
; Close and delete .netBOOT (which will close .ATBOOT)
lea -$32(SP),SP
move.l SP,A0
move.w $18(A4),$18(A0) ; ioRefNum
dc.w $A001 ; _Close
lea $32(SP),SP
move.w $18(A4),D0 ; ioRefNum
dc.w $A03E ; _DrvrRemove
move.w #-52,D0 ; ioRefNum ; also delete .ATBOOT for neatness
dc.w $A03E ; _DrvrRemove
; A3 = our driver in sysheap (plus 574 bytes for the user record)
move.l #DrvrEnd-DrvrBase+574,D0
dc.w $A51E ; NewPtrSys
move.l A0,A1
lea DrvrBase,A0
move.l #DrvrEnd-DrvrBase+574,D0
dc.w $A02E ; BlockMove
move.l A1,A3
; Install the driver in the unit table. Take over netBOOT's old unit number.
move.w $18(A4),D0 ; ioRefNum
dc.w $A43D ; _DrvrInstall ReserveMem
; That call created a driver control entry (DCE). Find and lock.
move.l $11C,A0 ; UTableBase
move.w $18(A4),D0 ; ioRefNum
not.w D0
lsl.w #2,D0
add.w D0,A0
move.l (A0),A0
dc.w $A029 ; _HLock
move.l (A0),A0
; Populate the empty DCE that DrvrInstall left us (forget fields related desk accessories)
move.l A3,(A0) ; dCtlDriver = driver pointer (not handle)
move.w (A3),4(A0) ; dCtlFlags = drvrFlags
; Open our driver
lea -$32(SP),SP
move.l SP,A0
bsr clearblock
lea DrvrName,A1
move.l A1,$12(A0) ; IOFileName
dc.w $A000 ; _Open
lea $32(SP),SP
; Create & add a drive queue entry (DQE).
move.l #$16,D0
dc.w $A71E ; _NewPtrSysClear
add.l #4,A0 ; has some cheeky flags at negative offset
move.l #$00080000,-4(A0) ; secret flags, see http://mirror.informatimago.com/next/developer.apple.com/documentation/mac/Files/Files-112.html
move.w #1,4(A0) ; qType
;move.w #0,$A(A0) ; dQFSID should be for a native fs
;move.l #0,$C(A0) ; dQDrvSz/dQDrvSz2 ; whoa, better fix this!
move.l $16(A4),D0 ; scoop drivenum & driver refnum from _Read PB
dc.w $A04E ; _AddDrive (A0=DQE, D0=drvnum/drefnum)
; Open .MPP (still open?) & our DDP socket
lea -$32(SP),SP
move.l SP,A0
bsr clearblock
pea MPPName
move.l (SP)+,$12(A0) ; ioNamePtr
dc.w $A000 ; _Open
move.w #248,$1A(A0) ; csCode = openSkt
move.b #10,$1C(A0) ; socket = 10, same as ATBOOT uses
pea DrvrSockListener-DrvrBase(A3)
move.l (SP)+,$1E(A0) ; listener
dc.w $A004 ; _Control
lea $32(SP),SP
; Re-execute the _Read trap in ROM
movem.l (SP)+,A0-A6/D0-D7
rts
MPPName dc.b 4, '.MPP', 0
clearblock move.w #$32/2-1,D0
.loop clr.w (A0)+
dbra D0,.loop
lea -$32(A0),A0
rts
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
@ -28,7 +182,7 @@ DrvrBase
dc.w DrvrControl-DrvrBase dc.w DrvrControl-DrvrBase
dc.w DrvrStatus-DrvrBase dc.w DrvrStatus-DrvrBase
dc.w DrvrClose-DrvrBase dc.w DrvrClose-DrvrBase
DrvrName dc.b 8, ".LANDisk", 0 DrvrName dc.b 8, ".netBOOT", 0
g g
gNumBlks dc.l 0 ; the source of all truth gNumBlks dc.l 0 ; the source of all truth
@ -562,303 +716,8 @@ DrvrIcon
dc.l %11111111111111111111111111111111 dc.l %11111111111111111111111111111111
dc.l %11111111111111111111111111111111 dc.l %11111111111111111111111111111111
dc.b 22, "AppleTalk NetBoot Disk", 0 dc.b 22, "AppleTalk NetBoot Disk", 0
gUserRec ; append some 574 zeroes here later on
DrvrEnd DrvrEnd
CodeEnd
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
OneTimeInitCode
cmp.l #1,4(SP)
beq getBootBlocks
cmp.l #2,4(SP)
beq getSysVol
cmp.l #3,4(SP)
beq mountSysVol
move.l #-1,d0
rts
getBootBlocks
; Now is the time to install our DRVR because we are guaranteed an opportunity to boot if we don't fuck up.
link A6,#-$32
movem.l A2-A4/D3-D7,-(SP)
; Patch the server address into the DRVR code (TODO: concentrate all global patches here)
move.l 12(A6),A0 ; global pointer
move.l 24(A0),D0 ; AddrBlock
lea gSaveAddr,A0
move.b #10,15(A0) ; hardcode DDP protocol ID
move.b D0,13(A0) ; socket
lsr.w #4,D0
lsr.w #4,D0
move.b D0,11(A0) ; node
swap D0
move.w D0,7(A0) ; network
; Patch the disk image name and size into the DRVR code
; bsr BootPicker ; A0 = pstring ptr
; lea gNumBlks,A1
; move.l -4(A0),(A1) ; the size is underneath the pstring ptr
; move.l -4(A0),D6 ; D6 = block count, needed for DQE
; lea gQFilename,A1 ; A1 = dest
; moveq.l #1,D0
; add.b (A0),D0
; dc.w $A22E ; _BlockMoveData
; Install the driver in the unit table
lea DrvrBase,A0
move.l #myDRefNum,D0
dc.w $A43D ; _DrvrInstall ReserveMem
; That call created a DCE. Find and lock.
move.l $11C,A0 ; UTableBase
move.l myUnitNum*4(A0),A0
dc.w $A029 ; _HLock
move.l (A0),A0
; Populate the empty DCE that DrvrInstall left us (forget fields related desk accessories)
lea DrvrBase,A2
move.l A2,0(A0) ; dCtlDriver = driver pointer (not handle)
move.w 0(A2),4(A0) ; dCtlFlags = drvrFlags
; Open the driver
lea -$32(SP),SP
move.l SP,A0
bsr clearblock
lea DrvrName,A1
move.l A1,$12(A0) ; IOFileName
dc.w $A000 ; _Open
lea $32(SP),SP
; Create a DQE. The fate of this exact DQE is to be copied and deleted by ROM code.
move.l #$16,D0
dc.w $A71E ; _NewPtr ,Sys,Clear
add.l #4,A0 ; has some cheeky flags at negative offset
move.l A0,A3
lea gDQEAddr,A0
move.l A3,(A0)
; Populate the DQE
move.l D6,D0 ; needs fixing for Ruby Slipper
lsl.l #5,D0 ; convert to bytes
lsl.l #4,D0
swap D0
move.l D0,$C(A3) ; dQDrvSz/dQDrvSz2
move.l #$00080000,-4(A3) ; secret flags, see http://mirror.informatimago.com/next/developer.apple.com/documentation/mac/Files/Files-112.html
move.w #1,4(A3) ; qType
move.w #0,$A(A3) ; dQFSID should be for a native fs
; Into the drive queue (which will further populate the DQE)
bsr findFreeDriveNum ; get drvnum in D0
lea gDriveNum,A0
move.w D0,(A0)
swap D0
move.w #myDRefNum,D0 ; D0.H = drvnum, D0.L = drefnum
move.l D0,D3 ; we need this in a sec
move.l A3,A0
dc.w $A04E ; _AddDrive
; Open our socket
lea -$32(SP),SP
move.l SP,A0
bsr clearblock
move.w #-10,$18(A0) ; ioRefNum = .MPP
move.w #248,$1A(A0) ; csCode = openSkt
move.b #10,$1C(A0) ; socket = 10, same as ATBOOT uses
lea DrvrSockListener,A2
move.l A2,$1E(A0) ; listener
dc.w $A004 ; _Control
lea $32(SP),SP
; Get the real 1024k of boot blocks to a temp location
; (it will eventually get trashed, but we have time)
lea 4096(A5),A4 ; above BootGlobals
lea -$32(SP),SP
move.l SP,A0
bsr clearblock
move.l D3,22(A0) ; IOVRefNum=drvnum, IORefNum=drefnum
move.l A4,32(A0) ; IOBuffer
move.l #1024,36(A0) ; IOReqCount = 2 blocks
move.l #0,46(A0) ; IOPosOffset = 0
move.w #1,44(A0) ; IOPosMode = from start
dc.w $A002 ; _Read
lea $32(SP),SP
; Put the boot blocks in netBOOT's global data structure as requested
move.l A4,A0
move.l 12(A6),A1
lea $BA(A1),A1
move.l #$138,D0
dc.w $A22E ; _BlockMoveData
move.l A1,A0 ; A0 = truncated BBs
move.l A4,A1 ; A1 = full-length BBs
bsr HealInjuredBootBlocks
; Clean up our stack frame
movem.l (SP)+,A2-A4/D3-D7
unlk A6
move.l #0,D0
rts
getSysVol ; pointless call :(
move.l #0,D0
rts
mountSysVol
link A6,#-$32
movem.l A2-A4/D3,-(SP)
lea gDriveNum,A0
move.w (A0),D3
; System 7 needs MountVol to return the right vRefNum
move.l $366,A0 ; Steal existing PB from FSQHead
; Set aside the FS queue to stop MountVol deadlocking
move.w $360,-(SP) ; FSBusy
move.l $362,-(SP) ; FSQHead
move.l $366,-(SP) ; FSQTail
clr.w $360
clr.l $362
clr.l $366
; MountVol
bsr clearblock
move.w D3,$16(A0) ; ioVRefNum = ioDrvNum = the drive number
dc.w $A00F ; _MountVol
bne error
; Restore the FS queue
move.l (SP)+,$366
move.l (SP)+,$362
move.w (SP)+,$360
; Tattle about the DQE and VCB
move.l 4+12(A6),A1
move.l $356+2,A0 ; VCBQHdr.QHead (maybe I should be clever-er)
move.l A0,(A1)
move.l 4+16(A6),A1
lea gDQEAddr,A0
move.l (A0),(A1)
lea Code,A0
move.l #OneTimeInitCode-Code,D0
dc.w $A020 ; Cut the unnecessary code off me
movem.l (SP)+,A2-A4/D3
unlk A6
move.l #0,d0
rts
error
move.w #$7777,D0
dc.w $A9C9
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
gDriveNum dc.w 0
gDQEAddr dc.l 0
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
clearblock
move.w #$32/2-1,D0
.loop clr.w (A0)+
dbra D0,.loop
lea -$32(A0),A0
rts
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
findFreeDriveNum ; and return it in D0. Free to trash the usual registers
; Find a free drive number (nicked this code from BootUtils.a:AddMyDrive)
LEA $308,A0 ; [DrvQHdr]
MOVEQ #4,D0 ; start with drive number 4
.CheckDrvNum
MOVE.L 2(A0),A1 ; [qHead] start with first drive
.CheckDrv
CMP.W 6(A1),D0 ; [dqDrive] does this drive already have our number?
BEQ.S .NextDrvNum ; yep, bump the number and try again.
CMP.L 6(A0),A1 ; [qTail] no, are we at the end of the queue?
BEQ.S .GotDrvNum ; if yes, our number's unique! Go use it.
MOVE.L 0(A1),A1 ; [qLink] point to next queue element
BRA.S .CheckDrv ; go check it.
.NextDrvNum
; this drive number is taken, pick another
ADDQ.W #1,D0 ; bump to next possible drive number
BRA.S .CheckDrvNum ; try the new number
.GotDrvNum
rts
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
HealInjuredBootBlocks ; patch the BBs to fix themselves if executed
; Args: A0 = truncated boot blocks (138b), A1 = correct boot blocks (1024b)
; If these boot blocks are executable (from offset 2), then the 138 bytes of
; declarative data copied by the netBOOT driver are not enough. We edit the boot
; blocks with a stub that copies the entire 1k into place. System 7 needs this.
; This unfortunately clobbers the declarative part of the boot blocks, so we need to
; check for declarative boot blocks and leave them unchanged
move.l A0,-(SP) ; Save A1 to a global, but need to keep A0
lea .gFullLoc,A0
move.l A1,(A0)
move.l (SP)+,A0
move.b 6(A0),D0 ; BBVersion
cmp.b #$44,D0
beq.s .executable
and.b #$C0,D0
cmp.b #$C0,D0
beq.s .executable
rts
; Relevant structure of the boot blocks:
; 0-1 bbID always 'LK'
; 2-5 bbEntry BRA.W base+128
; 6-7 bbVersion interpreted as above
; 8-137 data
; 138-1023 code (MISSING from netBOOT's short version)
; Our self-repairing boot blocks:
; 0-1 bbID always 'LK'
; 2-5 bbEntry BRA.W base+8
; 6-7 bbVersion interpreted as above
; 8-13 JSR .inPlaceFixRoutine
; 14-137 junk
.executable ; Need to leave bytes 6,7 intact
move.l #$60000004,2(A0) ; BB+2: BRA.W BB+8
move.w #$4EB9,8(A0) ; BB+8: JSR .inPlaceFixRoutine (abs)
lea .inPlaceFixRoutine,A1
move.l A1,10(A0)
move.l A0,A1 ; Clear the icache with a BlockMove
move.l #138,D0
dc.w $A02E ; _BlockMove
rts
.inPlaceFixRoutine ; The BB stub JSRs to here
move.l (SP)+,A1 ; so the return address will be at BB+14
lea -14(A1),A1 ; "Rewind" to the start of the BB
move.l .gFullLoc,A0 ; And here are our full boot blocks
move.l #1024,D0
dc.w $A02E ; _BlockMove (needs to clear cache)
jmp 2(A1) ; Jump to the fixed-up BB
.gFullLoc dc.l 0 ; Stuff addr of full-length BB in here