Slice Protection, Issue #366

- Dean Jenkins has motivated me to implement additional protection from using a slice that does not fit within the capacity of the physical disk being used. You can still assign an unusable slice, but when you try to refer to it, you will immediately get a "no disk" error from the OS.
2026-02-06 14:11:48 -06:00 · 2023-10-07 15:15:10 -07:00
parent d98547dea3
commit 93dcfe9610
4 changed files with 126 additions and 18 deletions
--- a/Source/CBIOS/cbios.asm
+++ b/Source/CBIOS/cbios.asm
@@ -1511,8 +1511,8 @@ DSK_MBR3:
 ;
 DSK_MBR4:
 	; IF BOOT FROM PARTITION, USE NEW SECTORS PER SLICE VALUE
-	LD	HL,16384		; NEW SECTORS PER SLICE
-	LD	(SPS),HL		; SAVE IT
+	LD	HL,16384	; NEW SECTORS PER SLICE
+	LD	(SPS),HL	; SAVE IT

 	; UPDATE MEDIA ID
 	LD	A,MID_HDNEW	; NEW MEDIA ID
@@ -1520,20 +1520,79 @@ DSK_MBR4:
 ;
 DSK_MBR5:
 	; ADJUST LBA OFFSET BASED ON TARGET SLICE
-	LD	A,(SLICE)		; GET SLICE, A IS LOOP CNT
-	LD	HL,(SEKLBA)		; SET DE:HL
-	LD	DE,(SEKLBA+2)		; ... TO STARTING LBA
-	LD	BC,(SPS)		; SECTORS PER SLICE
-DSK_MBR6:
-	OR	A			; SET FLAGS TO CHECK LOOP CNTR
-	JR	Z,DSK_MBR8		; DONE IF COUNTER EXHAUSTED
-	ADD	HL,BC			; ADD ONE SLICE TO LOW WORD
-	JR	NC,DSK_MBR7		; CHECK FOR CARRY
-	INC	DE			; IF SO, BUMP HIGH WORD
-DSK_MBR7:
-	DEC	A			; DEC LOOP DOWNCOUNTER
-	JR	DSK_MBR6		; AND LOOP
+	LD	A,(SLICE)	; GET SLICE, A IS LOOP CNT
+	LD	HL,(SEKLBA)	; SET DE:HL
+	LD	DE,(SEKLBA+2)	; ... TO STARTING LBA
+	LD	BC,(SPS)	; SECTORS PER SLICE
+DSK_MBR6:                       
+	OR	A		; SET FLAGS TO CHECK LOOP CNTR
+	JR	Z,DSK_MBR8	; DONE IF COUNTER EXHAUSTED
+	ADD	HL,BC		; ADD ONE SLICE TO LOW WORD
+	JR	NC,DSK_MBR7	; CHECK FOR CARRY
+	INC	DE		; IF SO, BUMP HIGH WORD
+DSK_MBR7:                       
+	DEC	A		; DEC LOOP DOWNCOUNTER
+	JR	DSK_MBR6	; AND LOOP
 DSK_MBR8:
+	; LBA OFFSET OF DESIRED SLICE IS NOW IN DE:HL
+	; NEED TO CHECK IF THE SLICE IS BEYOND CAPACITY OF MEDIA
+	; IF LBA_OFF + SPS >= DSK_CAP, ERROR!
+
+	; SAVE LBA_OFF
+	PUSH	DE		; MSW
+	PUSH	HL		; LSW
+	
+	; ADD SPS TO COMPUTE LBA_REQ
+	LD	BC,(SPS)	; SECTORS PER SLICE
+	ADD	HL,BC		; ADD ONE SLICE TO LOW WORD
+	JR	NC,DSK_MBR9	; CHECK FOR CARRY
+	INC	DE		; IF SO, BUMP HIGH WORD
+DSK_MBR9:
+	; SAVE CAP_REQ
+	LD	(CAP_REQ),HL	; LSW
+	LD	(CAP_REQ+2),DE	; MSW
+;
+#IFDEF PLTWBW
+	; GET DSK_CAP (DE:HL)
+	LD	B,BF_DIOCAP	; HBIOS DISK CAPACITY FUNC
+	LD	A,(SEKUNIT)	; DISK UNIT NUMBER
+	LD	C,A		; ... INTO C
+	RST	08		; HBIOS CALL (DE:HL = CAPACITY)
+#ENDIF
+;
+#IFDEF PLTUNA
+	; GET DSK_CAP (DE:HL)
+	LD	C,$45		; UBIOS DISK INFO FUNC
+	LD	A,(SEKUNIT)	; DISK UNIT NUMBER
+	LD	B,A		; ... INTO B
+	RST	08		; CALL UNA (DE:HL = CAPACITY)
+#ENDIF
+;
+	; SAVE DSK_CAP (DE:HL)
+	PUSH	DE		; SAVE DSK_CAP (MSW)
+	PUSH	HL		; SAVE DSK_CAP (LSW)
+;
+	; CHECK DSK_CAP >= CAP_REQ, CF SET ON OVERFLOW
+	; NO NEED SAVE ACTUAL RESULT
+	OR	A		; CLEAR CARRY FOR SBC
+	POP	HL		; DSK_CAP LSW
+	LD	DE,(CAP_REQ)	; CAP_REQ LSW
+	SBC	HL,DE		; DSK_CAP - LBA_REQ (LSW)
+	POP	HL		; DSK_CAP MSW
+	LD	DE,(CAP_REQ+2)	; CAP_REQ MSW
+	SBC	HL,DE		; DSK_CAP - LBA_REQ (MSW)
+;
+	; RESTORE LBA_OFF
+	POP	HL		; LSW
+	POP	DE		; MSW
+;
+	; ABORT ON OVERFLOW WITH ERROR!
+	JR	NC,DSK_MBR10	; IF NO OVERFLOW, CONTINUE
+	OR	$FF		; SIGNAL ERROR
+	RET			; DONE
+;
+DSK_MBR10:
+	; FINALIZE SLICE LBA
 	SET	7,D		; SET LBA ACCESS FLAG
 	; RESAVE IT
 	LD	(SEKLBA),HL	; LOWORD
@@ -1758,6 +1817,7 @@ CCPBUF		.DW	0		; ADDRESS OF CCP BUF IN BIOS BANK
 MEDID		.DB	0		; TEMP STORAGE FOR MEDIA ID
 SLICE		.DB	0		; CURRENT SLICE
 SPS		.DW	0		; SECTORS PER SLICE
+CAP_REQ		.DW	0,0		; LBA CAP REQUIRED FOR SLICE
 STKSAV		.DW	0		; TEMP SAVED STACK POINTER
 ;
 #IFDEF PLTWBW
--- a/Source/CPM3/diskio.z80
+++ b/Source/CPM3/diskio.z80
@@ -38,7 +38,7 @@
 	
 	extrn	?bnkxlt
 	
-	extrn	phex8, cout
+	extrn	phex16, phex8, cout, crlf, crlf2


    ; CP/M 3 Disk definition macros
@@ -600,6 +600,53 @@ boot7:
 	dec	a			; dec loop downcounter
 	jr	boot6			; and loop
 boot8:
+
+	; LBA offset of desired slice is now in DE:HL.
+	; Need to check if the slice is beyond capacity of media.
+	; If lba_off + sps >= dsk_cap, error!
+
+	; Save lba_off
+	push	de		; msw
+	push	hl		; lsw
+	
+	; Add sps to compute lba_req
+	ld	bc,(sps)	; sectors per slice
+	add	hl,bc		; add one slice to low word
+	jr	nc,dsk_mbr9	; check for carry
+	inc	de		; if so, bump high word
+dsk_mbr9:
+	; Save cap_req
+	ld	(cap_req),hl	; lsw
+	ld	(cap_req+2),de	; msw
+
+	; Get dsk_cap (de:hl)
+	ld	b,1Ah		; hbios disk capacity func
+	ld	a,(unit)	; disk unit number
+	ld	c,a		; ... into c
+	rst	08		; hbios call (de:hl = capacity)
+
+	; Save dsk_cap (de:hl)
+	push	de		; save dsk_cap (msw)
+	push	hl		; save dsk_cap (lsw)
+
+	; Check dsk_cap >= cap_req, cf set on overflow
+	; No need save actual result
+	or	a		; clear carry for sbc
+	pop	hl		; dsk_cap lsw
+	ld	de,(cap_req)	; cap_req lsw
+	sbc	hl,de		; dsk_cap - lba_req (lsw)
+	pop	hl		; dsk_cap msw
+	ld	de,(cap_req+2)	; cap_req msw
+	sbc	hl,de		; dsk_cap - lba_req (msw)
+
+	; Restore lba_off
+	pop	hl		; lsw
+	pop	de		; msw
+
+	; Abort on overflow with error!
+	jp	c,err_noslice	; slice too high, error exit
+
+	; Finalize slice lba
 	set	7,d			; set LBA access flag
 	ld	(lba),hl		; save new lba, low word
 	ld	(lba+2),de		; save new lba, high word
@@ -870,6 +917,7 @@ unit		db	0		; working disk unit num
 slice		db	0		; working slice num
 lba		dw	0,0		; working  lba
 sps		dw	0		; sectors per slice
+cap_req		dw	0,0		; lba cap required for slice
 mbrsec		ds	512		; MBR sector buffer
 dma		dw	0		; current DMA address
 bank		db	0		; HBIOS DMA bank
--- a/Source/ver.inc
+++ b/Source/ver.inc
@@ -2,7 +2,7 @@
 #DEFINE	RMN	4
 #DEFINE	RUP	0
 #DEFINE	RTP	0
-#DEFINE BIOSVER	"3.4.0-dev.1"
+#DEFINE BIOSVER	"3.4.0-dev.2"
 #define rmj	RMJ
 #define rmn	RMN
 #define rup	RUP
--- a/Source/ver.lib
+++ b/Source/ver.lib
@@ -3,5 +3,5 @@ rmn	equ	4
 rup	equ	0
 rtp	equ	0
 biosver	macro
-	db	"3.4.0-dev.1"
+	db	"3.4.0-dev.2"
 	endm