Changeset 78

Timestamp:

Apr 8, 2017, 12:26:16 AM (8 years ago)

Author:

Ben Rietbroek

Message:

More hard-coded '80h' corrections [v1.1.1-testing]

Code in 'partmain.asm' around line 1350 needs some more attention.
Possibly the whole 'boot-flag' stuff is not needed with modern BIOSses.
Updating them is disabled for now, which should only affect very old
BIOSses that don't leave this checking to the MBR code.

CAUTION:
This is a testbuild !
AirBoot uses the BIOS to access disks and a small coding error can trash
partition tables or other vital disk structures. You are advised to make
backups of TRACK0 and EBRs before using this testbuild. More info at:
​https://rousseaux.github.io/netlabs.air-boot/pdf/AirBoot-v1.1.0-manual.pdf

Location:

trunk

Files:

• bootcode/airboot.asm (modified) (1 diff)
• bootcode/regular/driveio.asm (modified) (5 diffs)
• bootcode/regular/other.asm (modified) (2 diffs)
• bootcode/regular/partmain.asm (modified) (2 diffs)
• bootcode/regular/partscan.asm (modified) (2 diffs)
• include/version.h (modified) (1 diff)
• include/version.inc (modified) (1 diff)

trunk/bootcode/airboot.asm

@@ -120 +120 @@
 BIOS_AUXPARMS_DEFAULT   EQU     (AUX_INIT_PARMS SHL 8) OR BIOS_COM_PORT
 
-; Default byte value for BIOS_BootDisk variabls
+; Default byte value for BIOS_BootDisk variable
 BIOS_BOOTDISK_DEFAULT   EQU     80h
 

trunk/bootcode/regular/driveio.asm

@@ -39 +39 @@
         mov     es, ax
         mov     bx, offset Configuration
-        mov     dx, 0080h                     ; First harddrive, Sector 55...
-        mov     cx, 0037h
+        xor     dh, dh
+        mov     dl, [BIOS_BootDisk]           ; Disk we booted from
+        mov     cx, 0037h                     ; Sector 55 (CHS)
         mov     ax, 0201h                     ; Function 02, read 1 sector...
         int     13h
@@ -86 +87 @@
         ; ES == CS
         mov     bx, offset Configuration
-        mov     dx, 0080h                     ; First harddrive, Sector 55...
-        mov     cx, 0037h
+        xor     dh, dh
+        mov     dl, [BIOS_BootDisk]           ; Disk we booted from
+        mov     cx, 0037h                     ; Sector 55 (CHS)
 
         ; Changed from 5 to calculated value
@@ -173 +175 @@
         mov     di, offset LBASwitchTable
         mov     dh, [TotalHarddiscs]
-        mov     dl, 80h
+        mov     dl, 80h        ; First disk to process
     DIOILUT_DriveLoop:
         push    dx
@@ -197 +199 @@
         mov     bptr ds:[di], ah  ; Save that value
         inc     di                ; Go to next BYTE
-        inc     dl
-        dec     dh
-        jnz     DIOILUT_DriveLoop
+        inc     dl                ; Next disk
+        dec     dh                ; Decrease disks to process
+        jnz     DIOILUT_DriveLoop ; Next disk if DH != 0
         ret
 DriveIO_InitLBASwitchTable  EndP
@@ -800 +802 @@
         ; checking the AiR-BOOT MBR.
         ;
-        cmp     dl,80h
-        ja      DriveIO_ProtectMBR_is_not_bootdisk
+        cmp     dl, [BIOS_BootDisk]
+        jne     DriveIO_ProtectMBR_is_not_bootdisk
 
         ;

trunk/bootcode/regular/other.asm

@@ -166 +166 @@
         call    MBR_TeletypeNL
 
+        ;
+        ; Write MBR back to disk to sync MBR variables.
+        ; Otherwise subsequent MBR loads will differ from the RAM stored one,
+        ; which is used by MBR protection to validate parts of the MBR.
+        ;
+        xor     bx, bx
+        mov     cx, 1
+        xor     dh, dh
+        mov     dl, [BIOS_BootDisk]
+        mov     al, 1
+        mov     ah, 03h
+        int     13h
+
+
+        ; Start with disk at index 0
         xor     cx,cx
+
     PRECRAP_Main_next_disk:
 
+        ; Get next disk and convert to BIOS disk-number
         mov     dl,cl
         or      dl,80h
@@ -431 +448 @@
         mov     ah, 41h
         mov     bx, 55AAh
-        mov     dl, 80h
+        mov     dl, [BIOS_BootDisk]     ; We check using the boot-disk
         int     13h
         cmp     bx, 0AA55h

trunk/bootcode/regular/partmain.asm

@@ -1318 +1318 @@
         ; --- HIDE COMPLETED ---
         ; So something got hidden and we have to remark a primary partition,
-        ;  if we are booting something non-primary from 1st hdd.
-        cmp     bptr [si+LocIPT_Drive], 80h
-        ja      PSP_HideAdjustPrimaryMark  ; When booting any hdd, but 1st
+        ;  if we are booting something non-primary from the boot-disk.
+        mov     al, [BIOS_BootDisk]
+        cmp     bptr [si+LocIPT_Drive], al
+        jne     PSP_HideAdjustPrimaryMark  ; When booting any hdd, but boot-disk
         mov     ax, wptr [si+LocIPT_AbsolutePartTable]
         mov     bx, wptr [si+LocIPT_AbsolutePartTable+2]
         or      ax, ax
         jnz     PSP_HideAdjustPrimaryMark  ; or booting non-primary partition
-        or      bx, bx                     ;  on 1st harddrive.
+        or      bx, bx                     ;  on boot-disk.
         jz      PSP_NoHideAdjustPrimaryMark
 
@@ -1333 +1334 @@
         xor     bx, bx
         mov     cx, 0001h                  ; Cylinder 0, Sector 1
-        mov     dx, 0080h                  ; First HD, Head 0
-                                                                     ; Load MBR
+        xor     dh, dh                     ; Head 0
+        mov     dl, [BIOS_BootDisk]        ; Boot Disk
+
+        ; This uses the boot-disk and alters 'CurPartition_Location'.
+        ; CHECKME: How does 81h being the boot-disk influences this ?
         call    DriveIO_LoadPartition      ; Load Primary Partition Table
+
+        ; This would only be needed for very old BIOSses
         call    PART_MarkFirstGoodPrimary
-        call    DriveIO_SavePartition       ; Saves the Partition-Table
+
+        ; CHECKME: Disabled writing back MBR with modified boot flags
+        ; This is a safety measure now that booting AirBoot from other disks
+        ; than 80h can occur.
+        ;~ call    DriveIO_SavePartition       ; Saves the Partition-Table
 
 

trunk/bootcode/regular/partscan.asm

@@ -305 +305 @@
         ; Clearing the boot-flags on other disks would prevent booting them
         ; from the BIOS. (TRAC ticket #6)
-        cmp     dl, 080h                            ; See if this is boot-disk
+        cmp     dl, [BIOS_BootDisk]                 ; See if this is boot-disk
         jne     PSSP_Skip_Clear_BootFlag            ; Nope, skip clear flag
         and     byte ptr [si+LocBRPT_Flags], 7Fh    ; Reset the Active-Flag
@@ -313 +313 @@
         jb      PSSP_ScanLoop
         ; If we are on first HDD and in primary partition table -> mark primary
-        cmp     bptr [CurPartition_Location+4], 80h ; Drive
+        mov     al, [BIOS_BootDisk]
+        cmp     bptr [CurPartition_Location+4], al  ; Drive
         jne     PSSP_NoMarkPrimary
         cmp     wptr [CurPartition_Location+0], 0
         jne     PSSP_NoMarkPrimary
-        cmp     wptr [CurPartition_Location+2], 0 ; Absolute Location
+        cmp     wptr [CurPartition_Location+2], 0   ; Absolute Location
         jne     PSSP_NoMarkPrimary
         call    PART_MarkFirstGoodPrimary

trunk/include/version.h

@@ -32 +32 @@
 #define     BLDLVL_YEAR             "2017"
 #define     BLDLVL_MONTH            "03"
-#define     BLDLVL_DAY              "18"
+#define     BLDLVL_DAY              "19"
 // Build time
 //~ #define     BLDLVL_HOURS            "01"

trunk/include/version.inc

@@ -70 +70 @@
 AB_YEAR             EQU     2017h
 AB_MONTH            EQU     03h
-AB_DAY              EQU     18h
+AB_DAY              EQU     19h
 
 ; The Hours, Minutes and Seconds, again in BCD for easy manipulation.