Changeset 100

Timestamp:

Apr 8, 2017, 12:26:54 AM (8 years ago)

Author:

Ben Rietbroek

Message:

Redone LVM sector validation [v1.1.1-testing]

AL.0 is 1 when a valid signature is found..
AH.0 is 1 when the CRC was OK.
ZF is 0 when LVM sector is valid.

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/bootcode

Files:

• regular/driveio.asm (modified) (2 diffs)
• special/lvm.asm (modified) (1 diff)

trunk/bootcode/regular/driveio.asm

@@ -1176 +1176 @@
 
         ; See if this is a valid LVM-sector
-        ; CY=1 if valid
-        call    DriveIO_LVMSectorValid
+        ; ZF=0 if valid
+        call    LVM_ValidateSector
 
 ;        pushf
@@ -1192 +1192 @@
 
         ; Yep, we found the master LVM-sector
-        jc      DriveIO_LoadMasterLVMSector_Found
+        jnz     DriveIO_LoadMasterLVMSector_Found
         ; Try next location
         loop    DriveIO_LoadMasterLVMSector_NextTry

trunk/bootcode/special/lvm.asm

@@ -125 +125 @@
 LVM_CheckSectorCRC              EndP
 
-; See if a LVM-sector is valid.
-; In  : si, pointer to sector
-; Out : CY if valid LVM sector, NC if not
-DriveIO_LVMSectorValid           Proc  Near
-        pusha
-
-        call    LVM_CheckSectorSignature
-        ; NC if no signature found
-        jnc     DriveIO_LVMSectorValid_End
-
-        call    LVM_CheckSectorCRC
-        ; Force valid !!!
-        ;~ stc
-
-    DriveIO_LVMSectorValid_End:
-        popa
-        ret
-DriveIO_LVMSectorValid           EndP
+; Checks if a sector is a valid LVM-sector
+;  Sector is considered valid LVM-sector if both signature and CRC are correct.
+;        In: DS:SI - Sector that needs to get checked...
+;       Out: AL = 1 -> LVM Signature found
+;            AH = 1 -> CRC OK
+;            ZF = 0 -> Signature found and CRC OK, ZF = 1 -> Invalid LVM sector
+;      Note: AL thus indicates a valid signature and AH a valid CRC
+; Destroyed: None
+LVM_ValidateSector              Proc Near
+        xor     ax, ax                      ; Start with all zero bits
+        call    LVM_CheckSectorSignature    ; CF=1 -> Signature OK
+        rcl     al, 1                       ; Store CF in AL
+        call    LVM_CheckSectorCRC          ; CF=1 -> Checksum OK
+        rcl     ah, 1                       ; Store CF in AH
+        test    al, ah                      ; ZF=0 if both AL and AH are 1
+        ret
+LVM_ValidateSector              EndP
 
 ; Updates Sector with valid LVM CRC