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ntfsboot.asm
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page ,132
title ntfsboot - NTFS boot loader
name ntfsboot
; The ROM in the IBM PC starts the boot process by performing a hardware
; initialization and a verification of all external devices. If all goes
; well, it will then load from the boot drive the sector from track 0, head 0,
; sector 1. This sector is placed at physical address 07C00h.
;
; The boot code's sole resposiblity is to find NTLDR, load it at
; address 2000:0000, and then jump to it.
;
; The boot code understands the structure of the NTFS root directory,
; and is capable of reading files. There is no contiguity restriction.
;
MASM equ 1
.xlist
.286
A_DEFINED EQU 1
include ntfs.inc
DoubleWord struc
lsw dw ?
msw dw ?
DoubleWord ends
;
; The following are various segments used by the boot loader. The first
; two are the segments where the boot sector is initially loaded and where
; the boot sector is relocated to. The third is the static location
; where the NTLDR is loaded.
;
BootSeg segment at 07c0h ; this is where the ROM loads us initially.
BootSeg ends
NewSeg segment at 0d00h ; this is where we'll relocate to.
NewSeg ends ; enough for 16 boot sectors +
; 4-sector scratch
; below where we'll load NTLDR.
LdrSeg segment at 2000h ; we want to load the loader at 2000:0000
LdrSeg ends
;/********************** START OF SPECIFICATIONS ************************/
;/* */
;/* SUBROUTINE NAME: ntfsboot */
;/* */
;/* DESCRIPTIVE NAME: Bootstrap loader */
;/* */
;/* FUNCTION: To load NTLDR into memory. */
;/* */
;/* NOTES: ntfsboot is loaded by the ROM BIOS (Int 19H) at */
;/* physical memory location 0000:7C00H. */
;/* ntfsboot runs in real mode. */
;/* This boot record is for NTFS volumes only. */
;/* */
;/* ENTRY POINT: ntfsboot */
;/* LINKAGE: Jump (far) from Int 19H */
;/* */
;/* INPUT: CS:IP = 0000:7C00H */
;/* SS:SP = 0030:00FAH (CBIOS dependent) */
;/* */
;/* EXIT-NORMAL: DL = INT 13 drive number we booted from */
;/* Jmp to main in NTLDR */
;/* */
;/* EXIT-ERROR: None */
;/* */
;/* EFFECTS: NTLDR is loaded into the physical memory */
;/* location 00020000H */
;/* */
;/* MESSAGES: A disk read error occurred. */
;/* The file NTLDR cannot be found. */
;/* Insert a system diskette and restart the system. */
;/* */
;/*********************** END OF SPECIFICATIONS *************************/
BootCode segment ;would like to use BootSeg here, but LINK flips its lid
assume cs:BootCode,ds:nothing,es:nothing,ss:nothing
org 0 ; start at beginning of segment, not 0100h.
public cstart
cstart proc far
jmp start
.errnz ($-cstart) GT (3),<FATAL PROBLEM: JMP is more than three bytes>
org 3
;
; This is a template BPB--anyone who writes boot code to disk
; should either preserve the existing BPB and NTFS information
; or create it anew.
;
Version db "NTFS " ; Must be 8 characters
BPB label byte
BytesPerSector dw 0 ; Size of a physical sector
SectorsPerCluster db 0 ; Sectors per allocation unit
ReservedSectors dw 0 ; Number of reserved sectors
Fats db 0 ; Number of fats
DirectoryEntries dw 0 ; Number of directory entries
Sectors dw 0 ; No. of sectors - no. of hidden sectors
Media db 0 ; Media byte
FatSectors dw 0 ; Number of fat sectors
SectorsPerTrack dw 0 ; Sectors per track
Heads dw 0 ; Number of surfaces
HiddenSectors dd 0 ; Number of hidden sectors
SectorsLong dd 0 ; Number of sectors iff Sectors = 0
;
; The following is the rest of the NTFS Sector Zero information.
; The position and order of DriveNumber and CurrentHead are especially
; important, since those two variables are loaded into a single 16-bit
; register for the BIOS with one instruction.
;
DriveNumber db 80h ; Physical drive number (0 or 80h)
CurrentHead db ? ; Variable to store current head no.
SectorZeroPad1 dw 0
SectorsOnVolume db (size LARGE_INTEGER) dup (0)
MftStartLcn db (size LARGE_INTEGER) dup (0)
Mft2StartLcn db (size LARGE_INTEGER) dup (0)
ClustersPerFrs dd 0
DefClustersPerBuf dd 0
SerialNumber db (size LARGE_INTEGER) dup (0)
CheckSum dd 0
;
; The following variables are not part of the Extended BPB; they're just
; scratch variables for the boot code.
;
SectorBase dd ? ; next sector to read
CurrentTrack dw ? ; current track
CurrentSector db ? ; current sector
SectorCount dw ? ; number of sectors to read
;****************************************************************************
start:
;
; First of all, set up the segments we need (stack and data).
;
cli
xor ax, ax ; Set up the stack to just before
mov ss, ax ; this code. It'll be moved after
mov sp, 7c00h ; we relocate.
sti
mov ax, Bootseg ; Address our BPB with DS.
mov ds, ax
assume ds:BootCode
;
; Now read the 16-sector boot block into memory. Then jump to that
; new version of the boot block, starting in the second sector
; (after the bootrecord sig).
;
mov SectorBase.lsw, 0 ; read sector zero.
mov SectorBase.msw, 0
mov word ptr [SectorCount], 16 ; read boot area
mov ax, NewSeg ; read it at NewSeg.
mov es, ax
sub bx, bx ; at NewSeg:0000.
call DoReadLL ; Call low-level DoRead routine
;
push NewSeg ; we'll jump to NewSeg:0200h.
push offset mainboot ; (the second sector).
ret ; "return" to the second sector.
cstart endp
;*******************************************************************************
;
; Low-level read routine that doesn't work across a 64k addr boundary.
;
; Read SectorCount sectors (starting at SectorBase) to es:bx.
;
; As a side effect, SectorBase is updated (but es:bx are not)
; and SectorCount is reduced to zero.
;
DoReadLL proc
push ax ; save important registers
push bx
push cx
push dx
push es
DoRead$Loop:
.386
mov eax, SectorBase
add eax, HiddenSectors
xor edx,edx
;EDX:EAX = absolute sector number
movzx ecx,word ptr SectorsPerTrack ; get into 32 bit value
div ecx ; (EDX) = sector within track, (EAX)=track
inc dl ; sector numbers are 1-based, not 0
mov CurrentSector, dl
mov edx,eax
shr edx,16
.286
div Heads ; (DX) = head no., (AX) = cylinder
mov CurrentHead, dl
mov CurrentTrack, ax
; CurrentHead is the head for this next disk request
; CurrentTrack is the track for this next request
; CurrentSector is the beginning sector number for this request
;
; Compute the number of sectors that we may be able to read in a single ROM
; request.
;
mov ax, SectorsPerTrack ; could read up to this much
sub al, CurrentSector ; offset within this track
inc ax ; CurrentSector was 1-based
;
; AX is the number of sectors that we may read.
;
cmp ax, SectorCount ; do we need to read whole trk?
jbe DoRead$FullTrack ; yes we do.
mov ax, SectorCount ; no, read a partial track.
;
; AX is now the number of sectors that we SHOULD read.
;
DoRead$FullTrack:
push ax ; save sector count for later calc.
mov ah, 2 ; "read sectors"
mov dx, CurrentTrack ; at this cylinder
mov cl, 6
shl dh, cl ; high 2 bits of DH = bits 8,9 of DX
or dh, CurrentSector ; (DH)=cyl bits | 6-bit sector no.
mov cx, dx ; (CX)=cylinder/sector no. combination
xchg ch, cl ; in the right order
mov dh, CurrentHead
mov dl, 80h ; should be DriveNumber, but...
int 13h ; call BIOS.
pop ax
jb BootErr$he ; If errors report
add SectorBase.lsw, ax ; increment logical sector position
adc SectorBase.msw, 0
sub SectorCount, ax ; exhausted entire sector run?
jbe DoRead$Exit ; yes, we're all done.
shl ax, 9 - 4 ; (AX)=paragraphs read from last track
mov dx, es ; (DX)=segment we last read at
add dx, ax ; (DX)=segment right after last read
mov es, dx ; (ES)=segment to read next track at
jmp DoRead$Loop
;
DoRead$Exit:
pop es
pop dx
pop cx
pop bx
pop ax
ret
DoReadLL endp
;****************************************************************************
;
; BootErr - print error message and hang the system.
;
BootErr proc
BootErr$fnf:
mov si,offset TXT_MSG_SYSINIT_FILE_NOT_FD +2
jmp short BootErr2
BootErr$ntc:
mov si,offset TXT_MSG_SYSINIT_NTLDR_CMPRS +2
jmp short BootErr2
BootErr$he:
mov si,offset TXT_MSG_SYSINIT_BOOT_ERROR +2
BootErr2:
call BootErr$print
mov si,offset TXT_MSG_SYSINIT_INSER_DK +2
call BootErr$print
sti
jmp $ ;Wait forever
BootErr$print:
lodsb ; Get next character
cmp al, 0
je BootErr$Done
mov ah,14 ; Write teletype
mov bx,7 ; Attribute
int 10h ; Print it
jmp BootErr$print
BootErr$Done:
ret
BootErr endp
;****************************************************************************
include ntfsboot.inc ;suck in the message text
ReservedForFuture DB 2 dup(?) ;reserve remaining bytes to prevent NLS
;messages from using them
.errnz ($-cstart) GT (512-2),<FATAL PROBLEM: first sector is too large>
org 512-2
db 55h,0aah
; Name we look for. ntldr_length is the number of characters,
; ntldr_name is the name itself. Note that it is not NULL
; terminated, and doesn't need to be.
;
ntldr_name_length dw 4
ntldr_name dw 'B', 'O', 'O', 'T'
; Predefined name for index-related attributes associated with an
; index over $FILE_NAME
;
index_name_length dw 4
index_name dw '$', 'I', '3', '0'
; Global variables. These offsets are all relative to NewSeg.
;
AttrList dd 0e000h; Offset of buffer to hold attribute list
MftFrs dd 3000h; Offset of first MFT FRS
SegmentsInMft dd ? ; number of FRS's with MFT Data attribute records
RootIndexFrs dd ? ; Offset of Root Index FRS
AllocationIndexFrs dd ? ; Offset of Allocation Index FRS ; KPeery
BitmapIndexFrs dd ? ; Offset of Bitmap Index FRS ; KPeery
IndexRoot dd ? ; Offset of Root Index $INDEX_ROOT attribute
IndexAllocation dd ? ; Offset of Root Index $INDEX_ALLOCATION attribute
IndexBitmap dd ? ; Offset of Root Index $BITMAP attribute
NtldrFrs dd ? ; Offset of NTLDR FRS
NtldrData dd ? ; Offset of NTLDR $DATA attribute
IndexBlockBuffer dd ? ; Offset of current index buffer
IndexBitmapBuffer dd ? ; Offset of index bitmap buffer
NextBuffer dd ? ; Offset of next free byte in buffer space
BytesPerCluster dd ? ; Bytes per cluster
BytesPerFrs dd ? ; Bytes per File Record Segment
SectorsPerFrs dd ? ; Sectors per File Record Segment
BytesPerIndexBlock dd ? ; Bytes per index alloc block in root index
ClustersPerIndexBlock dd ? ; Clusters per index alloc block in root index
SectorsPerIndexBlock dd ? ; Sectors per index block in root index
.386
SAVE_ALL macro
push es
push ds
pushad
endm
RESTORE_ALL macro
popad
nop
pop ds
pop es
endm
;****************************************************************************
;
; mainboot -
;
;
mainboot proc far
; Get the new ds and the new stack. Note that ss is zero.
;
mov ax, cs ; Set DS to CS
mov ds, ax
shl ax, 4 ; convert to an offset.
cli
mov sp, ax ; load new stack, just before boot code.
sti
; Set up the FRS buffers. The MFT buffer is in a fixed
; location, and the other three come right after it. The
; buffer for index allocation blocks comes after that.
;
; Compute the useful constants associated with the volume
;
movzx eax, BytesPerSector ; eax = Bytes per Sector
movzx ebx, SectorsPerCluster ; ebx = Sectors Per Cluster
mul ebx ; eax = Bytes per Cluster
mov BytesPerCluster, eax
mov ecx, ClustersPerFrs ; ecx = clusters per frs
cmp cl, 0 ; is ClustersPerFrs less than zero?
jg mainboot$1
; If the ClustersPerFrs field is negative, we calculate the number
; of bytes per FRS by negating the value and using that as a shif count.
;
neg cl
mov eax, 1
shl eax, cl ; eax = bytes per frs
jmp mainboot$2
mainboot$1:
; Otherwise if ClustersPerFrs was positive, we multiply by bytes
; per cluster.
mov eax, BytesPerCluster
mul ecx ; eax = bytes per frs
mainboot$2:
mov BytesPerFrs, eax
movzx ebx, BytesPerSector
xor edx, edx ; zero high part of dividend
div ebx ; eax = sectors per frs
mov SectorsPerFrs, eax
; Set up the MFT FRS's---this will read all the $DATA attribute
; records for the MFT.
;
call SetupMft
; Set up the remaining FRS buffers. The RootIndex FRS comes
; directly after the last MFT FRS, followed by the NTLdr FRS
; and the Index Block buffer.
;
mov ecx, NextBuffer
mov RootIndexFrs, ecx
add ecx, BytesPerFrs ; AllocationFrs may be different
mov AllocationIndexFrs, ecx ; from RootIndexFrs - KPeery
add ecx, BytesPerFrs ; BitmapFrs may be different
mov BitmapIndexFrs, ecx ; from RootIndexFrs - KPeery
add ecx, BytesPerFrs
mov NtldrFrs, ecx
add ecx, BytesPerFrs
mov IndexBlockBuffer, ecx
;
; Read the root index, allocation index and bitmap FRS's and locate
; the interesting attributes.
;
mov eax, $INDEX_ROOT
mov ecx, RootIndexFrs
call LoadIndexFrs
or eax, eax
jz BootErr$he
mov IndexRoot, eax ; offset in Frs buffer
mov eax, $INDEX_ALLOCATION ; Attribute type code
mov ecx, AllocationIndexFrs ; FRS to search
call LoadIndexFrs
mov IndexAllocation, eax
mov eax, $BITMAP ; Attribute type code
mov ecx, BitmapIndexFrs ; FRS to search
call LoadIndexFrs
mov IndexBitmap, eax
; Consistency check: the index root must exist, and it
; must be resident.
;
mov eax, IndexRoot
or eax, eax
jz BootErr$he
cmp [eax].ATTR_FormCode, RESIDENT_FORM
jne BootErr$he
; Determine the size of the index allocation buffer based
; on information in the $INDEX_ROOT attribute. The index
; bitmap buffer comes immediately after the index block buffer.
;
; eax -> $INDEX_ROOT attribute record
;
lea edx, [eax].ATTR_FormUnion ; edx -> resident info
add ax, [edx].RES_ValueOffset ; eax -> value of $INDEX_ROOT
movzx ecx, [eax].IR_ClustersPerBuffer
mov ClustersPerIndexBlock, ecx
mov ecx, [eax].IR_BytesPerBuffer
mov BytesPerIndexBlock, ecx
mov eax, BytesPerIndexBlock
movzx ecx, BytesPerSector
xor edx, edx
div ecx ; eax = sectors per index block
mov SectorsPerIndexBlock, eax
mov eax, IndexBlockBuffer
add eax, BytesPerIndexBlock
mov IndexBitmapBuffer, eax
; Next consistency check: if the $INDEX_ALLOCATION attribute
; exists, the $INDEX_BITMAP attribute must also exist.
;
cmp IndexAllocation, 0
je mainboot30
cmp IndexBitmap, 0 ; since IndexAllocation exists, the
je BootErr$he ; bitmap must exist, too.
; Since the bitmap exists, we need to read it into the bitmap
; buffer. If it's resident, we can just copy the data.
;
mov ebx, IndexBitmap ; ebx -> index bitmap attribute
push ds
pop es
mov edi, IndexBitmapBuffer ; es:edi -> index bitmap buffer
call ReadWholeAttribute
mainboot30:
;
; OK, we've got the index-related attributes.
;
movzx ecx, ntldr_name_length ; ecx = name length in characters
mov eax, offset ntldr_name ; eax -> name
call FindFile
or eax, eax
jz BootErr$fnf
; Read the FRS for NTLDR and find its data attribute.
;
; eax -> Index Entry for NTLDR.
;
mov eax, [eax].IE_FileReference.REF_LowPart
push ds
pop es ; es:edi = target buffer
mov edi, NtldrFrs
call ReadFrs
mov eax, NtldrFrs ; pointer to FRS
mov ebx, $DATA ; requested attribute type
mov ecx, 0 ; attribute name length in characters
mov edx, 0 ; attribute name (NULL if none)
call LocateAttributeRecord
; eax -> $DATA attribute for NTLDR
;
or eax, eax ; if eax is zero, attribute not found.
jz BootErr$fnf
; Get the attribute record header flags, and make sure none of the
; `compressed' bits are set
movzx ebx, [eax].ATTR_Flags
and ebx, ATTRIBUTE_FLAG_COMPRESSION_MASK
jnz BootErr$ntc
mov ebx, eax ; ebx -> $DATA attribute for NTLDR
push LdrSeg
pop es ; es = segment addres to read into
sub edi, edi ; es:edi = buffer address
call ReadWholeAttribute
;
; We've loaded NTLDR--jump to it.
;
; Before we go to NTLDR, set up the registers the way it wants them:
; DL = INT 13 drive number we booted from
;
mov dl, DriveNumber
mov ax,1000
mov es, ax ; we don't really need this
lea si, BPB
sub ax,ax
push LdrSeg
push ax
retf ; "return" to NTLDR.
mainboot endp
;****************************************************************************
;
; DoRead - read SectorCount sectors into ES:BX starting from sector
; SectorBase.
;
; NOTE: This code WILL NOT WORK if ES:BX does not point to an address whose
; physical address (ES * 16 + BX) MOD 512 != 0.
;
; DoRead adds to ES rather than BX in the main loop so that runs longer than
; 64K can be read with a single call to DoRead.
;
; Note that DoRead (unlike DoReadLL) saves and restores SectorCount
; and SectorBase
;
.286
DoRead proc
push ax ; save important registers
push bx
push cx
push dx
push es
push SectorCount ; save state variables too
push SectorBase.lsw
push SectorBase.msw
;
; Calculate how much we can read into what's left of the current 64k
; physical address block, and read it.
;
;
mov ax,bx
shr ax,4
mov cx,es
add ax,cx ; ax = paragraph addr
;
; Now calc maximum number of paragraphs that we can read safely:
; 4k - ( ax mod 4k )
;
and ax,0fffh
sub ax,1000h
neg ax
;
; Calc CX = number of paragraphs to be read
;
mov cx,SectorCount ; convert SectorCount to paragraph cnt
shl cx,9-4
DoRead$Loop64:
push cx ; save cpRead
cmp ax,cx ; ax = min(cpReadSafely, cpRead)
jbe @F
mov ax,cx
@@:
push ax
;
; Calculate new SectorCount from amount we can read
;
shr ax,9-4
mov SectorCount,ax
call DoReadLL
pop ax ; ax = cpActuallyRead
pop cx ; cx = cpRead
sub cx,ax ; Any more to read?
jbe DoRead$Exit64 ; Nope.
;
; Adjust ES:BX by amount read
;
mov dx,es
add dx,ax
mov es,dx
;
; Since we're now reading on a 64k byte boundary, cpReadSafely == 4k.
;
mov ax,01000h ; 16k paragraphs per 64k segment
jmp short DoRead$Loop64 ; and go read some more.
DoRead$Exit64:
pop SectorBase.msw ; restore all this crap
pop SectorBase.lsw
pop SectorCount
pop es
pop dx
pop cx
pop bx
pop ax
ret
DoRead endp
.386
;****************************************************************************
;
; ReadClusters - Reads a run of clusters from the disk.
;
; ENTRY: eax == LCN to read
; edx == clusters to read
; es:edi -> Target buffer
;
; USES: none (preserves all registers)
;
ReadClusters proc near
SAVE_ALL
mov ebx, edx ; ebx = clusters to read.
movzx ecx, SectorsPerCluster ; ecx = cluster factor
mul ecx ; Convert LCN to sectors (wipes out edx!)
mov SectorBase, eax ; Store starting sector in SectorBase
mov eax, ebx ; eax = number of clusters
mul ecx ; Convert EAX to sectors (wipes out edx!)
mov SectorCount, ax ; Store number of sectors in SectorCount
; Note that ReadClusters gets its target buffer in es:edi but calls
; the DoRead worker function that takes a target in es:bx--we need
; to normalize es:edi so that we don't overflow bx.
;
mov bx, di
and bx, 0Fh
mov ax, es
shr edi, 4
add ax, di ; ax:bx -> target buffer
push ax
pop es ; es:bx -> target buffer
call DoRead
RESTORE_ALL
ret
ReadClusters endp
;
;****************************************************************************
;
; LocateAttributeRecord -- Find an attribute record in an FRS.
;
; ENTRY: EAX -- pointer to FRS
; EBX -- desired attribute type code
; ECX -- length of attribute name in characters
; EDX -- pointer to attribute name
;
; EXIT: EAX points at attribute record (0 indicates not found)
;
; USES: All
;
LocateAttributeRecord proc near
; get the first attribute record.
;
add ax, word ptr[eax].FRS_FirstAttribute
; eax -> next attribute record to investigate.
; ebx == desired type
; ecx == name length
; edx -> pointer to name
;
lar10:
cmp [eax].ATTR_TypeCode, 0ffffffffh
je lar99
cmp dword ptr[eax].ATTR_TypeCode, ebx
jne lar80
; this record is a potential match. Compare the names:
;
; eax -> candidate record
; ebx == desired type
; ecx == name length
; edx -> pointer to name
;
or ecx, ecx ; Did the caller pass in a name length?
jnz lar20
; We want an attribute with no name--the current record is
; a match if and only if it has no name.
;
cmp [eax].ATTR_NameLength, 0
jne lar80 ; Not a match.
; It's a match, and eax is set up correctly, so return.
;
ret
; We want a named attribute.
;
; eax -> candidate record
; ebx == desired type
; ecx == name length
; edx -> pointer to name
;
lar20:
cmp cl, [eax].ATTR_NameLength
jne lar80 ; Not a match.
; Convert name in current record to uppercase.
;
mov esi, eax
add si, word ptr[eax].ATTR_NameOffset
call UpcaseName
; eax -> candidate record
; ebx == desired type
; ecx == name length
; edx -> pointer to name
; esi -> Name in current record (upcased)
;
push ecx ; save cx
push ds ; Copy data segment into es
pop es
mov edi, edx ; note that esi is already set up.
repe cmpsw ; zero flag is set if equal
pop ecx ; restore cx
jnz lar80 ; not a match
; eax points at a matching record.
;
ret
;
; This record doesn't match; go on to the next.
;
; eax -> rejected candidate attribute record
; ebx == desired type
; ecx == Name length
; edx -> desired name
;
lar80: cmp [eax].ATTR_RecordLength, 0 ; if the record length is zero
je lar99 ; the FRS is corrupt.
add eax, [eax].ATTR_RecordLength; Go to next record
jmp lar10 ; and try again
; Didn't find it.
;
lar99: sub eax, eax
ret
LocateAttributeRecord endp
;****************************************************************************
;
; LocateIndexEntry -- Find an index entry in a file name index
;
; ENTRY: EAX -> pointer to index header
; EBX -> file name to find
; ECX == length of file name in characters
;
; EXIT: EAX points at index entry. NULL to indicate failure.
;
; USES: All
;
LocateIndexEntry proc near
; Convert the input name to upper-case
;
mov esi, ebx
call UpcaseName
; DEBUG CODE
;
; call PrintName
; call Debug2
;
; END DEBUG CODE
add eax, [eax].IH_FirstIndexEntry
; EAX -> current entry
; EBX -> file name to find
; ECX == length of file name in characters
;
lie10: test [eax].IE_Flags, INDEX_ENTRY_END ; Is it the end entry?
jnz lie99
lea edx, [eax].IE_Value ; edx -> FILE_NAME attribute value
; DEBUG CODE -- list file names as they are examined
;
; SAVE_ALL
;
; call Debug3
; movzx ecx, [edx].FN_FileNameLength ; ecx = chars in name
; lea esi, [edx].FN_FileName ; esi -> name
; call PrintName
;
; RESTORE_ALL
;
; END DEBUG CODE
; EAX -> current entry
; EBX -> file name to find
; ECX == length of file name in characters
; EDX -> FILE_NAME attribute
;
cmp cl, [edx].FN_FileNameLength ; Is name the right length?
jne lie80
lea esi, [edx].FN_FileName ; Get name from FILE_NAME structure
call UpcaseName
push ecx ; save ecx
push ds
pop es ; copy data segment into es for cmpsw
mov edi, ebx ; edi->search name (esi already set up)
repe cmpsw ; zero flag is set if they're equal
pop ecx ; restore ecx
jnz lie80
; the current entry matches the search name, and eax points at it.
;
ret
; The current entry is not a match--get the next one.
; EAX -> current entry
; EBX -> file name to find
; ECX == length of file name in characters
;
lie80: cmp [eax].IE_Length, 0 ; If the entry length is zero
je lie99 ; then the index block is corrupt.
add ax, [eax].IE_Length ; Get the next entry.
jmp lie10
; Name not found in this block. Set eax to zero and return
;
lie99: xor eax, eax
ret
LocateIndexEntry endp
;****************************************************************************
;
; ReadWholeAttribute - Read an entire attribute value
;
; ENTRY: ebx -> attribute
; es:edi -> target buffer
;
; USES: ALL
;
ReadWholeAttribute proc near
cmp [ebx].ATTR_FormCode, RESIDENT_FORM
jne rwa10
; The attribute is resident.
; ebx -> attribute
; es:edi -> target buffer
;
SAVE_ALL
lea edx, [ebx].ATTR_FormUnion ; edx -> resident form info
mov ecx, [edx].RES_ValueLength ; ecx = bytes in value
mov esi, ebx ; esi -> attribute
add si, [edx].RES_ValueOffset ; esi -> attribute value
rep movsb ; copy bytes from value to buffer
RESTORE_ALL
ret ; That's all!
rwa10:
;
; The attribute type is non-resident. Just call
; ReadNonresidentAttribute starting at VCN 0 and
; asking for the whole thing.
;
; ebx -> attribute
; es:edi -> target buffer
;
lea edx, [ebx].ATTR_FormUnion ; edx -> nonresident form info
mov ecx, [edx].NONRES_HighestVcn.LowPart; ecx = HighestVcn
inc ecx ; ecx = clusters in attribute
sub eax, eax ; eax = 0 (first VCN to read)
call ReadNonresidentAttribute
ret
ReadWholeAttribute endp