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Added LBA support to FAT12/16 boot sector

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Now the FAT12/16 boot sector properly works on all FAT12/16 partition types (1, 4, 6, 0xe)
Fixed a few small bugs

svn path=/trunk/; revision=2852
This commit is contained in:
Brian Palmer 2002-04-16 06:11:08 +00:00
parent 3730336e4d
commit c44d02099d
17 changed files with 798 additions and 567 deletions
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14
freeldr/bootsect/Makefile
View file

@ -26,12 +26,10 @@ export NASM_CMD = nasm
.PHONY : clean
all: fat.bin fat32.bin bin2c.exe split.exe stubit.exe
all: fat.bin fat32.bin bin2c.exe
fat.bin: fat.asm bin2c.exe split.exe
$(NASM_CMD) -o fat_tmp.bin -f bin fat.asm
split fat_tmp.bin fat.bin fatstub.bin 512
$(RM) fat_tmp.bin
fat.bin: fat.asm bin2c.exe
$(NASM_CMD) -o fat.bin -f bin fat.asm
bin2c fat.bin fat.h fat_data
@ -42,12 +40,6 @@ fat32.bin: fat32.asm bin2c.exe
bin2c.exe: bin2c.c
$(CC) -o bin2c.exe bin2c.c
split.exe: split.c
$(CC) -o split.exe split.c
stubit.exe: stubit.c
$(CC) -o stubit.exe stubit.c
clean:
$(RM) *.bin
$(RM) *.exe

2
freeldr/bootsect/bin2c.c
View file

@ -45,4 +45,4 @@ int main(int argc, char *argv[])
fclose(out);
return 0;
}
}

661
freeldr/bootsect/fat.asm
View file

@ -1,6 +1,6 @@
; FAT.ASM
; FAT12/16 Boot Sector
; Copyright (c) 1998, 2001 Brian Palmer
; Copyright (c) 1998, 2001, 2002 Brian Palmer
@ -9,11 +9,27 @@
; for the file freeldr.sys and loads it into
; memory.
;
; The stack is set to 0000:7C00 so that the first
; DWORD pushed will be placed at 0000:7BFC
; The stack is set to 0000:7BF2 so that the first
; WORD pushed will be placed at 0000:7BF0
;
; The DWORD at 0000:7BFC or BP-04h is the logical
; sector number of the start of the data area.
;
; The DWORD at 0000:7BF8 or BP-08h is the total
; sector count of the boot drive as reported by
; the computers bios.
;
; The WORD at 0000:7BF6 or BP-0ah is the offset
; of the ReadSectors function in the boot sector.
;
; The WORD at 0000:7BF4 or BP-0ch is the offset
; of the ReadCluster function in the boot sector.
;
; The WORD at 0000:7BF2 or BP-0eh is the offset
; of the PutChars function in the boot sector.
;
; When it locates freeldr.sys on the disk it will
; load the first sector of the file to 0000:7E00
; load the first sector of the file to 0000:8000
; With the help of this sector we should be able
; to load the entire file off the disk, no matter
; how fragmented it is.
@ -23,6 +39,16 @@
; boots dramatically.
BootSectorStackTop equ 0x7bf2
DataAreaStartHigh equ 0x2
DataAreaStartLow equ 0x4
BiosCHSDriveSize equ 0x6
BiosCHSDriveSizeHigh equ 0x6
BiosCHSDriveSizeLow equ 0x8
ReadSectorsOffset equ 0xa
ReadClusterOffset equ 0xc
PutCharsOffset equ 0xe
org 7c00h
@ -55,180 +81,150 @@ VolumeLabel db 'NO NAME '
FileSystem db 'FAT12 '
main:
cli
cld
xor ax,ax
mov ss,ax
mov bp,7c00h
mov sp,bp ; Setup a stack
mov ax,cs ; Setup segment registers
mov ds,ax ; Make DS correct
mov es,ax ; Make ES correct
mov sp,BootSectorStackTop ; Setup a stack
mov ds,ax ; Make DS correct
mov es,ax ; Make ES correct
sti ; Enable ints now
mov [BYTE bp+BootDrive],dl ; Save the boot drive
xor ax,ax ; Zero out AX
mov [BYTE bp+BootDrive],dl ; Save the boot drive
GetDriveParameters:
mov ah,08h
mov dl,[BYTE bp+BootDrive] ; Get boot drive in dl
int 13h ; Request drive parameters from the bios
jnc CalcDriveSize ; If the call succeeded then calculate the drive size
; If we get here then the call to the BIOS failed
; so just set CHS equal to the maximum addressable
; size
mov cx,0ffffh
mov dh,cl
CalcDriveSize:
; Now that we have the drive geometry
; lets calculate the drive size
mov bl,ch ; Put the low 8-bits of the cylinder count into BL
mov bh,cl ; Put the high 2-bits in BH
shr bh,6 ; Shift them into position, now BX contains the cylinder count
and cl,3fh ; Mask off cylinder bits from sector count
; CL now contains sectors per track and DH contains head count
movzx eax,dh ; Move the heads into EAX
movzx ebx,bx ; Move the cylinders into EBX
movzx ecx,cl ; Move the sectors per track into ECX
inc eax ; Make it one based because the bios returns it zero based
inc ebx ; Make the cylinder count one based also
mul ecx ; Multiply heads with the sectors per track, result in edx:eax
mul ebx ; Multiply the cylinders with (heads * sectors) [stored in edx:eax already]
; We now have the total number of sectors as reported
; by the bios in eax, so store it in our variable
mov [BYTE bp-BiosCHSDriveSize],eax
; Reset disk controller
int 13h
jnc Continue1
jmp BadBoot ; Reset failed...
Continue1:
; Now we must find our way to the first sector of the root directory
xor ax,ax
xor dx,dx
mov al,[BYTE bp+NumberOfFats] ; Number of fats
mul WORD [BYTE bp+SectorsPerFat] ; Times sectors per fat
xor cx,cx
mov al,[BYTE bp+NumberOfFats] ; Number of fats
mul WORD [BYTE bp+SectorsPerFat] ; Times sectors per fat
add ax,WORD [BYTE bp+HiddenSectors]
adc dx,WORD [BYTE bp+HiddenSectors+2] ; Add the number of hidden sectors
add ax,WORD [BYTE bp+ReservedSectors] ; Add the number of reserved sectors
adc dx,byte 0 ; Add carry bit
push ax ; Store it on the stack
push dx ; Save 32-bit logical start sector
push ax
push dx ; Save it for later use also
adc dx,WORD [BYTE bp+HiddenSectors+2] ; Add the number of hidden sectors
add ax,WORD [BYTE bp+ReservedSectors] ; Add the number of reserved sectors
adc dx,cx ; Add carry bit
mov WORD [BYTE bp-DataAreaStartLow],ax ; Save the starting sector of the root directory
mov WORD [BYTE bp-DataAreaStartHigh],dx ; Save it in the first 4 bytes before the boot sector
mov si,WORD [BYTE bp+MaxRootEntries] ; Get number of root dir entries in SI
pusha ; Save 32-bit logical start sector of root dir
; DX:AX now has the number of the starting sector of the root directory
; Now calculate the size of the root directory
mov ax,0020h ; Size of dir entry
mul WORD [BYTE bp+MaxRootEntries] ; Times the number of entries
mov ax,0020h ; Size of dir entry
mul si ; Times the number of entries
mov bx,[BYTE bp+BytesPerSector]
add ax,bx
dec ax
div bx ; Divided by the size of a sector
; AX now has the number of root directory sectors
div bx ; Divided by the size of a sector
; AX now has the number of root directory sectors
xchg ax,cx ; Now CX has number of sectors
pop dx
pop ax ; Restore logical sector start
push cx ; Save number of root dir sectors for later use
mov bx,7c0h ; We will load the root directory
add bx,byte 20h ; Right after the boot sector in memory
mov es,bx
xor bx,bx ; We will load it to [0000:7e00h]
call ReadSectors ; Read the sectors
add [BYTE bp-DataAreaStartLow],ax ; Add the number of sectors of the root directory to our other value
adc [BYTE bp-DataAreaStartHigh],cx ; Now the first 4 bytes before the boot sector contain the starting sector of the data area
popa ; Restore root dir logical sector start to DX:AX
LoadRootDirSector:
mov bx,7e0h ; We will load the root directory sector
mov es,bx ; Right after the boot sector in memory
xor bx,bx ; We will load it to [0000:7e00h]
xor cx,cx ; Zero out CX
inc cx ; Now increment it to 1, we are reading one sector
xor di,di ; Zero out di
push es ; Save ES because it will get incremented by 20h
call ReadSectors ; Read the first sector of the root directory
pop es ; Restore ES (ES:DI = 07E0:0000)
; Now we have to find our way through the root directory to
; The OSLOADER.SYS file
mov bx,[BYTE bp+MaxRootEntries]; Search entire root directory
mov ax,7e0h ; We loaded at 07e0:0000
mov es,ax
xor di,di
mov si,filename
mov cx,11
rep cmpsb ; Compare filenames
jz FoundFile ; If same we found it
dec bx
jnz FindFile
jmp ErrBoot
SearchRootDirSector:
cmp [es:di],ch ; If the first byte of the directory entry is zero then we have
jz ErrBoot ; reached the end of the directory and FREELDR.SYS is not here so reboot
pusha ; Save all registers
mov cl,0xb ; Put 11 in cl (length of filename in directory entry)
mov si,filename ; Put offset of filename string in DS:SI
repe cmpsb ; Compare this directory entry against 'FREELDR SYS'
popa ; Restore all the registers
jz FoundFreeLoader ; If we found it then jump
dec si ; SI holds MaxRootEntries, subtract one
jz ErrBoot ; If we are out of root dir entries then reboot
add di,BYTE +0x20 ; Increment DI by the size of a directory entry
cmp di,0200h ; Compare DI to 512 (DI has offset to next dir entry, make sure we haven't gone over one sector)
jc SearchRootDirSector ; If DI is less than 512 loop again
jmp LoadRootDirSector ; Didn't find FREELDR.SYS in this directory sector, try again
FindFile:
mov ax,es ; We didn't find it in the previous dir entry
add ax,byte 2 ; So lets move to the next one
mov es,ax ; And search again
xor di,di
mov si,filename
mov cx,11
rep cmpsb ; Compare filenames
jz FoundFile ; If same we found it
dec bx ; Keep searching till we run out of dir entries
jnz FindFile ; Last entry?
jmp ErrBoot
FoundFile:
FoundFreeLoader:
; We found freeldr.sys on the disk
; so we need to load the first 512
; bytes of it to 0000:7E00
xor di,di ; ES:DI has dir entry
xor dx,dx
mov ax,WORD [es:di+1ah]; Get start cluster
dec ax ; Adjust start cluster by 2
dec ax ; Because the data area starts on cluster 2
xor ch,ch
mov cl,BYTE [BYTE bp+SectsPerCluster] ; Times sectors per cluster
mul cx
pop cx ; Get number of sectors for root dir
add ax,cx ; Add it to the start sector of freeldr.sys
adc dx,byte 0
pop cx ; Get logical start sector of
pop bx ; Root directory
add ax,bx ; Now we have DX:AX with the logical start
adc dx,cx ; Sector of OSLOADER.SYS
mov cx,1 ; We will load 1 sector
push WORD [es:di+1ah] ; Save start cluster
mov bx,7e0h
mov es,bx
xor bx,bx
call ReadSectors ; Load it
pop ax ; Restore start cluster
jmp LoadFile
; bytes of it to 0000:8000
; ES:DI has dir entry (ES:DI == 07E0:XXXX)
mov ax,WORD [es:di+1ah] ; Get start cluster
push ax ; Save start cluster
push WORD 800h ; Put 800h on the stack and load it
pop es ; Into ES so that we load the cluster at 0000:8000
call ReadCluster ; Read the cluster
pop ax ; Restore start cluster of FreeLoader
; Save the addresses of needed functions so
; the helper code will know where to call them.
mov WORD [BYTE bp-ReadSectorsOffset],ReadSectors ; Save the address of ReadSectors
mov WORD [BYTE bp-ReadClusterOffset],ReadCluster ; Save the address of ReadCluster
mov WORD [BYTE bp-PutCharsOffset],PutChars ; Save the address of PutChars
; Now AX has start cluster of FreeLoader and we
; have loaded the helper code in the first 512 bytes
; of FreeLoader to 0000:8000. Now transfer control
; to the helper code. Skip the first three bytes
; because they contain a jump instruction to skip
; over the helper code in the FreeLoader image.
;jmp 0000:8003h
jmp 8003h
; Reads cluster number in AX into [ES:0000]
ReadCluster:
; StartSector = ((Cluster - 2) * SectorsPerCluster) + ReservedSectors + HiddenSectors;
dec ax ; Adjust start cluster by 2
dec ax ; Because the data area starts on cluster 2
xor ch,ch
mov cl,BYTE [BYTE bp+SectsPerCluster]
mul cx ; Times sectors per cluster
add ax,[BYTE bp-DataAreaStartLow] ; Add start of data area
adc dx,[BYTE bp-DataAreaStartHigh] ; Now we have DX:AX with the logical start sector of OSLOADER.SYS
xor bx,bx ; We will load it to [ES:0000], ES loaded before function call
mov cl,BYTE [BYTE bp+SectsPerCluster]
call ReadSectors
ret
; Reads logical sectors into [ES:BX]
; DX:AX has logical sector number to read
; CX has number of sectors to read
; CarryFlag set on error
ReadSectors:
push ax
push dx
push cx
xchg ax,cx
xchg ax,dx
xor dx,dx
div WORD [BYTE bp+SectorsPerTrack]
xchg ax,cx
div WORD [BYTE bp+SectorsPerTrack] ; Divide logical by SectorsPerTrack
inc dx ; Sectors numbering starts at 1 not 0
xchg cx,dx
div WORD [BYTE bp+NumberOfHeads] ; Number of heads
mov dh,dl ; Head to DH, drive to DL
mov dl,[BYTE bp+BootDrive] ; Drive number
mov ch,al ; Cylinder in CX
ror ah,1 ; Low 8 bits of cylinder in CH, high 2 bits
ror ah,1 ; in CL shifted to bits 6 & 7
or cl,ah ; Or with sector number
mov ax,0201h
int 13h ; DISK - READ SECTORS INTO MEMORY
; AL = number of sectors to read, CH = track, CL = sector
; DH = head, DL = drive, ES:BX -> buffer to fill
; Return: CF set on error, AH = status (see AH=01h), AL = number of sectors read
jc BadBoot
pop cx
pop dx
pop ax
inc ax ;Increment Sector to Read
jnz NoCarry
inc dx
NoCarry:
push bx
mov bx,es
add bx,byte 20h
mov es,bx
pop bx
; Increment read buffer for next sector
loop ReadSectors ; Read next sector
ret
; Displays a bad boot message
; And reboots
BadBoot:
mov si,msgDiskError ; Bad boot disk message
call PutChars ; Display it
mov si,msgAnyKey ; Press any key message
call PutChars ; Display it
jmp Reboot
; Displays an error message
; And reboots
@ -254,246 +250,131 @@ PutChars:
Done:
retn
; Displays a bad boot message
; And reboots
BadBoot:
mov si,msgDiskError ; Bad boot disk message
call PutChars ; Display it
mov si,msgAnyKey ; Press any key message
call PutChars ; Display it
jmp Reboot
; Reads logical sectors into [ES:BX]
; DX:AX has logical sector number to read
; CX has number of sectors to read
ReadSectors:
cmp dx,WORD [BYTE bp-BiosCHSDriveSizeHigh]; Check if they are reading a sector within CHS range
jb ReadSectorsCHS ; Yes - go to the old CHS routine
cmp ax,WORD [BYTE bp-BiosCHSDriveSizeLow]; Check if they are reading a sector within CHS range
jbe ReadSectorsCHS ; Yes - go to the old CHS routine
ReadSectorsLBA:
pushad ; Save logical sector number & sector count
o32 push byte 0
push dx ; Put 64-bit logical
push ax ; block address on stack
push es ; Put transfer segment on stack
push bx ; Put transfer offset on stack
push byte 1 ; Set transfer count to 1 sector
push byte 0x10 ; Set size of packet to 10h
mov si,sp ; Setup disk address packet on stack
; We are so totally out of space here that I am forced to
; comment out this very beautifully written piece of code
; It would have been nice to have had this check...
;CheckInt13hExtensions: ; Now make sure this computer supports extended reads
; mov ah,0x41 ; AH = 41h
; mov bx,0x55aa ; BX = 55AAh
; mov dl,[BYTE bp+BootDrive] ; DL = drive (80h-FFh)
; int 13h ; IBM/MS INT 13 Extensions - INSTALLATION CHECK
; jc PrintDiskError ; CF set on error (extensions not supported)
; cmp bx,0xaa55 ; BX = AA55h if installed
; jne PrintDiskError
; test cl,1 ; CX = API subset support bitmap
; jz PrintDiskError ; Bit 0, extended disk access functions (AH=42h-44h,47h,48h) supported
; Good, we're here so the computer supports LBA disk access
; So finish the extended read
mov dl,[BYTE bp+BootDrive] ; Drive number
mov ah,42h ; Int 13h, AH = 42h - Extended Read
int 13h ; Call BIOS
jc BadBoot ; If the read failed then abort
add sp,0x10 ; Remove disk address packet from stack
popad ; Restore sector count & logical sector number
inc ax ; Increment Sector to Read
jnz NoCarry
inc dx
NoCarry:
mov dx,es
add dx,byte 20h ; Increment read buffer for next sector
mov es,dx
loop ReadSectorsLBA ; Read next sector
ret
; Reads logical sectors into [ES:BX]
; DX:AX has logical sector number to read
; CX has number of sectors to read
; CarryFlag set on error
ReadSectorsCHS:
pushad
xchg ax,cx
xchg ax,dx
xor dx,dx
div WORD [BYTE bp+SectorsPerTrack]
xchg ax,cx
div WORD [BYTE bp+SectorsPerTrack] ; Divide logical by SectorsPerTrack
inc dx ; Sectors numbering starts at 1 not 0
xchg cx,dx
div WORD [BYTE bp+NumberOfHeads] ; Number of heads
mov dh,dl ; Head to DH, drive to DL
mov dl,[BYTE bp+BootDrive] ; Drive number
mov ch,al ; Cylinder in CX
ror ah,1 ; Low 8 bits of cylinder in CH, high 2 bits
ror ah,1 ; in CL shifted to bits 6 & 7
or cl,ah ; Or with sector number
mov ax,0201h
int 13h ; DISK - READ SECTORS INTO MEMORY
; AL = number of sectors to read, CH = track, CL = sector
; DH = head, DL = drive, ES:BX -> buffer to fill
; Return: CF set on error, AH = status (see AH=01h), AL = number of sectors read
jc BadBoot
popad
inc ax ;Increment Sector to Read
jnz NoCarryCHS
inc dx
NoCarryCHS:
push bx
mov bx,es
add bx,byte 20h
mov es,bx
pop bx
; Increment read buffer for next sector
loop ReadSectorsCHS ; Read next sector
ret
msgDiskError db 'Disk error',0dh,0ah,0
msgFreeLdr db 'FREELDR.SYS not found',0dh,0ah,0
msgAnyKey db 'Press any key to restart',0dh,0ah,0
; Sorry, need the space...
;msgAnyKey db 'Press any key to restart',0dh,0ah,0
msgAnyKey db 'Press any key',0dh,0ah,0
filename db 'FREELDR SYS'
times 510-($-$$) db 0 ; Pad to 510 bytes
dw 0aa55h ; BootSector signature
; End of bootsector
;
; Now starts the extra boot code that we will store
; in the first 512 bytes of freeldr.sys
LoadFile:
push ax ; First save AX - the start cluster of freeldr.sys
; Display "Loading FreeLoader..." message
mov si,msgLoading ; Loading message
call PutChars ; Display it
pop ax ; Restore AX
; AX has start cluster of freeldr.sys
push ax
call ReadFatIntoMemory
pop ax
mov bx,7e0h
mov es,bx
LoadFile2:
push ax
call IsFat12
pop ax
jnc LoadFile3
cmp ax,0ff8h ; Check to see if this is the last cluster in the chain
jmp LoadFile4
LoadFile3:
cmp ax,0fff8h
LoadFile4:
jae LoadFile_Done ; If so continue, if not then read then next one
push ax
xor bx,bx ; Load ROSLDR starting at 0000:8000h
push es
call ReadCluster
pop es
xor bx,bx
mov bl,BYTE [BYTE bp+SectsPerCluster]
shl bx,5 ; BX = BX * 512 / 16
mov ax,es ; Increment the load address by
add ax,bx ; The size of a cluster
mov es,ax
call IsFat12
pop ax
push es
jnc LoadFile5
call GetFatEntry12 ; Get the next entry
jmp LoadFile6
LoadFile5:
call GetFatEntry16
LoadFile6:
pop es
jmp LoadFile2 ; Load the next cluster (if any)
LoadFile_Done:
mov dl,BYTE [BYTE bp+BootDrive]
xor ax,ax
push ax
mov ax,8000h
push ax ; We will do a far return to 0000:8000h
retf ; Transfer control to ROSLDR
; Reads the entire FAT into memory at 7000:0000
ReadFatIntoMemory:
mov ax,WORD [BYTE bp+HiddenSectors]
mov dx,WORD [BYTE bp+HiddenSectors+2]
add ax,WORD [BYTE bp+ReservedSectors]
adc dx,byte 0
mov cx,WORD [BYTE bp+SectorsPerFat]
mov bx,7000h
mov es,bx
xor bx,bx
call ReadSectors
ret
; Returns the FAT entry for a given cluster number for 16-bit FAT
; On entry AX has cluster number
; On return AX has FAT entry for that cluster
GetFatEntry16:
xor dx,dx
mov cx,2 ; AX = AX * 2 (since FAT16 entries are 2 bytes)
mul cx
shl dx,0fh
mov bx,7000h
add bx,dx
mov es,bx
mov bx,ax ; Restore FAT entry offset
mov ax,WORD [es:bx] ; Get FAT entry
ret
; Returns the FAT entry for a given cluster number for 12-bit FAT
; On entry AX has cluster number
; On return AX has FAT entry for that cluster
GetFatEntry12:
push ax
mov cx,ax
shr ax,1
add ax,cx ; AX = AX * 1.5 (AX = AX + (AX / 2)) (since FAT12 entries are 12 bits)
mov bx,7000h
mov es,bx
mov bx,ax ; Put FAT entry offset into BX
mov ax,WORD [es:bx] ; Get FAT entry
pop cx ; Get cluster number from stack
and cx,1
jz UseLow12Bits
and ax,0fff0h
shr ax,4
jmp GetFatEntry12_Done
UseLow12Bits:
and ax,0fffh
GetFatEntry12_Done:
ret
; Reads cluster number in AX into [ES:0000]
ReadCluster:
; StartSector = ((Cluster - 2) * SectorsPerCluster) + + ReservedSectors + HiddenSectors;
dec ax
dec ax
xor dx,dx
movzx bx,BYTE [BYTE bp+SectsPerCluster]
mul bx
push ax
push dx
; Now calculate the size of the root directory
mov ax,0020h ; Size of dir entry
mul WORD [BYTE bp+MaxRootEntries] ; Times the number of entries
mov bx,WORD [BYTE bp+BytesPerSector]
add ax,bx
dec ax
div bx ; Divided by the size of a sector
mov cx,ax
; CX now has the number of root directory sectors
xor dx,dx
movzx ax,BYTE [BYTE bp+NumberOfFats]
mul WORD [BYTE bp+SectorsPerFat]
add ax,WORD [BYTE bp+ReservedSectors]
adc dx,byte 0
add ax,WORD [BYTE bp+HiddenSectors]
adc dx,WORD [BYTE bp+HiddenSectors+2]
add ax,cx
adc dx,byte 0
pop cx
pop bx
add ax,bx
adc dx,cx
xor bx,bx ; We will load it to [ES:0000], ES loaded before function call
movzx cx,BYTE [BYTE bp+SectsPerCluster]
call ReadSectors
ret
; Returns CF = 1 if this is a FAT12 file system
; Otherwise CF = 0 for FAT16
IsFat12:
; Now calculate the size of the root directory
mov ax,0020h ; Size of dir entry
mul WORD [BYTE bp+MaxRootEntries] ; Times the number of entries
mov bx,WORD [BYTE bp+BytesPerSector]
add ax,bx ; Plus (BytesPerSector - 1)
dec ax
div bx ; Divided by the size of a sector
; AX now has the number of root directory sectors
mov bx,ax
; Now we must find our way to the first sector of the root directory
xor ax,ax
xor dx,dx
mov al,BYTE [BYTE bp+NumberOfFats] ; Number of fats
mul WORD [BYTE bp+SectorsPerFat] ; Times sectors per fat
add ax,WORD [BYTE bp+HiddenSectors]
adc dx,WORD [BYTE bp+HiddenSectors+2] ; Add the number of hidden sectors
add ax,[BYTE bp+ReservedSectors] ; Add the number of reserved sectors
adc dx,byte 0 ; Add carry bit
add ax,bx
adc dx,byte 0 ; Add carry bit
; DX:AX now has the number of the starting sector of the data area
xor cx,cx
mov bx,WORD [BYTE bp+TotalSectors]
cmp bx,byte 0
jnz IsFat12_2
mov bx,WORD [BYTE bp+TotalSectorsBig]
mov cx,WORD [BYTE bp+TotalSectorsBig+2]
; CX:BX now contains the number of sectors on the volume
IsFat12_2:
sub bx,ax ; Subtract data area start sector
sub cx,dx ; from total sectors of volume
mov ax,bx
mov dx,cx
; DX:AX now contains the number of data sectors on the volume
movzx bx,BYTE [BYTE bp+SectsPerCluster]
div bx
; AX now has the number of clusters on the volume
stc
cmp ax,4085
jb IsFat12_Done
clc
IsFat12_Done:
ret
times 998-($-$$) db 0 ; Pad to 998 bytes
msgLoading db 'Loading FreeLoader...',0dh,0ah,0
dw 0aa55h ; BootSector signature

53
freeldr/bootsect/fat32.asm
View file

@ -1,9 +1,8 @@
; FAT32.ASM
; FAT32 Boot Sector
; Copyright (c) 1998, 2000, 2001 Brian Palmer
; Copyright (c) 1998, 2000, 2001, 2002 Brian Palmer
;org 7c00h
org 0
org 7c00h
segment .text
@ -43,32 +42,12 @@ VolumeLabel db 'NO NAME '
FileSystem db 'FAT32 '
main:
cli
cld
; Lets copy ourselves from 0000:7c00 to 9000:0000
; and transfer control to the new code
xor ax,ax
mov ds,ax
mov si,7c00h
mov ax,9000h
mov es,ax
xor di,di
mov cx,512
rep movsb
jmp 0x9000:RealMain
; Now we are executing at 9000:xxxx
; We are now free to load freeldr.sys at 0000:7e00
RealMain:
xor ax,ax
mov bp,ax
mov sp,ax ; Setup a stack
mov ax,cs ; Setup segment registers
xor ax,ax ; Setup segment registers
mov ds,ax ; Make DS correct
mov es,ax ; Make ES correct
mov ss,ax ; Make SS correct
sti ; Enable ints now
mov bp,7c00h
mov sp,7c00h ; Setup a stack
@ -121,13 +100,13 @@ CalcDriveSize:
LoadExtraBootCode:
; First we have to load our extra boot code at
; sector 14 into memory at [9000:0200h]
; sector 14 into memory at [0000:7e00h]
mov eax,0eh
add eax,DWORD [BYTE bp+HiddenSectors] ; Add the number of hidden sectors
mov cx,1
mov bx,9000h
mov es,bx ; Read sector to [9000:0200h]
mov bx,0200h
xor bx,bx
mov es,bx ; Read sector to [0000:7e00h]
mov bx,7e00h
call ReadSectors
jmp StartSearch
@ -291,8 +270,8 @@ StartSearch:
jb ContinueSearch ; If not continue, if so then we didn't find freeldr.sys
jmp PrintFileNotFound
ContinueSearch:
mov bx,7e0h
mov es,bx ; Read cluster to [0000:7e00h]
mov bx,800h
mov es,bx ; Read cluster to [0000:8000h]
call ReadCluster ; Read the cluster
@ -301,7 +280,7 @@ ContinueSearch:
xor bx,bx
mov bl,[BYTE bp+SectsPerCluster]
shl bx,4 ; BX = BX * 512 / 32
mov ax,7e0h ; We loaded at 07e0:0000
mov ax,800h ; We loaded at 0800:0000
mov es,ax
xor di,di
mov si,filename
@ -354,14 +333,14 @@ CheckEndCluster:
jmp PrintFileSystemError ; If so exit with error
InitializeLoadSegment:
mov bx,7e0h
mov bx,800h
mov es,bx
LoadFile:
cmp eax,0ffffff8h ; Check to see if this is the last cluster in the chain
jae LoadFileDone ; If so continue, if not then read the next one
push eax
xor bx,bx ; Load ROSLDR starting at 0000:7e00h
xor bx,bx ; Load ROSLDR starting at 0000:8000h
push es
call ReadCluster
pop es
@ -382,8 +361,8 @@ LoadFile:
LoadFileDone:
mov dl,[BYTE bp+BootDrive]
xor ax,ax ; We loaded at 0000:7e00 but the entry point is 0000:8000
push ax ; because the first 512 bytes is fat helper code
xor ax,ax
push ax ; We loaded at 0000:8000
push WORD 8000h ; We will do a far return to 0000:8000h
retf ; Transfer control to ROSLDR

55
freeldr/bootsect/split.c
View file

@ -1,55 +0,0 @@
#include <stdio.h>
FILE *in;
FILE *out;
FILE *new;
int main(int argc, char *argv[])
{
unsigned char ch;
int cnt;
int split_offset;
if (argc < 5)
{
printf("usage: split infile.bin outfile.bin newfile.bin split_offset\n");
return -1;
}
if ((in = fopen(argv[1], "rb")) == NULL)
{
printf("Couldn't open data file.\n");
return -1;
}
if ((out = fopen(argv[2], "wb")) == NULL)
{
printf("Couldn't open output file.\n");
return -1;
}
if ((new = fopen(argv[3], "wb")) == NULL)
{
printf("Couldn't open new file.\n");
return -1;
}
split_offset = atoi(argv[4]);
for (cnt=0; cnt<split_offset; cnt++)
{
ch = fgetc(in);
fputc(ch, out);
}
ch = fgetc(in);
while (!feof(in))
{
fputc(ch, new);
ch = fgetc(in);
}
fclose(in);
fclose(out);
fclose(new);
return 0;
}

52
freeldr/bootsect/stubit.c
View file

@ -1,52 +0,0 @@
#include <stdio.h>
FILE *in;
FILE *in2;
FILE *out;
int main(int argc, char *argv[])
{
unsigned char ch;
if (argc < 4)
{
printf("usage: stubit infile1.bin infile2.sys outfile.bin\n");
return -1;
}
if ((in = fopen(argv[1], "rb")) == NULL)
{
printf("Couldn't open data file.\n");
return -1;
}
if ((in2 = fopen(argv[2], "rb")) == NULL)
{
printf("Couldn't open data file.\n");
return -1;
}
if ((out = fopen(argv[3], "wb")) == NULL)
{
printf("Couldn't open output file.\n");
return -1;
}
ch = fgetc(in);
while (!feof(in))
{
fputc(ch, out);
ch = fgetc(in);
}
ch = fgetc(in2);
while (!feof(in2))
{
fputc(ch, out);
ch = fgetc(in2);
}
fclose(in);
fclose(in2);
fclose(out);
return 0;
}

4
freeldr/bootsect/win2k.asm
View file

@ -19,6 +19,8 @@
; sector number of the start of the data area.
;
org 7c00h
segment .text
bits 16
@ -49,7 +51,7 @@ FSInfoSector dw 0
BackupBootSector dw 6
Reserved1 times 12 db 0
; End FAT32 Inserted Info
BootDrive db 0
BootDrive db 80h
Reserved db 0
ExtendSig db 29h
SerialNumber dd 00000000h

249
freeldr/bootsect/wxpfat16.asm Normal file
View file

@ -0,0 +1,249 @@
;
; The BP register is initialized to 0x7c00, the start of
; the boot sector. The SP register is initialized to
; 0x7bf0, leaving 16 bytes of data storage space above
; the stack.
;
; The DWORD that gets stored at 0x7bfc is the logical
; sector number of the start of the data area.
;
; The DWORD that gets stored at 0x7bf8 is ????????
;
; The DWORD that gets stored at 0x7bf4 is ????????
;
; The DWORD that gets stored at 0x7bf0 is ????????
;
org 7c00h
segment .text
bits 16
start:
jmp short main
nop
OEMName db 'MSWIN4.0'
BytesPerSector dw 512
SectsPerCluster db 1
ReservedSectors dw 1
NumberOfFats db 2
MaxRootEntries dw 0 ;512 - Always zero for FAT32 volumes
TotalSectors dw 0 ;2880 - Always zero for FAT32 volumes
MediaDescriptor db 0f8h
SectorsPerFat dw 0 ;9 - Always zero for FAT32 volumes
SectorsPerTrack dw 18
NumberOfHeads dw 2
HiddenSectors dd 0
TotalSectorsBig dd 0
BootDrive db 80h
Reserved db 0
ExtendSig db 29h
SerialNumber dd 00000000h
VolumeLabel db 'NO NAME '
FileSystem db 'FAT16 '
main:
00007C3E 33C9 xor cx,cx
00007C40 8ED1 mov ss,cx ; Setup stack
00007C42 BCF07B mov sp,0x7bf0 ; Give us 16 bytes (4 dwords) of space above stack
00007C45 8ED9 mov ds,cx
00007C47 B80020 mov ax,0x2000
00007C4A 8EC0 mov es,ax ; Setup ES:0000 == 2000:0000
00007C4C FC cld
00007C4D BD007C mov bp,0x7c00
00007C50 384E24 cmp [bp+BootDrive],cl ; Compare the boot drive to zero (I think they are testing for a hard disk drive number)
00007C53 7D24 jnl floppy_boot ; Nope, it's a floppy, skip partition table tests
00007C55 8BC1 mov ax,cx ; Move zero to AX
00007C57 99 cwd ; DX:AX now contains zero
00007C58 E83C01 call read_one_sector ; Try to read in the MBR sector
00007C5B 721C jc floppy_boot ; Read failed, continue
00007C5D 83EB3A sub bx,byte +0x3a ; BX comes back with 512, make it equal to 454 (offset of partition table in MBR)
00007C60 66A11C7C mov eax,[HiddenSectors] ; Put HiddenSectors in EAX
find_our_partition:
00007C64 26663B07 cmp eax,[es:bx] ; Compare partition table entry's start sector to HiddenSectors
00007C68 268A57FC mov dl,[es:bx-0x4] ; Get partition type byte for this entry
00007C6C 7506 jnz next_partition_entry ; If partition start sector != HiddenSectors then skip this entry
00007C6E 80CA02 or dl,0x2 ; Set the second bit in partition type?? I guess this makes types 4 & 6 identical
00007C71 885602 mov [bp+0x2],dl ; Save it on top of nop instruction (3rd byte of boot sector)
next_partition_entry:
00007C74 80C310 add bl,0x10 ; Add 16 to bl (offset of next entry in partition table)
00007C77 73EB jnc find_our_partition ; Jump back until we hit the end of the partition table
; We now have our partition type at 0000:7C02
; If the type was 4 or 6 then that byte is 6
; I can't imagine why the boot sector needs to store
; this information, but hopefully I will uncover it
; as I further disassemble this boot sector.
floppy_boot:
00007C79 33C9 xor cx,cx ; Zero out CX
00007C7B 8A4610 mov al,[bp+NumberOfFats] ; Get the number of FATs in AL (usually 2)
00007C7E 98 cbw ; Sign extend it into AX (AX == 2)
00007C7F F76616 mul word [bp+NumberOfFats] ; Multiply it with NumberOfFats PLUS the low byte of MaxRootEntries!!??
00007C82 03461C add ax,[bp+HiddenSectors] ; Result is in DX:AX
00007C85 13561E adc dx,[bp+HiddenSectors+2] ; Add HiddenSectors to DX:AX
00007C88 03460E add ax,[bp+ReservedSectors] ; Add ReservedSectors to DX:AX
00007C8B 13D1 adc dx,cx ; CX still contains zero
00007C8D 8B7611 mov si,[bp+MaxRootEntries] ; Get MaxRootEntries in SI
00007C90 60 pusha ; Save all registers (right now DX:AX has starting sector of root dir)
00007C91 8946FC mov [bp-0x4],ax ; Save the starting sector of the root directory
00007C94 8956FE mov [bp-0x2],dx ; Save it in the first 4 bytes before the boot sector
00007C97 B82000 mov ax,0x20 ; AX == 32 (size of a directory entry)
00007C9A F7E6 mul si ; Multiply it with MaxRootEntries (DX:AX == length in bytes of root directory)
00007C9C 8B5E0B mov bx,[bp+BytesPerSector] ; Get the BytesPerSector in BX
00007C9F 03C3 add ax,bx ; Add it to AX (what if this addition carries? MS should 'adc dx,0' shouldn't they?)
00007CA1 48 dec ax ; Subtract one (basically rounding up)
00007CA2 F7F3 div bx ; Divide DX:AX (length of root dir in bytes) by the size of a sector
00007CA4 0146FC add [bp-0x4],ax ; Add the number of sectors of the root directory to our other value
00007CA7 114EFE adc [bp-0x2],cx ; Now the first 4 bytes before the boot sector contain the starting sector of the data area
00007CAA 61 popa ; Restore all registers (DX:AX has start sector of root dir)
load_root_dir_sector:
00007CAB BF0000 mov di,0x0 ; Zero out di
00007CAE E8E600 call read_one_sector ; Read the first sector of the root directory
00007CB1 7239 jc print_disk_error_message ; Read failed, print disk error and reboot
search_directory:
00007CB3 26382D cmp [es:di],ch ; If the first byte of the directory entry is zero then we have reached the end
00007CB6 7417 jz print_ntldr_error_message; of the directory and NTLDR is not here so reboot
00007CB8 60 pusha ; Save all registers
00007CB9 B10B mov cl,0xb ; Put 11 in cl (length of filename in directory entry)
00007CBB BEA17D mov si,NTLDR ; Put offset of filename string in DS:SI
00007CBE F3A6 repe cmpsb ; Compare this directory entry against 'NTLDR '
00007CC0 61 popa ; Restore all the registers
00007CC1 7432 jz found_ntldr ; If we found NTLDR then jump
00007CC3 4E dec si ; SI holds MaxRootEntries, subtract one
00007CC4 7409 jz print_ntldr_error_message; If we are out of root dir entries then reboot
00007CC6 83C720 add di,byte +0x20 ; Increment DI by the size of a directory entry
00007CC9 3BFB cmp di,bx ; Compare DI to BX (DI has offset to next dir entry, BX has address of end of directory sector in memory)
00007CCB 72E6 jc search_directory ; If DI is less than BX loop again
00007CCD EBDC jmp short load_root_dir_sector ; Didn't find NTLDR in this directory sector, try again
print_ntldr_error_message:
00007CCF A0FB7D mov al,[NTLDR_ERR_offset_from_0x7d00]
putchars:
00007CD2 B47D mov ah,0x7d
00007CD4 8BF0 mov si,ax
get_another_char:
00007CD6 AC lodsb
00007CD7 98 cbw
00007CD8 40 inc ax
00007CD9 740C jz print_reboot_message
00007CDB 48 dec ax
00007CDC 7413 jz reboot
00007CDE B40E mov ah,0xe
00007CE0 BB0700 mov bx,0x7
00007CE3 CD10 int 0x10
00007CE5 EBEF jmp short get_another_char
print_reboot_message:
00007CE7 A0FD7D mov al,[RESTART_ERR_offset_from_0x7d00]
00007CEA EBE6 jmp short putchars
print_disk_error_message:
00007CEC A0FC7D mov al,[DISK_ERR_offset_from_0x7d00]
00007CEF EBE1 jmp short putchars
reboot:
00007CF1 CD16 int 0x16
00007CF3 CD19 int 0x19
found_ntldr:
00007CF5 268B551A mov dx,[es:di+0x1a] ; Get NTLDR start cluster in DX
00007CF9 52 push dx ; Save it on the stack
00007CFA B001 mov al,0x1 ; Read 1 cluster? Or is this one sector?
00007CFC BB0000 mov bx,0x0 ; ES:BX is the load address (2000:0000)
00007CFF E83B00 call read_cluster ; Do the read
00007D02 72E8 jc print_disk_error_message ; If it failed then reboot
00007D04 5B pop bx ; Get the start cluster of NTLDR in BX
00007D05 8A5624 mov dl,[bp+BootDrive] ; Get boot drive in DL
00007D08 BE0B7C mov si,0x7c0b
00007D0B 8BFC mov di,sp
00007D0D C746F03D7D mov word [bp-0x10],read_cluster
00007D12 C746F4297D mov word [bp-0xc],0x7d29
00007D17 8CD9 mov cx,ds
00007D19 894EF2 mov [bp-0xe],cx
00007D1C 894EF6 mov [bp-0xa],cx
00007D1F C606967DCB mov byte [0x7d96],0xcb
00007D24 EA03000020 jmp 0x2000:0x3
00007D29 0FB6C8 movzx cx,al
00007D2C 668B46F8 mov eax,[bp-0x8]
00007D30 6603461C add eax,[bp+HiddenSectors]
00007D34 668BD0 mov edx,eax
00007D37 66C1EA10 shr edx,0x10
00007D3B EB5E jmp short 0x7d9b
read_cluster:
00007D3D 0FB6C8 movzx cx,al
00007D40 4A dec dx
00007D41 4A dec dx
00007D42 8A460D mov al,[bp+SectsPerCluster]
00007D45 32E4 xor ah,ah
00007D47 F7E2 mul dx
00007D49 0346FC add ax,[bp-0x4]
00007D4C 1356FE adc dx,[bp-0x2]
00007D4F EB4A jmp short 0x7d9b
read_sectors:
00007D51 52 push dx
00007D52 50 push ax
00007D53 06 push es
00007D54 53 push bx
00007D55 6A01 push byte +0x1
00007D57 6A10 push byte +0x10
00007D59 91 xchg ax,cx
00007D5A 8B4618 mov ax,[bp+SectorsPerTrack]
00007D5D 96 xchg ax,si
00007D5E 92 xchg ax,dx
00007D5F 33D2 xor dx,dx
00007D61 F7F6 div si
00007D63 91 xchg ax,cx
00007D64 F7F6 div si
00007D66 42 inc dx
00007D67 87CA xchg cx,dx
00007D69 F7761A div word [bp+NumberOfHeads]
00007D6C 8AF2 mov dh,dl
00007D6E 8AE8 mov ch,al
00007D70 C0CC02 ror ah,0x2
00007D73 0ACC or cl,ah
00007D75 B80102 mov ax,0x201
00007D78 807E020E cmp byte [bp+0x2],0xe
00007D7C 7504 jnz 0x7d82
00007D7E B442 mov ah,0x42
00007D80 8BF4 mov si,sp
00007D82 8A5624 mov dl,[bp+BootDrive]
00007D85 CD13 int 0x13
00007D87 61 popa
00007D88 61 popa
00007D89 720B jc 0x7d96
00007D8B 40 inc ax
00007D8C 7501 jnz 0x7d8f
00007D8E 42 inc dx
00007D8F 035E0B add bx,[bp+BytesPerSector]
00007D92 49 dec cx
00007D93 7506 jnz 0x7d9b
00007D95 F8 clc
00007D96 C3 ret
read_one_sector:
00007D97 41 inc cx
00007D98 BB0000 mov bx,0x0
00007D9B 60 pusha
00007D9C 666A00 o32 push byte +0x0
00007D9F EBB0 jmp short 0x7d51
NTLDR db 'NTLDR '
NTLDR_ERR db 0dh,0ah,'NTLDR is missing',0ffh
DISK_ERR db 0dh,0ah,'Disk error',0ffh
RESTART_ERR db 0dh,0ah,'Press any key to restart',0dh,0ah
filler times 18 db 0
NTLDR_offset_from_0x7d00 db 0
NTLDR_ERR_offset_from_0x7d00 db 0ach
DISK_ERR_offset_from_0x7d00 db 0bfh
RESTART_ERR_offset_from_0x7d00 db 0cch
dw 0
dw 0aa55h

3
freeldr/freeldr/Makefile
View file

@ -34,8 +34,7 @@ LIB_FILES2 = comm/comm.a disk/disk.a mm/mm.a cache/cache.a inifile/inifile.a
all: freeldr.sys
freeldr.sys: c_code.a end.o
$(LD) -N -Ttext=0x8000 --oformat=binary -s -o f.sys c_code.a end.o
../bootsect/stubit ../bootsect/fatstub.bin f.sys freeldr.sys
$(LD) -N -Ttext=0x8000 --oformat=binary -s -o freeldr.sys c_code.a end.o
freeldr.exe: asmcode.a c_code.a
$(LD) -o freeldr.exe asmcode.a c_code.a

5
freeldr/freeldr/arch/i386/Makefile
View file

@ -19,7 +19,7 @@
include ../../rules.mk
OBJS = arch.o boot.o mb.o mem.o disk.o
OBJS = fathelp.o arch.o boot.o mb.o mem.o disk.o
.PHONY : clean
@ -30,6 +30,9 @@ arch.a: $(OBJS)
- $(RM) ..\arch.a
$(CP) arch.a ..\arch.a
fathelp.o: fathelp.asm
$(NASM_CMD) -o fathelp.o -f coff fathelp.asm
arch.o: arch.S
$(CC) $(FLAGS) -o arch.o -c arch.S

2
freeldr/freeldr/arch/i386/arch.S
View file

@ -24,7 +24,7 @@
#include "arch.h"
EXTERN(start)
EXTERN(RealEntryPoint)
cli

226
freeldr/freeldr/arch/i386/fathelp.asm Normal file
View file

@ -0,0 +1,226 @@
; FATHELP.ASM
; FAT12/16 Boot Sector Helper Code
; Copyright (c) 1998, 2001, 2002 Brian Palmer
;org 8000h
segment .text
bits 16
BootSectorStackTop equ 0x7bf2
DataAreaStartHigh equ 0x2
DataAreaStartLow equ 0x4
BiosCHSDriveSize equ 0x6
BiosCHSDriveSizeHigh equ 0x6
BiosCHSDriveSizeLow equ 0x8
ReadSectorsOffset equ 0xa
ReadClusterOffset equ 0xc
PutCharsOffset equ 0xe
OEMName equ 3
BytesPerSector equ 11
SectsPerCluster equ 13
ReservedSectors equ 14
NumberOfFats equ 16
MaxRootEntries equ 17
TotalSectors equ 19
MediaDescriptor equ 21
SectorsPerFat equ 22
SectorsPerTrack equ 24
NumberOfHeads equ 26
HiddenSectors equ 28
TotalSectorsBig equ 32
BootDrive equ 36
Reserved equ 37
ExtendSig equ 38
SerialNumber equ 39
VolumeLabel equ 43
FileSystem equ 54
; This code will be stored in the first 512 bytes
; of freeldr.sys. The first 3 bytes will be a jmp
; instruction to skip past the FAT helper code
; that is stored in the rest of the 512 bytes.
;
; This code is loaded at 0000:8000 so we have to
; encode a jmp instruction to jump to 0000:8200
global start
start:
db 0xe9
db 0xfd
db 0x01
; Now starts the extra boot code that we will store
; in the first 512 bytes of freeldr.sys. This code
; allows the FAT12/16 bootsector to navigate the
; FAT table so that we can still load freeldr.sys
; even if it is fragmented.
FatHelperEntryPoint:
push ax ; First save AX - the start cluster of freeldr.sys
; Display "Loading FreeLoader..." message
mov esi,msgLoading ; Loading message
call [bp-PutCharsOffset] ; Display it
call ReadFatIntoMemory
pop ax ; Restore AX (start cluster)
; AX has start cluster of freeldr.sys
mov bx,800h
mov es,bx
LoadFile:
push ax
call IsFat12
pop ax
jnc LoadFile2
cmp ax,0ff8h ; Check to see if this is the last cluster in the chain
jmp LoadFile3
LoadFile2:
cmp ax,0fff8h
LoadFile3:
jae LoadFile_Done ; If so continue, if not then read then next one
push ax
xor bx,bx ; Load ROSLDR starting at 0000:8000h
push es
call [bp-ReadClusterOffset]
pop es
xor bx,bx
mov bl,BYTE [BYTE bp+SectsPerCluster]
shl bx,5 ; BX = BX * 512 / 16
mov ax,es ; Increment the load address by
add ax,bx ; The size of a cluster
mov es,ax
call IsFat12
pop ax
push es
jnc LoadFile4
call GetFatEntry12 ; Get the next entry
jmp LoadFile5
LoadFile4:
call GetFatEntry16
LoadFile5:
pop es
jmp LoadFile ; Load the next cluster (if any)
LoadFile_Done:
mov dl,BYTE [BYTE bp+BootDrive] ; Load the boot drive into DL
push WORD 0x0000
push WORD 0x8000 ; We will do a far return to 0000:8000h
retf ; Transfer control to ROSLDR
; Reads the entire FAT into memory at 7000:0000
ReadFatIntoMemory:
mov ax,WORD [BYTE bp+HiddenSectors]
mov dx,WORD [BYTE bp+HiddenSectors+2]
add ax,WORD [BYTE bp+ReservedSectors]
adc dx,byte 0
mov cx,WORD [BYTE bp+SectorsPerFat]
mov bx,7000h
mov es,bx
xor bx,bx
call [bp-ReadSectorsOffset]
ret
; Returns the FAT entry for a given cluster number for 16-bit FAT
; On entry AX has cluster number
; On return AX has FAT entry for that cluster
GetFatEntry16:
mov cx,2 ; AX = AX * 2 (since FAT16 entries are 2 bytes)
mul cx
shl dx,0fh
mov bx,7000h
add bx,dx
mov es,bx
mov bx,ax ; Restore FAT entry offset
mov ax,WORD [es:bx] ; Get FAT entry
ret
; Returns the FAT entry for a given cluster number for 12-bit FAT
; On entry AX has cluster number
; On return AX has FAT entry for that cluster
GetFatEntry12:
push ax
mov cx,ax
shr ax,1
add ax,cx ; AX = AX * 1.5 (AX = AX + (AX / 2)) (since FAT12 entries are 12 bits)
mov bx,7000h
mov es,bx
mov bx,ax ; Put FAT entry offset into BX
mov ax,WORD [es:bx] ; Get FAT entry
pop cx ; Get cluster number from stack
and cx,1
jz UseLow12Bits
and ax,0fff0h
shr ax,4
jmp GetFatEntry12_Done
UseLow12Bits:
and ax,0fffh
GetFatEntry12_Done:
ret
; Returns CF = 1 if this is a FAT12 file system
; Otherwise CF = 0 for FAT16
IsFat12:
mov bx,[BYTE bp-DataAreaStartLow]
mov cx,[BYTE bp-DataAreaStartHigh]
; CX:BX now has the number of the starting sector of the data area
xor dx,dx
mov ax,WORD [BYTE bp+TotalSectors]
cmp ax,byte 0
jnz IsFat12_2
mov ax,WORD [BYTE bp+TotalSectorsBig]
mov dx,WORD [BYTE bp+TotalSectorsBig+2]
; DX:AX now contains the number of sectors on the volume
IsFat12_2:
sub ax,bx ; Subtract data area start sector
sub dx,cx ; from total sectors of volume
; DX:AX now contains the number of data sectors on the volume
movzx bx,BYTE [BYTE bp+SectsPerCluster]
div bx
; AX now has the number of clusters on the volume
stc
cmp ax,4085
jb IsFat12_Done
clc
IsFat12_Done:
ret
msgLoading db 'Loading FreeLoader...',0dh,0ah,0
times 510-($-$$) db 0 ; Pad to 510 bytes
dw 0aa55h ; BootSector signature

6
freeldr/freeldr/debug.c
View file

@ -28,7 +28,7 @@
// DPRINT_UI | DPRINT_DISK | DPRINT_CACHE;
ULONG DebugPrintMask = DPRINT_WARNING | DPRINT_MEMORY | DPRINT_FILESYSTEM |
DPRINT_UI | DPRINT_DISK;
//ULONG DebugPrintMask = DPRINT_CACHE;
//ULONG DebugPrintMask = DPRINT_INIFILE;
#define SCREEN 0
#define RS232 1
@ -41,9 +41,9 @@ ULONG DebugPrintMask = DPRINT_WARNING | DPRINT_MEMORY | DPRINT_FILESYSTEM |
#define BOCHS_OUTPUT_PORT 0xe9
ULONG DebugPort = RS232;
//ULONG DebugPort = RS232;
//ULONG DebugPort = SCREEN;
//ULONG DebugPort = BOCHS;
ULONG DebugPort = BOCHS;
ULONG ComPort = COM1;
//ULONG BaudRate = 19200;
ULONG BaudRate = 115200;

1
freeldr/freeldr/freeldr.c
View file

@ -107,6 +107,7 @@ VOID BootMain(VOID)
MessageBox("Press ENTER to reboot.\n");
goto reboot;
}
TimeOut = -1;
// Try to open the operating system section in the .ini file
if (!IniOpenSection(OperatingSystemSectionNames[SelectedOperatingSystem], &SectionId))

14
freeldr/freeldr/mm/init.c
View file

@ -32,7 +32,6 @@ PVOID HeapBaseAddress = NULL;
ULONG HeapLengthInBytes = 0;
ULONG HeapMemBlockCount = 0;
PMEMBLOCK HeapMemBlockArray = NULL;
ULONG Stack;
VOID InitMemoryManager(VOID)
{
@ -42,6 +41,12 @@ VOID InitMemoryManager(VOID)
// Round up to the next page of memory
RealFreeLoaderModuleEnd = ROUND_UP(FreeLoaderModuleEnd, 4096);
// FIXME:
// Add extra space for .data & .bss sections
// which are listed after FreeLoaderModuleEnd
// because it is in the .text section.
// I need to have everything in one section...
RealFreeLoaderModuleEnd += 0x2000;
BaseAddress = RealFreeLoaderModuleEnd;
Length = (MAXLOWMEMADDR - RealFreeLoaderModuleEnd);
@ -64,22 +69,17 @@ VOID InitMemoryManager(VOID)
// Adjust the heap length so we can reserve
// enough storage space for the MEMBLOCK array
Length -= (MemBlocks * sizeof(MEMBLOCK));
DbgPrint((DPRINT_MEMORY, "We get here.\n"));
// Initialize our tracking variables
HeapBaseAddress = (PVOID)BaseAddress;
HeapLengthInBytes = Length;
HeapMemBlockCount = (HeapLengthInBytes / MEM_BLOCK_SIZE);
HeapMemBlockArray = (PMEMBLOCK)(HeapBaseAddress + HeapLengthInBytes);
DbgPrint((DPRINT_MEMORY, "We get here2.\n"));
// Clear the memory
__asm__("movl %esp,_Stack");
DbgPrint((DPRINT_MEMORY, "HeapBaseAddress: 0x%x HeapLengthInBytes: %d Stack: %d.\n", HeapBaseAddress, HeapLengthInBytes, Stack));
DbgPrint((DPRINT_MEMORY, "HeapBaseAddress: 0x%x HeapLengthInBytes: %d\n", HeapBaseAddress, HeapLengthInBytes));
RtlZeroMemory(HeapBaseAddress, HeapLengthInBytes);
DbgPrint((DPRINT_MEMORY, "We get here3.\n"));
RtlZeroMemory(HeapMemBlockArray, (HeapMemBlockCount * sizeof(MEMBLOCK)));
DbgPrint((DPRINT_MEMORY, "We get here4.\n"));
#ifdef DEBUG
DbgPrint((DPRINT_MEMORY, "Memory Manager initialized. BaseAddress = 0x%x Length = 0x%x. %d blocks in heap.\n", BaseAddress, Length, HeapMemBlockCount));

13
freeldr/freeldr/rules.mk
View file

@ -18,12 +18,13 @@
#
CC = gcc
LD = ld
AR = ar
RM = cmd /C del
CP = cmd /C copy
MAKE = make
CC = gcc
LD = ld
AR = ar
RM = cmd /C del
CP = cmd /C copy
MAKE = make
NASM_CMD = nasm
# For a release build uncomment this line
#FLAGS = -Wall -nostdlib -nostdinc -fno-builtin -I./ -I../ -I../../ -O3

5
freeldr/freeldr/ui/tui.c
View file

@ -724,6 +724,11 @@ void ShowMessageBoxesInSection(PUCHAR SectionName)
UCHAR SettingValue[80];
ULONG SectionId;
//
// Zero out message line text
//
strcpy(szMessageBoxLineText, "");
if (!IniOpenSection(SectionName, &SectionId))
{
sprintf(SettingName, "Section %s not found in freeldr.ini.\n", SectionName);