359 lines
10 KiB
NASM
359 lines
10 KiB
NASM
; Copyright (c) 2008-2009, diamond
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; All rights reserved.
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;
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; Redistribution and use in source and binary forms, with or without
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; modification, are permitted provided that the following conditions are met:
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; * Redistributions of source code must retain the above copyright
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; notice, this list of conditions and the following disclaimer.
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; * Redistributions in binary form must reproduce the above copyright
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; notice, this list of conditions and the following disclaimer in the
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; documentation and/or other materials provided with the distribution.
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; * Neither the name of the <organization> nor the
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; names of its contributors may be used to endorse or promote products
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; derived from this software without specific prior written permission.
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;
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; THIS SOFTWARE IS PROVIDED BY Alexey Teplov aka <Lrz> ''AS IS'' AND ANY
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; EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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; WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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; DISCLAIMED. IN NO EVENT SHALL <copyright holder> BE LIABLE FOR ANY
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; DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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; (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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; ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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; (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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; SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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;*****************************************************************************
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use_lba = 0
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org 0x7C00
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jmp start
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nop
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; FAT parameters, BPB
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; they must be changed at install, replaced with real values
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rb 8 ; BS_OEMName, ignored
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dw 200h ; BPB_BytsPerSec
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BPB_SecsPerClus db ?
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BPB_RsvdSecCnt dw ?
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BPB_NumFATs db ?
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BPB_RootEntCnt dw ?
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dw ? ; BPB_TotSec16
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db ? ; BPB_Media
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dw ? ; BPB_FATSz16 = 0 for FAT32
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BPB_SecPerTrk dw ?
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BPB_NumHeads dw ?
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BPB_HiddSec dd ?
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dd ? ; BPB_TotSec32
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BPB_FATSz32 dd ?
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BPB_ExtFlags dw ?
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dw ? ; BPB_FSVer
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BPB_RootClus dd ?
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dw ? ; BPB_FSInfo
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BPB_BkBootSec dw ?
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rb 12 ; BPB_Reserved
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BS_DrvNum db ?
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db ? ; BS_Reserved1
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db ? ; BS_BootSig
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dd ? ; BS_VolID
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rb 11 ; BS_VolLab
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rb 8 ;
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curseg dw 0x8000
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start:
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xor ax, ax
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mov ss, ax
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mov sp, 0x7C00
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mov ds, ax
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mov bp, sp
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cld
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sti
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push dx ; byte [bp-2] = boot drive
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if use_lba
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mov ah, 41h
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mov bx, 55AAh
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int 13h
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mov si, aNoLBA
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jc err_
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cmp bx, 0AA55h
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jnz err_
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test cl, 1
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jz err_
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else
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mov ah, 8
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int 13h
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jc @f
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movzx ax, dh
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inc ax
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mov [bp+BPB_NumHeads-0x7C00], ax
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and cx, 3Fh
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mov [bp+BPB_SecPerTrk-0x7C00], cx
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@@:
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end if
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; get FAT parameters
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xor bx, bx
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movzx eax, [bp+BPB_NumFATs-0x7C00]
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mul [bp+BPB_FATSz32-0x7C00]
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movzx ecx, [bp+BPB_RsvdSecCnt-0x7C00]
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push ecx ; FAT start = dword [bp-6]
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add eax, ecx
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push eax ; data start = dword [bp-10]
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;push dword -1 ; dword [bp-14] = current sector for FAT cache
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db 66h
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push -1 ; dword [bp-14] = current sector for FAT cache
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mov eax, [bp+BPB_RootClus-0x7C00]
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mov si, main_loader
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call lookup_in_dir
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jnc kordldr_ok
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noloader:
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mov si, aLoaderNotFound
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err_:
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call out_string
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mov si, aPressAnyKey
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call out_string
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xor ax, ax
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int 16h
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int 18h
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jmp $
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kordldr_ok:
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mov eax, [es:di+20-2] ; hiword(eax) = hiword(cluster)
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mov ax, [es:di+26] ; loword(eax) = loword(cluster)
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mov es, bx ; es = 0
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mov bx, 0x7E00
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push bx ; save return address: bx = 7E00
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; fall through - 'ret' in read_cluster will return to 7E00
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read_cluster:
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; ss:bp = 0:7C00
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; es:bx = pointer to data
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; eax = cluster
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sub eax, 2
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movzx ecx, [bp+BPB_SecsPerClus-0x7C00]
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mul ecx
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read_sectors2:
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; same as read_sectors32, but eax is relative to start of data
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add eax, [bp-10]
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read_sectors32:
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; ss:bp = 0:7C00
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; es:bx = pointer to data
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; eax = first sector
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; cx = number of sectors
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; some high words of 32-bit registers are destroyed!
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pusha
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add eax, [bp+BPB_HiddSec-0x7C00]
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if use_lba
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push ds
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do_read_sectors:
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push ax
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push cx
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cmp cx, 0x7F
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jbe @f
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mov cx, 0x7F
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@@:
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; create disk address packet on the stack
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; dq starting LBA
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push 0
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push 0
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push eax
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; dd buffer
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push es
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push bx
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; dw number of blocks to transfer (no more than 0x7F)
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push cx
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; dw packet size in bytes
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push 10h
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; issue BIOS call
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push ss
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pop ds
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mov si, sp
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mov dl, [bp-2]
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mov ah, 42h
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int 13h
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mov si, aReadError
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jc err_
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; restore stack
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add sp, 10h
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; increase current sector & buffer; decrease number of sectors
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movzx esi, cx
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mov ax, es
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shl cx, 5
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add ax, cx
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mov es, ax
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pop cx
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pop ax
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add eax, esi
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sub cx, si
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jnz do_read_sectors
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pop ds
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popa
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ret
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else
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do_read_sectors:
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pusha
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pop edi ; loword(edi) = di, hiword(edi) = si
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push bx
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; eax / (SectorsPerTrack) -> eax, remainder bx
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movzx esi, [bp+BPB_SecPerTrk-0x7C00]
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xor edx, edx
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div esi
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mov bx, dx ; bx=sector-1
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; eax -> dx:ax
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push eax
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pop ax
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pop dx
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; (dword in dx:ax) / (NumHeads) -> (word in ax), remainder dx
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div [bp+BPB_NumHeads-0x7C00]
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; number of sectors: read no more than to end of track
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sub si, bx
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cmp cx, si
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jbe @f
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mov cx, si
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@@:
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inc bx
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; now ax=track, dl=head, dh=0, cl=number of sectors, ch=0, bl=sector; convert to int13 format
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movzx edi, cx
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mov dh, dl
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mov dl, [bp-2]
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shl ah, 6
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mov ch, al
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mov al, cl
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mov cl, bl
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or cl, ah
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pop bx
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mov si, 3
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mov ah, 2
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@@:
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push ax
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int 13h
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jnc @f
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xor ax, ax
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int 13h ; reset drive
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pop ax
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dec si
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jnz @b
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mov si, aReadError
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jmp err_
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@@:
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pop ax
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mov ax, es
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mov cx, di
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shl cx, 5
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add ax, cx
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mov es, ax
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push edi
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popa
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add eax, edi
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sub cx, di
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jnz do_read_sectors
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popa
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ret
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end if
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lookup_in_dir:
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; in: ds:si -> 11-bytes FAT name
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; in: eax = cluster
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; in: bx = 0
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; out: if found: CF=0, es:di -> directory entry
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; out: if not found: CF=1
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; push 0x8000
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; pop es
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; read current cluster: first cluster goes to 8000:0000, others - to 8200:0000
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mov es, [bp-7C00h + curseg]
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push es
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push eax
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call read_cluster
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mov ax, es
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cmp ah, 82h
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jb @f
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mov ax, 8200h
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@@:
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mov [bp-7C00h + curseg], ax
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pop eax
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pop es
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; scan for filename
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shl cx, 4
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xor di, di
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sloop:
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cmp byte [es:di], bl
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jz snotfound
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test byte [es:di+11], 8 ; volume label?
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jnz scont ; ignore volume labels
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pusha
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mov cx, 11
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repz cmpsb
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popa
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jz sdone
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scont:
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add di, 0x20
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loop sloop
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; next cluster
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push 0x6000
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pop es
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push es ax
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shr eax, 7
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cmp eax, [bp-14]
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mov [bp-14], eax
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jz @f
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add eax, [bp-6]
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mov cx, 1
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call read_sectors32
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@@:
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pop di es
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and di, 0x7F
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shl di, 2
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and byte [es:di+3], 0x0F
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mov eax, [es:di]
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;and eax, 0x0FFFFFFF
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cmp eax, 0x0FFFFFF7
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jb lookup_in_dir
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snotfound:
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stc
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sdone:
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ret
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out_string:
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; in: ds:si -> ASCIIZ string
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lodsb
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test al, al
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jz sdone
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mov ah, 0Eh
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mov bx, 7
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int 10h
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jmp out_string
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aReadError db 'Read error',0
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if use_lba
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aNoLBA db 'The drive does not support LBA!',0
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end if
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aLoaderNotFound db 'Loader not found',0
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aPressAnyKey db 13,10,'Press any key...',13,10,0
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main_loader db 'KORDLDR F32'
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db 56h
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; just to make file 512 bytes long :)
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db 'd' xor 'i' xor 'a' xor 'm' xor 'o' xor 'n' xor 'd'
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; bootsector signature
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dw 0xAA55
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; display offsets of all procedures used by kordldr.f12.asm
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macro show [procedure]
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{
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bits = 16
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display `procedure,' = '
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repeat bits/4
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d = '0' + procedure shr (bits - %*4) and 0Fh
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if d > '9'
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d = d + 'A'-'9'-1
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end if
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display d
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end repeat
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display 13,10
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}
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show read_sectors32, read_sectors2, err_, noloader
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