690 lines
21 KiB
NASM
690 lines
21 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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org 0x7E00
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; the KordOS FAT12/FAT16 bootsector loads first cluster of this file to 0:7E00 and transfers control to here
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; ss:bp = 0:7C00
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virtual at bp
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rb 3 ; BS_jmpBoot
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rb 8 ; BS_OEMName, ignored
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dw ? ; 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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BPB_TotSec16 dw ?
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db ? ; BPB_Media
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BPB_FATSz16 dw ?
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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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BPB_TotSec32 dd ?
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BS_DrvNum db ?
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fat_type db ? ; this is BS_Reserved1,
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; we use it to save FS type: 0=FAT12, 1=FAT16
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db ? ; BS_BootSig
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num_sectors dd ? ; BS_VolID
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; rb 11 ; BS_VolLab
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; rb 3 ; BS_FilSysType, first 3 bytes
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read_sectors dw ?
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read_sectors2 dw ?
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lookup_in_root_dir dw ?
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scan_for_filename dw ?
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err_ dw ?
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noloader dw ?
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cachelimit dw ?
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filesize: ; will be used to save file size
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rb 5 ; BS_FilSysType, last 5 bytes
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; following variables are located in the place of starting code;
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; starting code is no more used at this point
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sect_per_clus dw ?
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cur_cluster dw ?
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next_cluster dw ?
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flags dw ?
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cur_delta dd ?
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end virtual
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; procedures from boot sector
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; LBA version
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lba_read_sectors = 7CE2h
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lba_read_sectors2 = 7CDCh
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lba_lookup_in_root_dir = 7D4Fh
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lba_scan_for_filename = 7D2Dh
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lba_err = 7CB5h
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lba_noloader = 7CB2h
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; CHS version
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chs_read_sectors = 7CDEh
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chs_read_sectors2 = 7CD8h
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chs_lookup_in_root_dir = 7D70h
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chs_scan_for_filename = 7D4Eh
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chs_err = 7CB1h
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chs_noloader = 7CAEh
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push ax cx ; save our position on disk
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push ss
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pop es
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; determine version of bootsector (LBA vs CHS)
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; mov [read_sectors], chs_read_sectors
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; mov [read_sectors2], chs_read_sectors2
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; mov [lookup_in_root_dir], chs_lookup_in_root_dir
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; mov [scan_for_filename], chs_scan_for_filename
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; mov [err], chs_err
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; mov [noloader], chs_noloader
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lea di, [read_sectors]
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mov si, chs_proc_addresses
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mov cx, 6*2
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cmp word [chs_scan_for_filename], 0xFF31 ; 'xor di,di'
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jz @f
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add si, cx
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; mov [read_sectors], lba_read_sectors
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; mov [read_sectors2], lba_read_sectors2
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; mov [lookup_in_root_dir], lba_lookup_in_root_dir
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; mov [scan_for_filename], lba_scan_for_filename
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; mov [err], lba_err
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; mov [noloader], lba_noloader
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@@:
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rep movsb
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mov cl, [BPB_SecsPerClus]
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mov [sect_per_clus], cx
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xor bx, bx
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; determine size of cache for folders
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int 12h ; ax = size of available base memory in Kb
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sub ax, 94000h / 1024
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jae @f
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nomem:
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mov si, nomem_str
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jmp [err_]
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@@:
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shr ax, 3
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mov [cachelimit], ax ; size of cache - 1
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; get type of file system - FAT12 or FAT16?
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; calculate number of clusters
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mov ax, [BPB_TotSec16]
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xor dx, dx
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test ax, ax
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jnz @f
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mov ax, word [BPB_TotSec32]
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mov dx, word [BPB_TotSec32+2]
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@@:
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sub ax, [bp-8] ; dword [bp-8] = first data sector
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sbb dx, [bp-6]
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jb j_noloader
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div [sect_per_clus]
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; ax = number of clusters
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; note: this is loader for FAT12/FAT16, so 'div' does not overflow on correct volumes
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mov [fat_type], ch
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cmp ax, 0xFF5
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jb init_fat12
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inc [fat_type]
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init_fat16:
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; no sectors loaded
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mov di, 0x8200
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xor ax, ax
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mov cx, 0x100/2
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rep stosw
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jmp init_fat_done
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init_fat12:
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; read FAT
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push 0x6000
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pop es
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mov ax, [BPB_RsvdSecCnt]
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mov cx, [BPB_FATSz16]
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cmp cx, 12
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jb @f
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mov cx, 12
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@@:
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xor dx, dx
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call [read_sectors]
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init_fat_done:
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; if cluster = sector, we need to read second part of our file
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; (bootsector loads only first cluster of kordldr.f1x)
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pop cx ax ; restore our position on disk
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cmp cx, 1
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ja kordldr_full
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sub ax, [bp-8]
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inc ax
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inc ax ; ax = first cluster of kordldr.f12
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call get_next_cluster
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jc @f
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j_noloader:
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jmp [noloader]
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@@:
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dec ax
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dec ax
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push 0x800
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pop es
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call [read_sectors2]
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kordldr_full:
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; ...continue loading...
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mov di, secondary_loader_info
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call load_file
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test bx, bx
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mov bx, [err_]
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jz @f
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mov si, aKernelNotFound
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jmp bx
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@@:
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; for subsequent calls to callback function, hook error handler
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; mov byte [bx], 0xE9 ; 'jmp' opcode
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; mov ax, hooked_err - 3
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; sub ax, bx
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; mov word [bx+1], ax
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; push hooked_err / ret
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mov word [bx], 0x68 + ((hooked_err and 0xFF) shl 8)
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mov word [bx+2], (hooked_err shr 8) + (0xC3 shl 8)
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; set registers for secondary loader
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mov ah, [BS_DrvNum]
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mov al, 'f'
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test ah, ah
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jns @f
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sub ah, 80h
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mov al, 'h'
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@@:
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mov bx, '12'
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cmp [fat_type], 0
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jz @f
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mov bh, '6'
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@@:
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mov si, callback ; ds:si = far pointer to callback procedure
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jmp far [si-callback+secondary_loader_info] ; jump to 1000:0000
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nomem_str db 'No memory',0
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chs_proc_addresses:
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dw chs_read_sectors
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dw chs_read_sectors2
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dw chs_lookup_in_root_dir
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dw chs_scan_for_filename
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dw chs_err
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dw chs_noloader
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lba_proc_addresses:
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dw lba_read_sectors
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dw lba_read_sectors2
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dw lba_lookup_in_root_dir
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dw lba_scan_for_filename
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dw lba_err
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dw lba_noloader
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get_next_cluster:
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; in: ax = cluster
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; out: if there is next cluster: CF=1, ax = next cluster
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; out: if there is no next cluster: CF=0
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push si
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cmp [fat_type], 0
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jnz gnc16
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; for FAT12
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push ds
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push 0x6000
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pop ds
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mov si, ax
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shr si, 1
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add si, ax
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test al, 1
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lodsw
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jz @f
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shr ax, 4
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@@:
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and ax, 0xFFF
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cmp ax, 0xFF7
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pop ds si
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ret
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; for FAT16
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gnc16:
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; each sector contains 200h bytes = 100h FAT entries
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; so ah = # of sector, al = offset in sector
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mov si, ax
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mov ah, 0
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shr si, 8
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; calculate segment for this sector of FAT table
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; base for FAT table is 6000:0000, so the sector #si has to be loaded to (60000 + 200*si)
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; segment = 6000 + 20*si, offset = 0
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push es
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push si
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shl si, 5
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add si, 0x6000
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mov es, si
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pop si
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cmp byte [ss:0x8200+si], ah ; sector already loaded?
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jnz @f
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; load corresponding sector
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pusha
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push es
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xor bx, bx
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mov ax, [BPB_RsvdSecCnt]
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xor dx, dx
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add ax, si
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adc dx, bx
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mov cx, 1 ; read 1 sector
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call [read_sectors]
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pop es
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popa
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@@:
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mov si, ax
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add si, si
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; mov ax, [es:si]
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lods word [es:si]
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pop es
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cmp ax, 0xFFF7
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pop si
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ret
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if $ > 0x8000
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error 'get_next_cluster must fit in first sector of kordldr.f1x!'
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end if
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load_file:
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; in: ss:bp = 0:7C00
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; in: ds:di -> information structure
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; dw:dw address
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; dw limit in 4Kb blocks (0x1000 bytes) (must be non-zero and not greater than 0x100)
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; ASCIIZ name
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; out: bx = status: bx=0 - ok, bx=1 - file is too big, only part of file was loaded, bx=2 - file not found
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; out: dx:ax = file size (0xFFFFFFFF if file not found)
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xor ax, ax ; start from root directory
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mov dx, -1
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mov word [filesize], dx
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mov word [filesize+2], dx ; initialize file size with invalid value
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lea si, [di+6]
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parse_dir_loop:
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; convert name to FAT name
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push di
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push ax
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push ss
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pop es
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; convert ASCIIZ filename to FAT name
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mov di, filename
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push di
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mov cx, 8+3
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mov al, ' '
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rep stosb
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pop di
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mov cl, 8 ; 8 symbols per name
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mov bl, 1
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nameloop:
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lodsb
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test al, al
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jz namedone
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cmp al, '/'
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jz namedone
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cmp al, '.'
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jz namedot
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dec cx
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js badname
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cmp al, 'a'
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jb @f
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cmp al, 'z'
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ja @f
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sub al, 'a'-'A'
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@@:
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stosb
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jmp nameloop
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namedot:
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inc bx
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jp badname
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add di, cx
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mov cl, 3
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jmp nameloop
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badname: ; do not make direct js/jp to notfound_pop:
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; this generates long forms of conditional jumps and results in longer code
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jmp notfound_pop
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namedone:
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; scan directory
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pop ax ; ax = cluster of directory or 0 for root
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push ds
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push si
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push es
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pop ds
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mov si, filename ; ds:si -> filename in FAT style
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test ax, ax
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jnz lookup_in_notroot_dir
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; for root directory, use the subroutine from bootsector
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call [lookup_in_root_dir]
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jmp lookup_done
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lookup_in_notroot_dir:
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; for other directories, read a folder sector-by-sector and scan
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; first, try to use the cache
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push ds
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push cs
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pop ds
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mov bx, [cachelimit]
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add bx, bx
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mov di, foldcache_mark
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@@:
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mov dx, [foldcache_clus+di-foldcache_mark+bx]
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cmp dx, ax
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jz cacheok
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test dx, dx
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jz cacheadd ; the cache has place for new entry
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dec bx
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dec bx
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jns @b
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; the folder is not present in the cache, so add it
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; the cache is full; find the oldest entry and replace it with the new one
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mov dx, [cachelimit]
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@@:
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inc bx
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inc bx
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cmp word [di+bx], dx ; marks have values 0 through [cachelimit]
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jnz @b
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cacheadd:
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or word [di+bx], 0xFFFF ; very big value, it will be changed soon
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mov [foldcache_clus+di-foldcache_mark+bx], ax
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and [foldcache_size+di-foldcache_mark+bx], 0 ; no folder items yet
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cacheok:
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; update cache marks
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mov dx, [di+bx]
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mov cx, [foldcache_size+di-foldcache_mark+bx]
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mov di, [cachelimit]
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add di, di
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cacheupdate:
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cmp [foldcache_mark+di], dx
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adc [foldcache_mark+di], 0
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dec di
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dec di
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jns cacheupdate
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and [foldcache_mark+bx], 0
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; done, bx contains (position in cache)*2
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pop ds
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; mov dx, bx
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; shl dx, 8 ; dx = (position in cache)*0x2000/0x10
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; add dx, 0x9200
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lea dx, [bx+0x92]
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xchg dl, dh
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mov es, dx
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jcxz not_in_cache
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call [scan_for_filename]
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jz lookup_done
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not_in_cache:
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; cache miss, read folder data from disk
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mov bx, cx
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shr bx, 4
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shl cx, 5
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mov di, cx ; es:di -> free space in cache entry
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; external loop: scan clusters
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folder_next_cluster:
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; internal loop: scan sectors in cluster
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mov cx, [sect_per_clus]
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push ax
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dec ax
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dec ax
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mul cx
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add ax, [bp-8]
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adc dx, [bp-6] ; dx:ax = absolute sector
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folder_next_sector:
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; skip first bx sectors
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dec bx
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jns folder_skip_sector
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push cx
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push es di
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push 0x8000
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pop es
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xor bx, bx
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mov cx, 1
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push es
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call [read_sectors]
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; copy data to the cache...
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pop ds
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pop di es
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cmp di, 0x2000 ; ...if there is free space, of course
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jae @f
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push si di
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mov cx, 0x100
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xor si, si
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rep movsw
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mov di, es
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shr di, 8
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add [ss:foldcache_size+di-0x92], 0x10 ; 0x10 new entries in the cache
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pop di si
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@@:
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push es
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push 0x8000
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pop es
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push cs
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pop ds
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mov cx, 0x10
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call [scan_for_filename]
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pop es
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pop cx
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jz lookup_done_pop
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folder_skip_sector:
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inc ax
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jnz @f
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inc dx
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@@:
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loop folder_next_sector
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pop ax ; ax = current cluster
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call get_next_cluster
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jc folder_next_cluster
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stc
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push ax
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lookup_done_pop:
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pop ax
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lookup_done:
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pop si
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pop ds
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; CF=1 <=> failed
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jnc found
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notfound:
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pop di
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mov bx, 2 ; file not found
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mov ax, 0xFFFF
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mov dx, ax ; invalid file size
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ret
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notfound_pop:
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pop ax
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jmp notfound
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found:
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mov ax, [es:di+26] ; get cluster
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test byte [es:di+11], 10h ; directory?
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jz regular_file
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cmp byte [si-1], 0
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jz notfound ; don't read directories as a regular files
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; ok, we have found a directory and the caller requested a file into it
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pop di
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jmp parse_dir_loop ; restart with new cluster in ax
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regular_file:
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cmp byte [si-1], 0
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jnz notfound ; file does not contain another files
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; ok, we have found a regular file and the caller requested it
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; save file size
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mov dx, [es:di+28]
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mov [filesize], dx
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mov dx, [es:di+30]
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mov [filesize+2], dx
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pop di
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mov si, [di+4]
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shl si, 3
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push si ; [ds:di+4] = limit in 4K blocks
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les bx, [di] ; es:bx -> buffer
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clusloop:
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; ax = first cluster, top of stack contains limit in sectors
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mov si, ax ; remember current cluster
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xor cx, cx ; cx will contain number of consecutive clusters
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mov word [cur_delta], cx
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mov word [cur_delta+2], cx
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mov di, ax
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clusfind:
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inc di
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inc cx
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call get_next_cluster
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jnc clusread
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cmp ax, di
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jz clusfind
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|
stc
|
|
clusread:
|
|
pop di ; limit in sectors
|
|
push ax ; save next cluster
|
|
pushf ; save flags
|
|
; read cx clusters, starting from si
|
|
; calculate number of sectors
|
|
xchg ax, cx
|
|
mul [sect_per_clus]
|
|
; dx:ax = number of sectors; compare with limit
|
|
mov word [num_sectors], ax
|
|
mov word [num_sectors+2], dx
|
|
jmp @f
|
|
continue_load_file:
|
|
les bx, [di] ; es:bx -> buffer
|
|
mov di, [di+4] ; ds:di = limit in 4K blocks
|
|
shl di, 3 ; now di = limit in sectors
|
|
mov ax, word [num_sectors]
|
|
mov dx, word [num_sectors+2]
|
|
mov si, [cur_cluster]
|
|
push [next_cluster]
|
|
push [flags]
|
|
or ax, dx
|
|
jz nextclus
|
|
@@:
|
|
test dx, dx
|
|
jnz clusdecrease
|
|
push dx ; limit was not exceeded
|
|
cmp ax, di
|
|
jbe @f
|
|
pop ax
|
|
clusdecrease:
|
|
push 1 ; limit was exceeded
|
|
mov ax, di
|
|
@@:
|
|
sub di, ax ; calculate new limit
|
|
sub word [num_sectors], ax
|
|
sbb word [num_sectors+2], 0
|
|
readloop:
|
|
push ax
|
|
; buffer should not cross a 64K boundary
|
|
push bx
|
|
shr bx, 4
|
|
mov cx, es
|
|
add bx, cx
|
|
neg bx
|
|
and bh, 0xF
|
|
shr bx, 5
|
|
jnz @f
|
|
mov bl, 0x80
|
|
@@:
|
|
cmp ax, bx
|
|
jbe @f
|
|
xchg ax, bx
|
|
@@:
|
|
pop bx
|
|
xchg ax, cx
|
|
; calculate starting sector
|
|
lea ax, [si-2]
|
|
mul [sect_per_clus]
|
|
add ax, word [cur_delta]
|
|
adc dx, word [cur_delta+2]
|
|
add word [cur_delta], cx
|
|
adc word [cur_delta+2], 0
|
|
; read
|
|
call [read_sectors2]
|
|
pop ax
|
|
sub ax, cx
|
|
jnz readloop
|
|
pop dx
|
|
; next cluster?
|
|
nextclus:
|
|
popf
|
|
pop ax
|
|
mov [cur_cluster], si
|
|
mov [next_cluster], ax
|
|
pushf
|
|
pop [flags]
|
|
jnc @f ; no next cluster => return
|
|
mov dl, 1 ; dh=0 in any case
|
|
test di, di
|
|
jz @f ; if there is next cluster but current limit is 0 => return: limit exceeded
|
|
push di
|
|
jmp clusloop ; all is ok, continue
|
|
hooked_err:
|
|
mov sp, 7C00h-12-2 ; restore stack
|
|
mov dx, 3 ; return: read error
|
|
@@:
|
|
mov bx, dx
|
|
mov ax, [filesize]
|
|
mov dx, [filesize+2]
|
|
ret
|
|
|
|
; Callback function for secondary loader
|
|
callback:
|
|
; in: ax = function number; only functions 1 and 2 are defined for now
|
|
; save caller's stack
|
|
mov dx, ss
|
|
mov cx, sp
|
|
; set our stack (required because we need ss=0)
|
|
xor si, si
|
|
mov ss, si
|
|
mov sp, 7C00h-8
|
|
mov bp, 7C00h
|
|
push dx
|
|
push cx
|
|
; call our function
|
|
stc ; unsupported function
|
|
dec ax
|
|
jz callback_readfile
|
|
dec ax
|
|
jnz callback_ret
|
|
; function 2: continue loading file
|
|
; can be called only after function 1 returned value bx=1 (only part of file was loaded)
|
|
; in: ds:di -> information structure
|
|
; dw:dw address
|
|
; dw limit in 4Kb blocks (0x1000 bytes) (must be non-zero and not greater than 0x100)
|
|
; out: bx=0 - ok, bx=1 - still only part of file was loaded, bx=3 - read error
|
|
; out: dx:ax = file size
|
|
call continue_load_file
|
|
jmp callback_ret_succ
|
|
callback_readfile:
|
|
; function 1: read file
|
|
; in: ds:di -> information structure
|
|
; dw:dw address
|
|
; dw limit in 4Kb blocks (0x1000 bytes) (must be non-zero and not greater than 0x100)
|
|
; ASCIIZ name
|
|
; out: bx=0 - ok, bx=1 - file is too big, only part of file was loaded, bx=2 - file not found, bx=3 - read error
|
|
; out: dx:ax = file size (0xFFFFFFFF if file was not found)
|
|
call load_file
|
|
callback_ret_succ:
|
|
clc ; function is supported
|
|
callback_ret:
|
|
; restore caller's stack
|
|
pop cx
|
|
pop ss
|
|
mov sp, cx
|
|
; return to caller
|
|
retf
|
|
|
|
secondary_loader_info:
|
|
dw 0, 0x1000
|
|
dw 0x30000 / 0x1000
|
|
db 'kernel.mnt',0
|
|
aKernelNotFound db 'Fatal error: cannot load the kernel',0
|
|
|
|
foldcache_clus dw 0,0,0,0,0,0,0 ; start with no folders in cache
|
|
foldcache_mark rw 7
|
|
foldcache_size rw 7
|
|
filename rb 11
|
|
if $ > 0x8200
|
|
error:
|
|
table overwritten
|
|
end if
|