445 lines
11 KiB
PHP
445 lines
11 KiB
PHP
; -----------------------------------------------------------------------
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;
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; Copyright 1994-2009 H. Peter Anvin - All Rights Reserved
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; Copyright 2009-2011 Intel Corporation; author: H. Peter Anvin
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;
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; This program is free software; you can redistribute it and/or modify
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; it under the terms of the GNU General Public License as published by
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; the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
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; Boston MA 02110-1301, USA; either version 2 of the License, or
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; (at your option) any later version; incorporated herein by reference.
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;
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; -----------------------------------------------------------------------
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;
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; diskboot.inc
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;
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; Common boot sector code for harddisk-based Syslinux derivatives.
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;
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; Requires macros z[bwd], labels ldlinux_ent, ldlinux_magic, ldlinux_sys
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; and constants BS_MAGIC_VER, LDLINUX_MAGIC, retry_count, Sect1Ptr[01]_VAL,
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; STACK_TOP
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;
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section .init
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;
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; Some of the things that have to be saved very early are saved
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; "close" to the initial stack pointer offset, in order to
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; reduce the code size...
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;
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global StackBuf, PartInfo, Hidden, OrigESDI, DriveNumber
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global OrigFDCTabPtr
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StackBuf equ STACK_TOP-44-92 ; Start the stack here (grow down - 4K)
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PartInfo equ StackBuf
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.mbr equ PartInfo
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.gptlen equ PartInfo+16
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.gpt equ PartInfo+20
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FloppyTable equ PartInfo+76
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; Total size of PartInfo + FloppyTable == 76+16 = 92 bytes
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Hidden equ StackBuf-24 ; Partition offset (qword)
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OrigFDCTabPtr equ StackBuf-16 ; Original FDC table
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OrigDSSI equ StackBuf-12 ; DS:SI -> partinfo
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OrigESDI equ StackBuf-8 ; ES:DI -> $PnP structure
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DriveNumber equ StackBuf-4 ; Drive number
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StackHome equ Hidden ; The start of the canonical stack
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;
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; Primary entry point. Tempting as though it may be, we can't put the
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; initial "cli" here; the jmp opcode in the first byte is part of the
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; "magic number" (using the term very loosely) for the DOS superblock.
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;
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bootsec equ $
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_start: jmp short start ; 2 bytes
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nop ; 1 byte
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;
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; "Superblock" follows -- it's in the boot sector, so it's already
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; loaded and ready for us
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;
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bsOemName db MY_NAME ; The SYS command sets this, so...
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zb 8-($-bsOemName)
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;
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; These are the fields we actually care about. We end up expanding them
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; all to dword size early in the code, so generate labels for both
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; the expanded and unexpanded versions.
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;
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%macro superb 1
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bx %+ %1 equ SuperInfo+($-superblock)*8+4
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bs %+ %1 equ $
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zb 1
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%endmacro
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%macro superw 1
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bx %+ %1 equ SuperInfo+($-superblock)*8
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bs %+ %1 equ $
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zw 1
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%endmacro
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%macro superd 1
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bx %+ %1 equ $ ; no expansion for dwords
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bs %+ %1 equ $
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zd 1
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%endmacro
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superblock equ $
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superw BytesPerSec
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superb SecPerClust
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superw ResSectors
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superb FATs
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superw RootDirEnts
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superw Sectors
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superb Media
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superw FATsecs
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superw SecPerTrack
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superw Heads
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superinfo_size equ ($-superblock)-1 ; How much to expand
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superd Hidden
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superd HugeSectors
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;
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; This is as far as FAT12/16 and FAT32 are consistent
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;
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; FAT12/16 need 26 more bytes,
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; FAT32 need 54 more bytes
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;
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superblock_len_fat16 equ $-superblock+26
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superblock_len_fat32 equ $-superblock+54
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zb 54 ; Maximum needed size
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superblock_max equ $-superblock
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SecPerClust equ bxSecPerClust
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;
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; Note we don't check the constraints above now; we did that at install
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; time (we hope!)
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;
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start:
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cli ; No interrupts yet, please
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cld ; Copy upwards
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;
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; Set up the stack
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;
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xor cx,cx
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mov ss,cx
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mov sp,StackBuf-2 ; Just below BSS (-2 for alignment)
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push dx ; Save drive number (in DL)
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push es ; Save initial ES:DI -> $PnP pointer
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push di
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push ds ; Save original DS:SI -> partinfo
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push si
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mov es,cx
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;
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; DS:SI may contain a partition table entry and possibly a GPT entry.
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; Preserve it for us. This saves 56 bytes of the GPT entry, which is
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; currently the maximum we care about. Total is 76 bytes.
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;
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mov cl,(16+4+56)/2 ; Save partition info
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mov di,PartInfo
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rep movsw ; This puts CX back to zero
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mov ds,cx ; Now we can initialize DS...
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;
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; Now sautee the BIOS floppy info block to that it will support decent-
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; size transfers; the floppy block is 11 bytes and is stored in the
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; INT 1Eh vector (brilliant waste of resources, eh?)
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;
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; Of course, if BIOSes had been properly programmed, we wouldn't have
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; had to waste precious space with this code.
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;
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mov bx,fdctab
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lfs si,[bx] ; FS:SI -> original fdctab
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push fs ; Save on stack in case we need to bail
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push si
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; Save the old fdctab even if hard disk so the stack layout
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; is the same. The instructions above do not change the flags
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and dl,dl ; If floppy disk (00-7F), assume no
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; partition table
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js harddisk
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floppy:
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xor ax,ax
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mov cl,6 ; 12 bytes (CX == 0)
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; es:di -> FloppyTable already
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; This should be safe to do now, interrupts are off...
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mov [bx],di ; FloppyTable
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mov [bx+2],ax ; Segment 0
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fs rep movsw ; Faster to move words
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mov cl,[bsSecPerTrack] ; Patch the sector count
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mov [di-12+4],cl
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push ax ; Partition offset == 0
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push ax
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push ax
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push ax
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int 13h ; Some BIOSes need this
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; Using xint13 costs +1B
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jmp short not_harddisk
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;
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; The drive number and possibly partition information was passed to us
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; by the BIOS or previous boot loader (MBR). Current "best practice" is to
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; trust that rather than what the superblock contains.
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;
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; Note: di points to beyond the end of PartInfo
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; Note: false negatives might slip through the handover area's sanity checks,
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; if the region is very close (less than a paragraph) to
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; PartInfo ; no false positives are possible though
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;
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harddisk:
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mov dx,[di-76-10] ; Original DS
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mov si,[di-76-12] ; Original SI
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shr si,4
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add dx,si
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cmp dx,4fh ; DS:SI < 50h:0 (BDA or IVT) ?
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jbe .no_partition
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cmp dx,(PartInfo-75)>>4 ; DS:SI in overwritten memory?
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jae .no_partition
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test byte [di-76],7Fh ; Sanity check: "active flag" should
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jnz .no_partition ; be 00 or 80
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cmp [di-76+4],cl ; Sanity check: partition type != 0
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je .no_partition
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cmp eax,'!GPT' ; !GPT signature?
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jne .mbr
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cmp byte [di-76+4],0EDh ; Synthetic GPT partition entry?
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jne .mbr
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.gpt: ; GPT-style partition info
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push dword [di-76+20+36]
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push dword [di-76+20+32]
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jmp .gotoffs
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.mbr: ; MBR-style partition info
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push cx ; Upper half partition offset == 0
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push cx
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push dword [di-76+8] ; Partition offset (dword)
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jmp .gotoffs
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.no_partition:
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;
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; No partition table given... assume that the Hidden field in the boot sector
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; tells the truth (in particular, is zero if this is an unpartitioned disk.)
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;
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push cx
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push cx
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push dword [bsHidden]
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.gotoffs:
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;
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; Get disk drive parameters (don't trust the superblock.) Don't do this for
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; floppy drives -- INT 13:08 on floppy drives will (may?) return info about
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; what the *drive* supports, not about the *media*. Fortunately floppy disks
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; tend to have a fixed, well-defined geometry which is stored in the superblock.
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;
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; DL == drive # still
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mov ah,08h
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call xint13
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jc no_driveparm
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and ah,ah
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jnz no_driveparm
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shr dx,8
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inc dx ; Contains # of heads - 1
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mov [bsHeads],dx
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and cx,3fh
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mov [bsSecPerTrack],cx
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no_driveparm:
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not_harddisk:
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;
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; Ready to enable interrupts, captain
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;
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sti
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;
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; Do we have EBIOS (EDD)?
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;
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eddcheck:
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mov bx,55AAh
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mov ah,41h ; EDD existence query
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call xint13
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jc .noedd
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cmp bx,0AA55h
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jne .noedd
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test cl,1 ; Extended disk access functionality set
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jz .noedd
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;
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; We have EDD support...
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;
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mov byte [getonesec.jmp+1],(getonesec_ebios-(getonesec.jmp+2))
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.noedd:
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;
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; Load the first sector of LDLINUX.SYS; this used to be all proper
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; with parsing the superblock and root directory; it doesn't fit
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; together with EBIOS support, unfortunately.
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;
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Sect1Load:
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mov eax,strict dword Sect1Ptr0_VAL ; 0xdeadbeef
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Sect1Ptr0 equ $-4
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mov edx,strict dword Sect1Ptr1_VAL ; 0xfeedface
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Sect1Ptr1 equ $-4
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mov bx,ldlinux_sys ; Where to load it
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call getonesec
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; Some modicum of integrity checking
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cmp dword [ldlinux_magic+4],LDLINUX_MAGIC^HEXDATE
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jne kaboom
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; Go for it!
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jmp ldlinux_ent
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;
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; getonesec: load a single disk linear sector EDX:EAX into the buffer
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; at ES:BX.
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;
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; This routine assumes CS == DS == SS, and trashes most registers.
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;
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; Stylistic note: use "xchg" instead of "mov" when the source is a register
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; that is dead from that point; this saves space. However, please keep
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; the order to dst,src to keep things sane.
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;
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getonesec:
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add eax,[Hidden] ; Add partition offset
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adc edx,[Hidden+4]
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mov cx,retry_count
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.jmp: jmp strict short getonesec_cbios
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;
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; getonesec_ebios:
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;
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; getonesec implementation for EBIOS (EDD)
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;
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getonesec_ebios:
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.retry:
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; Form DAPA on stack
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push edx
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push eax
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push es
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push bx
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push word 1
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push word 16
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mov si,sp
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pushad
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mov ah,42h ; Extended Read
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call xint13
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popad
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lea sp,[si+16] ; Remove DAPA
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jc .error
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ret
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.error:
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; Some systems seem to get "stuck" in an error state when
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; using EBIOS. Doesn't happen when using CBIOS, which is
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; good, since some other systems get timeout failures
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; waiting for the floppy disk to spin up.
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pushad ; Try resetting the device
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xor ax,ax
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call xint13
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popad
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loop .retry ; CX-- and jump if not zero
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; Total failure. Try falling back to CBIOS.
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mov byte [getonesec.jmp+1],(getonesec_cbios-(getonesec.jmp+2))
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;
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; getonesec_cbios:
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;
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; getlinsec implementation for legacy CBIOS
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;
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getonesec_cbios:
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.retry:
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pushad
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movzx esi,word [bsSecPerTrack]
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movzx edi,word [bsHeads]
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;
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; Dividing by sectors to get (track,sector): we may have
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; up to 2^18 tracks, so we need to use 32-bit arithmetric.
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;
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div esi
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xor cx,cx
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xchg cx,dx ; CX <- sector index (0-based)
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; EDX <- 0
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; eax = track #
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div edi ; Convert track to head/cyl
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cmp eax,1023 ; Outside the CHS range?
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ja kaboom
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;
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; Now we have AX = cyl, DX = head, CX = sector (0-based),
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; SI = bsSecPerTrack, ES:BX = data target
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;
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shl ah,6 ; Because IBM was STOOPID
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; and thought 8 bits were enough
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; then thought 10 bits were enough...
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inc cx ; Sector numbers are 1-based, sigh
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or cl,ah
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mov ch,al
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mov dh,dl
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mov ax,0201h ; Read one sector
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call xint13
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popad
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jc .error
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ret
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.error:
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loop .retry
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; Fall through to disk_error
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;
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; kaboom: write a message and bail out.
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;
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%ifdef BINFMT
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global kaboom
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%else
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global kaboom:function hidden
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%endif
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disk_error:
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kaboom:
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xor si,si
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mov ss,si
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mov sp,OrigFDCTabPtr ; Reset stack
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mov ds,si ; Reset data segment
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pop dword [fdctab] ; Restore FDC table
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.patch: ; When we have full code, intercept here
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mov si,bailmsg
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.loop: lodsb
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and al,al
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jz .done
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mov ah,0Eh ; Write to screen as TTY
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mov bx,0007h ; Attribute
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int 10h
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jmp short .loop
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.done:
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xor ax,ax
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.again: int 16h ; Wait for keypress
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; NB: replaced by int 18h if
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; chosen at install time..
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int 19h ; And try once more to boot...
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.norge: hlt ; If int 19h returned; this is the end
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jmp short .norge
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;
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; INT 13h wrapper function
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;
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xint13:
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mov dl,[DriveNumber]
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push es ; ES destroyed by INT 13h AH 08h
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int 13h
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pop es
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ret
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;
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; Error message on failure
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;
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bailmsg: db 'Boot error', 0Dh, 0Ah, 0
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; This fails if the boot sector overflowsg
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zb 1F8h-($-$$)
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bs_magic dd LDLINUX_MAGIC
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bs_link dw (Sect1Load - bootsec) | BS_MAGIC_VER
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bootsignature dw 0xAA55
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;
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; ===========================================================================
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; End of boot sector
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; ===========================================================================
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