ldlinux.lst

Windows上的精简Linux系统

   568                                  ;
   569                                  ; These are the fields we actually care about.  We end up expanding them
   570                                  ; all to dword size early in the code, so generate labels for both
   571                                  ; the expanded and unexpanded versions.
   572                                  ;;
   573                                  %macro		superb 1
   574                                  bx %+ %1	equ SuperInfo+($-superblock)*8+4
   575                                  bs %+ %1	equ $
   576                                  		zb 1
   577                                  %endmacro
   578                                  %macro		superw 1
   579                                  bx %+ %1	equ SuperInfo+($-superblock)*8
   580                                  bs %+ %1	equ $
   581                                  		zw 1
   582                                  %endmacro
   583                                  %macro		superd 1
   584                                  bx %+ %1	equ $			; no expansion for dwords
   585                                  bs %+ %1	equ $
   586                                  		zd 1
   587                                  %endmacro
   588                                  superblock	equ $
   589                                  		superw BytesPerSec
   590                              <1> bx %+ %1 equ SuperInfo+($-superblock)*8
   591                              <1> bs %+ %1 equ $
   592 0000000B 0000                <1>  zw 1
   593                                  		superb SecPerClust
   594                              <1> bx %+ %1 equ SuperInfo+($-superblock)*8+4
   595                              <1> bs %+ %1 equ $
   596 0000000D 00                  <1>  zb 1
   597                                  		superw ResSectors
   598                              <1> bx %+ %1 equ SuperInfo+($-superblock)*8
   599                              <1> bs %+ %1 equ $
   600 0000000E 0000                <1>  zw 1
   601                                  		superb FATs
   602                              <1> bx %+ %1 equ SuperInfo+($-superblock)*8+4
   603                              <1> bs %+ %1 equ $
   604 00000010 00                  <1>  zb 1
   605                                  		superw RootDirEnts
   606                              <1> bx %+ %1 equ SuperInfo+($-superblock)*8
   607                              <1> bs %+ %1 equ $
   608 00000011 0000                <1>  zw 1
   609                                  		superw Sectors
   610                              <1> bx %+ %1 equ SuperInfo+($-superblock)*8
   611                              <1> bs %+ %1 equ $
   612 00000013 0000                <1>  zw 1
   613                                  		superb Media
   614                              <1> bx %+ %1 equ SuperInfo+($-superblock)*8+4
   615                              <1> bs %+ %1 equ $
   616 00000015 00                  <1>  zb 1
   617                                  		superw FATsecs
   618                              <1> bx %+ %1 equ SuperInfo+($-superblock)*8
   619                              <1> bs %+ %1 equ $
   620 00000016 0000                <1>  zw 1
   621                                  		superw SecPerTrack
   622                              <1> bx %+ %1 equ SuperInfo+($-superblock)*8
   623                              <1> bs %+ %1 equ $
   624 00000018 0000                <1>  zw 1
   625                                  		superw Heads
   626                              <1> bx %+ %1 equ SuperInfo+($-superblock)*8
   627                              <1> bs %+ %1 equ $
   628 0000001A 0000                <1>  zw 1
   629                                  superinfo_size	equ ($-superblock)-1	; How much to expand
   630                                  		superd Hidden
   631                              <1> bx %+ %1 equ $
   632                              <1> bs %+ %1 equ $
   633 0000001C 00000000            <1>  zd 1
   634                                  		superd HugeSectors
   635                              <1> bx %+ %1 equ $
   636                              <1> bs %+ %1 equ $
   637 00000020 00000000            <1>  zd 1
   638                                  		superb DriveNumber
   639                              <1> bx %+ %1 equ SuperInfo+($-superblock)*8+4
   640                              <1> bs %+ %1 equ $
   641 00000024 00                  <1>  zb 1
   642                                  		superb Reserved1
   643                              <1> bx %+ %1 equ SuperInfo+($-superblock)*8+4
   644                              <1> bs %+ %1 equ $
   645 00000025 00                  <1>  zb 1
   646                                  		superb BootSignature	; 29h if the following fields exist
   647                              <1> bx %+ %1 equ SuperInfo+($-superblock)*8+4
   648                              <1> bs %+ %1 equ $
   649 00000026 00                  <1>  zb 1
   650                                  		superd VolumeID
   651                              <1> bx %+ %1 equ $
   652                              <1> bs %+ %1 equ $
   653 00000027 00000000            <1>  zd 1
   654 0000002B 00<rept>                bsVolumeLabel	zb 11
   655 00000036 00<rept>                bsFileSysType	zb 8			; Must be FAT12 or FAT16 for this version
   656                                  superblock_len	equ $-superblock
   657                                  
   658                                  SecPerClust	equ bxSecPerClust
   659                                  ;
   660                                  ; Note we don't check the constraints above now; we did that at install
   661                                  ; time (we hope!)
   662                                  ;
   663                                  
   664                                  ;floppy_table	equ $			; No sense in wasting memory, overwrite start
   665                                  
   666                                  start:
   667 0000003E FA                      		cli			; No interrupts yet, please
   668 0000003F FC                      		cld			; Copy upwards
   669                                  ;
   670                                  ; Set up the stack
   671                                  ;
   672 00000040 31C0                    		xor ax,ax
   673 00000042 8ED0                    		mov ss,ax
   674 00000044 BC[B4FF]                		mov sp,StackBuf		; Just below BSS
   675 00000047 8EC0                    		mov es,ax
   676                                  ;
   677                                  ; DS:SI may contain a partition table entry.  Preserve it for us.
   678                                  ;
   679 00000049 B90800                  		mov cx,8		; Save partition info
   680 0000004C 89E7                    		mov di,sp
   681 0000004E F3A5                    		rep movsw
   682                                  
   683 00000050 8ED8                    		mov ds,ax		; Now we can initialize DS...
   684                                  
   685 00000052 885560                  		mov [di+bsDriveNumber-FloppyTable],dl
   686                                  ;
   687                                  ; Now sautee the BIOS floppy info block to that it will support decent-
   688                                  ; size transfers; the floppy block is 11 bytes and is stored in the
   689                                  ; INT 1Eh vector (brilliant waste of resources, eh?)
   690                                  ;
   691                                  ; Of course, if BIOSes had been properly programmed, we wouldn't have
   692                                  ; had to waste precious space with this code.
   693                                  ;
   694 00000055 BB7800                  		mov bx,fdctab
   695 00000058 0FB437                  		lfs si,[bx]		; FS:SI -> original fdctab
   696 0000005B 0FA0                    		push fs			; Save on stack in case we need to bail
   697 0000005D 56                      		push si
   698                                  
   699                                  		; Save the old fdctab even if hard disk so the stack layout
   700                                  		; is the same.  The instructions above do not change the flags
   701 0000005E 20D2                    		and dl,dl		; If floppy disk (00-7F), assume no
   702                                  					; partition table
   703 00000060 7815                    		js harddisk
   704                                  
   705                                  floppy:
   706 00000062 B106                    		mov cl,6		; 12 bytes (CX == 0)
   707                                  		; es:di -> FloppyTable already
   708                                  		; This should be safe to do now, interrupts are off...
   709 00000064 893F                    		mov [bx],di		; FloppyTable
   710 00000066 894702                  		mov [bx+2],ax		; Segment 0
   711 00000069 64F3A5                  		fs rep movsw		; Faster to move words
   712 0000006C 8A0E[1800]              		mov cl,[bsSecPerTrack]  ; Patch the sector count
   713 00000070 884DF8                  		mov [di-8],cl
   714                                  		; AX == 0 here
   715 00000073 CD13                    		int 13h			; Some BIOSes need this
   716                                  
   717 00000075 EB27                    		jmp short not_harddisk
   718                                  ;
   719                                  ; The drive number and possibly partition information was passed to us
   720                                  ; by the BIOS or previous boot loader (MBR).  Current "best practice" is to
   721                                  ; trust that rather than what the superblock contains.
   722                                  ;
   723                                  ; Would it be better to zero out bsHidden if we don't have a partition table?
   724                                  ;
   725                                  ; Note: di points to beyond the end of PartInfo
   726                                  ;
   727                                  harddisk:
   728 00000077 F645F07F                		test byte [di-16],7Fh	; Sanity check: "active flag" should
   729 0000007B 7508                    		jnz no_partition	; be 00 or 80
   730 0000007D 668B45F8                		mov eax,[di-8]		; Partition offset (dword)
   731 00000081 66A3[1C00]              		mov [bsHidden],eax
   732                                  no_partition:
   733                                  ;
   734                                  ; Get disk drive parameters (don't trust the superblock.)  Don't do this for
   735                                  ; floppy drives -- INT 13:08 on floppy drives will (may?) return info about
   736                                  ; what the *drive* supports, not about the *media*.  Fortunately floppy disks
   737                                  ; tend to have a fixed, well-defined geometry which is stored in the superblock.
   738                                  ;
   739                                  		; DL == drive # still
   740 00000085 B408                    		mov ah,08h
   741 00000087 CD13                    		int 13h
   742 00000089 7213                    		jc no_driveparm
   743 0000008B 20E4                    		and ah,ah
   744 0000008D 750F                    		jnz no_driveparm
   745 0000008F C1EA08                  		shr dx,8
   746 00000092 42                      		inc dx			; Contains # of heads - 1
   747 00000093 8916[1A00]              		mov [bsHeads],dx
   748 00000097 83E13F                  		and cx,3fh
   749 0000009A 890E[1800]              		mov [bsSecPerTrack],cx
   750                                  no_driveparm:
   751                                  not_harddisk:
   752                                  ;
   753                                  ; Ready to enable interrupts, captain
   754                                  ;
   755 0000009E FB                      		sti
   756                                  ;