ldlinux.lst

Windows上的精简Linux系统

   757                                  ; Insane hack to expand the superblock to dwords
   758                                  ;
   759                                  expand_super:
   760 0000009F 6631C0                  		xor eax,eax
   761 000000A2 8EC0                    		mov es,ax			; INT 13:08 destroys ES
   762 000000A4 BE[0B00]                		mov si,superblock
   763 000000A7 BFB056                  		mov di,SuperInfo
   764 000000AA B110                    		mov cl,superinfo_size		; CH == 0
   765                                  .loop:
   766 000000AC AD                      		lodsw
   767 000000AD 4E                      		dec si
   768 000000AE 66AB                    		stosd				; Store expanded word
   769 000000B0 30E4                    		xor ah,ah
   770 000000B2 66AB                    		stosd				; Store expanded byte
   771 000000B4 E2F6                    		loop .loop
   772                                  
   773                                  ;
   774                                  ; Now we have to do some arithmetric to figure out where things are located.
   775                                  ; If Micro$oft had had brains they would already have done this for us,
   776                                  ; and stored it in the superblock at format time, but here we go,
   777                                  ; wasting precious boot sector space again...
   778                                  ;
   779                                  %define		Z di-superinfo_size*8-SuperInfo
   780                                  debugentrypt:
   781 000000B6 A1DC56                  		mov ax,[bxFATs]		; Number of FATs (eax<31:16> == 0)
   782 000000B9 668B55D8                		mov edx,[Z+bxFATsecs]	; Sectors/FAT
   783 000000BD 66F7E2                  		mul edx			; Get the size of the FAT area
   784                                  		; edx <- 0
   785 000000C0 660306[1C00]            		add eax,[bxHidden]		; Add hidden sectors
   786 000000C5 66034598                		add eax,[Z+bxResSectors]	; And reserved sectors
   787                                  
   788 000000C9 66A33057                		mov [RootDir],eax	; Location of root directory
   789 000000CD 66A33457                		mov [DataArea],eax	; First data sector
   790 000000D1 6650                    		push eax
   791                                  
   792 000000D3 668B45B0                		mov eax,[Z+bxRootDirEnts]
   793 000000D7 C1E005                  		shl ax,5		; Size of a directory entry
   794 000000DA 8B5D80                  		mov bx,[Z+bxBytesPerSec]
   795 000000DD 01D8                    		add ax,bx		; Round up, not down
   796 000000DF 48                      		dec ax
   797 000000E0 F7F3                    		div bx			; Now we have the size of the root dir
   798 000000E2 A33857                  		mov [RootDirSize],ax
   799 000000E5 A33A57                  		mov [DirScanCtr],ax
   800 000000E8 81C3E10F                		add bx,trackbuf-31
   801 000000EC 895D0C                  		mov [Z+EndofDirSec],bx	; End of a single directory sector
   802 000000EF 66014504                		add [Z+DataArea],eax
   803 000000F3 6658                    		pop eax			; Reload root directory starting point
   804                                  
   805                                  ;
   806                                  ; Now the fun begins.  We have to search the root directory for
   807                                  ; LDLINUX.SYS and load the first sector, so we have a little more
   808                                  ; space to have fun with.  Then we can go chasing through the FAT.
   809                                  ; Joy!!
   810                                  ;
   811 000000F5 6650                    sd_nextsec:	push eax
   812 000000F7 BB0010                  		mov bx,trackbuf
   813 000000FA 53                      		push bx
   814 000000FB E88200                  		call getonesec
   815 000000FE 5E                      		pop si
   816 000000FF B90B00                  sd_nextentry:	mov cx,11
   817 00000102 382C                    		cmp [si],ch		; Directory high water mark
   818 00000104 741C                    		je kaboom
   819                                  ; This no longer fits... since we'd be dead anyway if there
   820                                  ; was a nonfile named LDLINUX.SYS on the disk, it shouldn't
   821                                  ; matter...
   822                                  ;		test byte [si+11],18h	; Must be a file
   823                                  ;		jnz sd_not_file
   824 00000106 BF[EF01]                		mov di,ldlinux_name
   825 00000109 56                      		push si
   826 0000010A F3A6                    		repe cmpsb
   827 0000010C 5E                      		pop si
   828 0000010D 742E                    		je found_it
   829 0000010F 83C620                  sd_not_file:	add si,byte 32		; Distance to next
   830 00000112 3B363C57                		cmp si,[EndofDirSec]
   831 00000116 72E7                    		jb sd_nextentry
   832 00000118 6658                    		pop eax
   833 0000011A 6640                    		inc eax
   834 0000011C FF0E3A57                		dec word [DirScanCtr]
   835 00000120 75D3                    		jnz sd_nextsec
   836                                  ;
   837                                  ; kaboom: write a message and bail out.
   838                                  ;
   839                                  kaboom:
   840 00000122 31F6                    		xor si,si
   841 00000124 8ED6                    		mov ss,si		
   842 00000126 BC[B0FF]                		mov sp,StackBuf-4 	; Reset stack
   843 00000129 8EDE                    		mov ds,si		; Reset data segment
   844 0000012B 668F067800              		pop dword [fdctab]	; Restore FDC table
   845 00000130 BE[E001]                .patch:		mov si,bailmsg
   846 00000133 E83600                  		call writestr		; Returns with AL = 0
   847 00000136 98                      		cbw			; AH <- 0
   848 00000137 CD16                    		int 16h			; Wait for keypress
   849 00000139 CD19                    		int 19h			; And try once more to boot...
   850 0000013B EBFE                    .norge:		jmp short .norge	; If int 19h returned; this is the end
   851                                  
   852                                  ;
   853                                  ; found_it: now we compute the location of the first sector, then
   854                                  ;	    load it and JUMP (since we're almost out of space)
   855                                  ;
   856                                  found_it:	; Note: we actually leave two words on the stack here
   857                                  		; (who cares?)
   858 0000013D 66A1C456                		mov eax,[bxSecPerClust]
   859 00000141 89C5                    		mov bp,ax		; Load an entire cluster
   860 00000143 660FB75C1A              		movzx ebx,word [si+26]	; First cluster
   861 00000148 891E9257                		mov [RunLinClust],bx	; Save for later use
   862 0000014C 4B                      		dec bx			; First cluster is "cluster 2"
   863 0000014D 4B                      		dec bx
   864 0000014E 66F7E3                  		mul ebx
   865 00000151 6603063457              		add eax,[DataArea]
   866 00000156 BB[0002]                		mov bx,ldlinux_sys
   867 00000159 E82700                  		call getlinsec
   868 0000015C BE[EF01]                		mov si,bs_magic
   869 0000015F BF[1F02]                		mov di,ldlinux_magic
   870 00000162 B91100                  		mov cx,magic_len
   871 00000165 F3A6                    		repe cmpsb		; Make sure that the bootsector
   872 00000167 75B9                    		jne kaboom		; matches LDLINUX.SYS
   873                                  ;
   874                                  ; Done! Jump to the entry point!
   875                                  ;
   876 00000169 E9C800                  		jmp ldlinux_ent
   877                                  ;
   878                                  ;
   879                                  ; writestr: write a null-terminated string to the console
   880                                  ;	    This assumes we're on page 0.  This is only used for early
   881                                  ;           messages, so it should be OK.
   882                                  ;
   883                                  writestr:
   884 0000016C AC                      .loop:		lodsb
   885 0000016D 20C0                    		and al,al
   886 0000016F 7409                                    jz .return
   887 00000171 B40E                    		mov ah,0Eh		; Write to screen as TTY
   888 00000173 BB0700                  		mov bx,0007h		; Attribute
   889 00000176 CD10                    		int 10h
   890 00000178 EBF2                    		jmp short .loop
   891 0000017A C3                      .return:	ret
   892                                  
   893                                  ;
   894                                  ; disk_error: decrement the retry count and bail if zero.
   895                                  ;	      This gets patched once we have more space to try to
   896                                  ;             optimize transfer sizes on broken machines.
   897                                  ;
   898 0000017B 4E                      disk_error:	dec si			; SI holds the disk retry counter
   899 0000017C 74A4                    		jz kaboom
   900                                  		; End of patched "call" instruction!
   901 0000017E EB33                    		jmp short disk_try_again
   902                                  
   903                                  ;
   904                                  ; getonesec: like getlinsec, but pre-sets the count to 1
   905                                  ;
   906                                  getonesec:
   907 00000180 BD0100                  		mov bp,1
   908                                  		; Fall through to getlinsec
   909                                  
   910                                  ;
   911                                  ; getlinsec: load a sequence of BP floppy sector given by the linear sector
   912                                  ;	     number in EAX into the buffer at ES:BX.  We try to optimize
   913                                  ;	     by loading up to a whole track at a time, but the user
   914                                  ;	     is responsible for not crossing a 64K boundary.
   915                                  ;	     (Yes, BP is weird for a count, but it was available...)
   916                                  ;
   917                                  ;	     On return, BX points to the first byte after the transferred
   918                                  ;	     block.
   919                                  ;
   920                                  ;	     The "stupid patch area" gets replaced by the code
   921                                  ;	     mov bp,1 ; nop ... (BD 01 00 90 90...) when installing with
   922                                  ;	     the -s option.
   923                                  ;
   924                                  ;            This routine assumes CS == DS.
   925                                  ;
   926                                  ; Stylistic note: use "xchg" instead of "mov" when the source is a register
   927                                  ; that is dead from that point; this saves space.  However, please keep
   928                                  ; the order to dst,src to keep things sane.
   929                                  ;
   930                                  getlinsec:
   931 00000183 668B361857              		mov esi,[bxSecPerTrack]
   932                                  		;
   933                                  		; Dividing by sectors to get (track,sector): we may have
   934                                  		; up to 2^18 tracks, so we need to use 32-bit arithmetric.
   935                                  		;
   936 00000188 6631D2                  		xor edx,edx		; Zero-extend LBA to 64 bits
   937 0000018B 66F7F6                  		div esi
   938 0000018E 31C9                    		xor cx,cx
   939 00000190 87CA                    		xchg cx,dx		; CX <- sector index (0-based)
   940                                  					; EDX <- 0
   941                                  		; eax = track #
   942 00000192 66F7362857              		div dword [bxHeads]	; Con