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Assembly Source File | 1998-05-07 | 89.6 KB | 3,387 lines

; -*- fundamental -*- (asm-mode sucks) ; $Id: ldlinux.asm,v 1.36 1998/05/08 01:45:36 hpa Exp $ ; **************************************************************************** ; ; ldlinux.asm ; ; A program to boot Linux kernels off an MS-DOS formatted floppy disk. This ; functionality is good to have for installation floppies, where it may ; be hard to find a functional Linux system to run LILO off. ; ; This program allows manipulation of the disk to take place entirely ; from MS-LOSS, and can be especially useful in conjunction with the ; umsdos filesystem. ; ; This file is loaded in stages; first the boot sector at offset 7C00h, ; then the first sector (cluster, really, but we can only assume 1 sector) ; of LDLINUX.SYS at 7E00h and finally the remainder of LDLINUX.SYS at 8000h. ; ; Copyright (C) 1994-1998 H. Peter Anvin ; ; This program is free software; you can redistribute it and/or modify ; it under the terms of the GNU General Public License as published by ; the Free Software Foundation, Inc., 675 Mass Ave, Cambridge MA 02139, ; USA; either version 2 of the License, or (at your option) any later ; version; incorporated herein by reference. ; ; **************************************************************************** ; ; Some semi-configurable constants... change on your own risk ; max_cmd_len equ 255 ; Must be odd; 255 is the kernel limit retry_count equ 6 ; How patient are we with the disk? ; ; Should be updated with every release to avoid bootsector/SYS file mismatch ; %define version_str VERSION ; Must be 4 characters long! %define date DATE_STR ; Defined from the Makefile %define year '1998' ; ; Debgging stuff ; ; %define debug 1 ; Uncomment to enable debugging ; ; ID for SYSLINUX (reported to kernel) ; syslinux_id equ 031h ; SYSLINUX (3) version 1.x (1) ; ; Segments used by Linux ; real_mode_seg equ 9000h struc real_mode_seg_t resb 20h-($-$$) ; org 20h kern_cmd_magic resw 1 ; Magic # for command line kern_cmd_offset resw 1 ; Offset for kernel command line resb 497-($-$$) ; org 497d bs_setupsecs resb 1 ; Sectors for setup code (0 -> 4) bs_rootflags resw 1 ; Root readonly flag bs_syssize resw 1 bs_swapdev resw 1 ; Swap device (obsolete) bs_ramsize resw 1 ; Ramdisk flags, formerly ramdisk size bs_vidmode resw 1 ; Video mode bs_rootdev resw 1 ; Root device bs_bootsign resw 1 ; Boot sector signature (0AA55h) su_jump resb 1 ; 0EBh su_jump2 resb 1 su_header resd 1 ; New setup code: header su_version resw 1 ; See linux/arch/i386/boot/setup.S su_switch resw 1 su_setupseg resw 1 su_startsys resw 1 su_kver resw 1 ; Kernel version pointer su_loader resb 1 ; Loader ID su_loadflags resb 1 ; Load high flag su_movesize resw 1 su_code32start resd 1 ; Start of code loaded high su_ramdiskat resd 1 ; Start of initial ramdisk su_ramdisklen equ $ ; Length of initial ramdisk su_ramdisklen1 resw 1 su_ramdisklen2 resw 1 su_bsklugeoffs resw 1 su_bsklugeseg resw 1 su_heapend resw 1 resb (8000h-12)-($-$$) ; Were bootsect.S puts it... linux_stack equ $ linux_fdctab equ $ resb 8000h-($-$$) cmd_line_here equ $ ; Should be out of the way endstruc setup_seg equ 9020h struc setup_seg_t org 0h ; as 9020:0000, not 9000:0200 setup_entry equ $ endstruc ; ; Magic number of su_header field ; HEADER_ID equ 'HdrS' ; HdrS (in littleendian hex) ; ; Flags for the su_loadflags field ; LOAD_HIGH equ 01h ; Large kernel, load high CAN_USE_HEAP equ 80h ; Boot loader reports heap size ; ; The following structure is used for "virtual kernels"; i.e. LILO-style ; option labels. The options we permit here are `kernel' and `append ; Since there is no room in the bottom 64K for all of these, we ; stick them at 8000:0000 and copy them down before we need them. ; ; Note: this structure can be added to, but it must ; %define vk_power 7 ; log2(max number of vkernels) %define max_vk (1 << vk_power) ; Maximum number of vkernels %define vk_shift (16-vk_power) ; Number of bits to shift %define vk_size (1 << vk_shift) ; Size of a vkernel buffer struc vkernel vk_vname: resb 11 ; Virtual name **MUST BE FIRST!** vk_rname: resb 11 ; Real name vk_appendlen: resw 1 alignb 4 vk_append: resb max_cmd_len+1 ; Command line alignb 4 vk_end: equ $ ; Should be <= vk_size endstruc %if (vk_end > vk_size) || (vk_size*max_vk > 65536) %error "Too many vkernels defined, reduce vk_power" %endif ; ; Segment assignments in the bottom 640K ; 0000h - main code/data segment (and BIOS segment) ; 9000h - real_mode_seg ; vk_seg equ 8000h ; This is where we stick'em xfer_buf_seg equ 7000h ; Bounce buffer for I/O to high mem fat_seg equ 5000h ; 128K area for FAT (2x64K) comboot_seg equ 1000h ; COMBOOT image loading zone ; ; For our convenience: define macros for jump-over-unconditinal jumps ; %macro jmpz 1 jnz %%skip jmp %1 %%skip: %endmacro %macro jmpnz 1 jz %%skip jmp %1 %%skip: %endmacro %macro jmpe 1 jne %%skip jmp %1 %%skip: %endmacro %macro jmpne 1 je %%skip jmp %1 %%skip: %endmacro %macro jmpc 1 jnc %%skip jmp %1 %%skip: %endmacro %macro jmpnc 1 jc %%skip jmp %1 %%skip: %endmacro %macro jmpb 1 jnb %%skip jmp %1 %%skip: %endmacro %macro jmpnb 1 jb %%skip jmp %1 %%skip: %endmacro ; ; Macros similar to res[bwd], but which works in the code segment (after ; section .text) ; %macro zb 1 times %1 db 0 %endmacro %macro zw 1 times %1 dw 0 %endmacro %macro zd 1 times %1 dd 0 %endmacro ; --------------------------------------------------------------------------- ; BEGIN THE BIOS/CODE/DATA SEGMENT ; --------------------------------------------------------------------------- absolute 4*1Eh ; In the interrupt table fdctab equ $ fdctab1 resw 1 fdctab2 resw 1 %ifdef debug org 0100h ..start: ; ; Hook for debugger stuff. This gets automatically removed when ; generating the real thing. ; ; Initialize the registers for debugger operation ; cli mov ax,cs mov ds,ax mov es,ax mov ss,ax mov sp,StackBuf sti cld ; ; Load the actual boot sector so we can copy the data block ; xor ax,ax ; Reset floppy xor dx,dx int 13h mov cx,6 ; Retry count... debug_tryloop: push cx mov bx,trackbuf mov cx,0001h xor dx,dx mov ax,0201h int 13h pop cx jnc debug_okay loop debug_tryloop int 3 ; Halt! (Breakpoint) debug_okay: mov si,trackbuf+0bh mov di,bsBytesPerSec mov cx,33h rep movsb ; ; Save bogus "BIOS floppy block" info to the stack in case we hit kaboom ; push si push si push si ; Writing to the trackbuf is harmless ; ; Copy the BIOS data area ; push ds xor ax,ax mov ds,ax mov si,0400h mov di,si mov cx,0100h rep movsw pop ds ; ; ; A NOP where we can breakpoint, then jump into the code *after* ; the segment register initialization section ; nop jmp debugentrypt %endif absolute 0484h BIOS_vidrows resb 1 ; Number of screen rows ; ; Memory below this point is reserved for the BIOS and the MBR ; absolute 1000h trackbuf equ $ ; Track buffer goes here trackbufsize equ 16384 ; Safe size of track buffer ; trackbuf ends at 5000h absolute 6000h ; Here we keep our BSS stuff StackBuf equ $ ; Start the stack here (grow down - 4K) VKernelBuf: resb vk_size ; "Current" vkernel alignb 4 AppendBuf resb max_cmd_len+1 ; append= KbdMap resb 256 ; Keyboard map FKeyName resb 10*16 ; File names for F-key help NumBuf resb 16 ; Buffer to load number NumBufEnd equ NumBuf+15 ; Pointer to last byte in NumBuf alignb 4 PartInfo resb 16 ; Partition table entry InitRDat resd 1 ; Load address (linear) for initrd HiLoadAddr resd 1 ; Address pointer for high load loop KernelName resb 12 ; Mangled name for kernel ; (note the spare byte after!) RootDir equ $ ; Location of root directory RootDir1 resw 1 RootDir2 resw 1 DataArea equ $ ; Location of data area DataArea1 resw 1 DataArea2 resw 1 FBytes equ $ ; Used by open/getc FBytes1 resw 1 FBytes2 resw 1 RootDirSize resw 1 ; Root dir size in sectors DirScanCtr resw 1 ; Used while searching directory DirBlocksLeft resw 1 ; Ditto EndofDirSec resw 1 ; = trackbuf+bsBytesPerSec-31 RunLinClust resw 1 ; Cluster # for LDLINUX.SYS ClustSize resw 1 ; Bytes/cluster SecPerClust resw 1 ; Same as bsSecPerClust, but a word NextCluster resw 1 ; Pointer to "nextcluster" routine BufSafe resw 1 ; Clusters we can load into trackbuf BufSafeSec resw 1 ; = how many sectors? BufSafeBytes resw 1 ; = how many bytes? EndOfGetCBuf resw 1 ; = getcbuf+BufSafeBytes HighMemSize resw 1 ; High memory (K) KernelClust resw 1 ; Kernel size in clusters KernelK resw 1 ; Kernel size in kilobytes InitRDClust resw 1 ; Ramdisk size in clusters ClustPerMoby resw 1 ; Clusters per 64K FClust resw 1 ; Number of clusters in open/getc file FNextClust resw 1 ; Pointer to next cluster in d:o FPtr resw 1 ; Pointer to next char in buffer CmdOptPtr resw 1 ; Pointer to first option on cmd line KernelCNameLen resw 1 ; Length of unmangled kernel name InitRDCNameLen resw 1 ; Length of unmangled initrd name NextCharJump resw 1 ; Routine to interpret next print char SetupSecs resw 1 ; Number of setup sectors SavedSP resw 1 ; Our SP while running a COMBOOT image A20test resw 1 ; Counter for testing status of A20 TextAttrBX equ $ TextAttribute resb 1 ; Text attribute for message file TextPage resb 1 ; Active display page CursorDX equ $ CursorCol resb 1 ; Cursor column for message file CursorRow resb 1 ; Cursor row for message file ScreenSize equ $ VidCols resb 1 ; Columns on screen-1 VidRows resb 1 ; Rows on screen-1 RetryCount resb 1 ; Used for disk access retries KbdFlags resb 1 ; Check for keyboard escapes LoadFlags resb 1 ; Loadflags from kernel MNameBuf resb 11 ; Generic mangled file name buffer InitRD resb 11 ; initrd= mangled name KernelCName resb 13 ; Unmangled kernel name InitRDCName resb 13 ; Unmangled initrd name section .text org 7C00h ; ; Primary entry point. Tempting as though it may be, we can't put the ; initial "cli" here; the jmp opcode in the first byte is part of the ; "magic number" (using the term very loosely) for the DOS superblock. ; bootsec equ $ jmp short start ; 2 bytes nop ; 1 byte ; ; "Superblock" follows -- it's in the boot sector, so it's already ; loaded and ready for us ; bsOemName db 'SYSLINUX' ; The SYS command sets this, so... superblock equ $ bsBytesPerSec zw 1 bsSecPerClust zb 1 bsResSectors zw 1 bsFATs zb 1 bsRootDirEnts zw 1 bsSectors zw 1 bsMedia zb 1 bsFATsecs zw 1 bsSecPerTrack zw 1 bsHeads zw 1 bsHiddenSecs equ $ bsHidden1 zw 1 bsHidden2 zw 1 bsHugeSectors equ $ bsHugeSec1 zw 1 bsHugeSec2 zw 1 bsDriveNumber zb 1 bsReserved1 zb 1 bsBootSignature zb 1 ; 29h if the following fields exist bsVolumeID zd 1 bsVolumeLabel zb 11 bsFileSysType zb 8 ; Must be FAT12 for this version superblock_len equ $-superblock ; ; Note we don't check the constraints above now; we did that at install ; time (we hope!) ; ;floppy_table equ $ ; No sense in wasting memory, overwrite start start: cli ; No interrupts yet, please cld ; Copy upwards ; ; Set up the stack ; xor cx,cx mov ss,cx mov sp,StackBuf ; Just below BSS mov es,cx ; ; DS:SI may contain a partition table entry. Preserve it for us. ; mov cl,8 ; Save partition info (CH == 0) mov di,PartInfo rep movsw ; ; Now sautee the BIOS floppy info block to that it will support decent- ; size transfers; the floppy block is 11 bytes and is stored in the ; INT 1Eh vector (brilliant waste of resources, eh?) ; ; Of course, if BIOSes had been properly programmed, we wouldn't have ; had to waste precious boot sector space with this code. ; ; This code no longer fits. Hope that noone really needs it anymore. ; (If so, it needs serious updating.) In fact, some indications is that ; this code does more harm than good with all the new kinds of drives and ; media. ; %ifdef SUPPORT_REALLY_BROKEN_BIOSES lds si,[ss:fdctab] ; DS:SI -> original push ds ; Save on stack in case push si ; we have to bail push bx mov cx,6 ; 12 bytes mov di,floppy_table push di cld rep movsw ; Faster to move words pop di mov ds,ax ; Now we can point DS to here, too mov cl,[bsSecPerTrack] ; Patch the sector count mov [di+4],cl mov [fdctab+2],ax ; Segment 0 mov [fdctab],di ; offset floppy_block %else mov ds,cx ; CX == 0 %endif ; ; Ready to enable interrupts, captain ; sti ; ; The drive number and possibly partition information was passed to us ; by the BIOS or previous boot loader (MBR). Current "best practice" is to ; trust that rather than what the superblock contains. ; ; Would it be better to zero out bsHidden if we don't have a partition table? ; ; Note: di points to beyond the end of PartInfo ; mov [bsDriveNumber],dl test dl,80h ; If floppy disk (00-7F), assume no jz not_harddisk ; partition table test byte [di-16],7Fh ; Sanity check: "active flag" should jnz no_partition ; be 00 or 80 lea si,[di-8] ; Partition offset (dword) mov di,bsHidden1 mov cl,2 ; CH == 0 rep movsw no_partition: ; ; Get disk drive parameters (don't trust the superblock.) Don't do this for ; floppy drives -- INT 13:08 on floppy drives will (may?) return info about ; what the *drive* supports, not about the *media*. Fortunately floppy disks ; tend to have a fixed, well-defined geometry which is stored in the superblock. ; ; DL == drive # still mov ah,08h int 13h jc no_driveparm and ah,ah jnz no_driveparm inc dh ; Contains # of heads - 1 mov [bsHeads],dh and cx,3fh mov [bsSecPerTrack],cx no_driveparm: not_harddisk: ; ; Now we have to do some arithmetric to figure out where things are located. ; If Micro$oft had had brains they would already have done this for us, ; and stored it in the superblock at format time, but here we go, ; wasting precious boot sector space again... ; debugentrypt: xor ax,ax ; INT 13:08 destroys ES mov es,ax mov al,[bsFATs] ; Number of FATs (AH == 0) mul word [bsFATsecs] ; Get the size of the FAT area add ax,[bsHidden1] ; Add hidden sectors adc dx,[bsHidden2] add ax,[bsResSectors] ; And reserved sectors adc dx,byte 0 mov [RootDir1],ax ; Location of root directory mov [RootDir2],dx mov [DataArea1],ax mov [DataArea2],dx push ax push dx mov ax,32 ; Size of a directory entry mul word [bsRootDirEnts] mov bx,[bsBytesPerSec] add ax,bx ; Round up, not down dec ax div bx ; Now we have the size of the root dir mov [RootDirSize],ax mov [DirScanCtr],ax add bx,trackbuf-31 mov [EndofDirSec],bx ; End of a single directory sector add [DataArea1],ax adc word [DataArea2],byte 0 pop dx ; Reload root directory starting point pop ax ; ; Now the fun begins. We have to search the root directory for ; LDLINUX.SYS and load the first sector, so we have a little more ; space to have fun with. Then we can go chasing through the FAT. ; Joy!! ; sd_nextsec: push ax push dx mov bx,trackbuf push bx call getonesec pop si sd_nextentry: cmp byte [si],0 ; Directory high water mark je kaboom mov di,ldlinux_name mov cx,11 push si repe cmpsb pop si je found_it add si,byte 32 ; Distance to next cmp si,[EndofDirSec] jb sd_nextentry pop dx pop ax add ax,byte 1 adc dx,byte 0 dec word [DirScanCtr] jnz sd_nextsec ; ; kaboom: write a message and bail out. ; kaboom: xor si,si mov ss,si mov sp,StackBuf ; Reset stack mov ds,si ; Reset data segment mov si,bailmsg call writestr ; Returns with AL = 0 cbw ; AH <- 0 int 16h ; Wait for keypress int 19h ; And try once more to boot... norge: jmp short norge ; If int 19h returned; this is the end ; ; found_it: now we compute the location of the first sector, then ; load it and JUMP (since we're almost out of space) ; found_it: ; Note: we actually leave two words on the stack here ; (who cares?) xor ax,ax mov al,[bsSecPerClust] mov bp,ax ; Load an entire cluster mov bx,[si+26] ; First cluster mov [RunLinClust],bx ; Save for later use dec bx ; First cluster is "cluster 2" dec bx mul bx add ax,[DataArea1] adc dx,[DataArea2] mov bx,ldlinux_sys call getlinsec mov si,bs_magic mov di,ldlinux_magic mov cx,magic_len repe cmpsb ; Make sure that the bootsector jne kaboom ; matches LDLINUX.SYS ; ; Done! Jump to the entry point! ; jmp ldlinux_ent ; ; ; writestr: write a null-terminated string to the console ; writestr: wstr_1: lodsb and al,al jz return mov ah,0Eh ; Write to screen as TTY mov bx,0007h ; White on black, current page int 10h jmp short wstr_1 ; ; disk_error: decrement the retry count and bail if zero ; disk_error: dec si ; SI holds the disk retry counter jz kaboom xchg ax,bx ; Shorter than MOV pop bx ; pop cx ; <H> pop dx ; <G> jmp short disk_try_again return: ret ; ; getonesec: like getlinsec, but pre-sets the count to 1 ; getonesec: mov bp,1 ; Fall through to getlinsec ; ; getlinsec: load a sequence of BP floppy sector given by the linear sector ; number in DX:AX into the buffer at ES:BX. We try to optimize ; by loading up to a whole track at a time, but the user ; is responsible for not crossing a 64K boundary. ; (Yes, BP is weird for a count, but it was available...) ; ; On return, BX points to the first byte after the transferred ; block. ; ; The "stupid patch area" gets replaced by the code ; mov bp,1 ; nop ... (BD 01 00 90 90...) when installing with ; the -s option. ; ; Stylistic note: use "xchg" instead of "mov" when the source is a register ; that is dead from that point; this saves space. However, please keep ; the order to dst,src to keep things sane. ; getlinsec: mov si,[bsSecPerTrack] ; ; Dividing by sectors to get (track,sector): we may have ; up to 2^18 tracks, so we need to do this in two steps ; to produce a 32-bit quotient. ; xchg cx,ax ; CX <- LSW of LBA xchg ax,dx xor dx,dx ; DX:AX now == MSW of LBA div si ; Obtain MSW of track # xchg ax,cx ; Remainder -> MSW of new dividend ; LSW of LBA -> LSW of new dividend ; Quotient -> MSW of track # div si ; Obtain LSW of track #, remainder xchg cx,dx ; CX <- Sector index (0-based) ; DX <- MSW of track # div word [bsHeads] ; Convert track to head/cyl ; ; Now we have AX = cyl, DX = head, CX = sector (0-based), ; BP = sectors to transfer, SI = bsSecPerTrack, ; ES:BX = data target ; gls_nextchunk: push si ; <A> bsSecPerTrack push bp ; Sectors to transfer __BEGIN_STUPID_PATCH_AREA: sub si,cx ; Sectors left on track cmp bp,si jna gls_lastchunk mov bp,si ; No more than a trackful, please! __END_STUPID_PATCH_AREA: gls_lastchunk: push ax ; <C> Cylinder # push dx ; <D> Head # push bp ; <E> Number of sectors we're transferring push cx ; <F> Sector # mov cl,6 ; Because IBM was STOOPID shl ah,cl ; and thought 8 bits were enough ; then thought 10 bits were enough... pop cx ; <F> Sector # push cx inc cx ; Sector numbers are 1-based or cl,ah mov ch,al mov dh,dl mov dl,[bsDriveNumber] xchg ax,bp ; Sector to transfer count ; (xchg shorter than mov) mov ah,02h ; Read it! ; ; Do the disk transfer... save the registers in case we fail :( ; mov si,retry_count ; # of times to retry a disk access disk_try_again: push dx ; <G> push cx ; <H> push bx ; push ax ; <J> push si ; <K> int 13h pop si ; <K> pop bx ; <J> jc disk_error ; ; Disk access successful ; pop bx ; Buffer location pop ax ; <H> No longer needed pop ax ; <G> No longer needed pop cx ; <F> Sector # pop di ; <E> Sector transferred count mov ax,di ; Reduce sector left count mul word [bsBytesPerSec] ; Figure out how much to advance ptr add bx,ax ; Update buffer location pop dx ; <D> Head # pop ax ; <C> Cyl # pop bp ; Sectors left to transfer pop si ; <A> Number of sectors/track sub bp,di ; Reduce with # of sectors just read jz return ; Done! add cx,di cmp cx,si jb gls_nextchunk inc dx ; Next track on cyl cmp dx,[bsHeads] ; Was this the last one? jb gls_nonewcyl inc ax ; If so, new cylinder xor dx,dx ; First head on new cylinder gls_nonewcyl: sub cx,si ; First sector on new track jmp short gls_nextchunk bailmsg: db 'Boot failed', 0Dh, 0Ah, 0 bs_checkpt equ $ ; Must be <= 1EFh zb 1EFh-($-$$) bs_magic equ $ ; From here to the magic_len equ ; must match ldlinux_magic ldlinux_name: db 'LDLINUX SYS' ; Looks like this in the root dir dd HEXDATE ; Hopefully unique between compiles bootsignature dw 0AA55h magic_len equ $-bs_magic ; ; =========================================================================== ; End of boot sector ; =========================================================================== ; Start of LDLINUX.SYS ; =========================================================================== ldlinux_sys: syslinux_banner db 0Dh, 0Ah, 'SYSLINUX ', version_str, ' ', date, ' ', 0 db 0Dh, 0Ah, 1Ah ; EOF if we "type" this in DOS ldlinux_magic db 'LDLINUX SYS' dd HEXDATE dw 0AA55h align 4 ; ; Entry point. Note that some BIOSes are buggy and put the boot sector ; at 07C0:0000 instead of 0000:7C00 and the like. We don't want to add ; anything more to the boot sector, so it is written to not assume a fixed ; value in CS, but we don't want to deal with that anymore from now on. ; ldlinux_ent: jmp 0:ldlinux_ent2 ldlinux_ent2: ; ; Tell the user we got this far ; mov si,syslinux_banner call writestr ; ; Remember, the boot sector loaded only the first cluster of LDLINUX.SYS. ; We can really only rely on a single sector having been loaded. Hence ; we should load the FAT into RAM and start chasing pointers... ; mov dx,1 ; 64K xor ax,ax div word [bsBytesPerSec] ; sectors/64K mov si,ax push es mov bx,fat_seg ; Load into fat_seg:0000 mov es,bx mov ax,[bsHidden1] ; Hidden sectors mov dx,[bsHidden2] add ax,[bsResSectors] ; plus reserved sectors = FAT adc dx,byte 0 mov cx,[bsFATsecs] ; Sectors/FAT fat_load_loop: mov bp,cx cmp bp,si jna fat_load mov bp,si ; A full 64K moby fat_load: xor bx,bx ; Offset 0 in the current ES call getlinsecsr sub cx,bp jz fat_load_done ; Last moby? add ax,bp ; Advance sector count adc dx,byte 0 mov bx,es ; Next 64K moby add bx,1000h mov es,bx jmp short fat_load_loop fat_load_done: pop es ; ; Fine, now we have the FAT in memory. How big is a cluster, really? ; Also figure out how many clusters will fit in an 8K buffer, and how ; many sectors and bytes that is ; mov di,[bsBytesPerSec] ; Used a lot below mov al,[bsSecPerClust] ; We do this in the boot xor ah,ah ; sector, too, but there mov [SecPerClust],ax ; wasn't space to save it mov si,ax ; Also used a lot... mul di mov [ClustSize],ax ; Bytes/cluster mov bx,ax mov ax,trackbufsize xor dx,dx div bx mov [BufSafe],ax ; # of cluster in trackbuf mul word [SecPerClust] mov [BufSafeSec],ax mul di mov [BufSafeBytes],ax add ax,getcbuf ; Size of getcbuf is the same mov [EndOfGetCBuf],ax ; as for trackbuf ; ; FAT12 or FAT16? This computation is fscking ridiculous... ; xor dx,dx xor cx,cx mov ax,[bsSectors] and ax,ax jnz have_secs mov ax,[bsHugeSectors] mov dx,[bsHugeSectors+2] have_secs: sub ax,[bsResSectors] sbb dx,byte 0 mov cl,[bsFATs] sec_fat_loop: sub ax,[bsFATsecs] sbb dx,byte 0 loop sec_fat_loop push ax push dx mov ax,[bsRootDirEnts] mov bx,32 ; Smaller than shift since we mul bx ; need the doubleword product add ax,di adc dx,byte 0 sub ax,byte 1 sbb dx,byte 0 div di mov bx,ax pop dx pop ax sub ax,bx sbb dx,byte 0 div si cmp ax,4086 ; Right value? mov ax,nextcluster_fat16 ja have_fat_type have_fat12: mov ax,nextcluster_fat12 have_fat_type: mov word [NextCluster],ax ; ; Now we read the rest of LDLINUX.SYS. Don't bother loading the first ; cluster again, though. ; load_rest: mov cx,[ClustSize] mov bx,ldlinux_sys add bx,cx mov si,[RunLinClust] call [NextCluster] xor dx,dx mov ax,ldlinux_len-1 ; To be on the safe side add ax,cx div cx ; the number of clusters dec ax ; We've already read one jz all_read_jmp mov cx,ax call getfssec ; ; All loaded up ; all_read_jmp: jmp all_read ; ; ----------------------------------------------------------------------------- ; Subroutines that have to be in the first sector ; ----------------------------------------------------------------------------- ; ; getfssec: Get multiple clusters from a file, given the starting cluster. ; ; This routine makes sure the subtransfers do not cross a 64K boundary, ; and will correct the situation if it does, UNLESS *sectors* cross ; 64K boundaries. ; ; ES:BX -> Buffer ; SI -> Starting cluster number (2-based) ; CX -> Cluster count (0FFFFh = until end of file) ; ; 386 check getfssec: getfragment: xor bp,bp ; Fragment sector count mov ax,si ; Get sector address dec ax ; Convert to 0-based dec ax mul word [SecPerClust] add ax,[DataArea1] adc dx,[DataArea2] getseccnt: ; See if we can read > 1 clust add bp,[SecPerClust] dec cx ; Reduce clusters left to find mov di,si ; Predict next cluster inc di call [NextCluster] jc gfs_eof ; At EOF? jcxz endfragment ; Or was it the last we wanted? cmp si,di ; Is file continuous? jz getseccnt ; Yes, we can get endfragment: clc ; Not at EOF gfs_eof: pushf ; Remember EOF or not push si push cx gfs_getchunk: push ax push dx mov ax,es ; Check for 64K boundaries. mov cl,4 shl ax,cl add ax,bx xor dx,dx neg ax jnz gfs_partseg inc dx ; Full 64K segment gfs_partseg: div word [bsBytesPerSec] ; How many sectors fit? mov si,bp sub si,ax ; Compute remaining sectors jbe gfs_lastchunk mov bp,ax pop dx pop ax call getlinsecsr add ax,bp adc dx,byte 0 mov bp,si ; Remaining sector count jmp short gfs_getchunk gfs_lastchunk: pop dx pop ax call getlinsec pop cx pop si popf jcxz gfs_return ; If we hit the count limit jnc getfragment ; If we didn't hit EOF gfs_return: ret ; ; getlinsecsr: save registers, call getlinsec, restore registers ; getlinsecsr: push ax push dx push cx push bp push si push di call getlinsec pop di pop si pop bp pop cx pop dx pop ax ret ; ; nextcluster: Advance a cluster pointer in SI to the next cluster ; pointed at in the FAT tables (note: FAT12 assumed) ; Sets CF on return if end of file. ; ; The variable NextCluster gets set to the appropriate ; value here. ; nextcluster_fat12: push ax push ds mov ax,fat_seg mov ds,ax mov ax,si ; Multiply by 3/2 shr ax,1 pushf ; CF now set if odd add si,ax mov si,[si] popf jnc nc_even shr si,1 ; Needed for odd only shr si,1 shr si,1 shr si,1 nc_even: and si,0FFFh cmp si,0FF0h ; Clears CF if at end of file cmc ; But we want it SET... pop ds pop ax nc_return: ret ; ; FAT16 decoding routine. Note that a 16-bit FAT can be up to 128K, ; so we have to decide if we're in the "low" or the "high" 64K-segment... ; nextcluster_fat16: push ax push ds mov ax,fat_seg shl si,1 jnc .seg0 mov ax,fat_seg+1000h .seg0: mov ds,ax mov si,[si] cmp si,0FFF0h cmc pop ds pop ax ret ; ; Debug routine ; %ifdef debug safedumpregs: cmp word [Debug_Magic],0D00Dh jnz nc_return jmp dumpregs %endif rl_checkpt equ $ ; Must be <= 400h ; ---------------------------------------------------------------------------- ; End of code and data that have to be in the first sector ; ---------------------------------------------------------------------------- all_read: ; ; Let the user (and programmer!) know we got this far. This used to be ; in Sector 1, but makes a lot more sense here. ; mov si,copyright_str call writestr ; ; Check that no moron is trying to boot Linux on a 286 or so. According ; to Intel, the way to check is to see if the high 4 bits of the FLAGS ; register are either all stuck at 1 (8086/8088) or all stuck at 0 ; (286 in real mode), if not it is a 386 or higher. They didn't ; say how to check for a 186/188, so I *hope* it falls out as a 8086 ; or 286 in this test. ; ; Also, provide an escape route in case it doesn't work. ; check_escapes: mov ah,02h ; Check keyboard flags int 16h mov [KbdFlags],al ; Save for boot prompt check test al,04h ; Ctrl->skip 386 check jnz skip_checks test_8086: pushf ; Get flags pop ax and ax,0FFFh ; Clear top 4 bits push ax ; Load into FLAGS popf pushf ; And load back pop ax and ax,0F000h ; Get top 4 bits cmp ax,0F000h ; If set -> 8086/8088 je not_386 test_286: pushf ; Get flags pop ax or ax,0F000h ; Set top 4 bits push ax popf pushf pop ax and ax,0F000h ; Get top 4 bits jnz is_386 ; If not clear -> 386 not_386: mov si,err_not386 call writestr jmp kaboom is_386: ; Now we know it's a 386 or higher ; ; Now check that there is at least 608K of low (DOS) memory ; (608K = 9800h segments) ; int 12h cmp ax,608 jae enough_ram mov si,err_noram call writestr jmp kaboom enough_ram: skip_checks: ; ; Initialization that does not need to go into the any of the pre-load ; areas ; call adjust_screen ; ; Now we're all set to start with our *real* business. First load the ; configuration file (if any) and parse it. ; ; In previous versions I avoided using 32-bit registers because of a ; rumour some BIOSes clobbered the upper half of 32-bit registers at ; random. I figure, though, that if there are any of those still left ; they probably won't be trying to install Linux on them... ; ; The code is still ripe with 16-bitisms, though. Not worth the hassle ; to take'm out. In fact, we may want to put them back if we're going ; to boot ELKS at some point. ; mov si,linuxauto_cmd ; Default command: "linux auto" mov di,default_cmd mov cx,linuxauto_len rep movsb mov di,KbdMap ; Default keymap 1:1 xor al,al mov cx,256 mkkeymap: stosb inc al loop mkkeymap ; ; Load configuration file ; mov di,syslinux_cfg call open jz near no_config_file parse_config: call getkeyword jc near end_config_file ; Config file loaded cmp ax,'de' ; DEfault je pc_default cmp ax,'ap' ; APpend je pc_append cmp ax,'ti' ; TImeout je near pc_timeout cmp ax,'pr' ; PRompt je near pc_prompt cmp ax,'fo' ; FOnt je near pc_font cmp ax,'kb' ; KBd je near pc_kbd cmp ax,'di' ; DIsplay je near pc_display cmp ax,'la' ; LAbel je near pc_label cmp ax,'ke' ; KErnel je pc_kernel cmp ax,'im' ; IMplicit je near pc_implicit cmp al,'f' ; F-key jne parse_config jmp pc_fkey pc_default: mov di,default_cmd ; "default" command call getline mov si,auto_cmd ; add "auto"+null mov cx,auto_len rep movsb jmp short parse_config pc_append: cmp word [VKernelCtr],byte 0 ; "append" command ja pc_append_vk mov di,AppendBuf call getline sub di,AppendBuf pc_app1: mov [AppendLen],di jmp short parse_config pc_append_vk: mov di,VKernelBuf+vk_append ; "append" command (vkernel) call getline sub di,VKernelBuf+vk_append cmp di,byte 2 jne pc_app2 cmp byte [VKernelBuf+vk_append],'-' jne pc_app2 mov di,0 ; If "append -" -> null string pc_app2: mov [VKernelBuf+vk_appendlen],di jmp short parse_config_2 pc_kernel: cmp word [VKernelCtr],byte 0 ; "kernel" command je near parse_config ; ("label" section only) mov di,trackbuf push di call getline pop si mov di,VKernelBuf+vk_rname call mangle_name jmp short parse_config_2 pc_timeout: call getint ; "timeout" command jc parse_config_2 mov ax,0D215h ; There are approx 1.D215h mul bx ; clock ticks per 1/10 s add bx,dx mov [KbdTimeOut],bx jmp short parse_config_2 pc_display: call pc_getfile ; "display" command jz parse_config_2 ; File not found? call get_msg_file ; Load and display file parse_config_2: jmp parse_config pc_prompt: call getint ; "prompt" command jc parse_config_2 mov [ForcePrompt],bx jmp short parse_config_2 pc_implicit: call getint ; "implicit" command jc parse_config_2 mov [AllowImplicit],bx jmp short parse_config_2 pc_fkey: sub ah,'1' jnb pc_fkey1 mov ah,9 ; F10 pc_fkey1: xor cx,cx mov cl,ah push cx mov ax,1 shl ax,cl or [FKeyMap], ax ; Mark that we have this loaded mov di,trackbuf push di call getline ; Get filename to display pop si pop di shl di,4 ; Multiply number by 16 add di,FKeyName call mangle_name ; Mangle file name jmp short parse_config_2 pc_label: call commit_vk ; Commit any current vkernel mov di,trackbuf ; Get virtual filename push di call getline pop si mov di,VKernelBuf+vk_vname call mangle_name ; Mangle virtual name inc word [VKernelCtr] ; One more vkernel mov si,VKernelBuf+vk_vname ; By default, rname == vname mov di,VKernelBuf+vk_rname mov cx,11 rep movsb mov si,AppendBuf ; Default append==global append mov di,VKernelBuf+vk_append mov cx,[AppendLen] mov [VKernelBuf+vk_appendlen],cx rep movsb jmp short parse_config_2 pc_font: call pc_getfile ; "font" command jz parse_config_2 ; File not found? call loadfont ; Load and install font jmp short parse_config_3 pc_kbd: call pc_getfile ; "kbd" command jz parse_config_3 call loadkeys parse_config_3: jmp parse_config ; ; pc_getfile: For command line options that take file argument, this ; routine decodes the file argument and runs it through searchdir ; pc_getfile: mov di,trackbuf push di call getline pop si mov di,MNameBuf push di call mangle_name pop di jmp searchdir ; Tailcall ; ; commit_vk: Store the current VKernelBuf into buffer segment ; commit_vk: cmp word [VKernelCtr],byte 0 je cvk_ret ; No VKernel = return cmp word [VKernelCtr],max_vk ; Above limit? ja cvk_overflow mov di,[VKernelCtr] dec di shl di,vk_shift mov si,VKernelBuf mov cx,(vk_size >> 2) push es push word vk_seg pop es rep movsd ; Copy to buffer segment pop es cvk_ret: ret cvk_overflow: mov word [VKernelCtr],max_vk ; No more than max_vk, please ret ; ; End of configuration file ; end_config_file: call commit_vk ; Commit any current vkernel no_config_file: ; ; Check whether or not we are supposed to display the boot prompt. ; check_for_key: cmp word [ForcePrompt],byte 0 ; Force prompt? jnz enter_command test byte [KbdFlags],5Bh ; Caps, Scroll, Shift, Alt jz near auto_boot ; If neither, default boot enter_command: mov si,boot_prompt call writestr mov di,command_line ; ; get the very first character -- we can either time ; out, or receive a character press at this time. Some dorky BIOSes stuff ; a return in the buffer on bootup, so wipe the keyboard buffer first. ; clear_buffer: mov ah,1 ; Check for pending char int 16h jz get_char_time xor ax,ax ; Get char int 16h jmp short clear_buffer get_char_time: mov cx,[KbdTimeOut] and cx,cx jz get_char ; Timeout == 0 -> no timeout inc cx ; The first loop will happen ; immediately as we don't ; know the appropriate DX value time_loop: push cx tick_loop: push dx mov ah,1 ; Check for pending keystroke int 16h jnz get_char_pop xor ax,ax int 1Ah ; Get time "of day" pop ax cmp dx,ax ; Has the timer advanced? je tick_loop pop cx loop time_loop ; If so, decrement counter jmp command_done ; Timeout! get_char_pop: pop eax ; Clear the stack get_char: xor ax,ax ; Get char int 16h and al,al jz func_key mov bx,KbdMap ; Keyboard map translation xlatb cmp al,' ' ; ASCII? jb not_ascii ja enter_char cmp di,command_line ; Space must not be first je get_char enter_char: cmp di,max_cmd_len+command_line ; Check there's space jnb get_char stosb ; Save it call writechr ; Echo to screen jmp short get_char not_ascii: cmp al,0Dh ; Enter je command_done cmp al,08h ; Backspace jne get_char cmp di,command_line ; Make sure there is anything je get_char ; to erase dec di ; Unstore one character mov si,wipe_char ; and erase it from the screen call writestr jmp short get_char func_key: push di cmp ah,68 ; F10 ja get_char sub ah,59 ; F1 jb get_char mov cl,ah shr ax,4 ; Convert to x16 mov bx,1 shl bx,cl and bx,[FKeyMap] jz get_char ; Undefined F-key mov di,ax add di,FKeyName call searchdir jz fk_nofile call get_msg_file jmp short fk_wrcmd fk_nofile: mov si,crlf_msg call writestr fk_wrcmd: mov si,boot_prompt call writestr pop di ; Command line write pointer push di mov byte [di],0 ; Null-terminate command line mov si,command_line call writestr ; Write command line so far pop di jmp short get_char auto_boot: mov si,default_cmd mov di,command_line mov cx,(max_cmd_len+4) >> 2 rep movsd jmp short load_kernel command_done: mov si,crlf_msg call writestr cmp di,command_line ; Did we just hit return? je auto_boot xor al,al ; Store a final null stosb load_kernel: ; Load the kernel now ; ; First we need to mangle the kernel name the way DOS would... ; mov si,command_line mov di,KernelName push si push di call mangle_name pop di pop si ; ; Fast-forward to first option (we start over from the beginning, since ; mangle_name doesn't necessarily return a consistent ending state.) ; clin_non_wsp: lodsb cmp al,' ' ja clin_non_wsp clin_is_wsp: and al,al jz clin_opt_ptr lodsb cmp al,' ' jbe clin_is_wsp clin_opt_ptr: dec si ; Point to first nonblank mov [CmdOptPtr],si ; Save ptr to first option ; ; Now check if it is a "virtual kernel" ; mov cx,[VKernelCtr] push ds push word vk_seg pop ds cmp cx,byte 0 je not_vk xor si,si ; Point to first vkernel vk_check: pusha mov cx,11 repe cmpsb ; Is this it? je near vk_found popa add si,vk_size loop vk_check not_vk: pop ds ; ; Not a "virtual kernel" - check that's OK and construct the command line ; cmp word [AllowImplicit],byte 0 je bad_implicit push es push si push di mov di,real_mode_seg mov es,di mov si,AppendBuf mov di,cmd_line_here mov cx,[AppendLen] rep movsb mov [CmdLinePtr],di pop di pop si pop es mov bx,exten_count << 2 ; Alternates to try ; ; Find the kernel on disk ; get_kernel: mov byte [KernelName+11],0 ; Zero-terminate filename/extension mov eax,[KernelName+8] ; Save initial extension mov [OrigKernelExt],eax .search_loop: push bx mov di,KernelName ; Search on disk call searchdir pop bx jnz kernel_good mov eax,[exten_table+bx] ; Try a different extension mov [KernelName+8],eax sub bx,byte 4 jnb .search_loop bad_kernel: mov si,KernelName mov di,KernelCName push di call unmangle_name ; Get human form mov si,err_notfound ; Complain about missing kernel call writestr pop si ; KernelCName call writestr mov si,crlf_msg jmp abort_load ; Ask user for clue ; ; bad_implicit: The user entered a nonvirtual kernel name, with "implicit 0" ; bad_implicit: mov si,KernelName ; For the error message mov di,KernelCName call unmangle_name jmp short bad_kernel ; ; vk_found: We *are* using a "virtual kernel" ; vk_found: popa push di mov di,VKernelBuf mov cx,vk_size >> 2 rep movsd push es ; Restore old DS pop ds push es push word real_mode_seg pop es mov di,cmd_line_here mov si,VKernelBuf+vk_append mov cx,[VKernelBuf+vk_appendlen] rep movsb mov [CmdLinePtr],di ; Where to add rest of cmd pop es pop di ; DI -> KernelName push di mov si,VKernelBuf+vk_rname mov cx,11 ; We need ECX == CX later rep movsb pop di xor bx,bx ; Try only one version jmp get_kernel ; ; kernel_corrupt: Called if the kernel file does not seem healthy ; kernel_corrupt: mov si,err_notkernel jmp abort_load ; ; This is it! We have a name (and location on the disk)... let's load ; that sucker!! First we have to decide what kind of file this is; base ; that decision on the file extension. The following extensions are ; recognized: ; ; .COM - COMBOOT image ; .CBT - COMBOOT image ; .BS - Boot sector ; .BSS - Boot sector, but transfer over DOS superblock ; ; Anything else is assumed to be a Linux kernel. ; kernel_good: pusha mov si,KernelName mov di,KernelCName call unmangle_name ; Get human form sub di,KernelCName mov [KernelCNameLen],di popa mov ecx,[KernelName+8] ; Get (mangled) extension cmp ecx,'COM' je near is_comboot_image cmp ecx,'CBT' je near is_comboot_image cmp ecx,'BS ' je near is_bootsector cmp ecx,'BSS' je near is_bss_sector ; Otherwise Linux kernel ; ; A Linux kernel consists of three parts: boot sector, setup code, and ; kernel code. The boot sector is never executed when using an external ; booting utility, but it contains some status bytes that are necessary. ; The boot sector and setup code together form exactly 5 sectors that ; should be loaded at 9000:0. The subsequent code should be loaded ; at 1000:0. For simplicity, we load the whole thing at 0F60:0, and ; copy the latter stuff afterwards. ; ; NOTE: In the previous code I have avoided making any assumptions regarding ; the size of a sector, in case this concept ever gets extended to other ; media like CD-ROM (not that a CD-ROM would be bloody likely to use a FAT ; filesystem, of course). However, a "sector" when it comes to Linux booting ; stuff means 512 bytes *no matter what*, so here I am using that piece ; of knowledge. ; ; First check that our kernel is at least 64K and less than 8M (if it is ; more than 8M, we need to change the logic for loading it anyway...) ; is_linux_kernel: cmp dx,80h ; 8 megs ja kernel_corrupt and dx,dx jz kernel_corrupt kernel_sane: push ax push dx push si mov si,loading_msg call cwritestr ; ; Now start transferring the kernel ; push word real_mode_seg pop es push ax push dx div word [ClustSize] ; # of clusters total and dx,dx ; Round up setnz dl movzx dx,dl add ax,dx mov [KernelClust],ax pop dx pop ax add ax,1023 adc dx,byte 0 mov bx,1024 div bx ; Get number of kilobytes mov [KernelK],ax ; ; Now, if we transfer these straight, we'll hit 64K boundaries. Hence we ; have to see if we're loading more than 64K, and if so, load it step by ; step. ; mov dx,1 ; 10000h xor ax,ax div word [ClustSize] mov [ClustPerMoby],ax ; Clusters/64K ; ; Start by loading the bootsector/setup code, to see if we need to ; do something funky. It should fit in the first 32K (loading 64K won't ; work since we might have funny stuff up near the end of memory). ; If we have larger than 32K clusters, yes, we're hosed. ; call abort_check ; Check for abort key mov cx,[ClustPerMoby] shr cx,1 ; Half a moby sub [KernelClust],cx xor bx,bx pop si ; Cluster pointer on stack call getfssec jc near kernel_corrupt ; Failure in first 32K cmp word [es:bs_bootsign],0AA55h jne near kernel_corrupt ; Boot sec signature missing ; ; Get the BIOS' idea of what the size of high memory is ; push si ; Save our cluster pointer! mov ah,88h int 15h cmp ax,14*1024 ; Don't trust memory >15M jna hms_ok mov ax,14*1024 hms_ok: mov [HighMemSize],ax ; ; Construct the command line (append options have already been copied) ; mov word [es:kern_cmd_magic],0A33Fh ; Command line magic no mov word [es:kern_cmd_offset],cmd_line_here mov di,[CmdLinePtr] mov si,boot_image ; BOOT_IMAGE= mov cx,boot_image_len rep movsb mov si,KernelCName ; Unmangled kernel name mov cx,[KernelCNameLen] rep movsb mov al,' ' ; Space stosb mov si,[CmdOptPtr] ; Options from user input mov cx,(kern_cmd_len+3) >> 2 rep movsd ; %ifdef debug push ds ; DEBUG DEBUG DEBUG push es pop ds mov si,offset cmd_line_here call cwritestr pop ds mov si,offset crlf_msg call cwritestr %endif ; ; Scan through the command line for anything that looks like we might be ; interested in. The original version of this code automatically assumed ; the first option was BOOT_IMAGE=, but that is no longer certain. ; mov si,cmd_line_here mov byte [initrd_flag],0 push es ; Set DS <- real_mode_seg pop ds get_next_opt: lodsb and al,al jz near cmdline_end cmp al,' ' jbe get_next_opt dec si mov eax,[si] cmp eax,'vga=' je is_vga_cmd cmp eax,'mem=' je is_mem_cmd push es ; Save ES -> real_mode_seg push ss pop es ; Set ES <- normal DS mov di,initrd_cmd mov cx,initrd_cmd_len repe cmpsb jne not_initrd mov di,InitRD push si ; mangle_dir mangles si call mangle_name ; Mangle ramdisk name pop si cmp byte [es:InitRD],' ' ; Null filename? seta byte [es:initrd_flag] ; Set flag if not not_initrd: pop es ; Restore ES -> real_mode_seg skip_this_opt: lodsb ; Load from command line cmp al,' ' ja skip_this_opt dec si jmp short get_next_opt is_vga_cmd: add si,byte 4 mov eax,[si] mov bx,-1 cmp eax, 'norm' ; vga=normal je vc0 and eax,0ffffffh ; 3 bytes mov bx,-2 cmp eax, 'ext' ; vga=ext je vc0 mov bx,-3 cmp eax, 'ask' ; vga=ask je vc0 call parseint ; vga=<number> jc skip_this_opt ; Not an integer vc0: mov [bs_vidmode],bx ; Set video mode jmp short skip_this_opt is_mem_cmd: add si,byte 4 call parseint jc skip_this_opt ; Not an integer shr ebx,10 ; Convert to kilobytes sub ebx,1024 ; Don't count first meg cmp ebx,14*1024 ; Only trust < 15M point jna memcmd_fair mov bx,14*1024 memcmd_fair: mov [ss:HighMemSize],bx jmp short skip_this_opt cmdline_end: push ss ; Restore standard DS pop ds ; ; Now check if we have a large kernel, which needs to be loaded high ; cmp dword [es:su_header],HEADER_ID ; New setup code ID jne near old_kernel ; Old kernel, load low cmp word [es:su_version],0200h ; Setup code version 2.0 jb near old_kernel ; Old kernel, load low cmp word [es:su_version],0201h ; Version 2.01+? jb new_kernel ; If 2.00, skip this step mov word [es:su_heapend],linux_stack ; Set up the heap or byte [es:su_loadflags],80h ; Let the kernel know we care ; ; We definitely have a new-style kernel. Let the kernel know who we are, ; and that we are clueful ; new_kernel: mov byte [es:su_loader],syslinux_id ; Show some ID movzx ax,byte [es:bs_setupsecs] ; Variable # of setup sectors mov [SetupSecs],ax ; ; Now see if we have an initial RAMdisk; if so, do requisite computation ; test byte [initrd_flag],1 jz nk_noinitrd push es ; ES->real_mode_seg push ds pop es ; We need ES==DS mov si,InitRD mov di,InitRDCName call unmangle_name ; Create human-readable name sub di,InitRDCName mov [InitRDCNameLen],di mov di,InitRD call searchdir ; Look for it in directory pop es jz initrd_notthere mov [initrd_ptr],si ; Save cluster pointer mov [es:su_ramdisklen1],ax ; Ram disk length mov [es:su_ramdisklen2],dx div word [ClustSize] and dx,dx ; Round up setnz dl movzx dx,dl add ax,dx mov [InitRDClust],ax ; Ramdisk clusters movzx edx,word [HighMemSize] ; End of memory add edx,1024 ; Add "low" memory shl edx,10 ; Convert to bytes sub edx,[es:su_ramdisklen] ; Subtract size of ramdisk xor dx,dx ; Round down to 64K boundary mov [InitRDat],edx ; Load address call loadinitrd ; Load initial ramdisk jmp short initrd_end initrd_notthere: mov si,err_noinitrd call writestr mov si,InitRDCName call writestr mov si,crlf_msg jmp abort_load no_high_mem: mov si,err_nohighmem ; Error routine jmp abort_load ; ; About to load the kernel. This is a modern kernel, so use the boot flags ; we were provided. ; nk_noinitrd: initrd_end: mov al,[es:su_loadflags] mov [LoadFlags],al ; ; Load the kernel. We always load it at 100000h even if we're supposed to ; load it "low"; for a "low" load we copy it down to low memory right before ; jumping to it. ; read_kernel: mov si,KernelCName ; Print kernel name part of call cwritestr ; "Loading" message mov si,dotdot_msg ; Print dots call cwritestr mov ax,[HighMemSize] cmp ax,[KernelK] jb no_high_mem ; Not enough high memory ; ; Move the stuff beyond the setup code to high memory at 100000h ; movzx esi,word [SetupSecs] ; Setup sectors inc esi ; plus 1 boot sector shl esi,9 ; Convert to bytes mov ecx,108000h ; 108000h = 1M + 32K sub ecx,esi ; Adjust pointer to 2nd block mov [HiLoadAddr],ecx sub ecx,100000h ; Turn into a counter shr ecx,2 ; Convert to dwords add esi,90000h ; Pointer to source mov edi,100000h ; Copy to address 100000h call bcopy ; Transfer to high memory ; push word xfer_buf_seg ; Segment 7000h is xfer buffer pop es high_load_loop: mov si,dot_msg ; Progress report call cwritestr call abort_check mov cx,[KernelClust] cmp cx,[ClustPerMoby] jna high_last_moby mov cx,[ClustPerMoby] high_last_moby: sub [KernelClust],cx xor bx,bx ; Load at offset 0 pop si ; Restore cluster pointer call getfssec push si ; Save cluster pointer pushf ; Save EOF xor bx,bx mov esi,(xfer_buf_seg << 4) mov edi,[HiLoadAddr] ; Destination address mov ecx,4000h ; Cheating - transfer 64K call bcopy ; Transfer to high memory mov [HiLoadAddr],edi ; Point to next target area popf ; Restore EOF jc high_load_done ; If EOF we are done cmp word [KernelClust],byte 0 ; Are we done? jne high_load_loop ; Apparently not high_load_done: pop si ; No longer needed mov ax,real_mode_seg ; Set to real mode seg mov es,ax mov si,dot_msg call cwritestr ; ; Abandon hope, ye that enter here! We do no longer permit aborts. ; call abort_check ; Last chance!! ; ; Some kernels in the 1.2 ballpark but pre-bzImage have more than 4 ; setup sectors, but the boot protocol had not yet been defined. They ; rely on a signature to figure out if they need to copy stuff from ; the "protected mode" kernel area. Unfortunately, we used that area ; as a transfer buffer, so it's going to find the signature there. ; Hence, zero the low 32K beyond the setup area. ; mov di,[SetupSecs] inc di ; Setup + boot sector mov cx,32768/512 ; Sectors/32K sub cx,di ; Remaining sectors shl di,9 ; Sectors -> bytes shl cx,7 ; Sectors -> dwords xor eax,eax rep stosd ; Clear region ; ; Now, if we were supposed to load "low", copy the kernel down to 10000h ; test byte [LoadFlags],LOAD_HIGH jnz in_proper_place ; If high load, we're done movzx ecx,word [KernelK] shl ecx,8 ; K -> dword mov esi,100000h mov edi,10000h call bcopy in_proper_place: ; ; If the default root device is set to FLOPPY (0000h), change to ; /dev/fd0 (0200h) ; cmp word [es:bs_rootdev],byte 0 jne root_not_floppy mov word [es:bs_rootdev],0200h root_not_floppy: ; ; Copy the disk table to high memory, then re-initialize the floppy ; controller ; push ds lds si,[fdctab] mov di,linux_fdctab mov cx,3 ; 12 bytes push di rep movsd pop di cli mov [fdctab1],di ; Save new floppy tab pos mov [fdctab2],es sti xor ax,ax xor dx,dx int 13h pop ds ; ; Linux wants the floppy motor shut off before starting the kernel, ; at least bootsect.S seems to imply so ; kill_motor: mov dx,03F2h xor al,al out dx,al ; ; Now we're as close to be done as we can be and still use our normal ; routines, print a CRLF to end the row of dots ; mov si,crlf_msg call writestr ; ; If we're debugging, wait for a keypress so we can read any debug messages ; %ifdef debug xor ax,ax int 16h %endif ; ; Set up segment registers and the Linux real-mode stack ; mov ax,real_mode_seg mov ds,ax mov es,ax mov fs,ax mov gs,ax cli mov ss,ax mov sp,linux_stack sti ; ; We're done... now RUN THAT KERNEL!!!! ; jmp setup_seg:setup_entry ; ; Load an older kernel. Older kernels always have 4 setup sectors, can't have ; initrd, and are always loaded low. ; old_kernel: test byte [initrd_flag],1 ; Old kernel can't have initrd jz load_old_kernel mov si,err_oldkernel jmp abort_load load_old_kernel: mov word [SetupSecs],4 ; Always 4 setup sectors mov byte [LoadFlags],0 ; Always low jmp read_kernel ; ; Load a COMBOOT image. A COMBOOT image is basically a DOS .COM file, ; except that it may, of course, not contain any DOS system calls. We ; do, however, allow the execution of INT 20h to return to SYSLINUX. ; is_comboot_image: and dx,dx jnz comboot_too_large cmp ax,0ff00h ; Max size in bytes jae comboot_too_large ; ; Set up the DOS vectors in the IVT (INT 20h-3fh) ; mov dword [4*0x20],comboot_return ; INT 20h vector mov eax,comboot_bogus mov di,4*0x21 mov cx,31 ; All remaining DOS vectors rep stosd mov cx,comboot_seg mov es,cx mov bx,100h ; Load at <seg>:0100h mov cx,[ClustPerMoby] ; Absolute maximum # of clusters call getfssec xor di,di mov cx,64 ; 256 bytes (size of PSP) xor eax,eax ; Clear PSP rep stosd mov word [es:0], 020CDh ; INT 20h instruction ; First non-free paragraph mov word [es:02h], comboot_seg+1000h ; Copy the command line from high memory mov cx,125 ; Max cmdline len (minus space and CR) mov si,[CmdOptPtr] mov di,081h ; Offset in PSP for command line mov al,' ' ; DOS command lines begin with a space stosb comboot_cmd_cp: lodsb and al,al jz comboot_end_cmd stosb loop comboot_cmd_cp comboot_end_cmd: mov al,0Dh ; CR after last character stosb mov al,126 ; Include space but not CR sub al,cl mov [es:80h], al ; Store command line length mov ax,es mov ds,ax mov ss,ax xor sp,sp push word 0 ; Return to address 0 -> exit jmp comboot_seg:100h ; Run it ; Looks like a COMBOOT image but too large comboot_too_large: mov si,err_comlarge call writestr cb_enter: jmp enter_command ; Proper return vector comboot_return: cli ; Don't trust anyone xor ax,ax mov ss,ax mov sp,[ss:SavedSP] mov ds,ax mov es,ax sti cld jmp short cb_enter ; Attempted to execute DOS system call comboot_bogus: cli ; Don't trust anyone xor ax,ax mov ss,ax mov sp,[ss:SavedSP] mov ds,ax mov es,ax sti cld mov si,KernelCName call writestr mov si,err_notdos call writestr jmp short cb_enter ; ; Load a boot sector ; is_bootsector: ; Transfer zero bytes push word 0 jmp short load_bootsec is_bss_sector: ; Transfer the superblock push word superblock_len load_bootsec: and dx,dx jnz bad_bootsec mov bx,[bsBytesPerSec] cmp ax,bx jne bad_bootsec ; Make sure we don't test this uninitialized mov [bx+trackbuf-2],dx ; Note DX == 0 mov bx,trackbuf mov cx,1 ; 1 cluster >= 1 sector call getfssec mov bx,[bsBytesPerSec] mov ax,[bx+trackbuf-2] cmp ax,0AA55h ; Boot sector signature jne bad_bootsec mov si,superblock mov di,trackbuf+(superblock-bootsec) pop cx ; Transfer count rep movsb ; ; Okay, here we go... copy over our own boot sector and run the new one ; cli ; Point of no return mov dl,[bsDriveNumber] ; May not be in new bootsector! mov si,trackbuf mov di,bootsec mov cx,[bsBytesPerSec] rep movsb ; Copy the boot sector! mov si,PartInfo mov di,800h-18 ; Put partition info here push di mov cx,8 ; 16 bytes rep movsw pop si ; DS:SI points to partition info jmp bootsec bad_bootsec: mov si,err_bootsec call writestr jmp enter_command ; ; cwritestr: write a null-terminated string to the console, saving ; registers on entry (we can't use this in the boot sector, ; since we haven't verified 386-ness yet) ; cwritestr: pusha cwstr_1: lodsb and al,al jz cwstr_2 mov ah,0Eh ; Write to screen as TTY mov bx,0007h ; White on black, current page int 10h jmp short cwstr_1 cwstr_2: popa ret ; ; 32-bit bcopy routine for real mode ; ; We enter protected mode, set up a flat 32-bit environment, run rep movsd ; and then exit. IMPORTANT: This code assumes cs == ss == 0. ; ; This code is probably excessively anal-retentive in its handling of ; segments, but this stuff is painful enough as it is without having to rely ; on everything happening "as it ought to." ; align 2 bcopy_gdt_ptr: dw bcopy_gdt_size-1 dd bcopy_gdt align 4 bcopy_gdt: dd 0 ; Null descriptor dd 0 dd 0000ffffh ; Code segment, use16, readable, dd 00009b00h ; present, dpl 0, cover 64K dd 0000ffffh ; Data segment, use16, read/write, dd 008f9300h ; present, dpl 0, cover all 4G dd 0000ffffh ; Data segment, use16, read/write, dd 00009300h ; present, dpl 0, cover 64K bcopy_gdt_size: equ $-bcopy_gdt bcopy: push eax pushf ; Saves, among others, the IF flag push gs push fs push ds push es cli call enable_a20 o32 lgdt [bcopy_gdt_ptr] mov eax,cr0 or al,1 mov cr0,eax ; Enter protected mode jmp 8:.in_pm .in_pm: mov ax,16 ; Data segment selector mov es,ax mov ds,ax mov al,24 ; "Real-mode-like" data segment mov ss,ax mov fs,ax mov gs,ax a32 rep movsd ; Do our business mov es,ax ; Set to "real-mode-like" mov ds,ax mov eax,cr0 and al,0feh mov cr0,eax ; Disable protected mode jmp 0:.in_rm .in_rm: xor ax,ax ; Back in real mode mov ss,ax pop es pop ds pop fs pop gs call disable_a20 popf ; Re-enables interrupts pop eax ret ; ; Routines to enable and disable (yuck) A20. These routines are gathered ; from tips from a couple of sources, including the Linux kernel and ; http://www.x86.org/. The need for the delay to be as large as given here ; is indicated by Donnie Barnes of RedHat, the problematic system being an ; IBM ThinkPad 760EL. ; ; We typically toggle A20 twice for every 64K transferred. ; %define io_delay times 4 out 0EDh,al ; Invalid port (we hope) %define delaytime 256 ; 4 x ISA bus cycles (@ 1.5 ╡s) enable_a20: call empty_8042 mov al,0D1h ; Command write out 064h, al call empty_8042 mov al,0DFh ; A20 on out 060h, al call kbc_delay ; Verify that A20 actually is enabled. Do that by ; observing a word in low memory and the same word in ; the HMA until they are no longer coherent. Note that ; we don't do the same check in the disable case, because ; we don't want to *require* A20 masking (SYSLINUX should ; work fine without it, if the BIOS does.) push es mov ax,0FFFFh ; HMA mov es,ax .a20_wait: inc word [ss:A20test] mov ax,[es:A20test+10h] cmp ax,[ss:A20test] je .a20_wait pop es ret disable_a20: call empty_8042 mov al,0D1h out 064h, al ; Command write call empty_8042 mov al,0DDh ; A20 off out 060h, al jmp short kbc_delay kbc_delay: call empty_8042 push cx mov cx, delaytime .delayloop: io_delay loop .delayloop pop cx ret empty_8042: io_delay in al, 064h ; Status port test al,1 jz .no_output io_delay in al, 060h ; Read input jmp short empty_8042 .no_output: test al,2 jnz empty_8042 io_delay ret ; ; Load RAM disk into high memory ; loadinitrd: push es ; Save ES on entry mov ax,real_mode_seg mov es,ax mov si,[initrd_ptr] mov edi,[InitRDat] ; initrd load address mov [es:su_ramdiskat],edi ; Offset for ram disk push si mov si,InitRDCName ; Write ramdisk name call cwritestr mov si,dotdot_msg ; Write dots call cwritestr rd_load_loop: mov si,dot_msg ; Progress report call cwritestr pop si ; Restore cluster pointer call abort_check mov cx,[InitRDClust] cmp cx,[ClustPerMoby] jna rd_last_moby mov cx,[ClustPerMoby] rd_last_moby: sub [InitRDClust],cx xor bx,bx ; Load at offset 0 push word xfer_buf_seg ; Bounce buffer segment pop es push cx call getfssec pop cx push si ; Save cluster pointer mov esi,(xfer_buf_seg << 4) mov edi,[InitRDat] mov ecx,4000h ; Copy 64K call bcopy ; Does not change flags!! jc rd_load_done ; EOF? add dword [InitRDat],10000h ; Point to next 64K cmp word [InitRDClust],byte 0 ; Are we done? jne rd_load_loop ; Apparently not rd_load_done: pop si ; Clean up the stack mov si,crlf_msg call writestr mov si,loading_msg ; Write new "Loading " for call writestr ; the benefit of the kernel pop es ; Restore original ES ret ; ; abort_check: let the user abort with <ESC> or <Ctrl-C> ; abort_check: pusha ac1: mov ah,1 ; Check for pending keystroke int 16h jz ac_ret ; If no pending keystroke xor ax,ax ; Load pending keystroke int 16h mov bx,KbdMap xlatb cmp al,27 ; <ESC> aborts (DOS geeks) je ac2 cmp al,3 ; So does Ctrl-C (UNIX geeks) jne ac1 ; Unknown key... try again ac2: ; If we get here, ABORT! mov si,aborted_msg ; Fall through to abort_load ; ; abort_load: Called by various routines which wants to print a fatal ; error message and return to the command prompt. Since this ; may happen at just about any stage of the boot process, assume ; our state is messed up, and just reset the segment registers ; and the stack forcibly. ; ; SI = offset (in _text) of error message to print ; abort_load: mov ax,cs ; Restore CS = DS = ES mov ds,ax mov es,ax cli mov sp,StackBuf-2*3 ; Reset stack mov ss,ax ; Just in case... sti call writestr ; Expects SI -> error msg al_ok: jmp enter_command ; Return to command prompt ; ; End of abort_check ; ac_ret: popa ret ; ; searchdir: Search the root directory for a pre-mangled filename in ; DS:DI. This routine is similar to the one in the boot ; sector, but is a little less Draconian when it comes to ; error handling, plus it reads the root directory in ; larger chunks than a sector at a time (which is probably ; a waste of coding effort, but I like to do things right). ; ; FIXME: usually we can load the entire root dir in memory, ; and files are usually at the beginning anyway. It probably ; would be worthwhile to remember if we have the first chunk ; in memory and skip the load if that (it would speed up online ; help, mainly.) ; ; NOTE: This file considers finding a zero-length file an ; error. This is so we don't have to deal with that special ; case elsewhere in the program (most loops have the test ; at the end). ; ; If successful: ; ZF clear ; SI = cluster # for the first cluster ; DX:AX = file length in bytes ; If unsuccessful ; ZF set ; searchdir: mov ax,[bsRootDirEnts] mov [DirScanCtr],ax mov ax,[RootDirSize] mov [DirBlocksLeft],ax mov ax,[RootDir1] mov dx,[RootDir2] scan_group: mov bp,[DirBlocksLeft] and bp,bp jz dir_return cmp bp,[BufSafeSec] jna load_last mov bp,[BufSafeSec] load_last: sub [DirBlocksLeft],bp push ax push dx mov ax,[bsBytesPerSec] mul bp add ax,trackbuf-31 mov [EndofDirSec],ax ; End of loaded pop dx pop ax push bp ; Save number of sectors push ax ; Save present location push dx push di ; Save name mov bx,trackbuf call getlinsec pop di pop dx pop ax pop bp mov si,trackbuf dir_test_name: cmp byte [si],0 ; Directory high water mark je dir_return ; Failed test byte [si+11],018h ; Check it really is a file jnz dir_not_this push di push si mov cx,11 ; Filename = 11 bytes repe cmpsb pop si pop di je dir_success dir_not_this: add si,byte 32 dec word [DirScanCtr] jz dir_return ; Out of it... cmp si,[EndofDirSec] jb dir_test_name add ax,bp ; Increment linear sector number adc dx,byte 0 jmp short scan_group dir_success: mov ax,[si+28] ; Length of file mov dx,[si+30] mov si,[si+26] ; Cluster pointer mov bx,ax or bx,dx ; Sets ZF iff DX:AX is zero dir_return: ret ; ; writechr: Write a single character in AL to the screen without ; mangling any registers ; writechr: pusha mov ah,0Eh mov bx,0007h ; white text on this page int 10h popa ret ; ; adjust_screen: Set the internal variables associated with the screen size. ; This is a subroutine in case we're loading a custom font. ; adjust_screen: mov al,[BIOS_vidrows] and al,al jnz vidrows_is_ok mov al,24 ; No vidrows in BIOS, assume 25 ; (Remember: vidrows == rows-1) vidrows_is_ok: mov [VidRows],al mov ah,0fh int 10h ; Read video state mov [TextPage],bh dec ah ; Store count-1 (same as rows) mov [VidCols],ah bf_ret: ret ; ; loadfont: Load a .psf font file and install it onto the VGA console ; (if we're not on a VGA screen then ignore.) It is called with ; SI and DX:AX set by routine searchdir ; loadfont: mov bx,trackbuf ; The trackbuf is >= 16K; the part mov cx,[BufSafe] ; of a PSF file we care about is no call getfssec ; more than 8K+4 bytes mov ax,[trackbuf] ; Magic number cmp ax,0436h jne bf_ret mov al,[trackbuf+2] ; File mode cmp al,3 ; Font modes 0-3 supported ja bf_ret mov bh,byte [trackbuf+3] ; Height of font cmp bh,2 ; VGA minimum jb bf_ret cmp bh,32 ; VGA maximum ja bf_ret mov bp,trackbuf+4 ; Address of font data xor bl,bl mov cx,256 xor dx,dx mov ax,1110h int 10h ; Load into VGA RAM xor bl,bl mov ax,1103h ; Select page 0 int 10h jmp short adjust_screen ; ; loadkeys: Load a LILO-style keymap; SI and DX:AX set by searchdir ; loadkeys: and dx,dx ; Should be 256 bytes exactly jne loadkeys_ret cmp ax,256 jne loadkeys_ret mov bx,trackbuf mov cx,1 ; 1 cluster should be >= 256 bytes call getfssec mov si,trackbuf mov di,KbdMap mov cx,256 >> 2 rep movsd loadkeys_ret: ret ; ; get_msg_file: Load a text file and write its contents to the screen, ; interpreting color codes. Is called with SI and DX:AX ; set by routine searchdir ; get_msg_file: mov word [NextCharJump],msg_putchar ; State machine for color mov byte [TextAttribute],07h ; Default grey on white pusha mov bh,[TextPage] mov ah,03h ; Read cursor position int 10h mov [CursorDX],dx popa get_msg_chunk: push ax ; DX:AX = length of file push dx mov bx,trackbuf mov cx,[BufSafe] call getfssec pop dx pop ax push si ; Save current cluster mov si,trackbuf mov cx,[BufSafeBytes] ; No more than many bytes print_msg_file: push cx push ax push dx lodsb cmp al,1Ah ; ASCII EOF? je msg_done_pop call [NextCharJump] ; Do what shall be done pop dx pop ax pop cx sub ax,byte 1 sbb dx,byte 0 mov bx,ax or bx,dx jz msg_done loop print_msg_file pop si jmp short get_msg_chunk msg_done_pop: add sp,byte 6 ; Lose 3 words on the stack msg_done: pop si ret msg_putchar: ; Normal character cmp al,0Fh ; ^O = color code follows je msg_ctrl_o cmp al,0Dh ; Ignore <CR> je msg_ignore cmp al,0Ah ; <LF> = newline je msg_newline cmp al,0Ch ; <FF> = clear screen je msg_formfeed mov bx,[TextAttrBX] mov ah,09h ; Write character/attribute mov cx,1 ; One character only int 10h ; Write to screen mov al,[CursorCol] inc ax cmp al,[VidCols] ja msg_newline mov [CursorCol],al msg_gotoxy: mov bh,[TextPage] mov dx,[CursorDX] mov ah,02h ; Set cursor position int 10h msg_ignore: ret msg_ctrl_o: ; ^O = color code follows mov word [NextCharJump],msg_setbg ret msg_newline: ; Newline char or end of line mov byte [CursorCol],0 mov al,[CursorRow] inc ax cmp al,[VidRows] ja msg_scroll mov [CursorRow],al jmp short msg_gotoxy msg_scroll: xor cx,cx ; Upper left hand corner mov dx,[ScreenSize] mov [CursorRow],dh ; New cursor at the bottom mov bh,[TextAttribute] mov ax,0601h ; Scroll up one line int 10h jmp short msg_gotoxy msg_formfeed: ; Form feed character xor cx,cx mov [CursorDX],cx ; Upper lefthand corner mov dx,[ScreenSize] mov bh,[TextAttribute] mov ax,0600h ; Clear screen region int 10h jmp short msg_gotoxy msg_setbg: ; Color background character call unhexchar jc msg_color_bad shl al,4 mov [TextAttribute],al mov word [NextCharJump],msg_setfg ret msg_setfg: ; Color foreground character call unhexchar jc msg_color_bad or [TextAttribute],al ; setbg set foreground to 0 mov word [NextCharJump],msg_putchar ret msg_color_bad: mov byte [TextAttribute],07h ; Default attribute mov word [NextCharJump],msg_putchar ret ; ; open,getc: Load a file a character at a time for parsing in a manner ; similar to the C library getc routine. Only one simultaneous ; use is supported. Note: "open" trashes the trackbuf. ; ; open: Input: mangled filename in DS:DI ; Output: ZF set on file not found or zero length ; ; getc: Output: CF set on end of file ; Character loaded in AL ; open: call searchdir jz open_return pushf mov [FBytes1],ax mov [FBytes2],dx add ax,[ClustSize] adc dx,byte 0 sub ax,byte 1 sbb dx,byte 0 div word [ClustSize] mov [FClust],ax ; Number of clusters mov [FNextClust],si ; Cluster pointer mov ax,[EndOfGetCBuf] ; Pointer at end of buffer -> mov [FPtr],ax ; nothing loaded yet popf ; Restore no ZF open_return: ret ; getc: stc ; If we exit here -> EOF mov ecx,[FBytes] jecxz getc_ret mov si,[FPtr] cmp si,[EndOfGetCBuf] jb getc_loaded ; Buffer empty -- load another set mov cx,[FClust] cmp cx,[BufSafe] jna getc_oksize mov cx,[BufSafe] getc_oksize: sub [FClust],cx ; Reduce remaining clusters mov si,[FNextClust] mov bx,getcbuf push bx push es ; ES may be != DS, save old ES push ds ; Trackbuf is in DS, not ES pop es call getfssec ; Load a trackbuf full of data mov [FNextClust],si ; Store new next pointer pop es ; Restore ES pop si ; SI -> newly loaded data getc_loaded: lodsb ; Load a byte mov [FPtr],si ; Update next byte pointer dec dword [FBytes] ; Update bytes left counter (CF = 1) clc ; Not EOF getc_ret: ret ; ; ungetc: Push a character (in AL) back into the getc buffer ; Note: if more than one byte is pushed back, this may cause ; bytes to be written below the getc buffer boundary. If there ; is a risk for this to occur, the getcbuf base address should ; be moved up. ; ungetc: mov si,[FPtr] dec si mov [si],al mov [FPtr],si inc dword [FBytes] ret ; ; skipspace: Skip leading whitespace using "getc". If we hit end-of-line ; or end-of-file, return with carry set; ZF = true of EOF ; ZF = false for EOLN; otherwise CF = ZF = 0. ; ; Otherwise AL = first character after whitespace ; skipspace: skipspace_loop: call getc jc skipspace_eof cmp al,1Ah ; DOS EOF je skipspace_eof cmp al,0Ah je skipspace_eoln cmp al,' ' jbe skipspace_loop ret ; CF = ZF = 0 skipspace_eof: cmp al,al ; Set ZF stc ; Set CF ret skipspace_eoln: add al,0FFh ; Set CF, clear ZF ret ; ; getkeyword: Get a keyword from the current "getc" file; only the two ; first characters are considered significant. ; ; Lines beginning with ASCII characters 33-47 are treated ; as comments and ignored; other lines are checked for ; validity by scanning through the keywd_table. ; ; The keyword and subsequent whitespace is skipped. ; ; On EOF, CF = 1; otherwise, CF = 0, AL:AH = lowercase char pair ; getkeyword: gkw_find: call skipspace jz gkw_eof ; end of file jc gkw_find ; end of line: try again cmp al,'0' jb gkw_skipline ; skip comment line push ax call getc pop bx jc gkw_eof mov bh,al ; Move character pair into BL:BH or bx,2020h ; Lower-case it mov si,keywd_table gkw_check: lodsw and ax,ax jz gkw_badline ; Bad keyword, write message cmp ax,bx jne gkw_check push ax gkw_skiprest: call getc jc gkw_eof_pop cmp al,'0' ja gkw_skiprest call ungetc call skipspace jz gkw_eof_pop jc gkw_missingpar ; Missing parameter after keyword call ungetc ; Return character to buffer clc ; Successful return gkw_eof_pop: pop ax gkw_eof: ret ; CF = 1 on all EOF conditions gkw_missingpar: pop ax mov si,err_noparm call writestr jmp gkw_find gkw_badline_pop: pop ax gkw_badline: mov si,err_badcfg call writestr jmp short gkw_find gkw_skipline: cmp al,10 ; Scan for LF je gkw_find call getc jc gkw_eof jmp short gkw_skipline ; ; getint: Load an integer from the getc file. ; Return CF if error; otherwise return integer in EBX ; getint: mov di,NumBuf gi_getnum: cmp di,NumBufEnd ; Last byte in NumBuf jae gi_loaded push di call getc pop di jc gi_loaded stosb cmp al,'-' jnb gi_getnum call ungetc ; Unget non-numeric gi_loaded: mov byte [di],0 mov si,NumBuf ; Fall through to parseint ; ; parseint: Convert an integer to a number in EBX ; Get characters from string in DS:SI ; Return CF on error ; DS:SI points to first character after number ; ; Syntaxes accepted: [-]dec, [-]0+oct, [-]0x+hex, val+K, val+M ; parseint: push eax push ecx push bp xor eax,eax ; Current digit (keep eax == al) mov ebx,eax ; Accumulator mov ecx,ebx ; Base xor bp,bp ; Used for negative flag pi_begin: lodsb cmp al,'-' jne pi_not_minus xor bp,1 ; Set unary minus flag jmp short pi_begin pi_not_minus: cmp al,'0' jb pi_err je pi_octhex cmp al,'9' ja pi_err mov cl,10 ; Base = decimal jmp short pi_foundbase pi_octhex: lodsb cmp al,'0' jb pi_km ; Value is zero or al,20h ; Downcase cmp al,'x' je pi_ishex cmp al,'7' ja pi_err mov cl,8 ; Base = octal jmp short pi_foundbase pi_ishex: mov al,'0' ; No numeric value accrued yet mov cl,16 ; Base = hex pi_foundbase: call unhexchar jc pi_km ; Not a (hex) digit cmp al,cl jae pi_km ; Invalid for base imul ebx,ecx ; Multiply accumulated by base add ebx,eax ; Add current digit lodsb jmp short pi_foundbase pi_km: dec si ; Back up to last non-numeric lodsb or al,20h cmp al,'k' je pi_isk cmp al,'m' je pi_ism dec si ; Back up pi_fini: and bp,bp jz pi_ret ; CF=0! neg ebx ; Value was negative pi_done: clc pi_ret: pop bp pop ecx pop eax ret pi_err: stc jmp short pi_ret pi_isk: shl ebx,10 ; x 2^10 jmp short pi_done pi_ism: shl ebx,20 ; x 2^20 jmp short pi_done ; ; unhexchar: Convert a hexadecimal digit in AL to the equivalent number; ; return CF=1 if not a hex digit ; unhexchar: cmp al,'0' jb uxc_ret ; If failure, CF == 1 already cmp al,'9' ja uxc_1 sub al,'0' ; CF <- 0 ret uxc_1: or al,20h ; upper case -> lower case cmp al,'a' jb uxc_ret ; If failure, CF == 1 already cmp al,'f' ja uxc_err sub al,'a'-10 ; CF <- 0 ret uxc_err: stc uxc_ret: ret ; ; ; getline: Get a command line, converting control characters to spaces ; and collapsing streches to one; a space is appended to the ; end of the string, unless the line is empty. ; The line is terminated by ^J, ^Z or EOF and is written ; to ES:DI. On return, DI points to first char after string. ; CF is set if we hit EOF. ; getline: call skipspace mov dl,1 ; Empty line -> empty string. jz gl_eof ; eof jc gl_eoln ; eoln call ungetc gl_fillloop: push dx push di call getc pop di pop dx jc gl_ret ; CF set! cmp al,' ' jna gl_ctrl xor dx,dx gl_store: stosb jmp short gl_fillloop gl_ctrl: cmp al,10 je gl_ret ; CF clear! cmp al,26 je gl_eof and dl,dl jnz gl_fillloop ; Ignore multiple spaces mov al,' ' ; Ctrl -> space inc dx jmp short gl_store gl_eoln: clc ; End of line is not end of file jmp short gl_ret gl_eof: stc gl_ret: pushf ; We want the last char to be space! and dl,dl jnz gl_xret mov al,' ' stosb gl_xret: popf ret %ifdef debug ; This code for debugging only ; ; dumpregs: Dumps the contents of all registers ; assume ds:_text, es:NOTHING, fs:NOTHING, gs:NOTHING dumpregs proc near ; When calling, IP is on stack pushf ; Store flags pusha push ds push es push fs push gs push cs ; Set DS <- CS pop ds cld ; Clear direction flag mov si,offset crlf_msg call writestr mov bx,sp add bx,byte 26 mov si,offset regnames mov cx,2 ; 2*7 registers to dump dump_line: push cx mov cx,7 ; 7 registers per line dump_reg: push cx mov cx,4 ; 4 characters/register name wr_reg_name: lodsb call writechr loop wr_reg_name mov ax,ss:[bx] dec bx dec bx call writehex pop cx loop dump_reg mov al,0Dh ; <CR> call writechr mov al,0Ah ; <LF> call writechr pop cx loop dump_line pop gs pop fs pop es pop ds popa ; Restore the remainder popf ; Restore flags ret dumpregs endp regnames db ' IP: FL: AX: CX: DX: BX: SP: BP: SI: DI: DS: ES: FS: GS:' ; ; writehex: Writes a 16-bit hexadecimal number (in AX) ; writehex proc near push bx push cx mov cx,4 ; 4 numbers write_hexdig: xor bx,bx push cx mov cx,4 ; 4 bits/digit xfer_digit: shl ax,1 rcl bx,1 loop xfer_digit push ax mov ax,bx or al,'0' cmp al,'9' jna ok_digit add al,'A'-'0'-10 ok_digit: call writechr pop ax pop cx loop write_hexdig pop cx pop bx ret writehex endp debug_magic dw 0D00Dh %endif ; debug ; ; mangle_name: Mangle a DOS filename pointed to by DS:SI into a buffer pointed ; to by ES:DI; ends on encountering any whitespace ; mangle_name: mov cx,11 ; # of bytes to write mn_loop: lodsb cmp al,' ' ; If control or space, end jna mn_end cmp al,'.' ; Period -> space-fill je mn_is_period cmp al,'a' jb mn_not_lower cmp al,'z' ja mn_not_uslower sub al,020h jmp short mn_not_lower mn_is_period: mov al,' ' ; We need to space-fill mn_period_loop: cmp cx,3 ; If <= 3 characters left jbe mn_loop ; Just ignore it stosb ; Otherwise, write a period loop mn_period_loop ; Dec CX and (always) jump mn_not_uslower: cmp al,ucase_low jb mn_not_lower cmp al,ucase_high ja mn_not_lower mov bx,ucase_tab-ucase_low cs xlatb mn_not_lower: stosb loop mn_loop ; Don't continue if too long mn_end: mov al,' ' ; Space-fill name rep stosb ; Doesn't do anything if CX=0 ret ; Done ; ; Upper-case table for extended characters; this is technically code page 865, ; but code page 437 users will probably not miss not being able to use the ; cent sign in kernel images too much :-) ; ; The table only covers the range 129 to 164; the rest we can deal with. ; ucase_low equ 129 ucase_high equ 164 ucase_tab db 154, 144, 'A', 142, 'A', 143, 128, 'EEEIII' db 142, 143, 144, 146, 146, 'O', 153, 'OUUY', 153, 154 db 157, 156, 157, 158, 159, 'AIOU', 165 ; ; unmangle_name: Does the opposite of mangle_name; converts a DOS-mangled ; filename to the conventional representation. This is needed ; for the BOOT_IMAGE= parameter for the kernel. ; NOTE: A 13-byte buffer is mandatory, even if the string is ; known to be shorter. ; ; DS:SI -> input mangled file name ; ES:DI -> output buffer ; ; On return, DI points to the first byte after the output name, ; which is set to a null byte. ; unmangle_name: push si ; Save pointer to original name mov cx,8 mov bp,di un_copy_body: lodsb call lower_case stosb cmp al,' ' jbe un_cb_space mov bp,di ; Position of last nonblank+1 un_cb_space: loop un_copy_body mov di,bp mov al,'.' ; Don't save stosb mov cx,3 un_copy_ext: lodsb call lower_case stosb cmp al,' ' jbe un_ce_space mov bp,di un_ce_space: loop un_copy_ext mov di,bp mov byte [es:di], 0 pop si ret ; ; lower_case: Lower case a character in AL ; lower_case: cmp al,'A' jb lc_ret cmp al,'Z' ja lc_1 or al,20h ret lc_1: cmp al,lcase_low jb lc_ret cmp al,lcase_high ja lc_ret push bx mov bx,lcase_tab-lcase_low cs xlatb pop bx lc_ret: ret ; ; Lower-case table for codepage 865 ; lcase_low equ 128 lcase_high equ 165 lcase_tab db 135, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138 db 139, 140, 141, 132, 134, 130, 145, 145, 147, 148, 149 db 150, 151, 152, 148, 129, 155, 156, 155, 158, 159, 160 db 161, 162, 163, 164, 164 ; ; Various initialized or semi-initialized variables ; copyright_str db ' Copyright (C) 1994-', year, ' H. Peter Anvin' db 0Dh, 0Ah, 0 boot_prompt db 'boot: ',0 wipe_char db 08h, ' ', 08h, 0 err_notfound db 'Could not find kernel image: ',0 err_notkernel db 0Dh, 0Ah, 'Invalid or corrupt kernel image.', 0Dh, 0Ah, 0 err_not386 db 'It appears your computer uses a 286 or lower CPU.' db 0Dh, 0Ah db 'You cannot run Linux unless you have a 386 or higher CPU' db 0Dh, 0Ah db 'in your machine. If you get this message in error, hold' db 0Dh, 0Ah db 'down the Ctrl key while booting, and I will take your' db 0Dh, 0Ah db 'word for it.', 0Dh, 0Ah, 0 err_noram db 'It appears your computer has less than 608K of low ("DOS")' db 0Dh, 0Ah db 'RAM. Linux needs at least this amount to boot. If you get' db 0Dh, 0Ah db 'this message in error, hold down the Ctrl key while' db 0Dh, 0Ah db 'booting, and I will take your word for it.', 0Dh, 0Ah, 0 err_badcfg db 'Unknown keyword in syslinux.cfg.', 0Dh, 0Ah, 0 err_noparm db 'Missing parameter in syslinux.cfg.', 0Dh, 0Ah, 0 err_noinitrd db 0Dh, 0Ah, 'Could not find ramdisk image: ', 0 err_nohighmem db 'Not enough memory to load specified kernel.', 0Dh, 0Ah, 0 err_highload db 0Dh, 0Ah, 'Kernel transfer failure.', 0Dh, 0Ah, 0 err_oldkernel db 'Cannot load a ramdisk with an old kernel image.' db 0Dh, 0Ah, 0 err_notdos db ': attempted DOS system call', 0Dh, 0Ah, 0 err_comlarge db 'COMBOOT image too large.', 0Dh, 0Ah, 0 err_bootsec db 'Invalid or corrupt boot sector image.', 0Dh, 0Ah, 0 loading_msg db 'Loading ', 0 dotdot_msg db '.' dot_msg db '.', 0 aborted_msg db ' aborted.' ; Fall through to crlf_msg! crlf_msg db 0Dh, 0Ah, 0 syslinux_cfg db 'SYSLINUXCFG' ; ; Command line options we'd like to take a look at ; ; mem= and vga= are handled as normal 32-bit integer values initrd_cmd db 'initrd=' initrd_cmd_len equ 7 ; ; Config file keyword table ; align 2 keywd_table db 'ap' ; append db 'de' ; default db 'ti' ; timeout db 'fo' ; font db 'kb' ; kbd db 'di' ; display db 'pr' ; prompt db 'la' ; label db 'im' ; implicit db 'ke' ; kernel db 'f1' ; F1 db 'f2' ; F2 db 'f3' ; F3 db 'f4' ; F4 db 'f5' ; F5 db 'f6' ; F6 db 'f7' ; F7 db 'f8' ; F8 db 'f9' ; F9 db 'f0' ; F10 dw 0 ; ; Extensions to search for (in *reverse* order). Note that the last ; (lexically first) entry in the table is a placeholder for the original ; extension, needed for error messages. The exten_table is shifted so ; the table is 1-based; this is because a "loop" cx is used as index. ; exten_table: OrigKernelExt: dd 0 ; Original extension db 'COM',0 ; COMBOOT (same as DOS) db 'BS ',0 ; Boot Sector db 'BSS',0 ; Boot Sector (add superblock) db 'CBT',0 ; COMBOOT (specific) exten_count equ (($-exten_table) >> 2) - 1 ; Number of alternates ; ; Misc initialized (data) variables ; AppendLen dw 0 ; Bytes in append= command KbdTimeOut dw 0 ; Keyboard timeout (if any) FKeyMap dw 0 ; Bitmap for F-keys loaded CmdLinePtr dw cmd_line_here ; Command line advancing pointer initrd_flag equ $ initrd_ptr dw 0 ; Initial ramdisk pointer/flag VKernelCtr dw 0 ; Number of registered vkernels ForcePrompt dw 0 ; Force prompt AllowImplicit dw 1 ; Allow implicit kernels ; ; Stuff for the command line; we do some trickery here with equ to avoid ; tons of zeros appended to our file and wasting space ; linuxauto_cmd db 'linux ' auto_cmd db 'auto',0 linuxauto_len equ $-linuxauto_cmd auto_len equ $-auto_cmd boot_image db 'BOOT_IMAGE=' boot_image_len equ $-boot_image align 4, db 0 ; For the good of REP MOVSD command_line equ $ default_cmd equ $+(max_cmd_len+2) ldlinux_end equ default_cmd+(max_cmd_len+1) kern_cmd_len equ ldlinux_end-command_line ldlinux_len equ ldlinux_end-ldlinux_magic ; ; Put the getcbuf right after the code, aligned on a sector boundary ; end_of_code equ (ldlinux_end-bootsec)+7C00h getcbuf equ (end_of_code + 511) & 0FE00h