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Assembly Source File | 2005-01-04 | 35.4 KB | 1,455 lines

; -*- fundamental -*- (asm-mode sucks) ; $Id: extlinux.asm,v 1.19 2005/01/04 22:17:17 hpa Exp $ ; **************************************************************************** ; ; extlinux.asm ; ; A program to boot Linux kernels off an ext2/ext3 filesystem. ; ; Copyright (C) 1994-2005 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., 53 Temple Place Ste 330, ; Boston MA 02111-1307, USA; either version 2 of the License, or ; (at your option) any later version; incorporated herein by reference. ; ; **************************************************************************** %define IS_EXTLINUX 1 %include "macros.inc" %include "config.inc" %include "kernel.inc" %include "bios.inc" %include "tracers.inc" %include "layout.inc" %include "ext2_fs.inc" ; ; Some semi-configurable constants... change on your own risk. ; my_id equ extlinux_id ; NASM 0.98.38 croaks if these are equ's rather than macros... FILENAME_MAX_LG2 equ 8 ; log2(Max filename size Including final null) FILENAME_MAX equ (1 << FILENAME_MAX_LG2) ; Max mangled filename size NULLFILE equ 0 ; Null character == empty filename NULLOFFSET equ 0 ; Position in which to look retry_count equ 6 ; How patient are we with the disk? %assign HIGHMEM_SLOP 0 ; Avoid this much memory near the top LDLINUX_MAGIC equ 0x3eb202fe ; A random number to identify ourselves with MAX_OPEN_LG2 equ 6 ; log2(Max number of open files) MAX_OPEN equ (1 << MAX_OPEN_LG2) SECTOR_SHIFT equ 9 SECTOR_SIZE equ (1 << SECTOR_SHIFT) ; ; This is what we need to do when idle ; %macro RESET_IDLE 0 ; Nothing %endmacro %macro DO_IDLE 0 ; Nothing %endmacro ; ; 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 vk_seg:0000 and copy them down before we need them. ; struc vkernel vk_vname: resb FILENAME_MAX ; Virtual name **MUST BE FIRST!** vk_rname: resb FILENAME_MAX ; 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 ; ; Segment assignments in the bottom 640K ; Stick to the low 512K in case we're using something like M-systems flash ; which load a driver into low RAM (evil!!) ; ; 0000h - main code/data segment (and BIOS segment) ; real_mode_seg equ 4000h cache_seg equ 3000h ; 64K area for metadata cache vk_seg equ 2000h ; Virtual kernels xfer_buf_seg equ 1000h ; Bounce buffer for I/O to high mem comboot_seg equ real_mode_seg ; COMBOOT image loading zone ; ; File structure. This holds the information for each currently open file. ; struc open_file_t file_left resd 1 ; Number of sectors left (0 = free) file_sector resd 1 ; Next linear sector to read file_in_sec resd 1 ; Sector where inode lives file_in_off resw 1 file_mode resw 1 endstruc %ifndef DEPEND %if (open_file_t_size & (open_file_t_size-1)) %error "open_file_t is not a power of 2" %endif %endif ; --------------------------------------------------------------------------- ; BEGIN CODE ; --------------------------------------------------------------------------- ; ; Memory below this point is reserved for the BIOS and the MBR ; section .earlybss trackbufsize equ 8192 trackbuf resb trackbufsize ; Track buffer goes here getcbuf resb trackbufsize ; ends at 4800h section .bss SuperBlock resb 1024 ; ext2 superblock SuperInfo resq 16 ; DOS superblock expanded ClustSize resd 1 ; Bytes/cluster ("block") SecPerClust resd 1 ; Sectors/cluster ClustMask resd 1 ; Sectors/cluster - 1 PtrsPerBlock1 resd 1 ; Pointers/cluster PtrsPerBlock2 resd 1 ; (Pointers/cluster)^2 DriveNumber resb 1 ; BIOS drive number ClustShift resb 1 ; Shift count for sectors/cluster ClustByteShift resb 1 ; Shift count for bytes/cluster alignb open_file_t_size Files resb MAX_OPEN*open_file_t_size ; ; Constants for the xfer_buf_seg ; ; The xfer_buf_seg is also used to store message file buffers. We ; need two trackbuffers (text and graphics), plus a work buffer ; for the graphics decompressor. ; xbs_textbuf equ 0 ; Also hard-coded, do not change xbs_vgabuf equ trackbufsize xbs_vgatmpbuf equ 2*trackbufsize section .text ; ; Some of the things that have to be saved very early are saved ; "close" to the initial stack pointer offset, in order to ; reduce the code size... ; StackBuf equ $-44-32 ; Start the stack here (grow down - 4K) PartInfo equ StackBuf ; Saved partition table entry FloppyTable equ PartInfo+16 ; Floppy info table (must follow PartInfo) OrigFDCTabPtr equ StackBuf-4 ; The high dword on the stack ; ; 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 'EXTLINUX' ; The SYS command sets this, so... ; ; These are the fields we actually care about. We end up expanding them ; all to dword size early in the code, so generate labels for both ; the expanded and unexpanded versions. ; %macro superb 1 bx %+ %1 equ SuperInfo+($-superblock)*8+4 bs %+ %1 equ $ zb 1 %endmacro %macro superw 1 bx %+ %1 equ SuperInfo+($-superblock)*8 bs %+ %1 equ $ zw 1 %endmacro %macro superd 1 bx %+ %1 equ $ ; no expansion for dwords bs %+ %1 equ $ zd 1 %endmacro superblock equ $ superw BytesPerSec superb SecPerClust superw ResSectors superb FATs superw RootDirEnts superw Sectors superb Media superw FATsecs superw SecPerTrack superw Heads superinfo_size equ ($-superblock)-1 ; How much to expand superd Hidden superd HugeSectors ; ; This is as far as FAT12/16 and FAT32 are consistent ; zb 54 ; FAT12/16 need 26 more bytes, ; FAT32 need 54 more bytes superblock_len equ $-superblock ; ; Note we don't check the constraints above now; we did that at install ; time (we hope!) ; start: cli ; No interrupts yet, please cld ; Copy upwards ; ; Set up the stack ; xor ax,ax mov ss,ax mov sp,StackBuf ; Just below BSS mov es,ax ; ; DS:SI may contain a partition table entry. Preserve it for us. ; mov cx,8 ; Save partition info mov di,sp rep movsw mov ds,ax ; Now we can initialize DS... ; ; 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 space with this code. ; mov bx,fdctab lfs si,[bx] ; FS:SI -> original fdctab push fs ; Save on stack in case we need to bail push si ; Save the old fdctab even if hard disk so the stack layout ; is the same. The instructions above do not change the flags mov [DriveNumber],dl ; Save drive number in DL and dl,dl ; If floppy disk (00-7F), assume no ; partition table js harddisk floppy: mov cl,6 ; 12 bytes (CX == 0) ; es:di -> FloppyTable already ; This should be safe to do now, interrupts are off... mov [bx],di ; FloppyTable mov [bx+2],ax ; Segment 0 fs rep movsw ; Faster to move words mov cl,[bsSecPerTrack] ; Patch the sector count mov [di-8],cl ; AX == 0 here int 13h ; Some BIOSes need this jmp short not_harddisk ; ; 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 ; harddisk: test byte [di-16],7Fh ; Sanity check: "active flag" should jnz no_partition ; be 00 or 80 mov eax,[di-8] ; Partition offset (dword) mov [bsHidden],eax 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 shr dx,8 inc dx ; Contains # of heads - 1 mov [bsHeads],dx and cx,3fh mov [bsSecPerTrack],cx no_driveparm: not_harddisk: ; ; Ready to enable interrupts, captain ; sti ; ; Do we have EBIOS (EDD)? ; eddcheck: mov bx,55AAh mov ah,41h ; EDD existence query mov dl,[DriveNumber] int 13h jc .noedd cmp bx,0AA55h jne .noedd test cl,1 ; Extended disk access functionality set jz .noedd ; ; We have EDD support... ; mov byte [getlinsec.jmp+1],getlinsec_ebios-(getlinsec.jmp+2) .noedd: ; ; Load the first sector of LDLINUX.SYS; this used to be all proper ; with parsing the superblock and root directory; it doesn't fit ; together with EBIOS support, unfortunately. ; mov eax,[FirstSector] ; Sector start mov bx,ldlinux_sys ; Where to load it call getonesec ; Some modicum of integrity checking cmp dword [ldlinux_magic],LDLINUX_MAGIC jne kaboom cmp dword [ldlinux_magic+4],HEXDATE jne kaboom ; Go for it... jmp ldlinux_ent ; ; kaboom: write a message and bail out. ; kaboom: xor si,si mov ss,si mov sp,StackBuf-4 ; Reset stack mov ds,si ; Reset data segment pop dword [fdctab] ; Restore FDC table .patch: 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 ; ; ; writestr: write a null-terminated string to the console ; This assumes we're on page 0. This is only used for early ; messages, so it should be OK. ; writestr: .loop: lodsb and al,al jz .return mov ah,0Eh ; Write to screen as TTY mov bx,0007h ; Attribute int 10h jmp short .loop .return: ret ; ; xint13: wrapper for int 13h which will retry 6 times and then die, ; AND save all registers except BP ; xint13: .again: mov bp,retry_count .loop: pushad int 13h popad jnc writestr.return dec bp jnz .loop .disk_error: jmp strict near kaboom ; Patched ; ; getonesec: get one disk sector ; getonesec: mov bp,1 ; One sector ; Fall through ; ; getlinsec: load a sequence of BP floppy sector given by the linear sector ; number in EAX 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. ; ; This routine assumes CS == DS, and trashes most registers. ; ; 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: add eax,[bsHidden] ; Add partition offset .jmp: jmp strict short getlinsec_cbios ; This is patched ; ; getlinsec_ebios: ; ; getlinsec implementation for EBIOS (EDD) ; getlinsec_ebios: mov si,dapa ; Load up the DAPA mov [si+4],bx mov [si+6],es mov [si+8],eax .loop: push bp ; Sectors left call maxtrans ; Enforce maximum transfer size .bp_ok: mov [si+2],bp mov dl,[DriveNumber] mov ah,42h ; Extended Read call xint13 pop bp movzx eax,word [si+2] ; Sectors we read add [si+8],eax ; Advance sector pointer sub bp,ax ; Sectors left shl ax,9 ; 512-byte sectors add [si+4],ax ; Advance buffer pointer and bp,bp jnz .loop mov eax,[si+8] ; Next sector mov bx,[si+4] ; Buffer pointer ret ; ; getlinsec_cbios: ; ; getlinsec implementation for legacy CBIOS ; getlinsec_cbios: .loop: push eax push bp push bx movzx esi,word [bsSecPerTrack] movzx edi,word [bsHeads] ; ; Dividing by sectors to get (track,sector): we may have ; up to 2^18 tracks, so we need to use 32-bit arithmetric. ; xor edx,edx ; Zero-extend LBA to 64 bits div esi xor cx,cx xchg cx,dx ; CX <- sector index (0-based) ; EDX <- 0 ; eax = track # div edi ; 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 ; call maxtrans ; Enforce maximum transfer size ; Must not cross track boundaries, so BP <= SI-CX sub si,cx cmp bp,si jna .bp_ok mov bp,si .bp_ok: shl ah,6 ; Because IBM was STOOPID ; and thought 8 bits were enough ; then thought 10 bits were enough... inc cx ; Sector numbers are 1-based, sigh or cl,ah mov ch,al mov dh,dl mov dl,[DriveNumber] xchg ax,bp ; Sector to transfer count mov ah,02h ; Read sectors call xint13 movzx ecx,al shl ax,9 ; Convert sectors in AL to bytes in AX pop bx add bx,ax pop bp pop eax add eax,ecx sub bp,cx jnz .loop ret ; ; Truncate BP to MaxTransfer ; maxtrans: cmp bp,[MaxTransfer] jna .ok mov bp,[MaxTransfer] .ok: ret ; ; Error message on failure ; bailmsg: db 'Boot failed', 0Dh, 0Ah, 0 ; ; EBIOS disk address packet ; align 4, db 0 dapa: dw 16 ; Packet size .count: dw 0 ; Block count .off: dw 0 ; Offset of buffer .seg: dw 0 ; Segment of buffer .lba: dd 0 ; LBA (LSW) dd 0 ; LBA (MSW) %if 1 bs_checkpt_off equ ($-$$) %ifndef DEPEND %if bs_checkpt_off > 1F8h %error "Boot sector overflow" %endif %endif zb 1F8h-($-$$) %endif FirstSector dd 0xDEADBEEF ; Location of sector 1 MaxTransfer dw 0x007F ; Max transfer size bootsignature dw 0AA55h ; ; =========================================================================== ; End of boot sector ; =========================================================================== ; Start of LDLINUX.SYS ; =========================================================================== ldlinux_sys: syslinux_banner db 0Dh, 0Ah db 'EXTLINUX ' db version_str, ' ', date, ' ', 0 db 0Dh, 0Ah, 1Ah ; EOF if we "type" this in DOS align 8, db 0 ldlinux_magic dd LDLINUX_MAGIC dd HEXDATE ; ; This area is patched by the installer. It is found by looking for ; LDLINUX_MAGIC, plus 8 bytes. ; patch_area: LDLDwords dw 0 ; Total dwords starting at ldlinux_sys LDLSectors dw 0 ; Number of sectors - (bootsec+this sec) CheckSum dd 0 ; Checksum starting at ldlinux_sys ; value = LDLINUX_MAGIC - [sum of dwords] CurrentDir dd 2 ; "Current" directory inode number ; Space for up to 64 sectors, the theoretical maximum SectorPtrs times 64 dd 0 ldlinux_ent: ; ; Note that some BIOSes are buggy and run 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. ; jmp 0:.next .next: ; ; Tell the user we got this far ; mov si,syslinux_banner call writestr ; ; Patch disk error handling ; mov word [xint13.disk_error+1],do_disk_error-(xint13.disk_error+3) ; ; Now we read the rest of LDLINUX.SYS. Don't bother loading the first ; sector again, though. ; load_rest: mov si,SectorPtrs mov bx,7C00h+2*SECTOR_SIZE ; Where we start loading mov cx,[LDLSectors] .get_chunk: jcxz .done xor bp,bp lodsd ; First sector of this chunk mov edx,eax .make_chunk: inc bp dec cx jz .chunk_ready inc edx ; Next linear sector cmp [esi],edx ; Does it match jnz .chunk_ready ; If not, this is it add esi,4 ; If so, add sector to chunk jmp short .make_chunk .chunk_ready: call getlinsecsr shl bp,SECTOR_SHIFT add bx,bp jmp .get_chunk .done: ; ; All loaded up, verify that we got what we needed. ; Note: the checksum field is embedded in the checksum region, so ; by the time we get to the end it should all cancel out. ; verify_checksum: mov si,ldlinux_sys mov cx,[LDLDwords] mov edx,-LDLINUX_MAGIC .checksum: lodsd add edx,eax loop .checksum and edx,edx ; Should be zero jz all_read ; We're cool, go for it! ; ; Uh-oh, something went bad... ; mov si,checksumerr_msg call writestr jmp kaboom ; ; ----------------------------------------------------------------------------- ; Subroutines that have to be in the first sector ; ----------------------------------------------------------------------------- ; ; getlinsecsr: save registers, call getlinsec, restore registers ; getlinsecsr: pushad call getlinsec popad ret ; ; This routine captures disk errors, and tries to decide if it is ; time to reduce the transfer size. ; do_disk_error: cmp ah,42h je .ebios shr al,1 ; Try reducing the transfer size mov [MaxTransfer],al jz kaboom ; If we can't, we're dead... jmp xint13 ; Try again .ebios: push ax mov ax,[si+2] shr ax,1 mov [MaxTransfer],ax mov [si+2],ax pop ax jmp xint13 ; ; Checksum error message ; checksumerr_msg db 'Load error - ', 0 ; Boot failed appended ; ; Debug routine ; %ifdef debug safedumpregs: cmp word [Debug_Magic],0D00Dh jnz nc_return jmp dumpregs %endif rl_checkpt equ $ ; Must be <= 8000h rl_checkpt_off equ ($-$$) %if 0 ; ndef DEPEND %if rl_checkpt_off > 400h %error "Sector 1 overflow" %endif %endif ; ---------------------------------------------------------------------------- ; 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 ; ; Insane hack to expand the DOS superblock to dwords ; expand_super: xor eax,eax mov si,superblock mov di,SuperInfo mov cx,superinfo_size .loop: lodsw dec si stosd ; Store expanded word xor ah,ah stosd ; Store expanded byte loop .loop ; ; Load the real (ext2) superblock; 1024 bytes long at offset 1024 ; mov bx,SuperBlock mov eax,1024 >> SECTOR_SHIFT mov bp,ax call getlinsec ; ; Compute some values... ; xor edx,edx inc edx ; s_log_block_size = log2(blocksize) - 10 mov cl,[SuperBlock+s_log_block_size] add cl,10 mov [ClustByteShift],cl mov eax,edx shl eax,cl mov [ClustSize],eax sub cl,SECTOR_SHIFT mov [ClustShift],cl shr eax,SECTOR_SHIFT mov [SecPerClust],eax dec eax mov [ClustMask],eax add cl,SECTOR_SHIFT-2 ; 4 bytes/pointer shl edx,cl mov [PtrsPerBlock1],edx shl edx,cl mov [PtrsPerBlock2],edx ; ; Common initialization code ; %include "init.inc" %include "cpuinit.inc" ; ; Initialize the metadata cache ; call initcache ; ; Now, everything is "up and running"... patch kaboom for more ; verbosity and using the full screen system ; ; E9 = JMP NEAR mov dword [kaboom.patch],0e9h+((kaboom2-(kaboom.patch+3)) << 8) ; ; 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. ; ; ; Load configuration file ; load_config: mov di,ConfigName call open jz no_config_file ; ; Now we have the config file open. Parse the config file and ; run the user interface. ; %include "ui.inc" ; ; Linux kernel loading code is common. ; %include "runkernel.inc" ; ; COMBOOT-loading code ; %include "comboot.inc" %include "com32.inc" %include "cmdline.inc" ; ; Boot sector loading code ; %include "bootsect.inc" ; ; abort_check: let the user abort with <ESC> or <Ctrl-C> ; abort_check: call pollchar jz ac_ret1 pusha call getchar cmp al,27 ; <ESC> je ac_kill cmp al,3 ; <Ctrl-C> jne ac_ret2 ac_kill: mov si,aborted_msg ; ; 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 cwritestr ; Expects SI -> error msg al_ok: jmp enter_command ; Return to command prompt ; ; End of abort_check ; ac_ret2: popa ac_ret1: ret ; ; allocate_file: Allocate a file structure ; ; If successful: ; ZF set ; BX = file pointer ; In unsuccessful: ; ZF clear ; allocate_file: TRACER 'a' push cx mov bx,Files mov cx,MAX_OPEN .check: cmp dword [bx], byte 0 je .found add bx,open_file_t_size ; ZF = 0 loop .check ; ZF = 0 if we fell out of the loop .found: pop cx ret ; ; open_inode: ; Open a file indicated by an inode number in EAX ; ; 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 = file pointer ; DX:AX = EAX = file length in bytes ; If unsuccessful ; ZF set ; open_inode.allocate_failure: xor eax,eax ret open_inode: call allocate_file jnz .allocate_failure push gs ; First, get the appropriate inode group and index dec eax ; There is no inode 0 xor edx,edx mov [bx+file_sector],edx div dword [SuperBlock+s_inodes_per_group] ; EAX = inode group; EDX = inode within group push edx ; Now, we need the block group descriptor. ; To get that, we first need the relevant descriptor block. shl eax, ext2_group_desc_lg2size ; Get byte offset in desc table xor edx,edx div dword [ClustSize] ; eax = block #, edx = offset in block add eax,dword [SuperBlock+s_first_data_block] inc eax ; s_first_data_block+1 mov cl,[ClustShift] shl eax,cl call getcachesector ; Get the group descriptor add si,dx mov esi,[gs:si+bg_inode_table] ; Get inode table block # pop eax ; Get inode within group movzx edx, word [SuperBlock+s_inode_size] mul edx ; edx:eax = byte offset in inode table div dword [ClustSize] ; eax = block # versus inode table, edx = offset in block add eax,esi shl eax,cl ; Turn into sector push dx shr edx,SECTOR_SHIFT add eax,edx mov [bx+file_in_sec],eax pop dx and dx,SECTOR_SIZE-1 mov [bx+file_in_off],dx call getcachesector add si,dx mov ax,[gs:si+i_mode] mov [bx+file_mode],ax mov eax,[gs:si+i_size] push eax add eax,SECTOR_SIZE-1 shr eax,SECTOR_SHIFT mov [bx+file_left],eax pop eax mov si,bx mov edx,eax shr edx,16 ; 16-bitism, sigh and eax,eax ; ZF clear unless zero-length file pop gs ret ; ; close: ; Deallocates a file structure (pointer in SI) ; Assumes CS == DS. ; close: mov dword [si],0 ; First dword == file_left ret ; ; searchdir: ; Search the root directory for a pre-mangled filename in DS:DI. ; ; 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 = file pointer ; DX:AX = EAX = file length in bytes ; If unsuccessful ; ZF set ; ; Assumes CS == DS == ES; *** IS THIS CORRECT ***? ; searchdir: push bx push cx push di mov eax,[CurrentDir] .leadingslash: cmp byte [di],'/' ; Absolute filename? jne .searchloop mov eax,EXT2_ROOT_INO inc di ; Skip slash .searchloop: ; At this point, EAX contains the directory inode, ; and DS:DI contains a pathname tail. call open_inode .readdir: mov bx,trackbuf push bx mov cx,[SecPerClust] call getfssec pop bx pushf ; Save EOF flag .getent: cmp dword [bx+d_inode],0 je .endblock push di movzx cx,byte [bx+d_name_len] lea si,[bx+d_name] repe cmpsb je .maybe .nope: pop di add bx,[bx+d_rec_len] jmp .getent .endblock: popf jnc .readdir ; There is more .failure: xor eax,eax jmp .done .maybe: mov eax,[bx+d_inode] cmp byte [di],0 je .finish ; It's a real file; done cmp byte [di],'/' jne .nope ; False alarm ; It's a match, but it's a directory. ; Repeat operation. call close pop si ; Adjust stack (di) pop si ; Adjust stack (flags) inc di ; Skip slash jmp .searchloop .finish: ; We found it; now we need to open the file call close ; Close directory pop si ; Adjust stack (di) pop si ; Adjust stack (flags) call open_inode .done: pop di pop cx pop bx ret ; ; mangle_name: Mangle a filename pointed to by DS:SI into a buffer pointed ; to by ES:DI; ends on encountering any whitespace. ; ; This verifies that a filename is < FILENAME_MAX characters, ; doesn't contain whitespace, zero-pads the output buffer, ; and removes redundant slashes, ; so "repe cmpsb" can do a compare, and the ; path-searching routine gets a bit of an easier job. ; ; FIX: we may want to support \-escapes here (and this would ; be the place.) ; mangle_name: push bx xor ax,ax mov cx,FILENAME_MAX-1 mov bx,di .mn_loop: lodsb cmp al,' ' ; If control or space, end jna .mn_end cmp al,ah ; Repeated slash? je .mn_skip xor ah,ah cmp al,'/' jne .mn_ok mov ah,al .mn_ok stosb .mn_skip: loop .mn_loop .mn_end: cmp bx,di ; At the beginning of the buffer? jbe .mn_zero cmp byte [di-1],'/' ; Terminal slash? jne .mn_zero .mn_kill: dec di ; If so, remove it inc cx jmp short .mn_end .mn_zero: inc cx ; At least one null byte xor ax,ax ; Zero-fill name rep stosb pop bx ret ; Done ; ; 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: call strcpy dec di ; Point to final null byte ret ; ; writechr: Write a single character in AL to the console without ; mangling any registers; handle video pages correctly. ; writechr: call write_serial ; write to serial port if needed pushfd test byte [cs:DisplayCon],01h jz .nothing pushad mov ah,0Eh mov bl,07h ; attribute mov bh,[cs:BIOS_page] ; current page int 10h popad .nothing: popfd ret ; ; ; kaboom2: once everything is loaded, replace the part of kaboom ; starting with "kaboom.patch" with this part kaboom2: mov si,err_bootfailed call cwritestr call getchar call vgaclearmode int 19h ; And try once more to boot... .norge: jmp short .norge ; If int 19h returned; this is the end ; ; linsector: Convert a linear sector index in a file to a linear sector number ; EAX -> linear sector number ; DS:SI -> open_file_t ; ; Returns next sector number in EAX; CF on EOF (not an error!) ; linsector: push gs push ebx push esi push edi push ecx push edx push ebp push eax ; Save sector index mov cl,[ClustShift] shr eax,cl ; Convert to block number push eax mov eax,[si+file_in_sec] mov bx,si call getcachesector ; Get inode add si,[bx+file_in_off] ; Get *our* inode pop eax lea ebx,[i_block+4*eax] cmp eax,EXT2_NDIR_BLOCKS jb .direct mov ebx,i_block+4*EXT2_IND_BLOCK sub eax,EXT2_NDIR_BLOCKS mov ebp,[PtrsPerBlock1] cmp eax,ebp jb .ind1 mov ebx,i_block+4*EXT2_DIND_BLOCK sub eax,ebp mov ebp,[PtrsPerBlock2] cmp eax,ebp jb .ind2 mov ebx,i_block+4*EXT2_TIND_BLOCK sub eax,ebp .ind3: ; Triple indirect; eax contains the block no ; with respect to the start of the tind area; ; ebx contains the pointer to the tind block. xor edx,edx div dword [PtrsPerBlock2] ; EAX = which dind block, EDX = pointer within dind block push ax shr eax,SECTOR_SHIFT-2 mov ebp,[gs:si+bx] shl ebp,cl add eax,ebp call getcachesector pop bx and bx,(SECTOR_SIZE >> 2)-1 shl bx,2 mov eax,edx ; The ind2 code wants the remainder... .ind2: ; Double indirect; eax contains the block no ; with respect to the start of the dind area; ; ebx contains the pointer to the dind block. xor edx,edx div dword [PtrsPerBlock1] ; EAX = which ind block, EDX = pointer within ind block push ax shr eax,SECTOR_SHIFT-2 mov ebp,[gs:si+bx] shl ebp,cl add eax,ebp call getcachesector pop bx and bx,(SECTOR_SIZE >> 2)-1 shl bx,2 mov eax,edx ; The int1 code wants the remainder... .ind1: ; Single indirect; eax contains the block no ; with respect to the start of the ind area; ; ebx contains the pointer to the ind block. push ax shr eax,SECTOR_SHIFT-2 mov ebp,[gs:si+bx] shl ebp,cl add eax,ebp call getcachesector pop bx and bx,(SECTOR_SIZE >> 2)-1 shl bx,2 .direct: mov ebx,[gs:bx+si] ; Get the pointer pop eax ; Get the sector index again shl ebx,cl ; Convert block number to sector and eax,[ClustMask] ; Add offset within block add eax,ebx pop ebp pop edx pop ecx pop edi pop esi pop ebx pop gs ret ; ; getfssec: Get multiple sectors from a file ; ; Same as above, except SI is a pointer to a open_file_t ; ; ES:BX -> Buffer ; DS:SI -> Pointer to open_file_t ; CX -> Sector count (0FFFFh = until end of file) ; Must not exceed the ES segment ; Returns CF=1 on EOF (not necessarily error) ; All arguments are advanced to reflect data read. ; getfssec: push ebp push eax push edx push edi .getfragment: mov eax,[si+file_sector] ; Current start index mov edi,eax call linsector push eax ; Fragment start sector mov edx,eax xor ebp,ebp ; Fragment sector count .getseccnt: inc bp dec cx jz .do_read xor eax,eax mov ax,es shl ax,4 add ax,bx ; Now DI = how far into 64K block we are not ax ; Bytes left in 64K block inc eax shr eax,SECTOR_SHIFT ; Sectors left in 64K block cmp bp,ax jnb .do_read ; Unless there is at least 1 more sector room... inc edi ; Sector index inc edx ; Linearly next sector mov eax,edi call linsector ; jc .do_read cmp edx,eax je .getseccnt .do_read: pop eax ; Linear start sector call getlinsecsr push bp shl bp,9 add bx,bp ; Adjust buffer pointer pop bp add [si+file_sector],ebp ; Next sector index sub [si],ebp ; Sectors consumed jz .done jcxz .done jmp .getfragment .done: cmp dword [si],1 ; Did we run out of file? ; CF set if [SI] < 1, i.e. == 0 pop edi pop edx pop eax pop ebp ret ; ----------------------------------------------------------------------------- ; Common modules ; ----------------------------------------------------------------------------- %include "getc.inc" ; getc et al %include "conio.inc" ; Console I/O %include "writestr.inc" ; String output %include "parseconfig.inc" ; High-level config file handling %include "parsecmd.inc" ; Low-level config file handling %include "bcopy32.inc" ; 32-bit bcopy %include "loadhigh.inc" ; Load a file into high memory %include "font.inc" ; VGA font stuff %include "graphics.inc" ; VGA graphics %include "highmem.inc" ; High memory sizing %include "strcpy.inc" ; strcpy() %include "cache.inc" ; ----------------------------------------------------------------------------- ; Begin data section ; ----------------------------------------------------------------------------- section .data copyright_str db ' Copyright (C) 1994-', year, ' H. Peter Anvin' db CR, LF, 0 boot_prompt db 'boot: ', 0 wipe_char db BS, ' ', BS, 0 err_notfound db 'Could not find kernel image: ',0 err_notkernel db CR, LF, 'Invalid or corrupt kernel image.', CR, LF, 0 err_noram db 'It appears your computer has less than ' asciidec dosram_k db 'K of low ("DOS")' db CR, LF db 'RAM. Linux needs at least this amount to boot. If you get' db CR, LF db 'this message in error, hold down the Ctrl key while' db CR, LF db 'booting, and I will take your word for it.', CR, LF, 0 err_badcfg db 'Unknown keyword in extlinux.conf.', CR, LF, 0 err_noparm db 'Missing parameter in extlinux.conf.', CR, LF, 0 err_noinitrd db CR, LF, 'Could not find ramdisk image: ', 0 err_nohighmem db 'Not enough memory to load specified kernel.', CR, LF, 0 err_highload db CR, LF, 'Kernel transfer failure.', CR, LF, 0 err_oldkernel db 'Cannot load a ramdisk with an old kernel image.' db CR, LF, 0 err_notdos db ': attempted DOS system call', CR, LF, 0 err_comlarge db 'COMBOOT image too large.', CR, LF, 0 err_bssimage db 'BSS images not supported.', CR, LF, 0 err_a20 db CR, LF, 'A20 gate not responding!', CR, LF, 0 err_bootfailed db CR, LF, 'Boot failed: please change disks and press ' db 'a key to continue.', CR, LF, 0 ready_msg db 'Ready.', CR, LF, 0 crlfloading_msg db CR, LF loading_msg db 'Loading ', 0 dotdot_msg db '.' dot_msg db '.', 0 aborted_msg db ' aborted.' ; Fall through to crlf_msg! crlf_msg db CR, LF null_msg db 0 crff_msg db CR, FF, 0 ConfigName db 'extlinux.conf',0 ; Unmangled form ; ; 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 ; %include "keywords.inc" ; ; Extensions to search for (in *forward* order). ; align 4, db 0 exten_table: db '.cbt' ; COMBOOT (specific) db '.img' ; Disk image db '.bs', 0 ; Boot sector db '.com' ; COMBOOT (same as DOS) db '.c32' ; COM32 exten_table_end: dd 0, 0 ; Need 8 null bytes here ; ; Misc initialized (data) variables ; %ifdef debug ; This code for debugging only debug_magic dw 0D00Dh ; Debug code sentinel %endif alignb 4, db 0 BufSafe dw trackbufsize/SECTOR_SIZE ; Clusters we can load into trackbuf BufSafeSec dw trackbufsize/SECTOR_SIZE ; = how many sectors? BufSafeBytes dw trackbufsize ; = how many bytes? EndOfGetCBuf dw getcbuf+trackbufsize ; = getcbuf+BufSafeBytes %ifndef DEPEND %if ( trackbufsize % SECTOR_SIZE ) != 0 %error trackbufsize must be a multiple of SECTOR_SIZE %endif %endif