compilers/linux86-0.16.17/bootblocks/minix.c

   1 /*
   2  * This bootblock loads the linux-8086 executable in the file 'boot'
   3  * from the root directory of a minix filesystem.
   4  *
   5  * Copyright (C) 1990-1998 Robert de Bath, distributed under the GPL Version 2
   6  * Based on minix filesystem definitions.
   7  *
   8  * TODO:
   9  *       Alter nogood() to do a mov sp,... so the helper program can override
  10  *       the panic message.
  11  */
  12
  13 #include <a.out.h>
  14 #include "minix.h"
  15
  16 /* #define DOTS         /* define to have dots printed */
  17 /* #define HARDDISK     /* Define for hard disk version */
  18 /* #define TRY_FLOPPY   /* To do trial reads to find floppy size */
  19
  20 /* #define MIN_SPACE       */
  21
  22 #define zone_shift 0    /* for any < 32M (!= 0 not supported yet, if ever) */
  23 #define seg_at(k) ((k)*64)
  24 #define seg_of(p) ((unsigned int)p >>4)
  25 #define BOOTSEG   (0x07c0)
  26 #define LOADSEG   (0x1000)
  27 #define ORGADDR   (0x0500)
  28
  29 #ifdef HARDDISK
  30 #define get_now()
  31 #endif
  32
  33 #ifdef zone_shift
  34 #if zone_shift == 0
  35 #define load_zone load_block
  36 #endif
  37 #else
  38 static short     zone_shift;
  39 #endif
  40
  41 #asm
  42 BOOTADDR = 0x7c00
  43
  44 .text
  45 ! Apparently on startup the only things we can assume are that we start at
  46 ! `start` (ABS addr $07C00) and the boot sector is in the segment.
  47
  48 ! So first set CS=DS=ES=SS=0
  49 ! The we move this to $0500 and put the stack at the top of the first 64k.
  50 ! The directory 'file' is loaded $1500 and scanned there.
  51 ! The final executable will be loaded in the 2nd 64k chunk.
  52 !
  53 org ORGADDR     ! The lowest available address.
  54 start:
  55 #ifndef MIN_SPACE
  56   include sysboot.s
  57
  58 org start       ! The lowest available address, again.
  59   j     skip_vars
  60
  61 org dos_sysid
  62   .ascii "MINIXFS BOOT (C) 1990-1999,  Robert de Bath"
  63
  64   org codestart
  65 #endif
  66
  67 ! A few variables we need to know the positions of for patching, so export
  68 ! them and as86_encaps will make some variables. Put them here at the start
  69 ! so they're in the same place for both Floppy and harddisk versions as they
  70 ! will be used by helper programs.
  71
  72 export  inode                   ! Inode to search
  73 inode:
  74 _inode: .word   1               ! ROOT_INODE
  75
  76 #ifndef MIN_SPACE
  77 export  dinode                  ! Inode of directory file was found in.
  78 dinode:
  79 _dinode: .word  1               ! ROOT_INODE
  80 #endif
  81
  82 export  bootfile                ! File to boot, make this whatever you like,
  83 bootfile:                       ! 'boot' is good, 'linux' too.
  84 _bootfile:
  85    .ascii       "boot"
  86    .byte        0,0,0,0,0,0,0,0,0,0
  87
  88 skip_vars:
  89 #ifdef HARDDISK
  90   mov   bx,[si+8]       ! Fetch the linear address of part from DS:SI
  91   mov   dh,[si+10]      ! DL is drive number
  92 #endif
  93
  94   xor   ax,ax           ! All segments are zero, first 64k of mem.
  95   mov   ds,ax
  96   mov   es,ax
  97   mov   ss,ax
  98   mov   sp,ax
  99
 100 #ifndef HARDDISK
 101 loopy:
 102   mov   ax,#$0203               ! Read 3 sectors, code + superblock.
 103   mov   bx,#start               ! Where this _should_ be
 104   mov   cx,#$0001               ! From sector 1
 105   xor   dx,dx                   ! Of the floppy drive head zero
 106   int   $13
 107   jc    loopy
 108 #else
 109
 110   mov   cx,#$100        ! Move 256 words
 111   mov   si,#BOOTADDR    ! From default BB
 112   mov   di,#ORGADDR     ! To the correct address.
 113   rep
 114    movsw
 115
 116   xchg  dl,dh
 117   mov   [bootpart],bx   ! Save the partition sector offset (and drive)
 118   mov   [bootpart+2],dx
 119
 120   ! Read next 2 sectors of hd.
 121   xor   dx,dx
 122   mov   cx,#1
 123   mov   bx,#ORGADDR+$200
 124   mov   al,#2
 125
 126   call  load_sect
 127 #endif
 128
 129   jmpi  code,#0
 130
 131 #endasm
 132
 133 /* \f/* */
 134 /****************************************************************************/
 135 /* Section cdef */
 136 /****************************************************************************/
 137
 138 /* The name of the file and inode to start */
 139 extern char bootfile[];
 140 extern inode_nr inode;
 141 extern inode_nr dinode;
 142
 143 /* For multi-sector reads */
 144 extern sect_nr lastsect;
 145 extern sect_nr firstsect;
 146 extern unsigned loadaddr;
 147 extern unsigned loadcount;
 148
 149 /* Keep track of zones to load */
 150 extern zone_nr * next_zone;
 151 extern zone_nr * end_zone;
 152 extern zone_nr   indirect;
 153
 154 /* Where to load zones */
 155 extern unsigned ldaddr;
 156
 157 /* Directory reading */
 158 extern dir_struct * dirptr;
 159 extern unsigned flength;
 160 extern unsigned dir_32;
 161
 162 #ifndef HARDDISK
 163 /* The 'shape' of the floppy - intuit from superblock or try to read max */
 164 extern unsigned n_sectors;
 165 #endif
 166
 167 extern struct super_block b_super;
 168 extern d_inode            b_inode[INODES_PER_BLOCK];
 169 extern zone_nr            b_zone[NR_INDIRECTS];
 170 extern dir_struct         directory[];
 171
 172 /* \f/* */
 173 /****************************************************************************/
 174 /* Section adef */
 175 /****************************************************************************/
 176
 177 #asm
 178 .text
 179
 180 #ifdef HARDDISK
 181 bootpart:   .long       0
 182 #else
 183 _loadcount: .word       0
 184 _firstsect: .word       0
 185 _loadaddr:  .word       0
 186 _lastsect:  .word       0
 187 #endif
 188
 189   block start+0x400
 190 _b_super:       .blkb 512
 191
 192 #ifndef MIN_SPACE
 193 export helper
 194 helper:         .blkb 1024
 195 export helper_end
 196 helper_end:
 197 #endif
 198
 199 _b_inode:       .blkb 1024
 200 _b_zone:        .blkb 1024
 201
 202 #ifdef MIN_SPACE
 203 temp_space:     .blkb 512
 204 #endif
 205 probe_buf:
 206 _directory:     .blkb 32768
 207   endb
 208
 209 #endasm
 210
 211 /* \f/* */
 212 /****************************************************************************/
 213 /* Section nogood */
 214 /****************************************************************************/
 215 /* #if defined(HARDDISK) && !defined(SKIPBOOT) */
 216 #ifndef SKIPBOOT
 217 static
 218 nogood()
 219 {
 220 #asm
 221   mov   si,#fail_fs
 222 min_nextc:
 223   lodsb
 224   cmp   al,#0
 225   jz    min_eos
 226   mov   bx,#7
 227   mov   ah,#$E          ! Can't use $13 cause that's AT+ only!
 228   int   $10
 229   jmp   min_nextc
 230 min_eos:                ! Wait for a key then reboot
 231   xor   ax,ax
 232   int   $16
 233   jmpi  $0,$FFFF        ! Reboot.
 234
 235 fail_fs:
 236   .byte         13,10
 237 #if defined(HARDDISK)
 238   .asciz        "Initial boot failed, press return to reboot\r\n"
 239 #else
 240   .asciz        "Boot failed:"
 241 #endif
 242 #endasm
 243 }
 244
 245 #else
 246
 247 static
 248 nogood()
 249 {
 250 /* This didn't work, chain the boot sector of the HD */
 251 #asm
 252   push  cs
 253   pop   es
 254 hcode:
 255   mov   ax,#$0201               ! Read 1 sector
 256   mov   bx,#BOOTADDR            ! In the boot area
 257   mov   cx,#$0001               ! From sector 1
 258   mov   dx,#$0080               ! Of the hard drive head zero
 259   int   $13
 260   jc    hcode                   ! Keep trying forever!
 261   jmpi  BOOTADDR,0
 262 #endasm
 263 }
 264 #endif
 265
 266 /* \f/* */
 267 /****************************************************************************/
 268 /* Section hd_sect */
 269 /****************************************************************************/
 270 #ifdef HARDDISK
 271 #asm
 272 !
 273 ! Load AL sectors from linear sector DX:CX into location ES:BX
 274 ! Linear sector zero is at [bootpart]
 275 ! This loads one sector at a time, but that's OK cause even in the _very_
 276 ! worst case it'll take no more that 5 seconds to load a 16 bit executable.
 277 !
 278 load_sect:
 279   add   cx,[bootpart]
 280   adc   dx,[bootpart+2]
 281 moresect:
 282   cmp   al,#0
 283   jnz   onesect
 284   clc
 285   ret
 286
 287 ! Load one sector...
 288 onesect:
 289   push  ax      ! Save lots
 290   push  di
 291   push  si
 292   push  cx      ! Drive and sector.
 293   push  dx
 294
 295   push  es      ! Load location
 296   push  bx
 297
 298   push  cx      ! Drive and sector again.
 299   push  dx
 300
 301   ! Fetch drive 'shape'
 302   mov   ah,#8
 303   mov   dl,dh
 304   int   $13     ! DX:CX = drive specification
 305   jc    _nogood
 306
 307   and   cx,#$3F ! Get sector count => DI
 308   mov   di,cx
 309
 310   xor   dl,dl   ! Get head count  => SI
 311   xchg  dl,dh
 312   inc   dx
 313   mov   si,dx
 314
 315   pop   dx      ! Get back drive and sector
 316   pop   ax
 317
 318   mov   bl,dh   ! Save drive
 319   xor   dh,dh
 320
 321   div   di      ! DX=sector, AX=track number
 322   mov   cx,dx
 323   inc   cl      ! CL=sector number
 324
 325   xor   dx,dx
 326   div   si      ! DX=head, AX=cylinder
 327
 328   mov   dh,dl
 329   mov   dl,bl   ! DX for int 1302
 330
 331   xchg  al,ah
 332   ror   al,#1
 333   ror   al,#1
 334   or    cx,ax   ! CX for int 1302
 335
 336   pop   bx      ! ES:BX for int 1302
 337   pop   es
 338
 339   mov   di,#5   ! Lots of retries for a hd
 340 retry:
 341   mov   ax,#$0201
 342   int   $13
 343   jnc   got_hd_sect
 344
 345   xor   ax,ax   ! Reset between each try.
 346   int   $13
 347
 348   dec   di
 349   jnz   retry
 350   br    _nogood
 351
 352 got_hd_sect:
 353   pop   dx
 354   pop   cx
 355   pop   si
 356   pop   di
 357   pop   ax
 358
 359   dec   al
 360   add   cx,#1
 361   adc   dh,#0
 362   add   bh,#2
 363   jmp   moresect
 364 #endasm
 365 #endif
 366
 367 /****************************************************************************/
 368 /* This is the end of the parts that MUST be in the first sector            */
 369 /* From here down the functions can safely be in any order.                 */
 370 /****************************************************************************/
 371
 372 /* \f/* */
 373 /****************************************************************************/
 374 /* Section fd_block */
 375 /****************************************************************************/
 376 #ifndef HARDDISK
 377 static
 378 load_block(address, blkno)
 379 unsigned address, blkno;
 380 {
 381    register sect_nr sectno;
 382    if(blkno == 0) { zero_block(address); return; }
 383 #ifdef DOTS
 384    prt_dot();
 385 #endif
 386
 387    sectno = (sect_nr)blkno * 2;
 388    load_sect(address,    sectno);
 389    load_sect(address+32, sectno+1);
 390 }
 391 #endif
 392
 393 /****************************************************************************/
 394 /* Section fd_bpb */
 395 /****************************************************************************/
 396 #ifndef HARDDISK
 397 #asm
 398 _set_bpb:
 399 #ifdef MIN_SPACE
 400 bios_tabl=temp_space            ! Temp space.
 401 bios_disk=temp_space+4          !
 402 #else
 403 bios_tabl=dosfs_stat            ! Temp space.
 404 bios_disk=dosfs_stat+4          !
 405 #endif
 406
 407 #ifndef __CALLER_SAVES__
 408   push  si
 409   push  di
 410 #endif
 411
 412   mov   di,#bios_disk
 413   mov   bx,#0x78
 414 ! 0:bx is parameter table address
 415
 416   push  ds
 417   push  di
 418
 419   mov   si,[bx]
 420   mov   ax,[bx+2]
 421   mov   [bios_tabl],si
 422   mov   [bios_tabl+2],ax
 423   push  ax
 424
 425   pop   ds
 426 ! ds:si is source
 427
 428 ! copy 12 bytes
 429   mov   cl,#6
 430   cld
 431   rep
 432   movsw
 433
 434   pop   di
 435   pop   ds
 436   mov   ax,[_n_sectors]
 437   movb  4[di],al                ! patch sector count
 438
 439   mov   [bx],di
 440   mov   2[bx],es
 441
 442 #ifndef __CALLER_SAVES__
 443   pop   si
 444   pop   di
 445 #endif
 446   ret
 447
 448 _unset_bpb:
 449 ! 0:0x78 is parameter table address
 450
 451   mov   ax,[bios_tabl]
 452   mov   [0x78],ax
 453   mov   ax,[bios_tabl+2]
 454   mov   [0x78+2],ax
 455   ret
 456
 457 #endasm
 458 #endif
 459
 460 /****************************************************************************/
 461 /* Section fd_get_now */
 462 /****************************************************************************/
 463 #ifndef HARDDISK
 464 static
 465 get_now()
 466 {
 467 #asm
 468   mov   si,#5
 469 retry_get:
 470   xor   dx,dx
 471   mov   cx,[_firstsect]
 472   shr   ch,#1
 473   adc   dh,#0
 474   mov   es,[_loadaddr]
 475   xor   bx,bx
 476   mov   ax,[_loadcount]
 477   test  ax,ax
 478   jz    no_load
 479   mov   ah,#2
 480   int   $13             ! Try fetch
 481   jnc   no_load
 482   xor   ax,ax           ! Bad, retry.
 483   int   $13
 484   dec   si
 485   jnz   retry_get
 486   br    _nogood
 487 no_load:
 488   xor   ax,ax
 489   mov   [_loadcount],ax
 490 #endasm
 491 }
 492 #endif
 493
 494 /****************************************************************************/
 495 /* Section fd_probe */
 496 /****************************************************************************/
 497 #ifndef HARDDISK
 498 #ifdef TRY_FLOPPY
 499 #asm
 500 !-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
 501 !
 502 ! These are the number of sectors per track that will be scanned for.
 503 ! For 3.5 inch floppies 36 is 2.88 Mb, 18 is 1.44Mb, 21 is 1.68Mb on
 504 ! a 1.44Mb floppy drive. 15 and 9 are for 5.25 inch floppies.
 505
 506 disksizes: .byte 36,21,18,15,9
 507
 508 ! It seems that there is no BIOS call to get the number of sectors.  Guess
 509 ! 36 sectors if sector 36 can be read, 18 sectors if sector 18 can be read,
 510 ! 15 if sector 15 can be read.  Otherwise guess 9.
 511
 512 _probe_sectors:
 513         mov     si,#disksizes           ! table of sizes to try
 514
 515 probe_loop:
 516         lodsb
 517         cbw                             ! extend to word
 518         mov     _n_sectors, ax
 519         cmp     al,#9
 520         je      got_sectors             ! if all else fails, try 9
 521         xchg    ax, cx                  ! cx = track and sector
 522         xor     dx, dx                  ! drive 0, head 0
 523         mov     bx,#probe_buf           ! address after setup (es = cs)
 524         mov     ax,#0x0201              ! service 2, 1 sector
 525         int     0x13
 526         jc      probe_loop              ! try next value
 527 got_sectors:
 528
 529         ret
 530 #endasm
 531 #else
 532 probe_sectors()
 533 {
 534    /* Guess the number of sectors based on the size of the file system */
 535    if( (n_sectors = b_super.s_nzones / 40) > 11 ) n_sectors /= 2;
 536 }
 537 #endif
 538 #endif
 539
 540 /****************************************************************************/
 541 /* Section fd_sect */
 542 /****************************************************************************/
 543 #ifndef HARDDISK
 544 static
 545 load_sect(address, sectno)
 546 unsigned address;
 547 sect_nr sectno;
 548 {
 549    register sect_nr nsect;
 550
 551    nsect   =  sectno%n_sectors +1;
 552    sectno /= n_sectors;
 553    nsect  |= (sectno<<8);
 554
 555    if( loadcount )
 556    {
 557       lastsect++;
 558       if( ( address & 4095 ) && nsect == lastsect )
 559       {
 560          loadcount++;
 561          return;
 562       }
 563       get_now();
 564    }
 565
 566    lastsect  = firstsect = nsect;
 567    loadaddr  = address;
 568    loadcount = 1;
 569 }
 570 #endif
 571
 572 /****************************************************************************/
 573 /* Section fd_zeroblk */
 574 /****************************************************************************/
 575 #ifndef HARDDISK
 576 static
 577 zero_block(address)
 578 {
 579 #asm
 580 #if __FIRST_ARG_IN_AX__
 581   mov   es,ax
 582 #else
 583   mov   bx,sp
 584   mov   es,[bx+2]
 585 #endif
 586   push  di
 587   mov   cx,#512
 588   xor   ax,ax
 589   mov   di,ax
 590   rep
 591    stosw
 592   pop   di
 593 #endasm
 594 }
 595 #endif
 596
 597 /****************************************************************************/
 598 /* Section hd_block */
 599 /****************************************************************************/
 600 #ifdef HARDDISK
 601 /*----------------------------------*/
 602 /* Hard disk block driver           */
 603 /*----------------------------------*/
 604
 605 #asm
 606 _load_block:
 607   push  bp
 608   mov   bp,sp
 609 #if __FIRST_ARG_IN_AX__
 610   ! Fetch load location
 611   mov   es,ax
 612
 613   ! Test for block zero
 614   mov   ax,4[bp]
 615 #else
 616   ! Fetch load location
 617   mov   ax,[bp+4]
 618   mov   es,ax
 619
 620   ! Test for block zero
 621   mov   ax,6[bp]
 622 #endif
 623   test  ax,ax
 624   jne   real_block
 625
 626   ! Iff block zero, zap memory
 627   push  di
 628   mov   cx,#512
 629   xor   ax,ax
 630   mov   di,ax
 631   rep
 632    stosw
 633   pop   di
 634
 635 func_exit:
 636   mov   sp,bp
 637   pop   bp
 638   ret
 639
 640 real_block:
 641 #ifdef DOTS
 642   push  ax
 643   call  _prt_dot
 644   pop   ax
 645 #endif
 646
 647 ! Load a real block.
 648   mov   cx,ax
 649   xor   dx,dx
 650   shl   cx,#1
 651   rcl   dx,#1
 652
 653   xor   bx,bx
 654   mov   al,#2
 655   call  load_sect
 656
 657   j     func_exit
 658 #endasm
 659 #endif
 660
 661 /****************************************************************************/
 662 /* Section main */
 663 /****************************************************************************/
 664 #asm
 665 code:
 666   call  _loadprog
 667   call  _runprog
 668   br    _nogood
 669
 670 #endasm
 671
 672 /****************************************************************************/
 673 /* Section prt_dots */
 674 /****************************************************************************/
 675 #ifdef DOTS
 676 #asm
 677 _prt_crlf:
 678   mov   al,#13
 679   call  outch
 680   mov   al,#10
 681   j     outch
 682 _prt_dot:
 683   mov   al,#'.
 684 outch:
 685   mov   ah,#$0E
 686   mov   bx,#7
 687   int   $10
 688   ret
 689 #endasm
 690 #endif
 691
 692 /****************************************************************************/
 693 /* Section end_1 */
 694 /****************************************************************************/
 695 #if defined(HARDDISK) || !defined(MIN_SPACE)
 696 #asm
 697 end_of_part1:
 698 #ifdef HARDDISK
 699   if *>start+0x1FE      ! Leave space for magic
 700 #else
 701   if *>start+0x200
 702 #endif
 703      fail! Part 1 too large!
 704   endif
 705   .blkb 0x200+start-*
 706 #endasm
 707 #endif
 708
 709 /****************************************************************************/
 710 /* Section prog_load */
 711 /****************************************************************************/
 712
 713 loadprog()
 714 {
 715 #ifdef DOTS
 716    prt_dot();
 717 #endif
 718    if( b_super.s_magic == SUPER_MAGIC2 )
 719       dir_32 = 1;
 720    else if( b_super.s_magic == SUPER_MAGIC )
 721       dir_32 = 0;
 722    else
 723       nogood();
 724
 725 #ifdef zone_shift
 726    if( zone_shift != b_super.s_log_zone_size) nogood();
 727 #else
 728    zone_shift = b_super.s_log_zone_size;
 729 #endif
 730
 731 #ifndef HARDDISK
 732    probe_sectors();
 733
 734    /* if( (n_sectors = b_super.s_nzones / 40) > 11 ) n_sectors /= 2; */
 735
 736    set_bpb();
 737 #endif
 738
 739 try_again:;
 740    inode--;
 741    load_block(seg_of(b_inode), inode/INODES_PER_BLOCK
 742                           + b_super.s_imap_blocks
 743                           + b_super.s_zmap_blocks
 744                           + 2);
 745    get_now();
 746
 747    ldaddr = LOADSEG;            /* Load at 64k mark */
 748
 749    {
 750       register d_inode * i_ptr;
 751       i_ptr = b_inode + inode%INODES_PER_BLOCK;
 752       next_zone = i_ptr->i_zone;
 753       flength   = i_ptr->i_size;
 754       if( (i_ptr->i_mode & I_TYPE) == I_DIRECTORY )
 755       {
 756          ldaddr = seg_of(directory);
 757 #ifndef MIN_SPACE
 758          dinode  = inode+1;     /* Remember current directory */
 759 #endif
 760          inode  = 0;            /* Mark - we've no _file_ inode yet */
 761       }
 762    }
 763
 764    end_zone = next_zone+NR_DZONE_NUM;
 765    load_zone(seg_of(b_zone), (indirect = next_zone[NR_DZONE_NUM]));
 766    get_now();
 767
 768    for(;;)
 769    {
 770       if( next_zone >= end_zone )
 771       {
 772          if( indirect != 0 )
 773          {
 774             next_zone = b_zone;
 775             end_zone  = next_zone + NR_INDIRECTS;
 776             indirect  = 0;
 777             continue;
 778          }
 779          break;
 780       }
 781       load_zone(ldaddr, *next_zone);
 782       next_zone++;
 783       ldaddr += (seg_at(1) << zone_shift);
 784    }
 785    get_now();
 786
 787 #ifdef DOTS
 788    prt_crlf();
 789 #endif
 790    if(!inode)
 791    {
 792       dirptr = directory;
 793       while(flength > 0)
 794       {
 795 register char * s = bootfile;
 796 register char * p = dirptr->d_name;
 797
 798          if( dirptr->d_inum )
 799          {
 800             for(;;)
 801             {
 802                if( *s == '\0')
 803                {
 804                   if(*p == '\0')
 805                   {
 806                      inode = dirptr->d_inum;
 807                      goto try_again;
 808                   }
 809                   break;
 810                }
 811                if( *s++ != *p++ ) break;
 812             }
 813          }
 814          flength -= 16;
 815          dirptr++;
 816          if( dir_32 )
 817          {
 818             flength -= 16;
 819             dirptr++;
 820          }
 821       }
 822       nogood();
 823    }
 824 #ifndef HARDDISK
 825    unset_bpb();
 826 #endif
 827 }
 828
 829 /****************************************************************************/
 830 /* Section prog_run */
 831 /****************************************************************************/
 832 static
 833 runprog()
 834 {
 835 /* It all worked, run the loaded executable */
 836 #asm
 837 #ifdef HARDDISK
 838   mov   dx,[bootpart+2]
 839   xchg  dh,dl           ! DX => hard drive
 840   push  [bootpart]      ! CX => partition offset
 841   xor   si,si
 842 #else
 843   xor   dx,dx           ! DX=0 => floppy drive
 844   push  dx              ! CX=0 => partition offset = 0
 845   mov   si,[_n_sectors] ! Save for monitor.out
 846 #endif
 847
 848   mov   bx,#LOADSEG
 849   mov   ds,bx           ! DS = loadaddress
 850   xor   di,di           ! Zero
 851   mov   ax,[di]
 852   cmp   ax,#0x0301      ! Right magic ?
 853   jnz   binfile         ! Yuk ... assume .SYS
 854   inc   bx
 855   inc   bx              ! bx = initial CS
 856   mov   ax,[di+2]
 857   and   ax,#$20         ! Is it split I/D ?
 858   jz    impure          ! No ...
 859   mov   cl,#4
 860   mov   ax,[di+8]
 861   shr   ax,cl
 862 impure:
 863   pop   cx
 864   add   ax,bx
 865   mov   ss,ax
 866   mov   sp,[di+24]      ! Chmem value
 867   mov   ds,ax
 868 binfile:
 869
 870   push  bx
 871   push  di              !  jmpi 0,#LOADSEG+2
 872   retf
 873 #endasm
 874 }
 875
 876 /****************************************************************************/
 877 /* Section sys_libs */
 878 /****************************************************************************/
 879 #asm
 880 ! These functions are pulled from the C library.
 881 libstuff:
 882 imodu:
 883         xor     dx,dx
 884         div     bx
 885         mov     ax,dx           ! instruction queue full so xchg slower
 886         ret
 887 idiv_u:
 888         xor     dx,dx
 889         div     bx
 890         ret
 891 #ifndef zone_shift
 892 isl:
 893 islu:
 894         mov     cl,bl
 895         shl     ax,cl
 896         ret
 897 #endif
 898 libend:
 899 #endasm
 900
 901 /****************************************************************************/
 902 /* Section sys_vars */
 903 /****************************************************************************/
 904 #asm
 905 #ifdef MIN_SPACE
 906   block temp_space+64
 907 #endif
 908 vars:
 909 #ifndef HARDDISK
 910 _n_sectors:     .blkw 1
 911 #endif
 912 _next_zone:     .blkw 1
 913 _end_zone:      .blkw 1
 914 _indirect:      .blkw 1
 915 _ldaddr:        .blkw 1
 916 _dirptr:        .blkw 1
 917 _flength:       .blkw 1
 918 _dir_32:        .blkw 1
 919 varend:
 920 #ifdef MIN_SPACE
 921   endb
 922 #endif
 923 #endasm
 924
 925 /****************************************************************************/
 926 /* Section end_2 */
 927 /****************************************************************************/
 928 #asm
 929 end_of_prog:
 930   if *>start+0x400
 931      fail! Part 2 too large!
 932   endif
 933
 934   if end_of_prog<start+0x201
 935   .blkb 0x400+start-*
 936   else
 937   .blkb 0x3FF+start-*
 938   .byte 0xFF
 939   endif
 940
 941 #endasm
 942
 943 /****************************************************************************/