arch/x86_64/boot/setup.S

   1 /*
   2  *      setup.S         Copyright (C) 1991, 1992 Linus Torvalds
   3  *
   4  * setup.s is responsible for getting the system data from the BIOS,
   5  * and putting them into the appropriate places in system memory.
   6  * both setup.s and system has been loaded by the bootblock.
   7  *
   8  * This code asks the bios for memory/disk/other parameters, and
   9  * puts them in a "safe" place: 0x90000-0x901FF, ie where the
  10  * boot-block used to be. It is then up to the protected mode
  11  * system to read them from there before the area is overwritten
  12  * for buffer-blocks.
  13  *
  14  * Move PS/2 aux init code to psaux.c
  15  * (troyer@saifr00.cfsat.Honeywell.COM) 03Oct92
  16  *
  17  * some changes and additional features by Christoph Niemann,
  18  * March 1993/June 1994 (Christoph.Niemann@linux.org)
  19  *
  20  * add APM BIOS checking by Stephen Rothwell, May 1994
  21  * (sfr@canb.auug.org.au)
  22  *
  23  * High load stuff, initrd support and position independency
  24  * by Hans Lermen & Werner Almesberger, February 1996
  25  * <lermen@elserv.ffm.fgan.de>, <almesber@lrc.epfl.ch>
  26  *
  27  * Video handling moved to video.S by Martin Mares, March 1996
  28  * <mj@k332.feld.cvut.cz>
  29  *
  30  * Extended memory detection scheme retwiddled by orc@pell.chi.il.us (david
  31  * parsons) to avoid loadlin confusion, July 1997
  32  *
  33  * Transcribed from Intel (as86) -> AT&T (gas) by Chris Noe, May 1999.
  34  * <stiker@northlink.com>
  35  *
  36  * Fix to work around buggy BIOSes which dont use carry bit correctly
  37  * and/or report extended memory in CX/DX for e801h memory size detection
  38  * call.  As a result the kernel got wrong figures.  The int15/e801h docs
  39  * from Ralf Brown interrupt list seem to indicate AX/BX should be used
  40  * anyway.  So to avoid breaking many machines (presumably there was a reason
  41  * to orginally use CX/DX instead of AX/BX), we do a kludge to see
  42  * if CX/DX have been changed in the e801 call and if so use AX/BX .
  43  * Michael Miller, April 2001 <michaelm@mjmm.org>
  44  *
  45  * Added long mode checking and SSE force. March 2003, Andi Kleen.
  46  */
  47
  48 #include <linux/config.h>
  49 #include <asm/segment.h>
  50 #include <linux/version.h>
  51 #include <linux/compile.h>
  52 #include <asm/boot.h>
  53 #include <asm/e820.h>
  54 #include <asm/page.h>
  55
  56 /* Signature words to ensure LILO loaded us right */
  57 #define SIG1    0xAA55
  58 #define SIG2    0x5A5A
  59
  60 INITSEG  = DEF_INITSEG          # 0x9000, we move boot here, out of the way
  61 SYSSEG   = DEF_SYSSEG           # 0x1000, system loaded at 0x10000 (65536).
  62 SETUPSEG = DEF_SETUPSEG         # 0x9020, this is the current segment
  63                                 # ... and the former contents of CS
  64
  65 DELTA_INITSEG = SETUPSEG - INITSEG      # 0x0020
  66
  67 .code16
  68 .globl begtext, begdata, begbss, endtext, enddata, endbss
  69
  70 .text
  71 begtext:
  72 .data
  73 begdata:
  74 .bss
  75 begbss:
  76 .text
  77
  78 start:
  79         jmp     trampoline
  80
  81 # This is the setup header, and it must start at %cs:2 (old 0x9020:2)
  82
  83                 .ascii  "HdrS"          # header signature
  84                 .word   0x0203          # header version number (>= 0x0105)
  85                                         # or else old loadlin-1.5 will fail)
  86 realmode_swtch: .word   0, 0            # default_switch, SETUPSEG
  87 start_sys_seg:  .word   SYSSEG
  88                 .word   kernel_version  # pointing to kernel version string
  89                                         # above section of header is compatible
  90                                         # with loadlin-1.5 (header v1.5). Don't
  91                                         # change it.
  92
  93 type_of_loader: .byte   0               # = 0, old one (LILO, Loadlin,
  94                                         #      Bootlin, SYSLX, bootsect...)
  95                                         # See Documentation/i386/boot.txt for
  96                                         # assigned ids
  97
  98 # flags, unused bits must be zero (RFU) bit within loadflags
  99 loadflags:
 100 LOADED_HIGH     = 1                     # If set, the kernel is loaded high
 101 CAN_USE_HEAP    = 0x80                  # If set, the loader also has set
 102                                         # heap_end_ptr to tell how much
 103                                         # space behind setup.S can be used for
 104                                         # heap purposes.
 105                                         # Only the loader knows what is free
 106 #ifndef __BIG_KERNEL__
 107                 .byte   0
 108 #else
 109                 .byte   LOADED_HIGH
 110 #endif
 111
 112 setup_move_size: .word  0x8000          # size to move, when setup is not
 113                                         # loaded at 0x90000. We will move setup
 114                                         # to 0x90000 then just before jumping
 115                                         # into the kernel. However, only the
 116                                         # loader knows how much data behind
 117                                         # us also needs to be loaded.
 118
 119 code32_start:                           # here loaders can put a different
 120                                         # start address for 32-bit code.
 121 #ifndef __BIG_KERNEL__
 122                 .long   0x1000          #   0x1000 = default for zImage
 123 #else
 124                 .long   0x100000        # 0x100000 = default for big kernel
 125 #endif
 126
 127 ramdisk_image:  .long   0               # address of loaded ramdisk image
 128                                         # Here the loader puts the 32-bit
 129                                         # address where it loaded the image.
 130                                         # This only will be read by the kernel.
 131
 132 ramdisk_size:   .long   0               # its size in bytes
 133
 134 bootsect_kludge:
 135                 .long   0               # obsolete
 136
 137 heap_end_ptr:   .word   modelist+1024   # (Header version 0x0201 or later)
 138                                         # space from here (exclusive) down to
 139                                         # end of setup code can be used by setup
 140                                         # for local heap purposes.
 141
 142 pad1:           .word   0
 143 cmd_line_ptr:   .long 0                 # (Header version 0x0202 or later)
 144                                         # If nonzero, a 32-bit pointer
 145                                         # to the kernel command line.
 146                                         # The command line should be
 147                                         # located between the start of
 148                                         # setup and the end of low
 149                                         # memory (0xa0000), or it may
 150                                         # get overwritten before it
 151                                         # gets read.  If this field is
 152                                         # used, there is no longer
 153                                         # anything magical about the
 154                                         # 0x90000 segment; the setup
 155                                         # can be located anywhere in
 156                                         # low memory 0x10000 or higher.
 157
 158 ramdisk_max:    .long 0xffffffff
 159
 160 trampoline:     call    start_of_setup
 161                 .align 16
 162                                         # The offset at this point is 0x240
 163                 .space  (0x7ff-0x240+1) # E820 & EDD space (ending at 0x7ff)
 164 # End of setup header #####################################################
 165
 166 start_of_setup:
 167 # Bootlin depends on this being done early
 168         movw    $0x01500, %ax
 169         movb    $0x81, %dl
 170         int     $0x13
 171
 172 #ifdef SAFE_RESET_DISK_CONTROLLER
 173 # Reset the disk controller.
 174         movw    $0x0000, %ax
 175         movb    $0x80, %dl
 176         int     $0x13
 177 #endif
 178
 179 # Set %ds = %cs, we know that SETUPSEG = %cs at this point
 180         movw    %cs, %ax                # aka SETUPSEG
 181         movw    %ax, %ds
 182 # Check signature at end of setup
 183         cmpw    $SIG1, setup_sig1
 184         jne     bad_sig
 185
 186         cmpw    $SIG2, setup_sig2
 187         jne     bad_sig
 188
 189         jmp     good_sig1
 190
 191 # Routine to print asciiz string at ds:si
 192 prtstr:
 193         lodsb
 194         andb    %al, %al
 195         jz      fin
 196
 197         call    prtchr
 198         jmp     prtstr
 199
 200 fin:    ret
 201
 202 # Space printing
 203 prtsp2: call    prtspc          # Print double space
 204 prtspc: movb    $0x20, %al      # Print single space (note: fall-thru)
 205
 206 prtchr:
 207         pushw   %ax
 208         pushw   %cx
 209         movw    $0007,%bx
 210         movw    $0x01, %cx
 211         movb    $0x0e, %ah
 212         int     $0x10
 213         popw    %cx
 214         popw    %ax
 215         ret
 216
 217 beep:   movb    $0x07, %al
 218         jmp     prtchr
 219
 220 no_sig_mess: .string    "No setup signature found ..."
 221
 222 good_sig1:
 223         jmp     good_sig
 224
 225 # We now have to find the rest of the setup code/data
 226 bad_sig:
 227         movw    %cs, %ax                        # SETUPSEG
 228         subw    $DELTA_INITSEG, %ax             # INITSEG
 229         movw    %ax, %ds
 230         xorb    %bh, %bh
 231         movb    (497), %bl                      # get setup sect from bootsect
 232         subw    $4, %bx                         # LILO loads 4 sectors of setup
 233         shlw    $8, %bx                         # convert to words (1sect=2^8 words)
 234         movw    %bx, %cx
 235         shrw    $3, %bx                         # convert to segment
 236         addw    $SYSSEG, %bx
 237         movw    %bx, %cs:start_sys_seg
 238 # Move rest of setup code/data to here
 239         movw    $2048, %di                      # four sectors loaded by LILO
 240         subw    %si, %si
 241         movw    %cs, %ax                        # aka SETUPSEG
 242         movw    %ax, %es
 243         movw    $SYSSEG, %ax
 244         movw    %ax, %ds
 245         rep
 246         movsw
 247         movw    %cs, %ax                        # aka SETUPSEG
 248         movw    %ax, %ds
 249         cmpw    $SIG1, setup_sig1
 250         jne     no_sig
 251
 252         cmpw    $SIG2, setup_sig2
 253         jne     no_sig
 254
 255         jmp     good_sig
 256
 257 no_sig:
 258         lea     no_sig_mess, %si
 259         call    prtstr
 260
 261 no_sig_loop:
 262         jmp     no_sig_loop
 263
 264 good_sig:
 265         movw    %cs, %ax                        # aka SETUPSEG
 266         subw    $DELTA_INITSEG, %ax             # aka INITSEG
 267         movw    %ax, %ds
 268 # Check if an old loader tries to load a big-kernel
 269         testb   $LOADED_HIGH, %cs:loadflags     # Do we have a big kernel?
 270         jz      loader_ok                       # No, no danger for old loaders.
 271
 272         cmpb    $0, %cs:type_of_loader          # Do we have a loader that
 273                                                 # can deal with us?
 274         jnz     loader_ok                       # Yes, continue.
 275
 276         pushw   %cs                             # No, we have an old loader,
 277         popw    %ds                             # die.
 278         lea     loader_panic_mess, %si
 279         call    prtstr
 280
 281         jmp     no_sig_loop
 282
 283 loader_panic_mess: .string "Wrong loader, giving up..."
 284
 285 loader_ok:
 286         /* check for long mode. */
 287         /* we have to do this before the VESA setup, otherwise the user
 288            can't see the error message. */
 289
 290         pushw   %ds
 291         movw    %cs,%ax
 292         movw    %ax,%ds
 293
 294         /* minimum CPUID flags for x86-64 */
 295         /* see http://www.x86-64.org/lists/discuss/msg02971.html */
 296 #define SSE_MASK ((1<<25)|(1<<26))
 297 #define REQUIRED_MASK1 ((1<<0)|(1<<3)|(1<<4)|(1<<5)|(1<<6)|(1<<8)|\
 298                                            (1<<13)|(1<<15)|(1<<24))
 299 #define REQUIRED_MASK2 (1<<29)
 300
 301         pushfl                          /* standard way to check for cpuid */
 302         popl    %eax
 303         movl    %eax,%ebx
 304         xorl    $0x200000,%eax
 305         pushl   %eax
 306         popfl
 307         pushfl
 308         popl    %eax
 309         cmpl    %eax,%ebx
 310         jz      no_longmode             /* cpu has no cpuid */
 311         movl    $0x0,%eax
 312         cpuid
 313         cmpl    $0x1,%eax
 314         jb      no_longmode             /* no cpuid 1 */
 315         xor     %di,%di
 316         cmpl    $0x68747541,%ebx        /* AuthenticAMD */
 317         jnz     noamd
 318         cmpl    $0x69746e65,%edx
 319         jnz     noamd
 320         cmpl    $0x444d4163,%ecx
 321         jnz     noamd
 322         mov     $1,%di                  /* cpu is from AMD */
 323 noamd:
 324         movl    $0x1,%eax
 325         cpuid
 326         andl    $REQUIRED_MASK1,%edx
 327         xorl    $REQUIRED_MASK1,%edx
 328         jnz     no_longmode
 329         movl    $0x80000000,%eax
 330         cpuid
 331         cmpl    $0x80000001,%eax
 332         jb      no_longmode             /* no extended cpuid */
 333         movl    $0x80000001,%eax
 334         cpuid
 335         andl    $REQUIRED_MASK2,%edx
 336         xorl    $REQUIRED_MASK2,%edx
 337         jnz     no_longmode
 338 sse_test:
 339         movl    $1,%eax
 340         cpuid
 341         andl    $SSE_MASK,%edx
 342         cmpl    $SSE_MASK,%edx
 343         je      sse_ok
 344         test    %di,%di
 345         jz      no_longmode     /* only try to force SSE on AMD */
 346         movl    $0xc0010015,%ecx        /* HWCR */
 347         rdmsr
 348         btr     $15,%eax        /* enable SSE */
 349         wrmsr
 350         xor     %di,%di         /* don't loop */
 351         jmp     sse_test        /* try again */
 352 no_longmode:
 353         call    beep
 354         lea     long_mode_panic,%si
 355         call    prtstr
 356 no_longmode_loop:
 357         jmp     no_longmode_loop
 358 long_mode_panic:
 359         .string "Your CPU does not support long mode. Use a 32bit distribution."
 360         .byte 0
 361
 362 sse_ok:
 363         popw    %ds
 364
 365 # tell BIOS we want to go to long mode
 366         movl  $0xec00,%eax      # declare target operating mode
 367         movl  $2,%ebx           # long mode
 368         int $0x15
 369
 370 # Get memory size (extended mem, kB)
 371
 372         xorl    %eax, %eax
 373         movl    %eax, (0x1e0)
 374 #ifndef STANDARD_MEMORY_BIOS_CALL
 375         movb    %al, (E820NR)
 376 # Try three different memory detection schemes.  First, try
 377 # e820h, which lets us assemble a memory map, then try e801h,
 378 # which returns a 32-bit memory size, and finally 88h, which
 379 # returns 0-64m
 380
 381 # method E820H:
 382 # the memory map from hell.  e820h returns memory classified into
 383 # a whole bunch of different types, and allows memory holes and
 384 # everything.  We scan through this memory map and build a list
 385 # of the first 32 memory areas, which we return at [E820MAP].
 386 # This is documented at http://www.teleport.com/~acpi/acpihtml/topic245.htm
 387
 388 #define SMAP  0x534d4150
 389
 390 meme820:
 391         xorl    %ebx, %ebx                      # continuation counter
 392         movw    $E820MAP, %di                   # point into the whitelist
 393                                                 # so we can have the bios
 394                                                 # directly write into it.
 395
 396 jmpe820:
 397         movl    $0x0000e820, %eax               # e820, upper word zeroed
 398         movl    $SMAP, %edx                     # ascii 'SMAP'
 399         movl    $20, %ecx                       # size of the e820rec
 400         pushw   %ds                             # data record.
 401         popw    %es
 402         int     $0x15                           # make the call
 403         jc      bail820                         # fall to e801 if it fails
 404
 405         cmpl    $SMAP, %eax                     # check the return is `SMAP'
 406         jne     bail820                         # fall to e801 if it fails
 407
 408 #       cmpl    $1, 16(%di)                     # is this usable memory?
 409 #       jne     again820
 410
 411         # If this is usable memory, we save it by simply advancing %di by
 412         # sizeof(e820rec).
 413         #
 414 good820:
 415         movb    (E820NR), %al                   # up to 32 entries
 416         cmpb    $E820MAX, %al
 417         jnl     bail820
 418
 419         incb    (E820NR)
 420         movw    %di, %ax
 421         addw    $20, %ax
 422         movw    %ax, %di
 423 again820:
 424         cmpl    $0, %ebx                        # check to see if
 425         jne     jmpe820                         # %ebx is set to EOF
 426 bail820:
 427
 428
 429 # method E801H:
 430 # memory size is in 1k chunksizes, to avoid confusing loadlin.
 431 # we store the 0xe801 memory size in a completely different place,
 432 # because it will most likely be longer than 16 bits.
 433 # (use 1e0 because that's what Larry Augustine uses in his
 434 # alternative new memory detection scheme, and it's sensible
 435 # to write everything into the same place.)
 436
 437 meme801:
 438         stc                                     # fix to work around buggy
 439         xorw    %cx,%cx                         # BIOSes which dont clear/set
 440         xorw    %dx,%dx                         # carry on pass/error of
 441                                                 # e801h memory size call
 442                                                 # or merely pass cx,dx though
 443                                                 # without changing them.
 444         movw    $0xe801, %ax
 445         int     $0x15
 446         jc      mem88
 447
 448         cmpw    $0x0, %cx                       # Kludge to handle BIOSes
 449         jne     e801usecxdx                     # which report their extended
 450         cmpw    $0x0, %dx                       # memory in AX/BX rather than
 451         jne     e801usecxdx                     # CX/DX.  The spec I have read
 452         movw    %ax, %cx                        # seems to indicate AX/BX
 453         movw    %bx, %dx                        # are more reasonable anyway...
 454
 455 e801usecxdx:
 456         andl    $0xffff, %edx                   # clear sign extend
 457         shll    $6, %edx                        # and go from 64k to 1k chunks
 458         movl    %edx, (0x1e0)                   # store extended memory size
 459         andl    $0xffff, %ecx                   # clear sign extend
 460         addl    %ecx, (0x1e0)                   # and add lower memory into
 461                                                 # total size.
 462
 463 # Ye Olde Traditional Methode.  Returns the memory size (up to 16mb or
 464 # 64mb, depending on the bios) in ax.
 465 mem88:
 466
 467 #endif
 468         movb    $0x88, %ah
 469         int     $0x15
 470         movw    %ax, (2)
 471
 472 # Set the keyboard repeat rate to the max
 473         movw    $0x0305, %ax
 474         xorw    %bx, %bx
 475         int     $0x16
 476
 477 # Check for video adapter and its parameters and allow the
 478 # user to browse video modes.
 479         call    video                           # NOTE: we need %ds pointing
 480                                                 # to bootsector
 481
 482 # Get hd0 data...
 483         xorw    %ax, %ax
 484         movw    %ax, %ds
 485         ldsw    (4 * 0x41), %si
 486         movw    %cs, %ax                        # aka SETUPSEG
 487         subw    $DELTA_INITSEG, %ax             # aka INITSEG
 488         pushw   %ax
 489         movw    %ax, %es
 490         movw    $0x0080, %di
 491         movw    $0x10, %cx
 492         pushw   %cx
 493         cld
 494         rep
 495         movsb
 496 # Get hd1 data...
 497         xorw    %ax, %ax
 498         movw    %ax, %ds
 499         ldsw    (4 * 0x46), %si
 500         popw    %cx
 501         popw    %es
 502         movw    $0x0090, %di
 503         rep
 504         movsb
 505 # Check that there IS a hd1 :-)
 506         movw    $0x01500, %ax
 507         movb    $0x81, %dl
 508         int     $0x13
 509         jc      no_disk1
 510
 511         cmpb    $3, %ah
 512         je      is_disk1
 513
 514 no_disk1:
 515         movw    %cs, %ax                        # aka SETUPSEG
 516         subw    $DELTA_INITSEG, %ax             # aka INITSEG
 517         movw    %ax, %es
 518         movw    $0x0090, %di
 519         movw    $0x10, %cx
 520         xorw    %ax, %ax
 521         cld
 522         rep
 523         stosb
 524 is_disk1:
 525
 526 # Check for PS/2 pointing device
 527         movw    %cs, %ax                        # aka SETUPSEG
 528         subw    $DELTA_INITSEG, %ax             # aka INITSEG
 529         movw    %ax, %ds
 530         movw    $0, (0x1ff)                     # default is no pointing device
 531         int     $0x11                           # int 0x11: equipment list
 532         testb   $0x04, %al                      # check if mouse installed
 533         jz      no_psmouse
 534
 535         movw    $0xAA, (0x1ff)                  # device present
 536 no_psmouse:
 537
 538 #include "../../i386/boot/edd.S"
 539
 540 # Now we want to move to protected mode ...
 541         cmpw    $0, %cs:realmode_swtch
 542         jz      rmodeswtch_normal
 543
 544         lcall   *%cs:realmode_swtch
 545
 546         jmp     rmodeswtch_end
 547
 548 rmodeswtch_normal:
 549         pushw   %cs
 550         call    default_switch
 551
 552 rmodeswtch_end:
 553 # we get the code32 start address and modify the below 'jmpi'
 554 # (loader may have changed it)
 555         movl    %cs:code32_start, %eax
 556         movl    %eax, %cs:code32
 557
 558 # Now we move the system to its rightful place ... but we check if we have a
 559 # big-kernel. In that case we *must* not move it ...
 560         testb   $LOADED_HIGH, %cs:loadflags
 561         jz      do_move0                        # .. then we have a normal low
 562                                                 # loaded zImage
 563                                                 # .. or else we have a high
 564                                                 # loaded bzImage
 565         jmp     end_move                        # ... and we skip moving
 566
 567 do_move0:
 568         movw    $0x100, %ax                     # start of destination segment
 569         movw    %cs, %bp                        # aka SETUPSEG
 570         subw    $DELTA_INITSEG, %bp             # aka INITSEG
 571         movw    %cs:start_sys_seg, %bx          # start of source segment
 572         cld
 573 do_move:
 574         movw    %ax, %es                        # destination segment
 575         incb    %ah                             # instead of add ax,#0x100
 576         movw    %bx, %ds                        # source segment
 577         addw    $0x100, %bx
 578         subw    %di, %di
 579         subw    %si, %si
 580         movw    $0x800, %cx
 581         rep
 582         movsw
 583         cmpw    %bp, %bx                        # assume start_sys_seg > 0x200,
 584                                                 # so we will perhaps read one
 585                                                 # page more than needed, but
 586                                                 # never overwrite INITSEG
 587                                                 # because destination is a
 588                                                 # minimum one page below source
 589         jb      do_move
 590
 591 end_move:
 592 # then we load the segment descriptors
 593         movw    %cs, %ax                        # aka SETUPSEG
 594         movw    %ax, %ds
 595
 596 # Check whether we need to be downward compatible with version <=201
 597         cmpl    $0, cmd_line_ptr
 598         jne     end_move_self           # loader uses version >=202 features
 599         cmpb    $0x20, type_of_loader
 600         je      end_move_self           # bootsect loader, we know of it
 601
 602 # Boot loader doesnt support boot protocol version 2.02.
 603 # If we have our code not at 0x90000, we need to move it there now.
 604 # We also then need to move the params behind it (commandline)
 605 # Because we would overwrite the code on the current IP, we move
 606 # it in two steps, jumping high after the first one.
 607         movw    %cs, %ax
 608         cmpw    $SETUPSEG, %ax
 609         je      end_move_self
 610
 611         cli                                     # make sure we really have
 612                                                 # interrupts disabled !
 613                                                 # because after this the stack
 614                                                 # should not be used
 615         subw    $DELTA_INITSEG, %ax             # aka INITSEG
 616         movw    %ss, %dx
 617         cmpw    %ax, %dx
 618         jb      move_self_1
 619
 620         addw    $INITSEG, %dx
 621         subw    %ax, %dx                        # this will go into %ss after
 622                                                 # the move
 623 move_self_1:
 624         movw    %ax, %ds
 625         movw    $INITSEG, %ax                   # real INITSEG
 626         movw    %ax, %es
 627         movw    %cs:setup_move_size, %cx
 628         std                                     # we have to move up, so we use
 629                                                 # direction down because the
 630                                                 # areas may overlap
 631         movw    %cx, %di
 632         decw    %di
 633         movw    %di, %si
 634         subw    $move_self_here+0x200, %cx
 635         rep
 636         movsb
 637         ljmp    $SETUPSEG, $move_self_here
 638
 639 move_self_here:
 640         movw    $move_self_here+0x200, %cx
 641         rep
 642         movsb
 643         movw    $SETUPSEG, %ax
 644         movw    %ax, %ds
 645         movw    %dx, %ss
 646 end_move_self:                                  # now we are at the right place
 647         lidt    idt_48                          # load idt with 0,0
 648         xorl    %eax, %eax                      # Compute gdt_base
 649         movw    %ds, %ax                        # (Convert %ds:gdt to a linear ptr)
 650         shll    $4, %eax
 651         addl    $gdt, %eax
 652         movl    %eax, (gdt_48+2)
 653         lgdt    gdt_48                          # load gdt with whatever is
 654                                                 # appropriate
 655
 656 # that was painless, now we enable a20
 657         call    empty_8042
 658
 659         movb    $0xD1, %al                      # command write
 660         outb    %al, $0x64
 661         call    empty_8042
 662
 663         movb    $0xDF, %al                      # A20 on
 664         outb    %al, $0x60
 665         call    empty_8042
 666
 667 #
 668 #       You must preserve the other bits here. Otherwise embarrasing things
 669 #       like laptops powering off on boot happen. Corrected version by Kira
 670 #       Brown from Linux 2.2
 671 #
 672         inb     $0x92, %al                      #
 673         orb     $02, %al                        # "fast A20" version
 674         outb    %al, $0x92                      # some chips have only this
 675
 676 # wait until a20 really *is* enabled; it can take a fair amount of
 677 # time on certain systems; Toshiba Tecras are known to have this
 678 # problem.  The memory location used here (0x200) is the int 0x80
 679 # vector, which should be safe to use.
 680
 681         xorw    %ax, %ax                        # segment 0x0000
 682         movw    %ax, %fs
 683         decw    %ax                             # segment 0xffff (HMA)
 684         movw    %ax, %gs
 685 a20_wait:
 686         incw    %ax                             # unused memory location <0xfff0
 687         movw    %ax, %fs:(0x200)                # we use the "int 0x80" vector
 688         cmpw    %gs:(0x210), %ax                # and its corresponding HMA addr
 689         je      a20_wait                        # loop until no longer aliased
 690
 691 # make sure any possible coprocessor is properly reset..
 692         xorw    %ax, %ax
 693         outb    %al, $0xf0
 694         call    delay
 695
 696         outb    %al, $0xf1
 697         call    delay
 698
 699 # well, that went ok, I hope. Now we mask all interrupts - the rest
 700 # is done in init_IRQ().
 701         movb    $0xFF, %al                      # mask all interrupts for now
 702         outb    %al, $0xA1
 703         call    delay
 704
 705         movb    $0xFB, %al                      # mask all irq's but irq2 which
 706         outb    %al, $0x21                      # is cascaded
 707
 708 # Well, that certainly wasn't fun :-(. Hopefully it works, and we don't
 709 # need no steenking BIOS anyway (except for the initial loading :-).
 710 # The BIOS-routine wants lots of unnecessary data, and it's less
 711 # "interesting" anyway. This is how REAL programmers do it.
 712 #
 713 # Well, now's the time to actually move into protected mode. To make
 714 # things as simple as possible, we do no register set-up or anything,
 715 # we let the gnu-compiled 32-bit programs do that. We just jump to
 716 # absolute address 0x1000 (or the loader supplied one),
 717 # in 32-bit protected mode.
 718 #
 719 # Note that the short jump isn't strictly needed, although there are
 720 # reasons why it might be a good idea. It won't hurt in any case.
 721         movw    $1, %ax                         # protected mode (PE) bit
 722         lmsw    %ax                             # This is it!
 723         jmp     flush_instr
 724
 725 flush_instr:
 726         xorw    %bx, %bx                        # Flag to indicate a boot
 727         xorl    %esi, %esi                      # Pointer to real-mode code
 728         movw    %cs, %si
 729         subw    $DELTA_INITSEG, %si
 730         shll    $4, %esi                        # Convert to 32-bit pointer
 731 # NOTE: For high loaded big kernels we need a
 732 #       jmpi    0x100000,__KERNEL_CS
 733 #
 734 #       but we yet haven't reloaded the CS register, so the default size
 735 #       of the target offset still is 16 bit.
 736 #       However, using an operant prefix (0x66), the CPU will properly
 737 #       take our 48 bit far pointer. (INTeL 80386 Programmer's Reference
 738 #       Manual, Mixing 16-bit and 32-bit code, page 16-6)
 739
 740         .byte 0x66, 0xea                        # prefix + jmpi-opcode
 741 code32: .long   0x1000                          # will be set to 0x100000
 742                                                 # for big kernels
 743         .word   __KERNEL_CS
 744
 745 # Here's a bunch of information about your current kernel..
 746 kernel_version: .ascii  UTS_RELEASE
 747                 .ascii  " ("
 748                 .ascii  LINUX_COMPILE_BY
 749                 .ascii  "@"
 750                 .ascii  LINUX_COMPILE_HOST
 751                 .ascii  ") "
 752                 .ascii  UTS_VERSION
 753                 .byte   0
 754
 755 # This is the default real mode switch routine.
 756 # to be called just before protected mode transition
 757 default_switch:
 758         cli                                     # no interrupts allowed !
 759         movb    $0x80, %al                      # disable NMI for bootup
 760                                                 # sequence
 761         outb    %al, $0x70
 762         lret
 763
 764
 765 # This routine checks that the keyboard command queue is empty
 766 # (after emptying the output buffers)
 767 #
 768 # Some machines have delusions that the keyboard buffer is always full
 769 # with no keyboard attached...
 770 #
 771 # If there is no keyboard controller, we will usually get 0xff
 772 # to all the reads.  With each IO taking a microsecond and
 773 # a timeout of 100,000 iterations, this can take about half a
 774 # second ("delay" == outb to port 0x80). That should be ok,
 775 # and should also be plenty of time for a real keyboard controller
 776 # to empty.
 777 #
 778
 779 empty_8042:
 780         pushl   %ecx
 781         movl    $100000, %ecx
 782
 783 empty_8042_loop:
 784         decl    %ecx
 785         jz      empty_8042_end_loop
 786
 787         call    delay
 788
 789         inb     $0x64, %al                      # 8042 status port
 790         testb   $1, %al                         # output buffer?
 791         jz      no_output
 792
 793         call    delay
 794         inb     $0x60, %al                      # read it
 795         jmp     empty_8042_loop
 796
 797 no_output:
 798         testb   $2, %al                         # is input buffer full?
 799         jnz     empty_8042_loop                 # yes - loop
 800 empty_8042_end_loop:
 801         popl    %ecx
 802         ret
 803
 804 # Read the cmos clock. Return the seconds in al
 805 gettime:
 806         pushw   %cx
 807         movb    $0x02, %ah
 808         int     $0x1a
 809         movb    %dh, %al                        # %dh contains the seconds
 810         andb    $0x0f, %al
 811         movb    %dh, %ah
 812         movb    $0x04, %cl
 813         shrb    %cl, %ah
 814         aad
 815         popw    %cx
 816         ret
 817
 818 # Delay is needed after doing I/O
 819 delay:
 820         outb    %al,$0x80
 821         ret
 822
 823 # Descriptor tables
 824 gdt:
 825         .word   0, 0, 0, 0                      # dummy
 826
 827         .word   0, 0, 0, 0                      # unused
 828
 829         .word   0xFFFF                          # 4Gb - (0x100000*0x1000 = 4Gb)
 830         .word   0                               # base address = 0
 831         .word   0x9A00                          # code read/exec
 832         .word   0x00CF                          # granularity = 4096, 386
 833                                                 #  (+5th nibble of limit)
 834
 835         .word   0xFFFF                          # 4Gb - (0x100000*0x1000 = 4Gb)
 836         .word   0                               # base address = 0
 837         .word   0x9200                          # data read/write
 838         .word   0x00CF                          # granularity = 4096, 386
 839                                                 #  (+5th nibble of limit)
 840 idt_48:
 841         .word   0                               # idt limit = 0
 842         .word   0, 0                            # idt base = 0L
 843 gdt_48:
 844         .word   0x8000                          # gdt limit=2048,
 845                                                 #  256 GDT entries
 846
 847         .word   0, 0                            # gdt base (filled in later)
 848
 849 # Include video setup & detection code
 850
 851 #include "video.S"
 852
 853 # Setup signature -- must be last
 854 setup_sig1:     .word   SIG1
 855 setup_sig2:     .word   SIG2
 856
 857 # After this point, there is some free space which is used by the video mode
 858 # handling code to store the temporary mode table (not used by the kernel).
 859
 860 modelist:
 861
 862 .text
 863 endtext:
 864 .data
 865 enddata:
 866 .bss
 867 endbss: