1 ;; -----------------------------------------------------------------------
3 ;; Copyright 1994-2007 H. Peter Anvin - All Rights Reserved
5 ;; This program is free software; you can redistribute it and/or modify
6 ;; it under the terms of the GNU General Public License as published by
7 ;; the Free Software Foundation, Inc., 53 Temple Place Ste 330,
8 ;; Boston MA 02111-1307, USA; either version 2 of the License, or
9 ;; (at your option) any later version; incorporated herein by reference.
11 ;; -----------------------------------------------------------------------
16 ;; 32-bit bcopy routine for real mode
20 ; 32-bit bcopy routine for real mode
22 ; We enter protected mode, set up a flat 32-bit environment, run rep movsd
23 ; and then exit. IMPORTANT: This code assumes cs == 0.
25 ; This code is probably excessively anal-retentive in its handling of
26 ; segments, but this stuff is painful enough as it is without having to rely
27 ; on everything happening "as it ought to."
29 ; NOTE: this code is relocated into low memory, just after the .earlybss
30 ; segment, in order to support to "bcopy over self" operation.
37 ; This is in the .text segment since it needs to be
38 ; contiguous with the rest of the bcopy stuff
40 ; GDT descriptor entry
43 PM_%1 equ bcopy_gdt.%1-bcopy_gdt
47 dw bcopy_gdt_size-1 ; Null descriptor - contains GDT
48 dd bcopy_gdt ; pointer for LGDT instruction
52 dd 0000ffffh ; 08h Code segment, use16, readable,
53 dd 00009b00h ; present, dpl 0, cover 64K
55 dd 0000ffffh ; 10h Data segment, use16, read/write,
56 dd 008f9300h ; present, dpl 0, cover all 4G
58 dd 0000ffffh ; 18h Data segment, use16, read/write,
59 dd 00009300h ; present, dpl 0, cover 64K
60 ; The next two segments are used for COM32 only
62 dd 0000ffffh ; 20h Code segment, use32, readable,
63 dd 00cf9b00h ; present, dpl 0, cover all 4G
65 dd 0000ffffh ; 28h Data segment, use32, read/write,
66 dd 00cf9300h ; present, dpl 0, cover all 4G
68 ; TSS segment to keep Intel VT happy. Intel VT is
69 ; unhappy about anything that doesn't smell like a
70 ; full-blown 32-bit OS.
72 dw 104-1, DummyTSS ; 30h 32-bit task state segment
73 dd 00008900h ; present, dpl 0, 104 bytes @DummyTSS
74 bcopy_gdt_size: equ $-bcopy_gdt
78 ; 32-bit copy, overlap safe
81 ; ESI - source pointer (-1 means do bzero rather than bcopy)
82 ; EDI - target pointer
87 ; ESI - first byte after source (garbage if ESI == -1 on entry)
88 ; EDI - first byte after target
96 pushf ; Saves, among others, the IF flag
105 mov byte [bcopy_gdt.TSS+5],89h ; Mark TSS unbusy
107 mov bx,ss ; Save the stack segment value!
109 o32 lgdt [cs:bcopy_gdt]
112 mov cr0,eax ; Enter protected mode
115 .in_pm: mov ax,PM_DS16_4G ; Data segment selector
119 ; Set ss, fs, and gs, in case we're on a virtual machine
120 ; running on Intel VT hardware -- it can't deal with a
121 ; partial transition, for no good reason. However,
122 ; ss is NOT zero in general, so we have to preserve
125 mov al,PM_DS16_RM ; Real-mode-like segment
130 mov al,PM_TSS ; Intel VT really doesn't want
131 ltr ax ; an invalid TR and LDTR, so give
132 xor ax,ax ; it something that it can use...
138 cmp esi,edi ; If source > destination, we might
139 ja .reverse ; have to copy backwards
142 mov al,cl ; Save low bits
144 shr ecx,2 ; Convert to dwords
145 a32 rep movsd ; Do our business
146 ; At this point ecx == 0
148 mov cl,al ; Copy any fractional dword
154 lea esi,[esi+ecx-1] ; Point to final byte
161 ; Change ESI/EDI to point to the last dword, instead
173 mov si,cx ; Save low bits
178 mov cx,si ; Write fractional dword
183 mov ax,PM_DS16_RM ; "Real-mode-like" data segment
189 mov cr0,eax ; Disable protected mode
192 .in_rm: ; Back in real mode
200 popf ; Re-enables interrupts
211 ; Routines to enable and disable (yuck) A20. These routines are gathered
212 ; from tips from a couple of sources, including the Linux kernel and
213 ; http://www.x86.org/. The need for the delay to be as large as given here
214 ; is indicated by Donnie Barnes of RedHat, the problematic system being an
215 ; IBM ThinkPad 760EL.
217 ; We typically toggle A20 twice for every 64K transferred.
219 %define io_delay call _io_delay
220 %define IO_DELAY_PORT 80h ; Invalid port (we hope!)
221 %define disable_wait 32 ; How long to wait for a disable
223 ; Note the skip of 2 here
224 %define A20_DUNNO 0 ; A20 type unknown
225 %define A20_NONE 2 ; A20 always on?
226 %define A20_BIOS 4 ; A20 BIOS enable
227 %define A20_KBC 6 ; A20 through KBC
228 %define A20_FAST 8 ; A20 through port 92h
230 slow_out: out dx, al ; Fall through
232 _io_delay: out IO_DELAY_PORT,al
238 mov byte [cs:A20Tries],255 ; Times to try to make this work
249 ; If the A20 type is known, jump straight to type
252 jmp word [cs:bp+A20List]
255 ; First, see if we are on a system with no A20 gate
259 mov byte [cs:A20Type], A20_NONE
264 ; Next, try the BIOS (INT 15h AX=2401h)
267 mov byte [cs:A20Type], A20_BIOS
269 pushf ; Some BIOSes muck with IF
277 ; Enable the keyboard controller A20 gate
280 mov dl, 1 ; Allow early exit
282 jnz a20_done ; A20 live, no need to use KBC
284 mov byte [cs:A20Type], A20_KBC ; Starting KBC command sequence
286 mov al,0D1h ; Command write
288 call empty_8042_uncond
292 call empty_8042_uncond
294 ; Verify that A20 actually is enabled. Do that by
295 ; observing a word in low memory and the same word in
296 ; the HMA until they are no longer coherent. Note that
297 ; we don't do the same check in the disable case, because
298 ; we don't want to *require* A20 masking (SYSLINUX should
299 ; work fine without it, if the BIOS does.)
309 ; Running out of options here. Final attempt: enable the "fast A20 gate"
312 mov byte [cs:A20Type], A20_FAST ; Haven't used the KBC yet
315 and al,~01h ; Don't accidentally reset the machine!
328 ; Oh bugger. A20 is not responding. Try frobbing it again; eventually give up
329 ; and report failure to the user.
333 dec byte [cs:A20Tries]
340 err_a20 db CR, LF, 'A20 gate not responding!', CR, LF, 0
344 ; A20 unmasked, proceed...
351 ; This routine tests if A20 is enabled (ZF = 0). This routine
352 ; must not destroy any register contents.
358 mov cx,0FFFFh ; HMA = segment 0FFFFh
360 mov cx,32 ; Loop count
364 io_delay ; Serialize, and fix delay
365 cmp ax,[es:A20Test+10h]
382 jmp word [cs:bp+A20DList]
386 pushf ; Some BIOSes muck with IF
389 jmp short a20d_snooze
392 ; Disable the "fast A20 gate"
398 jmp short a20d_snooze
401 ; Disable the keyboard controller A20 gate
404 call empty_8042_uncond
406 out 064h, al ; Command write
407 call empty_8042_uncond
408 mov al,0DDh ; A20 off
410 call empty_8042_uncond
411 ; Wait a bit for it to take effect
415 .delayloop: call a20_test
425 ; Routine to empty the 8042 KBC controller. If dl != 0
426 ; then we will test A20 in the loop and exit if A20 is
437 in al, 064h ; Status port
441 in al, 060h ; Read input
450 ; Execute a WBINVD instruction if possible on this CPU
461 ; This routine is used to shuffle memory around, followed by
462 ; invoking an entry point somewhere in low memory. This routine
463 ; can clobber any memory above 7C00h, we therefore have to move
464 ; necessary code into the trackbuf area before doing the copy,
465 ; and do adjustments to anything except BSS area references.
467 ; NOTE: Since PXELINUX relocates itself, put all these
468 ; references in the ".earlybss" segment.
470 ; After performing the copy, this routine resets the stack and
471 ; jumps to the specified entrypoint.
473 ; IMPORTANT: This routine does not canonicalize the stack or the
474 ; SS register. That is the responsibility of the caller.
477 ; DS:BX -> Pointer to list of (dst, src, len) pairs(*)
478 ; AX -> Number of list entries
479 ; [CS:EntryPoint] -> CS:IP to jump to
480 ; On stack - initial state (fd, ad, ds, es, fs, gs)
482 ; (*) If dst == -1, then (src, len) entry refers to a set of new
483 ; descriptors to load.
484 ; If src == -1, then the memory pointed to by (dst, len) is bzeroed;
485 ; this is handled inside the bcopy routine.
509 jmp far [cs:EntryPoint]
512 mov bx, trackbuf ; Next descriptor
514 push ecx ; Save byte count
519 div ecx ; Convert to descriptor count
525 ; This routine is chained to from shuffle_and_boot to invoke a
526 ; flat 32-bit protected mode operating system.
531 o32 lgdt [cs:bcopy_gdt]
534 mov cr0,eax ; Enter protected mode
535 jmp .next ; Near jump to synchronize on 386/486
536 .next: mov ax,PM_DS32 ; 32-bit data segment selector
542 jmp PM_CS32:TrampolineBuf
545 A20List dw a20_dunno, a20_none, a20_bios, a20_kbc, a20_fast
546 A20DList dw a20d_dunno, a20d_none, a20d_bios, a20d_kbc, a20d_fast
547 a20_adjust_cnt equ ($-A20List)/2
549 A20Type dw A20_NONE ; A20 type
551 ; Total size of .bcopy32 section
552 alignb 4, db 0 ; Even number of dwords
553 __bcopy_size equ $-__bcopy_start
557 EntryPoint resd 1 ; CS:IP for shuffle_and_boot
558 A20Test resw 1 ; Counter for testing status of A20
559 A20Tries resb 1 ; Times until giving up on A20
562 ; This buffer contains synthesized code for shuffle-and-boot.
563 ; For the PM case, it is 9*5 = 45 bytes long; for the RM case it is
564 ; 8*6 to set the GPRs, 6*5 to set the segment registers (including a dummy
565 ; setting of CS), 5 bytes to set CS:IP, for a total of 83 bytes.
567 TrampolineBuf resb 83 ; Shuffle and boot trampoline
570 ; Space for a dummy task state segment. It should never be actually
571 ; accessed, but just in case it is, point to a chunk of memory not used