"Undocumented" LOADALL instruction

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neonz

Joined: 02 Aug 2003
Posts: 62
Location: Latvia

neonz 02 May 2004, 12:09

FASM does not support neither 286 variation of LOADALL, neither 386+ variation. Maybe it should be added?

Info: http://www.nondot.org/sabre/os/files/ProtectedMode/LOADALL.txt

02 May 2004, 12:09

ShortCoder

Joined: 07 May 2004
Posts: 105

ShortCoder 07 May 2004, 04:40

Interesting.---this seems like it would be a useful thing to use if you were coding your own x86 OS, except for you would have to have different versions of this OS for a 286 or 386 through pentiums. Also, does this undocumented function work in 64-bit processors?

Hmm...maybe the mnemonics could be LOADALL286 and LOADALL386 since there are two different ones there.

Perhaps, instead of adding the undocumented opcodes to FASM, a new include file could be made which equates the undocumented opcodes to their values with some sort of macro?

07 May 2004, 04:40

comrade

Joined: 16 Jun 2003
Posts: 1150
Location: Russian Federation

comrade 07 May 2004, 04:58

maybe loadall 386 version with "use32" directive used and 286 version otherwise

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07 May 2004, 04:58

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8351
Location: Kraków, Poland

Tomasz Grysztar 07 May 2004, 05:33

Both LOADALL286 and LOADALL386 are supported since ages.

07 May 2004, 05:33

Adam Kachwalla

Joined: 01 Apr 2006
Posts: 150

Adam Kachwalla 26 Apr 2006, 08:21

Does anyone know how to do this?:

Mark Dixon wrote:

THE PROCEDURE FOR USING LOADALL
(the ultra-safe, long procedure)

1. Save the original machine state, so you have a state to return to.
This information can be saved in a Loadall table, which is the most
convenient form for later use.

2. Disable interrupts. Just in case. We want a clean copy of area 80.

3. Save the 102-byte (33h words) block of data located at 80:0h. Ver-
sions of DOS (both PC- and MS-) earlier than 3.3 use this area for
critical system code, and as of DOS 3.3, RamDrive.Sys, and Himem.Sys use
this area for their own Loadall tables.

4. Re-enable interrupts. Let the clock ticks, or whatever, through,
while we do the following step.

5. Set up the new Loadall table (new_reg_buf), which defines the new
state we want to warp to.

6. Disable Interrupts.

7. Copy the new Loadall table to 80:0h.

8. Execute a Loadall.

9. Do something or other with your new machine state. Read or write
extended memory, run code upstairs, or whatever.

10. Copy the "old" Loadall table, containing the saved machine state,
down to 80:0.

11. Do another Loadall (Un-Loadall.) This restores the original
machine state.

12. Copy the block of saved data back to 80:0h.

13. Re-enable interrupts.

I guess Mark means something like:

Code:

...             ;Step I
CLI             ;Step II
...             ;Step III
STI             ;Step IV
...             ;Step V
CLI             ;Step VI
...             ;Step VII
LOADALL286      ;Step VIII
STI             ;No other step: I added this in (I don't see the point of leaving INTs disabled)
,,,             ;Step IX (Don't know if this is where the code is executed...)
CLI             ;No other step: just re-disabling interrupts for the next instructions (See Step VI)
...             ;Step X
LOADALL286      ;Step XI
...             ;Step XII
STI             ;Step XIII
,,,
;I am not sure if the code was meant to go here.
;I have a feeling Mark must have said something wrong
;He starts to restore the machine state in Step X, and interrupts are enabled in Step XIII

26 Apr 2006, 08:21

El Tangas

Joined: 11 Oct 2003
Posts: 120
Location: Sunset Empire

El Tangas 01 May 2006, 19:47

I you want to play with loadall, check this link too:
http://www.rcollins.org/articles/loadall/tspec_a3_doc.html

There is lots of good reading in that site, but unfortunately it is no longer updated.

01 May 2006, 19:47

Adam Kachwalla

Joined: 01 Apr 2006
Posts: 150

Adam Kachwalla 02 May 2006, 06:34

Maybe there is a way to add "LOADALL" to FASM. If LOADALL was executed instead of LOADALL286 or LOADALL386, it will do one of the following?:

1. Find out which CPU you have and execute the corresponding LOADALL function

2. Execute both LOADALL functions (Only one of them can be correct).

02 May 2006, 06:34

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