Exit from Virtual 8086 Mode in Protected Mode

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neo-92

Joined: 26 Feb 2014
Posts: 25

neo-92 12 Aug 2014, 09:39

Hi, i post a simple code in protected mode that goes in virtual 8086 mode:

Code:

use16

vm86:
mov ax,0e41h
mov bx,7
int 10h             ;this here we go. Print a character 'A' as in real mode.

;here i problems to use a task switch return in protected mode.

use32

pmode:
push 0
push 0
push 0
push 0
push 0
push 0fffeh
push 20000h
push 0
push vm86
iret

How can i return in protected mode from a task virtual 8086 mode? Thanks all.

12 Aug 2014, 09:39

neo-92

Joined: 26 Feb 2014
Posts: 25

neo-92 13 Aug 2014, 16:23

Please, can someone help me?

13 Aug 2014, 16:23

BAiC

Joined: 22 Mar 2011
Posts: 272
Location: California

BAiC 14 Aug 2014, 00:45

FYI: the USE32 is in the wrong place. when you return from "int 10h" your still in 16bit mode.

14 Aug 2014, 00:45

neo-92

Joined: 26 Feb 2014
Posts: 25

neo-92 14 Aug 2014, 08:39

BAiC wrote:

FYI: the USE32 is in the wrong place. when you return from "int 10h" your still in 16bit mode.

Ok Stefan. But, how do i get out of a v86 task and return in pmode?
The code

14 Aug 2014, 08:39

BAiC

Joined: 22 Mar 2011
Posts: 272
Location: California

BAiC 14 Aug 2014, 11:35

what is the perspective of the code your dealing with? I mean; are you trying to jack the CPU from within a v86 task? Virtual-86 mode is a protected mode; your not supposed to "get out" of it. your supposed to finish your work then signal the OS/Hypervisor to terminate your task for you (an 'int' tied to a task gate would be the most ideal IMO).

- Stefan

_________________
byte me.

14 Aug 2014, 11:35

neo-92

Joined: 26 Feb 2014
Posts: 25

neo-92 14 Aug 2014, 13:18

How do i to return from a v86 task 'iret' in pmode?

14 Aug 2014, 13:18

neo-92

Joined: 26 Feb 2014
Posts: 25

neo-92 14 Aug 2014, 13:45

I want kill the v86 task, is there a solution?

14 Aug 2014, 13:45

BAiC

Joined: 22 Mar 2011
Posts: 272
Location: California

BAiC 14 Aug 2014, 14:00

from what I understand you don't 'return' from a v86 task. you invoke an OS service to end the task for you. this shit is complicated. why are you determined to do such work when you don't even know the simpler stuff?

14 Aug 2014, 14:00

BAiC

Joined: 22 Mar 2011
Posts: 272
Location: California

BAiC 14 Aug 2014, 14:19

look at this site:
http://css.csail.mit.edu/6.858/2013/readings/i386/s15_03.htm

14 Aug 2014, 14:19

neo-92

Joined: 26 Feb 2014
Posts: 25

neo-92 14 Aug 2014, 16:04

I looked the site, but using 'iret' in v86 through another task i get a triple fault. Why? Is right the task switch or wrong?

14 Aug 2014, 16:04

BAiC

Joined: 22 Mar 2011
Posts: 272
Location: California

BAiC 14 Aug 2014, 16:11

I gave you that link to help you learn. the patchwork methods you are using don't fucking work for anything as complex as a Hypervisor ("Monitor"). stop skipping the meat of the OS. your not helping yourself at all.

BTW: I'm not helping you patch together a petty v86 hypervisor. you need to build a system. a fucking function will not cut it.

- Stefan

14 Aug 2014, 16:11

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