flat assembler

Index > OS Construction > LDT

Author

Thread

BOTOKILLER

Joined: 07 Jan 2011
Posts: 154
Location: Ukraine

BOTOKILLER

Hi everyone!
Yeah, I figured out how paging interacts with segments - LDT Very Happy

Where can I find LDT tutorial???

_________________
_______________________________
NSOS

27 Jul 2011, 12:08

DJ Mauretto

Joined: 14 Mar 2007
Posts: 464
Location: Rome,Italy

DJ Mauretto

Always Intel Manuals Wink

_________________
Nil Volentibus Arduum Razz

27 Jul 2011, 12:17

BOTOKILLER

Joined: 07 Jan 2011
Posts: 154
Location: Ukraine

BOTOKILLER

Which one???

27 Jul 2011, 12:25

f2

Joined: 30 May 2010
Posts: 13
Location: France

BOTOKILLER wrote:

Which one???

Intel Architecture Software Developer’s Manual Volume 3: System Programming Guide

Hope you will search by yourself next time...

27 Jul 2011, 12:31

edfed

Joined: 20 Feb 2006
Posts: 4240
Location: 2018

edfed

BOTOKILLER wrote:

Which one???

the fact that you ask it means you did not read any.

hurry up! download ALL the manuals, don't forget to rename the pdf files with the true title of the volume, because a number is not very easy to remember.

and read all the manuals. you are not forced to read everything, but at least, try to overview the main topics of the manuals, and you will have a lot less question to ask.

_________________
Smile

fool gitlab fasmstuff
gitlab foolstuff

27 Jul 2011, 13:02

BOTOKILLER

Joined: 07 Jan 2011
Posts: 154
Location: Ukraine

BOTOKILLER

edfed wrote:

BOTOKILLER wrote:
Which one???

the fact that you ask it means you did not read any.

hurry up! download ALL the manuals, don't forget to rename the pdf files with the true title of the volume, because a number is not very easy to remember.

and read all the manuals. you are not forced to read everything, but at least, try to overview the main topics of the manuals, and you will have a lot less question to ask.

I read them, In fact they are opened in a few tabs of chrome which I never close...

_________________
_______________________________
NSOS

27 Jul 2011, 13:12

BOTOKILLER

Joined: 07 Jan 2011
Posts: 154
Location: Ukraine

BOTOKILLER

I cant find where LDT entry format is mentioned...

_________________
_______________________________
NSOS

27 Jul 2011, 16:11

f2

Joined: 30 May 2010
Posts: 13
Location: France

it's probably wiritten somewhere in Intel manuals (but I don't know where, I'm not interested about implementing such obsolete things like LDTs).

I have searched the Internet and I found an interesting page about segmentation on x86:
http://book.opensourceproject.org.cn/kernel/kernel3rd/opensource/0596005652/understandlk-chp-2-sect-2.html

27 Jul 2011, 17:02

BOTOKILLER

Joined: 07 Jan 2011
Posts: 154
Location: Ukraine

BOTOKILLER

f2 wrote:

it's probably wiritten somewhere in Intel manuals (but I don't know where, I'm not interested about implementing such obsolete things like LDTs).

I have searched the Internet and I found an interesting page about segmentation on x86:
http://book.opensourceproject.org.cn/kernel/kernel3rd/opensource/0596005652/understandlk-chp-2-sect-2.html

but LDT must somehow point to Page tables...

_________________
_______________________________
NSOS

28 Jul 2011, 11:53

qandrew

Joined: 21 Jan 2010
Posts: 3

qandrew

BOTOKILLER wrote:

but LDT must somehow point to Page tables...

The LDT isn't related to Paging!

Why? It just isn't. As Wikipedia mentions, "On x86 processors not having paging features, like the Intel 80286, the LDT is essential to implementing separate address spaces for multiple processes.".

You should choose what you want to use: it is either Paging or LDT. Not both at the same time.

28 Jul 2011, 12:23

BOTOKILLER

Joined: 07 Jan 2011
Posts: 154
Location: Ukraine

BOTOKILLER

Then what do I put into CS, DS, SS, etc when paging enabled???

_________________
_______________________________
NSOS

28 Jul 2011, 12:37

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17639
Location: In your JS exploiting you and your system

revolution

LDT/GDT defines segments and thus affects CS, DS, etc.

Paging defines access to memory pages and is independent of segments. Most modern OSes effectively disable segmentation by defining all segments to be 4GB (or run in 64 bit mode where there are no segments of consequence (except that pesky GS thing)).

28 Jul 2011, 12:44

BOTOKILLER

Joined: 07 Jan 2011
Posts: 154
Location: Ukraine

BOTOKILLER

So, I just have to put all segments to point to whole address space???
That simple Smile

Thanks guys!!!

Last edited by BOTOKILLER on 28 Jul 2011, 13:01; edited 1 time in total

28 Jul 2011, 12:59

f2

Joined: 30 May 2010
Posts: 13
Location: France

Hmm... Well.

I fully agree that you ask lot of questions about something you can't understand. But mostly, you can easily answer these questions:
- by reading carefully the Intel manuals,
- or by following all existing tutorials about OS development.
- and, of course, if you have a question, search on theOSDev Wiki, the FASM board, or on Google. Post here ONLY if you can't find an answer that question.

28 Jul 2011, 13:00

< Last Thread | Next Thread >

Forum Rules:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum