Re: [PLUG] ldt_modify and detailed information

[aglist@metashadow.com]

Kevin,

thanks for responding.  what i am trying to do is to be able to create a
memory segment  to have a hardware protected large block of memory (64M at
the bare minumum). i would rather my prog seg fault than have a run away
pointer problem if the memory is not properly accessed.  if use the
standard malloc in the default heap segment, that single area would not be
protected.  i would like to create in address space:

-------------------
| text segment    |
-------------------
| stack, heap seg |
-------------------
| my own seg      |
-------------------

but i did not know in depth how it works. that's why i want to look up how
linux handles/creates the default segments and user created segments.  i
have more questions like "if i malloc 64M+ of memory, are all the pages
automatically created, or does it only create pages and table entries as
the memory is accessed."  the same question goes for user created
segments.  i do not want to use all my swap space on empty pages and
really large page directories.

but instead of asking every question i have, i want to be find some good
resources i can read all i can about it, then ask any remaining questions.
 but i am having problems finding any good resources. (other than source
code, but that's my last resort)

and this is for an application in userland.

thanks,
-- adam grossman

>> howdy,
>>
>>  i want to write a programmer which create and uses it's own memory
>> segment
>>  on x86. the problem is i can not find much information on how to use
>> it.
>>  when i search for modify_ldt, i just get a lot of man pages. does
>> anybody
>>  know any books (online or dead tree), articles, stone tablets, etc,
>> that
>>  explains in detail how to use ldt_modify, how not to have mem segs
>> trample
>>  each other in the address space, how the loader places the different
>>  segments (code, text, etc) and how it access it during the program
>>  running. i hope it is a not more complicated than just saying "create
>> new
>>  mem seg" and loading the CR3 register whenever i want to use it...
>>
>>  this is not only for something i want to write, but an academic
>> exercise
>>  to see if i can do it and learn from it.
>>
>>  thanks,
>>  -- adam grossman
>
>
> Interesting question ... are you trying to study compilers and linkers
> or do some user application programming?  I wasn't sure, because your
> initial question asks about *ldt (which I'm not the familiar with, but a
> quick check shows it's a process memory management interface) but then
> you talk about the program accessing memory.  Generally program access
> to memory is handled by functions supplied by the language you are using
> (malloc/free in C, for example)
>
> If you wanted to study linkers/loaders you might want to do some
> searching on the linker (gnu ld on linux) or the loader (escapes me at
> the moment.)
>
> --
> Kevin Brosius
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