lkml.org 
[lkml]   [1996]   [Jul]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: LDT currently unused?
On 10 Jul 1996, Florian Weimer wrote:

> I'm currently developing an application which needs call gates to
> kernel mode. These call gates are stored in the LDT of a certain
> process at a fixed position (currently, the first six descriptors are
> used by my program). Do I have to expect any conflicts with existing
> software? Are there any libraries which use the LDT?

1. LDT is _NOT_ 'unused'. The kernel uses the first 3 ones in the default LDT.
'Wine' as well as 'DOSemu' use LDT-entries above those.
The default LDT is static, if you create your own entries, the kernel
will allocate a private 8K LDT for the process, taking over the contents
of the default LDT.

2. The syscall you need to fiddle with LTD-stuff is sys_modify_ldt (No.123).
You have to use it directly (no lib-function available)) by defining:

_syscall3(int, modify_ldt, int, func, void *, ptr, unsigned long, bytecount)

Have a look at Wine (memory/ldt.c) or DOSemu (src/dosext/dpmi/dpmi.c)

3. Though the CPU allowes you to have them in the LDT, Call-Gates are
refused by sys_modify_ldt (ldt_info.contents == 3), which will return
-EINVAL, if you anyway want to create one.

4. All other LDT manipulation than using sys_modify_ldt are
refused by the kernel.

Hans
<lermen@fgan.de>



\
 
 \ /
  Last update: 2005-03-22 13:38    [W:3.433 / U:0.004 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site