Re: doubt ?

[Angelo Dell'Aera <buffer@users.sourceforge.net>]

On Sat, 31 Aug 2002 10:39:20 -0700 (PDT)
Mcen navaraj <mcensamuel@yahoo.com> wrote:

>hi,
>
>what is the use of gates in the intel processors ?
>what is the use of interrupt gate ?

If you refer to Intel x86 arch you have to distinguish between three types
of interrupt gates which are inserted through three different functions in
the Global Descriptor Table:

- interrupt gates (which can NOT be accessed from User Mode processes. They
  are used for activate interrupt handlers);
- system gates (can be accessed from User Mode processes. The four exceptions
  3,4,5 and 128 are activated by means of system gates. In particular 128 is
  the well-known int 0x80 which is associated to the exception handler  
  system_call you refer to; 
- trap gates (can NOT be accessed from User Mode processes and all exception
  handlers except the four described before are activated through these ones).

>please tell me how many segments are created when a 
>process is created ?.What are the segments are created
>when we create a process ?

AFAIK Linux creates at boot time some segments.

-two for kernel : kernel data segment and kernel code segment;
-two for userland : user data segment and user code segment
	(this last ones are shared by all processes in User Mode);
-in Linux 2.2 a task state segment (TSS) for each process, in 
 Linux 2.4 simply one TSS per CPU;
-a default Local Descriptor Table segment usually shared by all
 processes (but very rarely used).


Regards,

Angelo Dell'Aera 'buffer' 
<buffer@users.sourceforge.net>
--
Kernelnewbies: Help each other learn about the Linux kernel.
Archive:       http://mail.nl.linux.org/kernelnewbies/
FAQ:           http://kernelnewbies.org/faq/