[plug] Query related to kernel mode and UML

raven at themaw.net raven at themaw.net
Tue Apr 20 21:12:19 WST 2004

On Tue, 20 Apr 2004, Parag Nemade wrote:

Assuming x86 arch.

> hello ,
>           I want to know 
> when i run a simple C program i am in kernel mode or
> in user mode?
> when system call is called in a C program in which
> mode i am ?

Goes like:

1. call system function xxx() - user mode
2. sys call does soft int 0x80 for call number 
   allocated to xxx() - switch to kernel mode
3. sys call entry point calls sys_xxx service
   routine - kernel mode
4. on completion call returns in reverse order changing
   mode as above.

> Also what is User Mode Linux(UML). what is difference
> between UML and Simple LINUX KERNEL?

Heard of it havn't checked it out.

> When i modify kernel and add some functions in kernel
> and boot it? my functions runs in kernel mode or user
> mode?

Huh. How you doing that?
There are 255 possible int 0x80 entry points.
It's not your call to mess with these.

> Is there any connection of modification of kernel to
> UML?

Don't know.

You need to be a little more specific with you questions. In any case I 
likely won't know unless it's VFS specific.


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