Re: [uml-devel] Using SKAS, any examples?

[Ian Rogers <ian.rogers@manchester.ac.uk>]

Jeff Dike wrote:

>On Wed, May 04, 2005 at 10:28:28AM +0100, Ian Rogers wrote:
>  
>
>>What I'm hoping to do is to use SKAS to create a second address 
>>space I can, map, unmap, peek and poke from the first. The reason for 
>>this is to allow an emulator to live in the first address space and the 
>>emulated data... to live in the second. 
>>    
>>
>
>UML obviously does this.  Look at arch/um/kernel/skas/mem_user.c for the
>basic primitives.  The creation and destruction of address spaces is done
>in arch/um/kernel/skas/mmu.c.
>  
>
I've had a play with a simple test, but I need to work further on it. 
mem_user.c seems clear enough but I am slightly baffled by what is 
happening with the file descriptors in mmu.c.

>  
>
>>I hope to be able to access the 
>>second by altering the i386 selector value.
>>    
>>
>
>What's the i386 selector value?
>  
>
I hope, for example, to set LDT 0 to point to the second address space. 
I can then swap the value of 7 (index 0, LDT, ring 3) into fs or gs 
whenever I hope to address the second address space. I can do similar 
code with modify_ldt but I'm restricted to using mmap to allocate memory 
and therefore I don't get a fully addressable 4gb address space.

Thanks for your help,

Ian Rogers



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