On Wednesday 04 May 2005 16:49, Ian Rogers wrote: > 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. You'll never get that, sadly, because the upper 1G is used by the kernel itself... This can be achieved on x86_64, even with 32bit binaries (if they are run with the right emulation). -- Paolo Giarrusso, aka Blaisorblade Skype user "PaoloGiarrusso" Linux registered user n. 292729 http://www.user-mode-linux.org/~blaisorblade
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