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[Xen-devel] Re: [RFC, PATCH 7/24] i386 Vmi memory hole

Chris Wright wrote:
* Zachary Amsden (zach@xxxxxxxxxx) wrote:
Allow creation of an compile time hole at the top of linear address space.

Extended to allow a dynamic hole in linear address space, 7/2005.  This
required some serious hacking to get everything perfect, but the end result
appears to function quite nicely.  Everyone can now share the appreciation
of pseudo-undocumented ELF OS fields, which means core dumps, debuggers
and even broken or obsolete linkers may continue to work.

Thanks.  Gerd did something similar (although I believe it's simpler,
don't recall the relocation magic) for Xen.  Either way, it's useful
from Xen perspective.

I believe Xen disables sysenter. The complications in my patch come from the fact that the vsyscall page has to be relocated dynamically, requiring, basically run time linking on the page and some tweaks to get sysenter to work. If you don't use vsyscall (say, non-TLS glibc), then you don't need that complexity. But I think it might be needed now, even for Xen.


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