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

[Zachary Amsden <zach@xxxxxxxxxx>]

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.
Zach

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