Date: Tue, 14 Mar 2006 20:31:08 -0800
From: Chris Wright <chrisw@sous-sol.org>
To: Zachary Amsden <zach@vmware.com>
Cc: Chris Wright <chrisw@sous-sol.org>, Linus Torvalds <torvalds@osdl.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Virtualization Mailing List <virtualization@lists.osdl.org>,
       Xen-devel <xen-devel@lists.xensource.com>,
       Andrew Morton <akpm@osdl.org>, Dan Hecht <dhecht@vmware.com>,
       Dan Arai <arai@vmware.com>, Anne Holler <anne@vmware.com>,
       Pratap Subrahmanyam <pratap@vmware.com>,
       Christopher Li <chrisl@vmware.com>, Joshua LeVasseur <jtl@ira.uka.de>,
       Rik Van Riel <riel@redhat.com>, Jyothy Reddy <jreddy@vmware.com>,
       Jack Lo <jlo@vmware.com>, Kip Macy <kmacy@fsmware.com>,
       Jan Beulich <jbeulich@novell.com>,
       Ky Srinivasan <ksrinivasan@novell.com>,
       Wim Coekaerts <wim.coekaerts@oracle.com>,
       Leendert van Doorn <leendert@watson.ibm.com>,
       Gerd Hoffmann <kraxel@suse.de>
Subject: Re: [RFC, PATCH 7/24] i386 Vmi memory hole
Message-ID: <20060315043108.GP12807@sorel.sous-sol.org>
References: <200603131804.k2DI4N6s005678@zach-dev.vmware.com> <20060314064107.GK12807@sorel.sous-sol.org> <44166D6B.4090701@vmware.com> <20060314215616.GM12807@sorel.sous-sol.org> <4417454F.2080908@vmware.com>
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* Zachary Amsden (zach@vmware.com) wrote:
> Chris Wright wrote:
> >* Zachary Amsden (zach@vmware.com) 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.

Yes, so vsyscall page has int80 implementation.

> 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.

I believe both Xen and execshield move vsyscall out of fixmap, and then
map into userspace as normal vma.

thanks,
-chris
-
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