>> 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. Yep, my patch (attached below for reference) moves the vsyscall page into user address space, just below PAGE_OFFSET. Works basically the same way the vsyscall page is mapped in the ia32 emulation of the x86_64 architecture. Address stays fixed, thus the relocation magic isn't needed. Once the vsyscall page is moved out of fixmap it's easy to make fixmap movable and thus have a runtime-resizable address space hole at the top of address space. Patch is attached too, although that one is more proof-of-concept, it doesn't make much sense as-is. It has a kernel command line option to specify the top of address space so you can play around with it ... Both patches are against -rc3 and most likely still apply just fine, havn't tested that though. cheers, Gerd -- Gerd 'just married' Hoffmann I'm the hacker formerly known as Gerd Knorr. http://www.suse.de/~kraxel/just-married.jpeg