[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] 2.6 changesets
More info on the TLS problems. I've added limited instruction emulation to Xen so that we can use the TLS libraries that come with e.g., Redhat 9 and Debian. Basically we take teh general protection fault, then decode the instruction and interpret it if it's trying to access a -ve segment offset. Unfortunately the emulation triggers _a lot_! So it will affect performance... However, I intend to add dynamic patching of the unexecutable instructions to Linux -- it will detect instructions of a particular limited class, and dynamically create fixup code, and patch the original execution site to call the fixup code. I originally thought this would be very hard, but I think I have a way of doing this in a reasonably simple manner (fingers crossed). This should get almost every drop of performance back. -- Keir > I'm not an expert or anything like that but I investigated this same > problem because UML (user mode linux) doesn't like (read: support) tls > too - either 2.4 and 2.6 umls. > > "various different tls implementations" -> No such thing. NPTL/TLS > support is stable and much the same in every linux distro. So if you > have problems with RH you'll have problems with debian unstable, i686 > and a 2.6 kernel (read below for explanation), etc... > > /lib/ld.so checks `uname` in 2.4 kernels. If extraversion begins with > "-ntpl" than this 2.4 kernel has nptl support. If extraversion doesn't > have that string it's assumed that the kernel doesn't have nptl support > (and tls support). > > If the kernel is 2.6+ then ld.so assumes that nptl support is present. > The way to remove it is to "mv /lib/tls /lib/tls.off". Other way to deal > with it is to use the environment var LD_ASSUME_KERNEL and set it to 2.4 > globally, wich may cause havoc :) > > I think that nptl requires at least i486, so if you install for i386, > nptl support won't be included in the installation. Another way is to > downgrade the VMM from i686 (or whatever processor you have) to plain > i386. I don't know if it's possible in xen... > > In my uml setups i choose the KISS method: mv /lib/tls /lib/tls.off > > With debian you can instruct dpkg (man dpkg-divert) to relocate > everything that would be installed to /lib/tls to another location > automagically. This saves troubles when apt-get upgrad'ing ;) > > Hope this helps, > Nuno Silva > > P.S. Great work! Keep going!! :) > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1.2.4 (GNU/Linux) > Comment: Using GnuPG with Thunderbird - http://enigmail.mozdev.org > > iD8DBQFA+KHUOPig54MP17wRAmQ6AKDJt+S34QrrzXN0Bm4hFlBkNpW4dgCgw55G > EFOTQDye2YnPA/foE9R0OUs= > =L05g > -----END PGP SIGNATURE----- > > > ------------------------------------------------------- > This SF.Net email is sponsored by BEA Weblogic Workshop > FREE Java Enterprise J2EE developer tools! > Get your free copy of BEA WebLogic Workshop 8.1 today. > http://ads.osdn.com/?ad_id=4721&alloc_id=10040&op=click > _______________________________________________ > Xen-devel mailing list > Xen-devel@xxxxxxxxxxxxxxxxxxxxx > https://lists.sourceforge.net/lists/listinfo/xen-devel ------------------------------------------------------- This SF.Net email is sponsored by BEA Weblogic Workshop FREE Java Enterprise J2EE developer tools! Get your free copy of BEA WebLogic Workshop 8.1 today. http://ads.osdn.com/?ad_id=4721&alloc_id=10040&op=click _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/xen-devel
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