Michael Richardson wrote: > Mark Morgan Lloyd <markmll....@telemetry.co.uk> wrote: > > The (unofficial?) FAQ at http://uml.devloop.org.uk/faq.html implies that > > it is possible to build UML on a 64-bit system to run a 32-bit guest. > > > The best that I can manage on e.g. Debian "Jessie" x86-64 is to use > > make ARCH=um SUBARCH=i386 which results in a 32-bit ELF to presumably > > run a 32-bit guest. Prerequisites appear to be the multiarch-support > > and gcc-multiarch packages. > > > Is it possible to build UML as a 64-bit binary, but to run a 32-bit > > guest? What I'd like to be able to do is to put it on a system which has > > no multiarch stuff, i.e. to completely sequester the 32-bit libraries > > etc. within the guest filesystem. > > You could try running that 64-bit kernel with a 32-bit binary. > Put a statically linked 32-bit busybox in the guest file system, or use a > 32-bit Debian initrd as a test case.. > > I suspect that it won't work because the enclosing ("dom0") kernel will have > set the process to be a 64-bit process to run your kernel, and thus I think > the entire address space will be 64-bit.
[Nod] Probably fragile at best. > > [Background: I used UML fairly heavily in the 2.4 era, but I'm a > > comparative newcomer to x86-64. I'm trying to avoid overuse of > > multi-arch stuff.] > > I am not sure why you are trying to avoid this, unless you are trying to run > the results on a system that doesn't have multi-arch. Trying to keep systems as clean as possible. I had little option but to install user-level multi-arch for Acrobat Reader, and there's always going to be oddities like Ken Thompson's APL that will never get ported to 64-bit, but knowing how robust UML is /if/ it had handled the shimming it would have been a very attractive alternative. > (I'm fighting/putting-off replacing a Fedora10 build system with a Jessie > system, in great part because the appliance system needs a 64-bit kernel now, > but my build environment is 32-bit, and not-multiarch capable. Build-root > is the proper answer) Jessie's got the expected number of Debianisms in it, even on something as ablutions-standard as i386. We're considering looking at Fedora... Anyway, thanks everybody for the comments, which if nothing else have confirmed that while I'd misinterpreted the original text I'd not overlooked anything obvious when building kernels etc. -- Mark Morgan Lloyd markMLl .AT. telemetry.co .DOT. uk [Opinions above are the author's, not those of his employers or colleagues] ------------------------------------------------------------------------------ _______________________________________________ User-mode-linux-user mailing list User-mode-linux-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-user