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.
> [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.
(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)
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