x32 abi support?

[Richard W.M. Jones]

On Wed, May 16, 2012 at 04:41:06PM +0200, Jakub Jelinek wrote:
> On Wed, May 16, 2012 at 04:28:31PM +0200, Lennart Poettering wrote:
> > Mhmm, so I was under the impression that x32 was mostly about increasing
> > the scalability of virtualized systems. i.e. run a higher number of
> > x32 containers/VM on an x86_64 host. Most server software that is run in
> > containers/VMs does not require 64bit address space, and hence using x32
> > for them should be quite benificial so that you can run more
> > containers/VMs per host. After all this would reduce memory and CPU
> > consumption of each, and due to smaller memory usage also result in less
> > IO?
> 
> Note that x32 is less secure than x86-64, the possible address space
> randomization is much more limited there, while there is ASCII armor, it
> can protect just a couple of libraries, unlikely all of them.  With LP64
> certain kinds of exploits are harder.
> 
> And, for various programs you usually don't need 64-bit address space,
> but in the case where you have say bigger input you are simply out of luck
> if you are limited to 32-bit address space.  Say with compilers/linkers,
> you can usually compile smaller stuff just fine with 32-bit compiler, but
> if you have some larger source code, x32 won't do it.  Similarly
> various other programs that don't have constant memory requirements, but
> linear (or worse) with the size of the input.

Also functional language runtimes tend to benefit from 64 bit, since
it gives more room to use tag bits and GC coloring bits.  The OCaml
runtime gets a major benefit here.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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