[PATCH 11/11] kernel/x86: enable x32 support for amd64

[Elliott Mitchell]

On Wed, Nov 15, 2023 at 10:36:21AM +0100, Stefan Lippers-Hollmann wrote:
> 
> On 2023-11-14, Elliott Mitchell wrote:
> 
> > I don't know the future, but enabling kernel support is the first step.
> 
> If you wanted to add it to Debian (with working a multi-arch
> implementation and organically grown repositories (which aren't
> rebuild aside from sourceful uploads or targeted binNMUs), you would
> be right - for OpenWrt, no, there really is no need to enable it,
> before you have the rest of the x32 subtarget ready to be merged (and
> I can't imagine any reason to enable it for the current OpenWrt x86_64
> subtarget at all).

So you would be against enabling the kernel support before userspace is
ready?  Meanwhile everyone else would be against working on userspace
without it being enabled in the kernel...

That doesn't really work too well.

> For OpenWrt, I could imagine only two approaches to this:
> - make the x86_64 subtarget x32-only
> - add a new x32-only subtarget and leave x86_64 as it is
> Neither would really be 'sensible', but the only workable approach
> would imho be the later, even if the intention was (I hope not to
> witness that) to kill off the old x86_64 target.

I agree with this.  One comment though, I suspect OpenWRT VM
installations will remain below 4GB of memory for quite some time.  As
such x32 would be a "free" performance boost/memory reduction if upstream
sources support x32 (yeah, this is a big if).

> So I really don't see any reason to enable x32 for the x86_64 subtarget,
> there's nothing to be gained, just major disadvantages.
> While I'm not a proponent for a pure-x32 subtarget either (at all), this
> would be the only workable approach to introduce it.

At a glance it looks like some useful gains for not too much cost.

>From my perspective though this isn't a crucial part of my goal.  So I'm
likely to drop further discussion as this the cost:benefit isn't there.


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