[PATCH 6/9] kernel/x86: enable x32 support for amd64

[Stefan Lippers-Hollmann]

Hi

On 2023-03-30, Elliott Mitchell wrote:
> Full amd64 support isn't really appropriate for most situations
> OpenWRT is deployed.  Whereas x86-x32 seems extremely appropriate for
> these situations.  As such enable x86-x32 support.
> 
> CONFIG_ARCH_MMAP_RND_COMPAT_BITS is required to follow along,
> otherwise the kernel build breaks.
> 
> Signed-off-by: Elliott Mitchell <ehem+openwrt at m5p.com>
> ---
> I suggest OpenWRT should be placing quite a bit of effort towards
> x86-x32.  x86-x32 seems a rather superior generic target for OpenWRT.
> Only issue is it could be valuable to have at least minimal amd64
> userland support alongside the x86-x32 version.

x86_32 is pretty much dead in the water, with almost zero deployment
by general purpose distributions - apart from VM data centre 
environments doing their own thing (least amount of RAM usage 
possible, everything else being secondary at best). At least Debian
did raise security concerns about the x86_32 ISA in the past.

While I might understand (understand, not support) a desire for this 
as a dedicated subtarget (to appease the virtualization crowd), 
although I still don't see a reason or sufficient uptake in more 
conventional Linux environments. I would not be happy (at all) to 
lose 'normal' x86_64 support (on real hardware) for this exotic 
fringe hybrid. I can imagine that actually building for this 
environment (with a 32 bit userland) might lead to 'funny' results 
as well (as in major toolchain changes necessary to get it working 
as expected).

Regards
	Stefan Lippers-Hollmann
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