Re: Can we drop upstream Linux x32 support?

On Wed, Jan 09, 2019 at 01:41:14PM +0100, Florian Weimer wrote:

* Thomas Schöbel-Theuer:

quoted

2) please _announce_ _now_ that after the _next_ LTS kernel (whichever
you want to declare as such), you will _afterwards_ drop the legacy
32bit support for 64 kernels (I am deliberately using "management
speak" here).

=> result: the industry should have to fair chance to deal with such a
roadmap. Yes, it will hurt some people, but they will have enough time
for their migration projects.

Example: I know that out of several millions of customers of
webhosting, a very low number of them have some very old legacy 32bit
software installed in their webspace. This cannot be supported
forever. But the number of such cases is very small, and there just
needs to be enough time for finding a solution for those few
customers.

3) the next development kernel _after_ that LTS release can then
immediately drop the 32bit support. Enterprise users should have
enough time for planning, and for lots of internal projects
modernizing their infrastructure. Usually, they will need to do this
anyway in the long term.

We've already phased out support for all 32-bit architectures except
i386 in our products, and i386 is obviously next.  (We never supported
x32 in the first place.)

It becomes increasingly difficult to build a 32-bit userspace that meets
backwards-compatibility needs.  We want to use SSE2 (to avoid excess
precision for double) and avoid relying on stack realignment (for
compatibility with applications that use the old i386 ABI which did not
require stack realignment).  We also have to build the distribution with
a full complement of hardening flags.  This results in a combination of
flags that is poorly tested in upstream GCC.  The i386 register file
isn't large enough to support all these features at the same time and
combine them with function arguments passed in registers (which some
programs enable manually via function attributes).

So even if we keep the kernel interface, in the forseeable future, I
expect that it will be difficult to build a full, contemporary 32-bit
userspace on i386.

I guess that's informative of how one company's distro process works,
but it's not representative. Your customers are enterprise and
big-server (probably mostly the former) oriented which is exactly the
domain where 32-bit is of course irrelevant except for running legacy
applications. Where it matters are embedded and other systems striving
for resource efficiency.

For what it's worth, 32-bit archs including i386 and many others are
well-supported in Debian with no forseeable EOL I'm aware of, and most
if not all of the musl-libc-based distros I'm familiar with support
32-bit archs including i386.

I don't think waning relevance of 32-bit is a reasonable argument
against x32 since x32's relevance is in exactly the places where
32-bit is already relevant and preferred for important reasons.

Rich