Hi,

On 2022-07-14 02:52, Wookey wrote:

On 2022-07-01 15:53 +0200, Ard Biesheuvel wrote:

quoted

The 32-bit ARM kernel implements fixups on behalf of user space when
using LDM/STM or LDRD/STRD instructions on addresses that are not 32-bit
aligned.

quoted

This feature is one of the remaining impediments to being able to switch
to 64-bit kernels on 64-bit capable hardware running 32-bit user space,
so let's implement it for the arm64 compat layer as well.

quoted

Note to cc'ees: if this is something you would like to see merged,
please indicate so. This stuff is unlikely to get in if there are no
users.

Decent 32-bit arm hardware is thin on the ground these days. Debian
still has some but it's getting old and flaky. Being able to build
reliably on 64-bit hardware is important and useful. Unaligned
accesses are much less of a problem than they used to be, but they can
still happen, so having these fixups available is definitely a good
thing.

Debian runs its 32-bit buildds with alignment fixups turned on. It
looks like the boxes still hit about 1 per day.

We also do 32 bit builds on 64-bit kernels (in 32-bit userspaces) and
it mostly works. We do have packages that fail on 64-bit kernels and
have to be built on real 32-bit hardware, but I don't know how much of
that would be fixed by this patch. Some, presumably.

So yes, cheers for this. It is helpful in the real world (or at least
it should be).

I confirm that this would be very helpful to Debian, so that 32-bit
binaries behaves the same with a 32-bit or a 64-bit kernel. Otherwise we
need to keep running (old) 32-bit hardware.

What's the status of those patches?

Thanks
Aurelien

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@aurel32.net                 http://www.aurel32.net