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Re: [PATCH v2] arm64: compat: Implement misalignment fixups formultiword loads

On 7/15/22 04:04, LinAdmin wrote:
Pi 4 has much more throughput in 32-bit modes but the so
called experts of Debian decided to abandon it :-(

On 14.07.22 03:52, Wookey wrote:
On 2022-07-01 15:53 +0200, Ard Biesheuvel wrote:
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
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.
I agree.  So far, raspios is still available in armhf flavor, and for running
heavy machinery with just a few microseconds to respond to an IRQ,
armhf builds are a given. LinuxCNC is such an application.

I built this kernel for an rpi4b quite a while ago, but none more recent
have been as usable. uname -a:

Linux rpi4.coyote.den 4.19.71-rt24-v7l+ #1 SMP PREEMPT RT Thu Feb 6 07:09:18 EST 2020 armv7l GNU/Linux

latency-test shows about 12 u-secs as long as I stay away from firefox.

That's good enough to run a cnc converted 80 yo 11x56 Sheldon lathe,
making it do dance steps that were not in its vocabulary 80 years ago.

Yet that raspios buster install is the full blown graphical install I also use
as a development platform, with big SSD's plugged into its usb3 ports for

Is it stable? Absolutely, no splats since the above date unless caused by
me, uptimes are in the many months category as I try newer stuff now
and then and find it wanting.

The exception is right now, as libc6 was replaced and I rebooted it
2 days ago.

It would be running bullseye but the last time I switched boot cards to try
it, the python was too new to build LinuxCNC with but the built on buster
version still worked and so did the above kernel.

What I'd like to know, is why is armhf such a dirty word to debian?

Take care and stay well everybody.
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
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

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).


Cheers, Gene Heskett.

"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/>

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