Re: Y2038 - best way forward in Debian?
On Tue, Feb 11, 2020 at 12:07 PM Marco d'Itri <md@linux.it> wrote:
>
> On Feb 11, Arnd Bergmann <arnd@linaro.org> wrote:
>
> > I agree that changing the i386 port is probably a bad idea at the moment,
> > let's see how the armhf port turns out and fix all the bugs first, as this
> > is clearly needed anyway. Once there is a working armhf version with
> > full time64 user space, there can be a separate discussion about what
> > to do with the i386 port (phase out i386 before y2038, migrate all of
> > i386 to time64 quickly, have two separate i386 ports, or something
> > else).
>
> I have still not seen any explanation about why we expect that 32 bit
> ARM systems will still be popular (as non-embedded) ~15 years from now.
I think most installations of Debian on 32-bit ARM are already for embedded
systems, but that doesn't make them less important IMHO. In some deeply
embedded systems, you'd be looking at installing a current version of Debian
(because why not) and then running it for decades beyond the end of support
without updates. While this is often no problem in the absence of attack
vectors, the time32 problem means that a piece of industrial equipment
may be created for a 40 year lifetime today and work flawlessly for the first
18 years before suddenly breaking. The sooner time64 gets supported in
Debian, the more of them have a chance of surviving.
I did some research last year to see how long these systems tend to
live before they are obsolete, here is a rough summary for each architecture
version:
* ARMv4 based chips were released between ~1997 and 2007, the last
supported released was Debian Lenny, originally in 2009, with support
ending in 2012.
* ARMv4T based chips were more popular and came out during the
same timeframe (1997 to 2007), last supported in Debian Stretch,
released in 2017 and LTS support ending in 2022.
* ARMv5 was introduced in ~2002 and is still supported, with a few
new chips still being taped out (Microchip SAM9X60, Allwinner
F-Series) and being actively deployed in large numbers for several
years to come. I expect the last Debian release with ARMv5 support
between 2025 and 2030, with the last users relying on Debian LTS
powering the hardware off well before 2038.
* ARMv6 was less popular, most chips (i.MX3, S3C64xx, OMAP2)
from 2005 to 2014 are obsolete or never ran Debian in the first
place (e.g. AST2500). The main exception is probably Raspbian
on BCM2835, which surely will be used as long as you can
fit Debian into 512MB of RAM, plus several years after support
ends, probably beyond 2038.
* ARMv7 chips came out between 2005 and 2015 but were more
popular than the above combined. Since Cortex-A5 is now part of
Arm's DesignStart program, we will see new tapeouts for years to
come, and some of them are likely to run Debian for longer than the
existing chips.
* ARMv7VE (first introduced in 2012) is still the most common
architecture for embedded designs today, we'll probably see new
Cortex-A7 based chips for another 5 to 10 years, followed by several
years of new boards based on those chips and a very long time
before these finally get powered off.
* ARMv8 is surely taking over the lead in the embedded space from
ARMv7/ARMv7VE over the next few years. Almost all of these
can run 64-bit code, but when shipping enough of them, the cost
of the on-board RAM means you are stuck with a single 4Gbit DDR3
chip (512MB), which in turn means you want to run 32-bit user
space to lower the memory consumption for the application.
The next sensible step up from 512MB DDR3 (on a single chip) is
probably 2GB of LP-DDR4 with 64-bit user space, but it will likely
take many years before that is actually cheap enough completely
obsolete DDR3 memory and 32-bit mode with it.
Arnd
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