On Fri, Aug 2, 2024 at 5:12 PM Arnd Bergmann [off-list ref] wrote:

Right, for us this is clearly only done for legacy user
binaries. It is still possible to run an OABI Debian-5.0
or older rootfs with a new kernel, but there are not a lot
of reasons to do so, other than ARMv4 (StrongARM)
hardware. The only times I ever tried using it were
to test kernel changes that impact OABI syscall handling.

I tried it with the old RedHat rootfs of the NetWinder. It "worked"
but you had to create e.g a sysfs directory for the thing to even
boot. Debian 5 got its last update 12 years or so ago.

Security-wise it must be strongly discouraged to connect
anything like that to a public network given the plethora of issues
in that old userspace, so I don't know if it can even be
useful for anything. The SSH agent will be refused by
contemporary servers. Maybe if you just have 1-2 old OABI
binaries without source code that you just have to keep running?
Is there any such system?

If people absolutely want to run these machines they should
probably port OpenWrt to them so they can run a modern
userspace, and OpenWrt uses EABI, albeit with a hack, but it's
the best I know of:
https://github.com/openwrt/openwrt/blob/main/toolchain/gcc/patches-14.x/840-armv4_pass_fix-v4bx_to_ld.patch

Yours,
Linus Walleij