On Fri, Jan 08, 2021 at 12:02:53PM -0800, Linus Torvalds wrote:

Well, honestly, I'm always in favor of having people not use ancient
compilers, but both of the issues at hand do seem to be specific to
arm64.

The "gcc before 5.1 generates incorrect stack pointer writes on arm64"
sounds pretty much deadly, and I think means that yes, for arm64 we
simply need to require 5.1 or newer.

I also suspect there is much less reason to use old gcc's on arm64. I
can't imagine that people really run very old setups, Is some old RHEL
version even relevant for arm64?

For me, six years old for a compiler is really not "very old" - and,
when I first encountered this problem, it was over 12 months ago.
Apart from the kernel, I am not in the habbit of upgrading stuff for
the sake of upgrading - I tend to stick with what I have and what
works. Not everyone on this planet has a desire to have the latest
and greatest all the time.

Since then, I've _not_ wanted to change the compiler in case the
problem vanishes without explanation - it had the feeling of being
way more serious than a compiler bug, potentially a memory ordering
bug.

It took about a year just to start being able to work out what was
going on - it would take up to about three months to show for me,
and when it did, it spat out an ext4 inode checksum error and made
the rootfs read-only.

To "hide" that by upgrading the compiler, and then to be in the
situation where you do not trust any aarch64 machine with your data
is no real solution. That's exactly where I was until this had been
found. The aarch64 architecture had completely lost my trust as a
viable computing platform - and I was at the point of considering
disposing of all my aarch64 hardware and replacing it with x86.

-- 
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