I think the only thing I'd love to see is to tell users in the commit message how to apply this as it seems this needs to be done manually.

The other question I have: does this work with gcc or do we need -mfix-cortex-a53-843419 there?

In D58212#1335515, @bz wrote:

I think the only thing I'd love to see is to tell users in the commit message how to apply this as it seems this needs to be done manually.

The fixup is applied automatically if your CPUTYPE is set to 'generic', 'armv8-a', 'cortex-a53' or if it is left empty.

The other question I have: does this work with gcc or do we need -mfix-cortex-a53-843419 there?

Yes, the linker flag is compatible with the GCC toolchain/linker.

Sure, enabling the -mfix-cortex-a53-843419 flag in clang also for FreeBSD will make things much cleaner. It's hard to say why it's not enabled yet.
Then enable all Cortex mitigations unconditionally (there are three others) and then leave all this dance to the compiler.

In D58212#1335516, @mmel wrote:

In D58212#1335515, @bz wrote:

I think the only thing I'd love to see is to tell users in the commit message how to apply this as it seems this needs to be done manually.

The fixup is applied automatically if your CPUTYPE is set to 'generic', 'armv8-a', 'cortex-a53' or if it is left empty.

It should also be applied to a CPUTYPE of cortex-a57.cortex-a53.

The world will need to be rebuilt, however as a limited number of cores are affected, and it seems difficult to hit the erratum I'm not planning on forcing a rebuild for everyone.