linker: Avoid invoking eventhandlers on incompletely loaded files

[markj]

Summary

We do not invoke the kld_load eventhandler until after the file is fully
linked, so don't invoke the kld_unload_try or kld_unload event handlers
unless the file is fully linked either.

In my case, the dtrace SDT kld unload handler was running before
relocations were processed against the file, and that caused problems
when sdt_kld_unload_probes() accesses elements of a linker set.

PR: 291238

[emaste]

LGTM. I do wonder if there's a reason the steps in the kld_unload EVENTHANDLER aren't (shouldn't be) handled in the same place as sysctls / sysuninits?

[cy]

No issues here.

[markj]

• Move the kld_unload eventhandler to immediately after sysuninits are invoked. This is more logically consistent and simplifies the patch.

[emaste]

Thanks. Thinking more about it, it does seem sensible to execute all of the teardown steps for this module before doing the dependencies.

[markj]

In D53938#1232616, @emaste wrote:

Thanks. Thinking more about it, it does seem sensible to execute all of the teardown steps for this module before doing the dependencies.

Yeah, I added these eventhandlers originally many years ago and I'm pretty sure I had no particular reason for invoking kld_unload so late.

[kib]

The difference now is in order in which dependencies are reported for unload.