gen_kobject_list.py is extremely slow

[arbrauns]

Describe the bug
With CONFIG_USERSPACE enabled, gen_kobject_list.py can take an obscenely long time to run, approximately 30s in our current (decently large) project.

To Reproduce

1. Set CONFIG_USERSPACE=y in a large project
2. Build with ninja -v
3. Watch the jobs for kobject_prebuilt_hash.gperf and kobject_hash.gperf take a very long time

This can even be observed in the barebones samples/userspace/hello_world_user, where each of those takes 0.6s.

Expected behavior
Generating these tables should not take up a significant part of the total build time.

Impact
For affected projects (large, with userspace enabled), this makes the already slow link times much, much worse. Touching a single file makes a subsequent build take 60 seconds, approximately 55 of which are spent waiting on the two invocations of gen_kobject_list.py.

Environment (please complete the following information):

• OS: Ubuntu 24.04
• Toolchain: Zephyr SDK 0.16.8
• Commit SHA or Version used: v3.7.0

[kartben]

@arbrauns is this something you were not observing in previous versions of Zephyr and you would then describe as a regression?

[ubieda]

Dropping link to related long-standing known issue: #8559

[arbrauns]

is this something you were not observing in previous versions of Zephyr and you would then describe as a regression?

No, I don't think this is particularly new, it's more that as the project grew larger it eventually got to a point where I got sick of just accepting and ignoring it.