llvm19 lld issue

[Michal Meloun]

While searching for the cause of armv7 kernel corruption after updating 
to llvm19 lld, I came across an interesting problem.

- The linker script does not list all generated sections. Specifically, 
the data sections created by the linker set are not listed.

- The linker can place these orphaned sections in any location (OK, with 
some restrictions). See 
https://maskray.me/blog/2024-06-02-understanding-orphan-sections.

- Creating symbols outside a section is fragile and subject to error; 
the linker may place an orphaned section between the symbol definition 
and the following section.

We ran into this problem many years ago, see 
https://github.com/freebsd/freebsd-src/commit/6e764e36da019837d90e3b4b712871ee4442637a. 
Unfortunately, we didn't fix it completely then, and we have to address 
the same corruption again.

I think we should be strict in this area and use 
'--orphan-handling=error' for kernel linking. However, I'm not sure we 
can handle linker sets gracefully.

Any comments, contrary opinion or better solution ? Does anyone know how 
to properly list all linker sets (mainly but not only 'set_<foo>_set') 
in linker script and which section is appropriate for them ? .rodata?

Thanks,
Michal