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__attribute__((constructor)) in kernel

What I've learned about it.

TL;DR - .not really useful for kernel


- It generates a .ctors (or .init_array on arm or something) section

- GCC has __attribute__((constructor(n))) where n is priority, and the
section entries are sorted in ascending order, which is a handy syntax

  - But not that great; easily replaced with ``sort'' function in linker script

- Userland needs this syntax, because userland applications have no
control about how it is linked; it sets function pointers in .ctors,
to ask ``system'' (linker, run-time) to call those functions before

- In kernel, this is not the case; kernel itself has to call the
functions by itself.  This way the section name (.ctors) doesn't
matter at all.

- To not confuse, ELF section (.ctors) is better to be hidden in final kernel.

- Rump will use link-set anyway.

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