[PATCH] D118490: [lld][ELF] add .note sections from linker scripts as SHT_NOTE

Sat Jan 29 00:46:24 PST 2022

MaskRay added a comment.

Non-SHF_ALLOC SHT_NOTE sections exists in the wild.

- https://fedoraproject.org/wiki/Toolchain/Watermark#Proposed_Specification_for_non-loaded_notes
- ghc `ghcLinkInfoSectionName = ".debug-ghc-link-info"`

I have created two patches to improve the propagating SHF_ALLOC situation.

---

For the section type, I have filed a feature request ld: Customize output section type <https://sourceware.org/bugzilla/show_bug.cgi?id=28841>.
If an arbitrary output section type is too difficult, supporting just `SHT_NOTE` seems good enough.

> We have considered compiled objects and discarded that option as unfeasible. It's an absolute nightmare to even get a simple linker script to work reliably across 30.000 packages with a huge variation of different build systems and setups, across half a dozen different architectures. Having to also take care of an additional compilation steps means the whole endeavor will simply fail due to complications, so it is not an option.

https://fedoraproject.org/wiki/Changes/Package_information_on_ELF_objects references https://github.com/systemd/package-notes/blob/main/hello.spec .
Can't we replace `-Wl,-dT,$PWD/notes.ld}` with an compiled .o?
Then it will work all linkers: GNU ld, gold, ld.lld, and mold, perhaps also the abandoned MCLinker.

>> (I think communication can usually be improved by informing the involved parties early.

An un-involved party may feel frustration, especially if you only started conversation with one camp and then essentially force the other camp to accept.)

> I'm sorry if you feel frustrated, but I cannot change the past. Also, I assure you there was no conversation with the bfd 'camp' on this topic, so there's no 'favoritism' - I don't think I even mentioned this specification when I sent the READONLY patch, as it was completely orthogonal. Please understand that this is a complex effort with a huge number of moving parts (that has been discussed many times in many public places where anybody could chime in, including tech press articles and conferences), and the critical and really complicated pieces are elsewhere in the stack.

(I did not want to make this review a blame place, but I have mentioned `READONLY` in two messages https://sourceware.org/pipermail/binutils/2021-May/116579.html https://sourceware.org/pipermail/binutils/2021-July/117492.html 
Perhaps I really should have kept more vigilance if I knew this going to be used in systemd, or, all Fedora packages?
I just raised https://sourceware.org/pipermail/binutils/2022-January/119537.html to question the error-prone `READONLY`
)

Repository:
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https://reviews.llvm.org/D118490