[PATCH] D70146: [ELF] Improve --gc-sections compatibility with GNU ld regarding section groups

[Peter Smith via Phabricator via llvm-commits]

peter.smith added a comment.

I'm broadly in favour of making this change. I recognise there are some concerns about the intent behind the ELF specification, which is largely written without garbage collection in mind. One reading of it is that garbage collection is orthogonal to group selection, and the all or nothing comments relate to group selection only. Will be good to wait a few days to see if there are any strong objections. I tend towards the conservative approach unless there are some demonstrable benefits from not doing so.

For upstream clang compiled objects I don't think that there would be a large impact for this change as the majority of groups have just one Section and a Relocation Section. ARM compiled groups also have .ARM.exidx and accompanying relocations but these are already all or nothing due to the way they are constructed, nothing refers to the .ARM.exidx and we rely on the SHF_LINK_ORDER reverse dependency for garbage collection protection.

I'm happy to separate out nextInGroup and dependentSections as while there are some similarities the former is used for ELF groups the latter is used for SHF_LINK_ORDER and keeping the concepts separate is reasonable.


Repository:
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  https://reviews.llvm.org/D70146/new/

https://reviews.llvm.org/D70146