[PATCH] D72197: [MC][ELF] Emit a relocation if target is defined in the same section and is non-local

[James Y Knight via Phabricator via llvm-commits]

jyknight added a comment.

In D72197#1806495 <https://reviews.llvm.org/D72197#1806495>, @dblaikie wrote:

> I think the question I have: What is the value (I don't mean to assume there is no value, but I want to understand the specific use case) of supporting this if the full generality of symbol interposition is not supported? (is there a well defined use case that is usable with this patch and doesn't need the full generality? Or is the use case going to be subtly broken if it changes even slighlty and happens to trip over another part of LLVM that doesn't support symbol interposition? (in which case this is a great patch, but only as part of an effort to fully support the general case))


IMO it's useful to differentiate the high-level desires, vs the low-level implementation details. Whatever clang/LLVM-IR wants its policy to be for semantic interposition, that choice needs to be represented somehow in assembly.

And it seems a reasonable choice (especially given gnu as compatibility) that on ELF platforms, referencing a global symbol in assembly should always use a relocation, as this patch implements. If we want to have the other behavior in some case, we can emit a local symbol alias for a function, and call via that, instead.

I hope the jmp difference doesn't cause an issue -- I think it makes more sense as you have, but that kind of thing always worries me. :)


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