[PATCH] D81784: [ELF] Resolve relocations in .debug_* referencing (discarded symbols or ICF folded section symbols) to tombstone values

[David Blaikie via Phabricator via llvm-commits]

dblaikie added inline comments.


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Comment at: lld/test/ELF/debug-dead-reloc-icf.s:2-5
+## Test we resolve symbolic relocations in .debug_* sections to a tombstone
+## if the referenced section symbol is folded into another section by ICF.
+## Otherwise, we would leave entries in multiple CUs claiming ownership of the
+## same range of code, which can confuse consumers.
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jhenderson wrote:
> One issue that I don't recall whether it was brought up previously: if we resolve one to -1, and the other has no debug data (e.g. they came from two different CUs, only one of which was compiled with -g), we could actually lose debug data for the function completely.
> 
> I don't know what the right thing to do is in this situation, as I don't know whether it's better than the risk of confusing consumers. I don't think we can reasonably attempt to identify whether there is matching debug data for the kept version after all.
Yeah, I'd accept that as an existing problem/not one that I think this tombstone work should necessarily address - the old solution or the new solution would be compatible with a linker making a more nuanced approach to this problem.

(but, in that separate discussion: I'm not sure this would be appropriate to fix - fixing this, I think, would mean having debug info influence which version of a function the linker chooses - increasing the risk of heisenbugs)


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  https://reviews.llvm.org/D81784/new/

https://reviews.llvm.org/D81784