[PATCH] D70398: [lld] Support copy relocations for TLS symbols

[James Clarke via Phabricator via llvm-commits]

jrtc27 added a subscriber: palmer-dabbelt.
jrtc27 added a comment.

I would agree that, for other architectures, not supporting copy relocations for TLS makes sense, and a world without copy relocations would be good. However, at the end of the day, this is what the RISC-V toolchains out there currently rely upon, and it would be very sad to force an incompatibility, especially since -fPIC introduces extra indirection in many cases that aren't needed, in particular because code generation has to assume symbol preemption. It does seem at least however that -fPIE yields the saner IE model again for both LLVM and GCC.... which begs the question why, as PIE vs non-PIE makes absolutely zero difference to the TLS addresses and semantics. I haven't yet found a discussion as to why this decision was made; the comment in the GCC source was the only reference I could even find that acknowledged this would require copy relocations. Ultimately, Clang+LLD can't currently be used to build FreeBSD as a result of this (nor can GCC+LLD), and telling people they can't use the default compiler mode that has always worked doesn't seem like the right answer; either LLVM and GCC need to stop forcing TLS copy relocations for position-dependent executables, or we need to support it here in LLD (or both...).

@palmer-dabbelt Do you have any comments about this?


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https://reviews.llvm.org/D70398