[PATCH] D63183: [ELF][RISCV] Treat R_RISCV_{ADD,SET,SUB}* as link-time constants

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added reviewers: asb, jrtc27, PkmX, ruiu.
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R_RISCV_{ADD,SET,SUB}* are expected to be used as local label
computation. Add a new RelExpr R_RISCV_ADD to represent them.

R_RISCV_ADD is treated as a link-time constant because otherwise
R_RISCV_{ADD,SET,SUB}* are not allowed in a non-writable section in
-pie/-shared mode.

In glibc Scrt1.o, .rela.eh_frame contains such relocations. With D63076 <https://reviews.llvm.org/D63076>
and this patch, I can run -pie/-shared programs linked against glibc.

Note llvm-mc cannot currently produce R_RISCV_SET* so they are not
tested.


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D63183

Files:
  ELF/Arch/RISCV.cpp
  ELF/InputSection.cpp
  ELF/Relocations.cpp
  ELF/Relocations.h
  test/ELF/riscv-reloc-add.s

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