[PATCH] D61613: [LLD][ELF] Add the -z ifunc-noplt option

[Mark Johnston via Phabricator via llvm-commits]

markj created this revision.
Herald added subscribers: llvm-commits, MaskRay, krytarowski, arichardson, emaste.
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markj added reviewers: emaste, arichardson, ruiu, MaskRay.

This is intended for use in freestanding environments where text
relocations are acceptable.  FreeBSD makes use of the option when
linking x86 kernels, which now make heavy use of ifuncs in hot paths.
Without the option, each ifunc results in the generation of a PLT entry,
so calls needlessly incur the extra overhead of an indirect jump.  With
the option, ifunc calls have the same cost as ordinary function calls.

Test Plan:
I added a couple of regression tests and tested the FreeBSD kernel
build using the latest lld sources.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D61613

Files:
  lld/ELF/Config.h
  lld/ELF/Driver.cpp
  lld/ELF/Relocations.cpp
  lld/docs/ld.lld.1
  lld/test/ELF/gnu-ifunc-noplt-i386.s
  lld/test/ELF/gnu-ifunc-noplt.s

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