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LLD 3.9 Release Notes


This document contains the release notes for the LLD linker, release 3.9. Here we describe the status of LLD, including major improvements from the previous release. All LLD releases may be downloaded from the LLVM releases web site.

What’s new in ELF Support?

LLD 3.9 is a major milestone for us. It is the first release that can link real-world large userland programs, including LLVM/Clang/LLD themselves. In fact, for example, it can now be used to produce most userland programs distributed as part of FreeBSD.

Many contributors have joined to the project to develop new features, port it to new architectures and fix issues since the last release.

Identical Code Folding

LLD 3.9 can now merge identical code sections to produce smaller output files. It is expected to be used with -ffunction-sections.

Symbol Versioning

LLD 3.9 is able to link against versioned symbols as well as produce versioned symbols. Both the original Sun’s symbol versioning scheme and the GNU extension are supported.

New Targets

LLD has expanded support for new targets, including ARM/Thumb, the x32 ABI and MIPS N64 ABI, in addition to the existing support for x86, x86-64, MIPS, PowerPC and PPC64.

TLS Relocation Optimizations

The ELF ABI specification of the thread-local variable define a few peephole optimizations linkers can do by rewriting instructions at the link-time to reduce run-time overhead to access TLS variables. That feature has been implemented.

New Linker Flags

Many command line options have been added in this release, including:

  • Symbol resolution and output options: -Bsymbolic-functions, -export-dynamic-symbol, -image-base, -pie, -end-lib, -start-lib, -build-id={md5,sha1,none,0x<hexstring>}.
  • Symbol versioning option: -dynamic-list.
  • LTO options: -lto-O, -lto-aa-pipeline, -lto-jobs, -lto-newpm-passes, -plugin, -plugin-eq, -plugin-opt, -plugin-opt-eq, -disable-verify, -mllvm.
  • Driver optionss: -help, -version, -unresolved-symbols.
  • Debug options: -demangle, -reproduce, -save-temps, -strip-debug, -trace, -trace-symbol, -warn-execstack.
  • Exception handling option: -eh-frame-hdr.
  • Identical Code Folding option: -icf.

Changes to the MIPS Target

  • Added support for MIPS N64 ABI.
  • Added support for TLS relocations for both O32 and N64 MIPS ABIs.

Building LLVM Toolchain with LLD

A new CMake variable, LLVM_ENABLE_LLD, has been added to use LLD to build the LLVM toolchain. If the varaible is true, -fuse-ld=lld option will be added to linker flags so that ld.lld is used instead of default ld. Because -fuse-ld=lld is a new compiler driver option, you need Clang 3.8 or newer to use the feature.