| ====================== |
| LLD 3.9 Release Notes |
| ====================== |
| |
| .. contents:: |
| :local: |
| |
| Introduction |
| ============ |
| |
| 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 <http://llvm.org/releases/>`_. |
| |
| 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. |
| |
| Link-Time Optimization |
| ---------------------- |
| |
| Initial support for LTO has been added. It is compatible with |
| `the LLVM gold plugin <http://llvm.org/docs/GoldPlugin.html>`_ in terms of |
| command line flags and input file format so that LLD is usable as a |
| drop-in replacement for GNU gold. LTO is implemented as a native |
| feature unlike the GNU gold's plugin mechanism. |
| |
| 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. |
