RPCS3/llvm
1
0
Fork 0
mirror of https://github.com/RPCS3/llvm.git synced 2024-11-30 23:21:04 +00:00
Code Issues Actions Packages Projects Releases Wiki Activity

[docs] Update GoldPlugin documentation

Browse Source 
Summary:
Updated and reorganized. Made the following additions:
1) How to see if ld.gold is installed, and whether it is the current
default.
2) How to install ld.gold as the default or alternatively use
-fuse-ld=gold.
3) Move the part about installing the newly built ld-new as the default
to the prior section and how to use --enable-gold=default to do it
automatically on install.
4) Add a note about ld.bfd supporting plugins but indicate that it is
not tested by the LLVM project and gold is the recommended linker for
use with the gold plugin.

Fixes PR32760.

Reviewers: davide

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D49490

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@337404 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Teresa Johnson 2018-07-18 17:10:17 +00:00
parent 19723d91b8
commit 7f233b7000
1 changed files with 30 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

47
docs/GoldPlugin.rst
View File

@ -6,13 +6,16 @@ Introduction
============
Building with link time optimization requires cooperation from
the system linker. LTO support on Linux systems requires that you use the
the system linker. LTO support on Linux systems is available via the
`gold linker`_ which supports LTO via plugins. This is the same mechanism
used by the `GCC LTO`_ project.
The LLVM gold plugin implements the gold plugin interface on top of
:ref:`libLTO`. The same plugin can also be used by other tools such as
``ar`` and ``nm``.
``ar`` and ``nm``. Note that ld.bfd from binutils version 2.21.51.0.2
and above also supports LTO via plugins. However, usage of the LLVM
gold plugin with ld.bfd is not tested and therefore not officially
supported or recommended.
.. _`gold linker`: http://sourceware.org/binutils
.. _`GCC LTO`: http://gcc.gnu.org/wiki/LinkTimeOptimization
@ -24,11 +27,20 @@ How to build it
===============
You need to have gold with plugin support and build the LLVMgold plugin.
Check whether you have gold running ``/usr/bin/ld -v``. It will report "GNU
gold" or else "GNU ld" if not. If you have gold, check for plugin support
by running ``/usr/bin/ld -plugin``. If it complains "missing argument" then
you have plugin support. If not, such as an "unknown option" error then you
will either need to build gold or install a version with plugin support.
The gold linker is installed as ld.gold. To see whether gold is the default
on your system, run ``/usr/bin/ld -v``. It will report "GNU
gold" or else "GNU ld" if not. If gold is already installed at
``/usr/bin/ld.gold``, one option is to simply make that the default by
backing up your existing ``/usr/bin/ld`` and creating a symbolic link
with ``ln -s /usr/bin/ld.gold /usr/bin/ld``. Alternatively, you can build
with clang's ``-fuse-ld=gold`` or add ``-fuse-ld=gold`` to LDFLAGS, which will
cause the clang driver to invoke ``/usr/bin/ld.gold`` directly.
If you have gold installed, check for plugin support by running
``/usr/bin/ld.gold -plugin``. If it complains "missing argument" then
you have plugin support. If not, and you get an error such as "unknown option",
then you will either need to build gold or install a version with plugin
support.
* Download, configure and build gold with plugin support:
@ -44,6 +56,14 @@ will either need to build gold or install a version with plugin support.
the ``-plugin`` option. Running ``make`` will additionally build
``build/binutils/ar`` and ``nm-new`` binaries supporting plugins.
Once you're ready to switch to using gold, backup your existing
``/usr/bin/ld`` then replace it with ``ld-new``. Alternatively, install
in ``/usr/bin/ld.gold`` and use ``-fuse-ld=gold`` as described earlier.
Optionally, add ``--enable=gold=default`` to the above configure invocation
to automatically install the newly built gold as the default linker with
``make install``.
* Build the LLVMgold plugin. Run CMake with
``-DLLVM_BINUTILS_INCDIR=/path/to/binutils/include``. The correct include
path will contain the file ``plugin-api.h``.
@ -51,19 +71,12 @@ will either need to build gold or install a version with plugin support.
Usage
=====
The linker takes a ``-plugin`` option that points to the path of
the plugin ``.so`` file. To find out what link command ``gcc``
would run in a given situation, run ``gcc -v [...]`` and
look for the line where it runs ``collect2``. Replace that with
``ld-new -plugin /path/to/LLVMgold.so`` to test it out. Once you're
ready to switch to using gold, backup your existing ``/usr/bin/ld``
then replace it with ``ld-new``.
You should produce bitcode files from ``clang`` with the option
``-flto``. This flag will also cause ``clang`` to look for the gold plugin in
the ``lib`` directory under its prefix and pass the ``-plugin`` option to
``ld``. It will not look for an alternate linker, which is why you need
gold to be the installed system linker in your path.
``ld``. It will not look for an alternate linker without ``-fuse-ld=gold``,
which is why you otherwise need gold to be the installed system linker in
your path.
``ar`` and ``nm`` also accept the ``-plugin`` option and it's possible to
to install ``LLVMgold.so`` to ``/usr/lib/bfd-plugins`` for a seamless setup.