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diff --git a/build/docs/sccache-dist.rst b/build/docs/sccache-dist.rst new file mode 100644 index 0000000000..edd9ead909 --- /dev/null +++ b/build/docs/sccache-dist.rst @@ -0,0 +1,199 @@ +.. _sccache_dist: + +================================== +Distributed sccache (sccache-dist) +================================== + +`sccache <https://github.com/mozilla/sccache>`_ is a ccache-like tool written in +Rust by Mozilla and many contributors. + +sccache-dist, its distributed variant, elevates this functionality by enabling +the distribution and caching of Rust compilations across multiple machines. +Please consider using sccache-dist when you have several machines +compiling Firefox on the same network. + +The steps for setting up your machine as an sccache-dist server are detailed below. + +In addition to improved security properties, distributed sccache offers +distribution and caching of rust compilation, so it should be an improvement +above and beyond what we see with icecc. Build servers run on Linux and +distributing builds is currently supported from Linux, macOS, and Windows. + + +Steps for distributing a build as an sccache-dist client +======================================================== + +Start by following the instructions at https://github.com/mozilla/sccache/blob/master/docs/DistributedQuickstart.md#configure-a-client +to configure your sccache distributed client. +*NOTE* If you're distributing from Linux a toolchain will be packaged +automatically and provided to the build server. If you're distributing from +Windows or macOS, start by using the cross-toolchains provided by +``./mach bootstrap`` rather than attempting to use ``icecc-create-env``. +sccache 0.2.12 or above is recommended, and the auth section of your config +must read:: + + [dist.auth] + type = "mozilla" + +* If you're compiling from a macOS client, there are a handful of additional + considerations outlined here: + https://github.com/mozilla/sccache/blob/master/docs/DistributedQuickstart.md#considerations-when-distributing-from-macos. + + Run ``./mach bootstrap`` to download prebuilt toolchains to + ``~/.mozbuild/clang-dist-toolchain.tar.xz`` and + ``~/.mozbuild/rustc-dist-toolchain.tar.xz``. This is an example of the paths + that should be added to your client config to specify toolchains to build on + macOS, located at ``~/Library/Application Support/Mozilla.sccache/config``:: + + [[dist.toolchains]] + type = "path_override" + compiler_executable = "/path/to/home/.rustup/toolchains/stable-x86_64-apple-darwin/bin/rustc" + archive = "/path/to/home/.mozbuild/rustc-dist-toolchain.tar.xz" + archive_compiler_executable = "/builds/worker/toolchains/rustc/bin/rustc" + + [[dist.toolchains]] + type = "path_override" + compiler_executable = "/path/to/home/.mozbuild/clang/bin/clang" + archive = "/path/to/home/.mozbuild/clang-dist-toolchain.tar.xz" + archive_compiler_executable = "/builds/worker/toolchains/clang/bin/clang" + + [[dist.toolchains]] + type = "path_override" + compiler_executable = "/path/to/home/.mozbuild/clang/bin/clang++" + archive = "/path/to/home/.mozbuild/clang-dist-toolchain.tar.xz" + archive_compiler_executable = "/builds/worker/toolchains/clang/bin/clang" + + Note that the version of ``rustc`` found in ``rustc-dist-toolchain.tar.xz`` + must match the version of ``rustc`` used locally. The distributed archive + will contain the version of ``rustc`` used by automation builds, which may + lag behind stable for a few days after Rust releases, which is specified by + the task definition in + `this file <https://hg.mozilla.org/mozilla-central/file/tip/taskcluster/ci/toolchain/dist-toolchains.yml>`_. + For instance, to specify 1.37.0 rather than the current stable, run + ``rustup toolchain add 1.37.0`` and point to + ``/path/to/home/.rustup/toolchains/1.37.0-x86_64-apple-darwin/bin/rustc`` in your + client config. + + The build system currently requires an explicit target to be passed with + ``HOST_CFLAGS`` and ``HOST_CXXFLAGS`` e.g.:: + + export HOST_CFLAGS="--target=x86_64-apple-darwin16.0.0" + export HOST_CXXFLAGS="--target=x86_64-apple-darwin16.0.0" + +* Compiling from a Windows client is supported but hasn't seen as much testing + as other platforms. The following example mozconfig can be used as a guide:: + + ac_add_options CCACHE="C:/Users/<USER>/.mozbuild/sccache/sccache.exe" + + export CC="C:/Users/<USER>/.mozbuild/clang/bin/clang-cl.exe --driver-mode=cl" + export CXX="C:/Users/<USER>/.mozbuild/clang/bin/clang-cl.exe --driver-mode=cl" + export HOST_CC="C:/Users/<USER>/.mozbuild/clang/bin/clang-cl.exe --driver-mode=cl" + export HOST_CXX="C:/Users/<USER>/.mozbuild/clang/bin/clang-cl.exe --driver-mode=cl" + + The client config should be located at + ``~/AppData/Roaming/Mozilla/sccache/config/config``, and as on macOS custom + toolchains should be obtained with ``./mach bootstrap`` and specified in the + client config, for example:: + + [[dist.toolchains]] + type = "path_override" + compiler_executable = "C:/Users/<USER>/.mozbuild/clang/bin/clang-cl.exe" + archive = "C:/Users/<USER>/.mozbuild/clang-dist-toolchain.tar.xz" + archive_compiler_executable = "/builds/worker/toolchains/clang/bin/clang" + + [[dist.toolchains]] + type = "path_override" + compiler_executable = "C:/Users/<USER>/.rustup/toolchains/stable-x86_64-pc-windows-msvc/bin/rustc.exe" + archive = "C:/Users/<USER>/.mozbuild/rustc-dist-toolchain.tar.xz" + archive_compiler_executable = "/builds/worker/toolchains/rustc/bin/rustc" + +* Add the following to your mozconfig:: + + ac_add_options CCACHE=/path/to/home/.mozbuild/sccache/sccache + + If you're compiling from a macOS client, you might need some additional configuration:: + + # Set the target flag to Darwin + export CFLAGS="--target=x86_64-apple-darwin16.0.0" + export CXXFLAGS="--target=x86_64-apple-darwin16.0.0" + export HOST_CFLAGS="--target=x86_64-apple-darwin16.0.0" + export HOST_CXXFLAGS="--target=x86_64-apple-darwin16.0.0" + + # Specify the macOS SDK to use + ac_add_options --with-macos-sdk=/path/to/MacOSX-SDKs/MacOSX13.3.sdk + + You can get the right macOS SDK by downloading an old version of XCode from + `developer.apple.com <https://developer.apple.com>`_ and unpacking the SDK + from it. + +* When attempting to get your client running, the output of ``sccache -s`` should + be consulted to confirm compilations are being distributed. To receive helpful + logging from the local daemon in case they aren't, run + ``SCCACHE_NO_DAEMON=1 SCCACHE_START_SERVER=1 SCCACHE_LOG=sccache=trace path/to/sccache`` + in a terminal window separate from your build prior to building. *NOTE* use + ``RUST_LOG`` instead of ``SCCACHE_LOG`` if your build of ``sccache`` does not + include `pull request 822 + <https://github.com/mozilla/sccache/pull/822>`_. (``sccache`` binaries from + ``mach bootstrap`` do include this PR.) + +* Run ``./mach build -j<value>`` with an appropriately large ``<value>``. + ``sccache --dist-status`` should provide the number of cores available to you + (or a message if you're not connected). In the future this will be integrated + with the build system to automatically select an appropriate value. + +This should be enough to distribute your build and replace your use of icecc. +Bear in mind there may be a few speedbumps, and please ensure your version of +sccache is current before investigating further. Please see the common questions +section below and ask for help if anything is preventing you from using it over +email (dev-builds), on slack in #sccache, or in #build on irc. + +Steps for setting up a server +============================= + +Build servers must run linux and use bubblewrap 0.3.0+ for sandboxing of compile +processes. This requires a kernel 4.6 or greater, so Ubuntu 18+, RHEL 8, or +similar. + +* Run ``./mach bootstrap`` or + ``./mach artifact toolchain --from-build linux64-sccache`` to acquire a recent + version of ``sccache-dist``. Please use a ``sccache-dist`` binary acquired in + this fashion to ensure compatibility with statically linked dependencies. + +* The instructions at https://github.com/mozilla/sccache/blob/master/docs/DistributedQuickstart.md#configure-a-build-server + should contain everything else required to configure and run the server. + + *NOTE* Port 10500 will be used by convention for builders. + Please use port 10500 in the ``public_addr`` section of your builder config. + + Extra logging may be helpful when setting up a server. To enable logging, + run your server with + ``sudo env SCCACHE_LOG=sccache=trace ~/.mozbuild/sccache/sccache-dist server --config ~/.config/sccache/server.conf`` + (or similar). *NOTE* ``sudo`` *must* come before setting environment variables + for this to work. *NOTE* use ``RUST_LOG`` instead of ``SCCACHE_LOG`` if your + build of ``sccache`` does not include `pull request 822 + <https://github.com/mozilla/sccache/pull/822>`_. (``sccache`` binaries from + ``mach bootstrap`` do include this PR.) + + +Common questions/considerations +=============================== + +* My build is still slow: scache-dist can only do so much with parts of the + build that aren't able to be parallelized. To start debugging a slow build, + ensure the "Successful distributed compilations" line in the output of + ``sccache -s`` dominates other counts. For a full build, at least a 2-3x + improvement should be observed. + +* My build output is incomprehensible due to a flood of warnings: clang will + treat some warnings differently when it's fed preprocessed code in a separate + invocation (preprocessing occurs locally with sccache-dist). Adding + ``rewrite_includes_only = true`` to the ``dist`` section of your client config + will improve this; however, setting this will cause build failures with a + commonly deployed version of ``glibc``. This option will default to ``true`` + once the fix is more widely available. Details of this fix can be found in + `this patch <https://sourceware.org/ml/libc-alpha/2019-11/msg00431.html>`_. + +* My build fails with a message about incompatible versions of rustc between + dependent crates: if you're using a custom toolchain check that the version + of rustc in your ``rustc-dist-toolchain.tar.xz`` is the same as the version + you're running locally. |