1 Android Clang/LLVM 2 ================== 3 4 For the latest version of this doc, please make sure to visit: 5 [Android Clang/LLVM Toolchain Readme Doc](https://android.googlesource.com/platform/external/clang/+/dev/ReadmeAndroid.md) 6 7 Platform Projects 8 ----------------- 9 10 The LLVM toolchain is primarily composed of the following projects: 11 12 * **external/clang** 13 * **external/compiler-rt** 14 * **external/llvm** 15 16 Each of these projects has three important branches: 17 18 * *aosp/master* 19 20 This is the branch that will be present in most platform trees. As such, 21 platform components that use clang or LLVM will build against the headers and 22 libraries in this branch. 23 24 This branch does not contain a full history. Updates to this are done via a 25 squashed merge from the *dev* branch. Aside from updates, patches usually 26 shouldn't be submitted to this branch. Any that are will need to be 27 cherry-picked to *dev*. 28 29 * *aosp/dev* 30 31 The primary purpose of this branch is allowing us to decouple the platform 32 compilers from RenderScript and other platform components that depend on LLVM 33 libraries. This means we can update the platform compilers even if 34 RenderScript will need substantial modification for API changes. 35 36 Updates are performed in this branch, and the platform compilers are built 37 from this branch. 38 39 * *aosp/upstream-master* 40 41 This branch is an automatically updated direct mirror of the upstream master 42 branch. This is a read only branch that is the merge source for updates to 43 *dev*. 44 45 46 Development Flow 47 ---------------- 48 49 Rebases take place in the **aosp/llvm** tree. This tree is a manifest that uses 50 the appropriate *dev* branches of each LLVM project and contains only the 51 projects needed to build the platform compilers. Updates are done by merging 52 from the *aosp/upstream-master* branch. 53 54 Conflicts are resolved manually and then a patch is produced to adapt 55 Android.mk files (as well as to add/delete any updated source files). 56 Prebuilts are then generated using these projects and placed into the proper 57 **prebuilts/clang/host** subprojects. 58 59 The prebuilt projects contain multiple versions to make it easy to check in a 60 new compiler that may not be ready to be enabled by default. Each new toolchain 61 will add the following paths: 62 63 prebuilts/clang/host/linux-x86/clang-$BUILD_NUMBER 64 prebuilts/clang/host/darwin-x86/clang-$BUILD_NUMBER 65 prebuilts/clang/host/windows-x86/clang-$BUILD_NUMBER 66 67 In order to prepare for the actual rebase (including updating dependent 68 projects), we will copy each **external/** *aosp/dev* project to its 69 corresponding **external/** *aosp/master* project as a squashed single CL. 70 This makes rollbacks simpler, and it also reduces churn on the Android build 71 servers. 72 This also has the side effect of not spamming non-Android @google.com 73 committers to upstream LLVM projects, since their commits will be batched up 74 into a single copy commit on each tracked **external/** project. 75 76 Prebuilts for llvm-rs-cc and bcc\_compat also need to be generated for 77 **prebuilts/sdk**. 78 This is done by running **frameworks/rs/update\_rs\_prebuilts.sh** on both Mac 79 and Linux. This is done from the normal AOSP platform tree rather than the LLVM 80 tree. 81 After this completes, the **prebuilts/sdk** project will have a prepared 82 branch/CL that can be uploaded for review/commit. 83 84 85 Fixing Bugs 86 ----------- 87 88 If we find a host-side bug that needs to be fixed, it may trigger an update of 89 the host prebuilts (i.e. rebase). 90 Device-side fixes can be pushed directly to **external/** *aosp/master* and then 91 copied to **external/** *aosp/dev* to speed up the process (assuming that it 92 doesnt affect the host builds). 93 94 95 Looking at Upstream 96 ------------------- 97 98 The upstream repositories are automatically mirrored to the 99 *aosp/upstream-master* branch. Update with `git fetch aosp upstream-master`. 100 101 102 Communication 103 ------------- 104 105 We have a public mailing list that you can subscribe to: 106 [android-llvm (a] googlegroups.com](https://groups.google.com/forum/#!forum/android-llvm) 107 108 109 Guides for Updating Toolchains 110 ------------------------------ 111 112 * [Updating platform toolchains](ToolchainPrebuilts.md) 113 * [Updating RenderScript prebuilts](RenderScriptPrebuilts.md) 114
