| andybons | 6eaa0c0d | 2015-08-26 20:12:52 | [diff] [blame] | 1 | # Clang |
| andybons | 3322f76 | 2015-08-24 21:37:09 | [diff] [blame] | 2 | |
| Nico Weber | b161701 | 2019-09-06 18:20:32 | [diff] [blame] | 3 | Chromium ships a prebuilt[clang](http://clang.llvm.org) binary. |
| 4 | It's just upstream clang built at a known-good revision that we |
| 5 | bump every two weeks or so. |
| andybons | 3322f76 | 2015-08-24 21:37:09 | [diff] [blame] | 6 | |
| Nico Weber | b161701 | 2019-09-06 18:20:32 | [diff] [blame] | 7 | This is the only supported compiler for building Chromium. |
| andybons | 6eaa0c0d | 2015-08-26 20:12:52 | [diff] [blame] | 8 | |
| 9 | [TOC] |
| andybons | 3322f76 | 2015-08-24 21:37:09 | [diff] [blame] | 10 | |
| Nico Weber | b161701 | 2019-09-06 18:20:32 | [diff] [blame] | 11 | ## Using gcc on Linux |
| andybons | 3322f76 | 2015-08-24 21:37:09 | [diff] [blame] | 12 | |
| Nico Weber | b161701 | 2019-09-06 18:20:32 | [diff] [blame] | 13 | `is_clang = false` will make the build use system gcc on Linux. There are no |
| 14 | bots that test this and there is no guarantee it will work, but we accept |
| 15 | patches for this configuration. |
| rnk | c052ba3 | 2016-04-13 21:13:00 | [diff] [blame] | 16 | |
| andybons | 3322f76 | 2015-08-24 21:37:09 | [diff] [blame] | 17 | ## Mailing List |
| andybons | 6eaa0c0d | 2015-08-26 20:12:52 | [diff] [blame] | 18 | |
| xiaoyin.l | 1003c0b | 2016-12-06 02:51:17 | [diff] [blame] | 19 | https://groups.google.com/a/chromium.org/group/clang/topics |
| andybons | 3322f76 | 2015-08-24 21:37:09 | [diff] [blame] | 20 | |
| 21 | ## Using plugins |
| 22 | |
| andybons | 6eaa0c0d | 2015-08-26 20:12:52 | [diff] [blame] | 23 | The |
| xiaoyin.l | 1003c0b | 2016-12-06 02:51:17 | [diff] [blame] | 24 | [chromium style plugin](https://dev.chromium.org/developers/coding-style/chromium-style-checker-errors) |
| andybons | 6eaa0c0d | 2015-08-26 20:12:52 | [diff] [blame] | 25 | is used by default when clang is used. |
| andybons | 3322f76 | 2015-08-24 21:37:09 | [diff] [blame] | 26 | |
| 27 | If you're working on the plugin, you can build it locally like so: |
| 28 | |
| Will Cassella | ee18027 | 2021-12-03 18:16:21 | [diff] [blame] | 29 | 1.Run`./tools/clang/scripts/build.py --without-android --without-fuchsia` |
| andybons | 6eaa0c0d | 2015-08-26 20:12:52 | [diff] [blame] | 30 | to build the plugin. |
| Tom Sepez | 7b8dfca | 2025-02-19 19:36:38 | [diff] [blame] | 31 | 1.Run`ninja -C third_party/llvm-build/Release+Asserts/` to build |
| 32 | incrementally after making changes. |
| 33 | 1.Run`(cd tools/clang/plugins/tests && ./test.py ../../../../third_party/llvm-build/Release+Asserts/bin/clang)` |
| 34 | to test the plugin after making changes. |
| 35 | 1.BuildChromiumwith clangas usual, but,if youuse reclient, disable it. |
| jyasskin | 37110bc | 2015-12-04 03:40:24 | [diff] [blame] | 36 | |
| Tom Sepez | 07b77e6 | 2025-05-05 17:41:52 | [diff] [blame] | 37 | Thelocal plugin willthen be usedforlocal buildsuntil thenext |
| 38 | `gclient sync` restores thedefault toolchain. |
| 39 | |
| Daniel Cheng | 7174602d | 2018-03-29 20:49:14 | [diff] [blame] | 40 | Since the pluginis rolledwith clang changes, behavior changes to the plugin |
| Tom Sepez | 07b77e6 | 2025-05-05 17:41:52 | [diff] [blame] | 41 | should be guardedby flags to make it easy to roll clang without introducing |
| 42 | unexpected breakage. A general outline: |
| 43 | 1.Implementnew plugin behavior behind a flag, disabledbydefault. |
| Daniel Cheng | 7174602d | 2018-03-29 20:49:14 | [diff] [blame] | 44 | 1.Waitfor a compiler roll to bringin the flag. |
| 45 | 1.Start passing thenew flagin`GN`and verify thenew behavior. |
| 46 | 1.Enable thenew plugin behavior unconditionallyand update the plugin to |
| 47 | ignore the flag. |
| 48 | 1.Waitfor another compiler roll. |
| 49 | 1.Stop passing the flagfrom`GN`. |
| 50 | 1.Remove the flag completely. |
| 51 | |
| andybons | 3322f76 | 2015-08-24 21:37:09 | [diff] [blame] | 52 | ## Using the clang static analyzer |
| 53 | |
| kirillbobyrev | eed2584d | 2015-11-02 14:38:29 | [diff] [blame] | 54 | See[clang_static_analyzer.md](clang_static_analyzer.md). |
| andybons | 3322f76 | 2015-08-24 21:37:09 | [diff] [blame] | 55 | |
| 56 | ## Windows |
| 57 | |
| Nico Weber | b161701 | 2019-09-06 18:20:32 | [diff] [blame] | 58 | clangis thedefault compiler onWindows.It uses MSVC's SDK, so you still need |
| 59 | to have Visual Studio with C++ support installed. |
| andybons | 3322f76 | 2015-08-24 21:37:09 | [diff] [blame] | 60 | |
| 61 | ## Using a custom clang binary |
| 62 | |
| thakis | 2a46c2d1 | 2016-11-29 22:41:38 | [diff] [blame] | 63 | Set `clang_base_path` in your args.gn to the llvm build directory containing |
| Nico Weber | 8699c056 | 2019-09-06 19:05:56 | [diff] [blame] | 64 | `bin/clang` (i.e. the directory you ran cmake). This must be an absolute |
| thakis | 2a46c2d1 | 2016-11-29 22:41:38 | [diff] [blame] | 65 | path. You also need to disable chromium's clang plugin. |
| andybons | 3322f76 | 2015-08-24 21:37:09 | [diff] [blame] | 66 | |
| andybons | 6eaa0c0d | 2015-08-26 20:12:52 | [diff] [blame] | 67 | Here's an example that also disables debug info and enables the component build |
| 68 | (both not strictly necessary, but they will speed up your build): |
| andybons | 3322f76 | 2015-08-24 21:37:09 | [diff] [blame] | 69 | |
| thakis | 2a46c2d1 | 2016-11-29 22:41:38 | [diff] [blame] | 70 | ``` |
| 71 | clang_base_path = getenv("HOME") + "/src/llvm-build" |
| 72 | clang_use_chrome_plugins = false |
| 73 | is_debug = false |
| 74 | symbol_level = 1 |
| 75 | is_component_build = true |
| andybons | 3322f76 | 2015-08-24 21:37:09 | [diff] [blame] | 76 | ``` |
| 77 | |
| Nico Weber | d9b4f45 | 2019-10-09 17:58:16 | [diff] [blame] | 78 | On Windows, for `clang_base_path` use something like this instead: |
| 79 | |
| 80 | ``` |
| 81 | clang_base_path = "c:/src/llvm-build" |
| 82 | ``` |
| 83 | |
| Lei Zhang | 4906c17c | 2021-05-12 11:31:01 | [diff] [blame] | 84 | You can then look in `out/gn/toolchain.ninja` and check that the `rule cc` and |
| 85 | `rule cxx` commands run your clang binary. If things look good, run `ninja |
| thakis | 2a46c2d1 | 2016-11-29 22:41:38 | [diff] [blame] | 86 | -C out/gn` to build. |
| andybons | 3322f76 | 2015-08-24 21:37:09 | [diff] [blame] | 87 | |
| Nico Weber | 1473512 | 2019-08-12 13:39:05 | [diff] [blame] | 88 | Chromium tries to be buildable with its currently pinned clang, and with clang |
| 89 | trunk. Set `llvm_force_head_revision = true` in your args.gn if the clang you're |
| 90 | trying to buildwithis closer to clang trunk than toChromium's pinned clang |
| 91 | (which `tools/clang/scripts/update.py --print-revision` prints). |
| Nico Weber | 46a1d77a | 2020-12-07 14:39:13 | [diff] [blame] | 92 | |
| 93 | ## Related documents |
| 94 | |
| 95 | * [Toolchain support](toolchain_support.md) gives an overview of clang |
| 96 | rolls, and documents when to revert clang rolls and how to file good |
| 97 | toolchain bugs. |
| 98 | |
| 99 | * [Updating clang](updating_clang.md) documents the mechanics of updating clang, |
| 100 | and which files are included in the default clang package. |
| 101 | |
| 102 | * [Clang Sheriffing](clang_sheriffing.md) contains instructions for how to debug |
| 103 | compiler bugs, for clang sheriffs. |
| Nico Weber | 6a992f3 | 2021-11-30 17:48:26 | [diff] [blame] | 104 | |
| 105 | * [Clang Tool Refactoring](clang_tool_refactoring.md) has notes on how to build |
| 106 | and run refactoring tools based on clang's libraries. |
| Hans Wennborg | 4eeedf79 | 2025-01-17 14:00:23 | [diff] [blame] | 107 | |
| 108 | *[UpdatingClang format binaries](updating_clang_format_binaries.md) has notes |
| 109 | on how to update clang-format. |
