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1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"2 "http://www.w3.org/TR/html4/strict.dtd">3<!-- Material used from: HTML 4.01 specs: http://www.w3.org/TR/html401/ -->4<html>5<head>6 <META http-equiv="Content-Type" content="text/html; charset=utf-8">7 <title>Hacking on clang</title>8 <link type="text/css" rel="stylesheet" href="menu.css">9 <link type="text/css" rel="stylesheet" href="content.css">10 <style type="text/css">11 pre { margin-left: 1.5em; }12 </style>13</head>14<body>15<!--#include virtual="menu.html.incl"-->16<div id="content">17 <!--*********************************************************************-->18 <h1>Hacking on Clang</h1>19 <!--*********************************************************************-->20 21 <p>This document provides some hints for how to get started hacking22 on Clang for developers who are new to the Clang and/or LLVM23 codebases.</p>24 <ul>25 <li><a href="#style">Coding Standards</a></li>26 <li><a href="#docs">Developer Documentation</a></li>27 <li><a href="#debugging">Debugging</a></li>28 <li><a href="#testing">Testing</a>29 <ul>30 <li><a href="#testingNonWindows">Testing on Unix-like Systems</a></li>31 <li><a href="#testingWindows">Testing using Visual Studio on Windows</a></li>32 <li><a href="#testingCommands">Testing on the Command Line</a></li>33 <li><a href="#testingLibc++">Testing changes affecting libc++</a></li>34 </ul>35 </li>36 <li><a href="#patches">Creating Patch Files</a></li>37 <li><a href="#irgen">LLVM IR Generation</a></li>38 </ul>39 40 <!--=====================================================================-->41 <h2 id="style">Coding Standards</h2>42 <!--=====================================================================-->43 44 <p>Clang follows the45 LLVM <a href="https://llvm.org/docs/CodingStandards.html">Coding46 Standards</a>. When submitting patches, please take care to follow these standards47 and to match the style of the code to that present in Clang (for example, in48 terms of indentation, bracing, and statement spacing).</p>49 50 <p>Clang has a few additional coding standards:</p>51 <ul>52 <li><i>cstdio is forbidden</i>: library code should not output diagnostics53 or other information using <tt>cstdio</tt>; debugging routines should54 use <tt>llvm::errs()</tt>. Other uses of <tt>cstdio</tt> impose behavior55 upon clients and block integrating Clang as a library. Libraries should56 support <tt>raw_ostream</tt> based interfaces for textual57 output. See <a href="https://llvm.org/docs/CodingStandards.html#use-raw-ostream">Coding58 Standards</a>.</li>59 </ul>60 61 <!--=====================================================================-->62 <h2 id="docs">Developer Documentation</h2>63 <!--=====================================================================-->64 65 <p>Both Clang and LLVM use doxygen to provide API documentation. Their66 respective web pages (generated nightly) are here:</p>67 <ul>68 <li><a href="https://clang.llvm.org/doxygen">Clang</a></li>69 <li><a href="https://llvm.org/doxygen">LLVM</a></li>70 </ul>71 72 <p>For work on the LLVM IR generation, the LLVM assembly language73 <a href="https://llvm.org/docs/LangRef.html">reference manual</a> is74 also useful.</p>75 76 <!--=====================================================================-->77 <h2 id="debugging">Debugging</h2>78 <!--=====================================================================-->79 80 <p>Inspecting data structures in a debugger:</p>81 <ul>82 <li>Many LLVM and Clang data structures provide83 a <tt>dump()</tt> method which will print a description of the84 data structure to <tt>stderr</tt>.</li>85 <li>The <a href="docs/InternalsManual.html#QualType"><tt>QualType</tt></a>86 structure is used pervasively. This is a simple value class for87 wrapping types with qualifiers; you can use88 the <tt>isConstQualified()</tt>, for example, to get one of the89 qualifiers, and the <tt>getTypePtr()</tt> method to get the90 wrapped <tt>Type*</tt> which you can then dump.</li>91 <li>For <a href="https://lldb.llvm.org"> <tt>LLDB</tt></a> users there are92 data formatters for LLVM data structures in93 <a href="https://github.com/llvm/llvm-project/blob/main/llvm/utils/lldbDataFormatters.py">94 <tt>llvm/utils/lldbDataFormatters.py</tt></a>.</li>95 </ul>96 97 <!--=====================================================================-->98 <h3 id="debuggingVisualStudio">Debugging using Visual Studio</h3>99 <!--=====================================================================-->100 101 <p>The files102 <a href="https://github.com/llvm/llvm-project/blob/main/llvm/utils/LLVMVisualizers/llvm.natvis">103 <tt>llvm/utils/LLVMVisualizers/llvm.natvis</tt></a> and104 <a href="https://github.com/llvm/llvm-project/blob/main/clang/utils/ClangVisualizers/clang.natvis">105 <tt>clang/utils/ClangVisualizers/clang.natvis</tt></a> provide debugger visualizers106 that make debugging of more complex data types much easier.</p>107 <p>Depending on how you configure the project, Visual Studio may automatically108 use these visualizers when debugging or you may be required to put the files109 into <tt>%USERPROFILE%\Documents\Visual Studio <version>\Visualizers</tt>110 or create a symbolic link so they update automatically. See111 <a href="https://learn.microsoft.com/en-us/visualstudio/debugger/create-custom-views-of-native-objects">112 Microsoft's documentation</a> for more details on use of NATVIS.</p>113 114 <!--=====================================================================-->115 <h2 id="testing">Testing</h2>116 <!--=====================================================================-->117 118 <!--=====================================================================-->119 <h3 id="testingNonWindows">Testing on Unix-like Systems</h3>120 <!--=====================================================================-->121 122 <p>Clang includes a basic regression suite in the tree which can be123 run with <tt>make test</tt> from the top-level clang directory, or124 just <tt>make</tt> in the <em>test</em> sub-directory.125 <tt>make VERBOSE=1</tt> can be used to show more detail126 about what is being run.</p>127 128 <p>If you built LLVM and Clang using CMake, the test suite can be run129 with <tt>make check-clang</tt> from the top-level LLVM directory.</p>130 131 <p>The tests primarily consist of a test runner script running the compiler132 under test on individual test files grouped in the directories under the133 test directory. The individual test files include comments at the134 beginning indicating the Clang compile options to use, to be read135 by the test runner. Embedded comments also can do things like telling136 the test runner that an error is expected at the current line.137 Any output files produced by the test will be placed under138 a created Output directory.</p>139 140 <p>During the run of <tt>make test</tt>, the terminal output will141 display a line similar to the following:</p>142 143 <pre>--- Running clang tests for i686-pc-linux-gnu ---</pre>144 145 <p>followed by a line continually overwritten with the current test146 file being compiled, and an overall completion percentage.</p>147 148 <p>After the <tt>make test</tt> run completes, the absence of any149 <tt>Failing Tests (count):</tt> message indicates that no tests150 failed unexpectedly. If any tests did fail, the151 <tt>Failing Tests (count):</tt> message will be followed by a list152 of the test source file paths that failed. For example:</p>153 154 <pre>155 Failing Tests (3):156 /home/john/llvm/tools/clang/test/SemaCXX/member-name-lookup.cpp157 /home/john/llvm/tools/clang/test/SemaCXX/namespace-alias.cpp158 /home/john/llvm/tools/clang/test/SemaCXX/using-directive.cpp159</pre>160 161 <p>If you used the <tt>make VERBOSE=1</tt> option, the terminal162 output will reflect the error messages from the compiler and163 test runner.</p>164 165 <p>The regression suite can also be run with Valgrind by running166 <tt>make test VG=1</tt> in the top-level clang directory.</p>167 168 <p>For more intensive changes, running169 the <a href="https://llvm.org/docs/TestingGuide.html#quick-start">LLVM170 Test Suite</a> with clang is recommended. Currently the best way to171 override LLVMGCC, as in: <tt>make LLVMGCC="clang -std=gnu89"172 TEST=nightly report</tt> (make sure <tt>clang</tt> is in your PATH or use the173 full path).</p>174 175 <!--=====================================================================-->176 <h3 id="testingWindows">Testing using Visual Studio on Windows</h3>177 <!--=====================================================================-->178 179 <p>The Clang test suite can be run from either Visual Studio or180 the command line.</p>181 182 <p>Note that the test runner is based on183 Python, which must be installed. Find Python at:184 <a href="https://www.python.org/downloads/">https://www.python.org/downloads/</a>.185 Download the latest stable version.</p>186 187 <p>The GnuWin32 tools are also necessary for running the tests.188 Get them from <a href="http://getgnuwin32.sourceforge.net/">189 http://getgnuwin32.sourceforge.net/</a>.190 If the environment variable <tt>%PATH%</tt> does not have GnuWin32,191 or if other grep(s) supercedes GnuWin32 on <tt>%PATH%,</tt>192 you should specify <tt>LLVM_LIT_TOOLS_DIR</tt>193 to CMake explicitly.</p>194 195 <p>The cmake build tool is set up to create Visual Studio project files196 for running the tests, "check-clang" being the root. Therefore, to197 run the test from Visual Studio, right-click the check-clang project198 and select "Build".</p>199 200 <p>201 Please see also202 <a href="https://llvm.org/docs/GettingStartedVS.html">Getting Started203 with the LLVM System using Microsoft Visual Studio</a> and204 <a href="https://llvm.org/docs/CMake.html">Building LLVM with CMake</a>.205 </p>206 207 <!--=====================================================================-->208 <h3 id="testingCommands">Testing on the Command Line</h3>209 <!--=====================================================================-->210 211 <p>If you want more control over how the tests are run, it may212 be convenient to run the test harness on the command-line directly. Before213 running tests from the command line, you will need to ensure that214 <tt>lit.site.cfg</tt> files have been created for your build. You can do215 this by running the tests as described in the previous sections. Once the216 tests have started running, you can stop them with control+C, as the217 files are generated before running any tests.</p>218 219 <p>Once that is done, to run all the tests from the command line,220 execute a command like the following:</p>221 222 <pre>223 python (path to llvm)\llvm\utils\lit\lit.py -sv224 --param=build_mode=Win32 --param=build_config=Debug225 --param=clang_site_config=(build dir)\tools\clang\test\lit.site.cfg226 (path to llvm)\llvm\tools\clang\test227</pre>228 229 <p>For CMake builds e.g. on Windows with Visual Studio, you will need230 to specify your build configuration (Debug, Release, etc.) via231 <tt>--param=build_config=(build config)</tt>. You may also need to specify232 the build mode (Win32, etc) via <tt>--param=build_mode=(build mode)</tt>.</p>233 234 <p>Additionally, you will need to specify the lit site configuration which235 lives in (build dir)\tools\clang\test, via236 <tt>--param=clang_site_config=(build dir)\tools\clang\test\lit.site.cfg</tt>.237 </p>238 239 <p>To run a single test:</p>240 241 <pre>242 python (path to llvm)\llvm\utils\lit\lit.py -sv243 --param=build_mode=Win32 --param=build_config=Debug244 --param=clang_site_config=(build dir)\tools\clang\test\lit.site.cfg245 (path to llvm)\llvm\tools\clang\test\(dir)\(test)246</pre>247 248 <p>For example:</p>249 250 <pre>251 python C:\Tools\llvm\utils\lit\lit.py -sv252 --param=build_mode=Win32 --param=build_config=Debug253 --param=clang_site_config=C:\Tools\build\tools\clang\test\lit.site.cfg254 C:\Tools\llvm\tools\clang\test\Sema\wchar.c255</pre>256 257 <p>The -sv option above tells the runner to show the test output if258 any tests failed, to help you determine the cause of failure.</p>259 260 <p>You can also pass in the --no-progress-bar option if you wish to disable261 progress indications while the tests are running.</p>262 263 <p>Your output might look something like this:</p>264 265 <pre>lit.py: lit.cfg:152: note: using clang: 'C:\Tools\llvm\bin\Release\clang.EXE'266-- Testing: Testing: 2534 tests, 4 threads --267Testing: 0 .. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80.. 90..268Testing Time: 81.52s269 Passed : 2503270 Expectedly Failed: 28271 Unsupported : 3272</pre>273 274 <p>The statistic, "Failed" (not shown if all tests pass), is the important one.</p>275 276 <!--=====================================================================-->277 <h3 id="testingLibc++">Testing changes affecting libc++</h3>278 <!--=====================================================================-->279 280 <p>Some changes in Clang affect <a href="https://libcxx.llvm.org">libc++</a>,281 for example:</p>282 <ul>283 <li>Changing the output of Clang's diagnostics.</li>284 <li>Changing compiler builtins, especially the builtins used for type traits285 or replacements of library functions like <tt>std::move</tt> or286 <tt>std::forward</tt>.</li>287 </ul>288 289 <p>After adjusting libc++ to work with the changes, the next revision will be290 tested by libc++'s291 <a href="https://buildkite.com/llvm-project/libcxx-ci">pre-commit CI</a>.292 293 <p>For most configurations, the pre-commit CI uses a recent294 <a href="https://apt.llvm.org/">nightly build</a> of Clang from LLVM's main295 branch. These configurations do <em>not</em> use the Clang changes in the296 patch. They only use the libc++ changes.</p>297 298 <p>The "Bootstrapping build" builds Clang and uses it to build and299 test libc++. This build <em>does</em> use the Clang changes in the patch.</p>300 301 <p>Libc++ supports multiple versions of Clang. Therefore when a patch changes302 the diagnostics it might be required to use a regex in the303 "expected" tests to make it pass the CI.</p>304 305 <p>Libc++ has more306 <a href="https://libcxx.llvm.org/Contributing.html#pre-commit-ci">307 documentation</a> about the pre-commit CI. For questions regarding308 libc++, the best place to ask is the <tt>#libcxx</tt> channel on309 <a href="https://discord.gg/jzUbyP26tQ">LLVM's Discord server</a>.</p>310 311 <!--=====================================================================-->312 <h2 id="patches">Creating Patch Files</h2>313 <!--=====================================================================-->314 315 <p>To contribute changes to Clang see316 <a href="https://llvm.org/docs/GettingStarted.html#sending-patches">LLVM's Getting Started page</a></p>317 318 <!--=====================================================================-->319 <h2 id="irgen">LLVM IR Generation</h2>320 <!--=====================================================================-->321 322 <p>The LLVM IR generation part of clang handles conversion of the323 AST nodes output by the Sema module to the LLVM Intermediate324 Representation (IR). Historically, this was referred to as325 "codegen", and the Clang code for this lives326 in <tt>lib/CodeGen</tt>.</p>327 328 <p>The output is most easily inspected using the <tt>-emit-llvm</tt>329 option to clang (possibly in conjunction with <tt>-o -</tt>). You330 can also use <tt>-emit-llvm-bc</tt> to write an LLVM bitcode file331 which can be processed by the suite of LLVM tools332 like <tt>llvm-dis</tt>, <tt>llvm-nm</tt>, etc. See the LLVM333 <a href="https://llvm.org/docs/CommandGuide/">Command Guide</a>334 for more information.</p>335 336</div>337</body>338</html>339