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=ISO-8859-1"> 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 hacking 22 on Clang for developers who are new to the Clang and/or LLVM 23 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 the 45 LLVM <a href="https://llvm.org/docs/CodingStandards.html">Coding 46 Standards</a>. When submitting patches, please take care to follow these standards 47 and to match the style of the code to that present in Clang (for example, in 48 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 diagnostics 53 or other information using <tt>cstdio</tt>; debugging routines should 54 use <tt>llvm::errs()</tt>. Other uses of <tt>cstdio</tt> impose behavior 55 upon clients and block integrating Clang as a library. Libraries should 56 support <tt>raw_ostream</tt> based interfaces for textual 57 output. See <a href="https://llvm.org/docs/CodingStandards.html#use-raw-ostream">Coding 58 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. Their 66 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 language 73 <a href="https://llvm.org/docs/LangRef.html">reference manual</a> is 74 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 provide 83 a <tt>dump()</tt> method which will print a description of the 84 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 for 87 wrapping types with qualifiers; you can use 88 the <tt>isConstQualified()</tt>, for example, to get one of the 89 qualifiers, and the <tt>getTypePtr()</tt> method to get the 90 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 are 92 data formatters for clang data structures in 93 <a href="https://github.com/llvm/llvm-project/blob/main/clang/utils/ClangDataFormat.py"> 94 <tt>clang/utils/ClangDataFormat.py</tt></a>.</li> 95 </ul> 96 97 <!--=====================================================================--> 98 <h3 id="debuggingVisualStudio">Debugging using Visual Studio</h3> 99 <!--=====================================================================--> 100 101 <p>The files 102 <a href="https://github.com/llvm/llvm-project/blob/main/llvm/utils/LLVMVisualizers/llvm.natvis"> 103 <tt>llvm/utils/LLVMVisualizers/llvm.natvis</tt></a> and 104 <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 visualizers 106 that make debugging of more complex data types much easier.</p> 107 <p>For Visual Studio 2013 only, put the files into 108 <tt>%USERPROFILE%\Documents\Visual Studio 2013\Visualizers</tt> or 109 create a symbolic link so they update automatically.</p> 110 <p>For later versions of Visual Studio, no installation is required. 111 Note also that later versions of Visual Studio also display better visualizations.</p> 112 113 <!--=====================================================================--> 114 <h2 id="testing">Testing</h2> 115 <!--=====================================================================--> 116 117 <!--=====================================================================--> 118 <h3 id="testingNonWindows">Testing on Unix-like Systems</h3> 119 <!--=====================================================================--> 120 121 <p>Clang includes a basic regression suite in the tree which can be 122 run with <tt>make test</tt> from the top-level clang directory, or 123 just <tt>make</tt> in the <em>test</em> sub-directory. 124 <tt>make VERBOSE=1</tt> can be used to show more detail 125 about what is being run.</p> 126 127 <p>If you built LLVM and Clang using CMake, the test suite can be run 128 with <tt>make clang-test</tt> from the top-level LLVM directory.</p> 129 130 <p>The tests primarily consist of a test runner script running the compiler 131 under test on individual test files grouped in the directories under the 132 test directory. The individual test files include comments at the 133 beginning indicating the Clang compile options to use, to be read 134 by the test runner. Embedded comments also can do things like telling 135 the test runner that an error is expected at the current line. 136 Any output files produced by the test will be placed under 137 a created Output directory.</p> 138 139 <p>During the run of <tt>make test</tt>, the terminal output will 140 display a line similar to the following:</p> 141 142 <pre>--- Running clang tests for i686-pc-linux-gnu ---</pre> 143 144 <p>followed by a line continually overwritten with the current test 145 file being compiled, and an overall completion percentage.</p> 146 147 <p>After the <tt>make test</tt> run completes, the absence of any 148 <tt>Failing Tests (count):</tt> message indicates that no tests 149 failed unexpectedly. If any tests did fail, the 150 <tt>Failing Tests (count):</tt> message will be followed by a list 151 of the test source file paths that failed. For example:</p> 152 153 <pre> 154 Failing Tests (3): 155 /home/john/llvm/tools/clang/test/SemaCXX/member-name-lookup.cpp 156 /home/john/llvm/tools/clang/test/SemaCXX/namespace-alias.cpp 157 /home/john/llvm/tools/clang/test/SemaCXX/using-directive.cpp 158</pre> 159 160 <p>If you used the <tt>make VERBOSE=1</tt> option, the terminal 161 output will reflect the error messages from the compiler and 162 test runner.</p> 163 164 <p>The regression suite can also be run with Valgrind by running 165 <tt>make test VG=1</tt> in the top-level clang directory.</p> 166 167 <p>For more intensive changes, running 168 the <a href="https://llvm.org/docs/TestingGuide.html#quick-start">LLVM 169 Test Suite</a> with clang is recommended. Currently the best way to 170 override LLVMGCC, as in: <tt>make LLVMGCC="clang -std=gnu89" 171 TEST=nightly report</tt> (make sure <tt>clang</tt> is in your PATH or use the 172 full path).</p> 173 174 <!--=====================================================================--> 175 <h3 id="testingWindows">Testing using Visual Studio on Windows</h3> 176 <!--=====================================================================--> 177 178 <p>The Clang test suite can be run from either Visual Studio or 179 the command line.</p> 180 181 <p>Note that the test runner is based on 182 Python, which must be installed. Find Python at: 183 <a href="https://www.python.org/downloads/">https://www.python.org/downloads/</a>. 184 Download the latest stable version.</p> 185 186 <p>The GnuWin32 tools are also necessary for running the tests. 187 Get them from <a href="http://getgnuwin32.sourceforge.net/"> 188 http://getgnuwin32.sourceforge.net/</a>. 189 If the environment variable <tt>%PATH%</tt> does not have GnuWin32, 190 or if other grep(s) supercedes GnuWin32 on <tt>%PATH%,</tt> 191 you should specify <tt>LLVM_LIT_TOOLS_DIR</tt> 192 to CMake explicitly.</p> 193 194 <p>The cmake build tool is set up to create Visual Studio project files 195 for running the tests, "clang-test" being the root. Therefore, to 196 run the test from Visual Studio, right-click the clang-test project 197 and select "Build".</p> 198 199 <p> 200 Please see also 201 <a href="https://llvm.org/docs/GettingStartedVS.html">Getting Started 202 with the LLVM System using Microsoft Visual Studio</a> and 203 <a href="https://llvm.org/docs/CMake.html">Building LLVM with CMake</a>. 204 </p> 205 206 <!--=====================================================================--> 207 <h3 id="testingCommands">Testing on the Command Line</h3> 208 <!--=====================================================================--> 209 210 <p>If you want more control over how the tests are run, it may 211 be convenient to run the test harness on the command-line directly. Before 212 running tests from the command line, you will need to ensure that 213 <tt>lit.site.cfg</tt> files have been created for your build. You can do 214 this by running the tests as described in the previous sections. Once the 215 tests have started running, you can stop them with control+C, as the 216 files are generated before running any tests.</p> 217 218 <p>Once that is done, to run all the tests from the command line, 219 execute a command like the following:</p> 220 221 <pre> 222 python (path to llvm)\llvm\utils\lit\lit.py -sv 223 --param=build_mode=Win32 --param=build_config=Debug 224 --param=clang_site_config=(build dir)\tools\clang\test\lit.site.cfg 225 (path to llvm)\llvm\tools\clang\test 226</pre> 227 228 <p>For CMake builds e.g. on Windows with Visual Studio, you will need 229 to specify your build configuration (Debug, Release, etc.) via 230 <tt>--param=build_config=(build config)</tt>. You may also need to specify 231 the build mode (Win32, etc) via <tt>--param=build_mode=(build mode)</tt>.</p> 232 233 <p>Additionally, you will need to specify the lit site configuration which 234 lives in (build dir)\tools\clang\test, via 235 <tt>--param=clang_site_config=(build dir)\tools\clang\test\lit.site.cfg</tt>. 236 </p> 237 238 <p>To run a single test:</p> 239 240 <pre> 241 python (path to llvm)\llvm\utils\lit\lit.py -sv 242 --param=build_mode=Win32 --param=build_config=Debug 243 --param=clang_site_config=(build dir)\tools\clang\test\lit.site.cfg 244 (path to llvm)\llvm\tools\clang\test\(dir)\(test) 245</pre> 246 247 <p>For example:</p> 248 249 <pre> 250 python C:\Tools\llvm\utils\lit\lit.py -sv 251 --param=build_mode=Win32 --param=build_config=Debug 252 --param=clang_site_config=C:\Tools\build\tools\clang\test\lit.site.cfg 253 C:\Tools\llvm\tools\clang\test\Sema\wchar.c 254</pre> 255 256 <p>The -sv option above tells the runner to show the test output if 257 any tests failed, to help you determine the cause of failure.</p> 258 259 <p>You can also pass in the --no-progress-bar option if you wish to disable 260 progress indications while the tests are running.</p> 261 262 <p>Your output might look something like this:</p> 263 264 <pre>lit.py: lit.cfg:152: note: using clang: 'C:\Tools\llvm\bin\Release\clang.EXE' 265-- Testing: Testing: 2534 tests, 4 threads -- 266Testing: 0 .. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80.. 90.. 267Testing Time: 81.52s 268 Passed : 2503 269 Expectedly Failed: 28 270 Unsupported : 3 271</pre> 272 273 <p>The statistic, "Failed" (not shown if all tests pass), is the important one.</p> 274 275 <!--=====================================================================--> 276 <h3 id="testingLibc++">Testing changes affecting libc++</h3> 277 <!--=====================================================================--> 278 279 <p>Some changes in Clang affect <a href="https://libcxx.llvm.org">libc++</a>, 280 for example:</p> 281 <ul> 282 <li>Changing the output of Clang's diagnostics.</li> 283 <li>Changing compiler builtins, especially the builtins used for type traits 284 or replacements of library functions like <tt>std::move</tt> or 285 <tt>std::forward</tt>.</li> 286 </ul> 287 288 <p>After adjusting libc++ to work with the changes, the next revision will be 289 tested by libc++'s 290 <a href="https://buildkite.com/llvm-project/libcxx-ci">pre-commit CI</a>. 291 292 <p>For most configurations, the pre-commit CI uses a recent 293 <a href="https://apt.llvm.org/">nightly build</a> of Clang from LLVM's main 294 branch. These configurations do <em>not</em> use the Clang changes in the 295 patch. They only use the libc++ changes.</p> 296 297 <p>The "Bootstrapping build" builds Clang and uses it to build and 298 test libc++. This build <em>does</em> use the Clang changes in the patch.</p> 299 300 <p>Libc++ supports multiple versions of Clang. Therefore when a patch changes 301 the diagnostics it might be required to use a regex in the 302 "expected" tests to make it pass the CI.</p> 303 304 <p>Libc++ has more 305 <a href="https://libcxx.llvm.org/Contributing.html#pre-commit-ci"> 306 documentation</a> about the pre-commit CI. For questions regarding 307 libc++, the best place to ask is the <tt>#libcxx</tt> channel on 308 <a href="https://discord.gg/jzUbyP26tQ">LLVM's Discord server</a>.</p> 309 310 <!--=====================================================================--> 311 <h2 id="patches">Creating Patch Files</h2> 312 <!--=====================================================================--> 313 314 <p>To contribute changes to Clang see 315 <a href="https://llvm.org/docs/GettingStarted.html#sending-patches">LLVM's Getting Started page</a></p> 316 317 <!--=====================================================================--> 318 <h2 id="irgen">LLVM IR Generation</h2> 319 <!--=====================================================================--> 320 321 <p>The LLVM IR generation part of clang handles conversion of the 322 AST nodes output by the Sema module to the LLVM Intermediate 323 Representation (IR). Historically, this was referred to as 324 "codegen", and the Clang code for this lives 325 in <tt>lib/CodeGen</tt>.</p> 326 327 <p>The output is most easily inspected using the <tt>-emit-llvm</tt> 328 option to clang (possibly in conjunction with <tt>-o -</tt>). You 329 can also use <tt>-emit-llvm-bc</tt> to write an LLVM bitcode file 330 which can be processed by the suite of LLVM tools 331 like <tt>llvm-dis</tt>, <tt>llvm-nm</tt>, etc. See the LLVM 332 <a href="https://llvm.org/docs/CommandGuide/">Command Guide</a> 333 for more information.</p> 334 335</div> 336</body> 337</html> 338