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 </ul> 34 </li> 35 <li><a href="#patches">Creating Patch Files</a></li> 36 <li><a href="#irgen">LLVM IR Generation</a></li> 37 </ul> 38 39 <!--=====================================================================--> 40 <h2 id="style">Coding Standards</h2> 41 <!--=====================================================================--> 42 43 <p>Clang follows the 44 LLVM <a href="http://llvm.org/docs/CodingStandards.html">Coding 45 Standards</a>. When submitting patches, please take care to follow these standards 46 and to match the style of the code to that present in Clang (for example, in 47 terms of indentation, bracing, and statement spacing).</p> 48 49 <p>Clang has a few additional coding standards:</p> 50 <ul> 51 <li><i>cstdio is forbidden</i>: library code should not output diagnostics 52 or other information using <tt>cstdio</tt>; debugging routines should 53 use <tt>llvm::errs()</tt>. Other uses of <tt>cstdio</tt> impose behavior 54 upon clients and block integrating Clang as a library. Libraries should 55 support <tt>raw_ostream</tt> based interfaces for textual 56 output. See <a href="http://llvm.org/docs/CodingStandards.html#ll_raw_ostream">Coding 57 Standards</a>.</li> 58 </ul> 59 60 <!--=====================================================================--> 61 <h2 id="docs">Developer Documentation</h2> 62 <!--=====================================================================--> 63 64 <p>Both Clang and LLVM use doxygen to provide API documentation. Their 65 respective web pages (generated nightly) are here:</p> 66 <ul> 67 <li><a href="http://clang.llvm.org/doxygen">Clang</a></li> 68 <li><a href="http://llvm.org/doxygen">LLVM</a></li> 69 </ul> 70 71 <p>For work on the LLVM IR generation, the LLVM assembly language 72 <a href="http://llvm.org/docs/LangRef.html">reference manual</a> is 73 also useful.</p> 74 75 <!--=====================================================================--> 76 <h2 id="debugging">Debugging</h2> 77 <!--=====================================================================--> 78 79 <p>Inspecting data structures in a debugger:</p> 80 <ul> 81 <li>Many LLVM and Clang data structures provide 82 a <tt>dump()</tt> method which will print a description of the 83 data structure to <tt>stderr</tt>.</li> 84 <li>The <a href="docs/InternalsManual.html#QualType"><tt>QualType</tt></a> 85 structure is used pervasively. This is a simple value class for 86 wrapping types with qualifiers; you can use 87 the <tt>isConstQualified()</tt>, for example, to get one of the 88 qualifiers, and the <tt>getTypePtr()</tt> method to get the 89 wrapped <tt>Type*</tt> which you can then dump.</li> 90 <li>For <a href="http://lldb.llvm.org"> <tt>LLDB</tt></a> users there are 91 data formatters for clang data structures in 92 <a href="http://llvm.org/svn/llvm-project/cfe/trunk/utils/ClangDataFormat.py"> 93 <tt>utils/ClangDataFormat.py</tt></a>.</li> 94 </ul> 95 96 <!--=====================================================================--> 97 <h3 id="debuggingVisualStudio">Debugging using Visual Studio</h3> 98 <!--=====================================================================--> 99 100 <p>The file <tt>utils/clangVisualizers.txt</tt> provides debugger visualizers that make debugging 101 of more complex data types much easier.</p> 102 <p>There are two ways to install them:</p> 103 104 <ul> 105 <li>Put the path to <tt>clangVisualizers.txt</tt> in the environment variable called 106 <tt>_vcee_autoexp</tt>. This method should work for Visual Studio 2008 and above. 107 </li> 108 <li>Edit your local <tt>autoexp.dat</tt> (make sure you make a backup first!), 109 located in <tt>Visual Studio Directory\Common7\Packages\Debugger</tt> and append 110 the contents of <tt>clangVisuailzers.txt</tt> to it. This method should work for 111 Visual Studio 2008 and above. 112 </li> 113 </ul> 114 115 <p><i>[Note: To disable the visualizer for any specific variable, type 116 <tt>variable_name,!</tt> inside the watch window.]</i></p> 117 118 <!--=====================================================================--> 119 <h2 id="testing">Testing</h2> 120 <!--=====================================================================--> 121 122 <p><i>[Note: The test running mechanism is currently under revision, so the 123 following might change shortly.]</i></p> 124 125 <!--=====================================================================--> 126 <h3 id="testingNonWindows">Testing on Unix-like Systems</h3> 127 <!--=====================================================================--> 128 129 <p>Clang includes a basic regression suite in the tree which can be 130 run with <tt>make test</tt> from the top-level clang directory, or 131 just <tt>make</tt> in the <em>test</em> sub-directory. 132 <tt>make VERBOSE=1</tt> can be used to show more detail 133 about what is being run.</p> 134 135 <p>If you built LLVM and Clang using CMake, the test suite can be run 136 with <tt>make clang-test</tt> from the top-level LLVM directory.</p> 137 138 <p>The tests primarily consist of a test runner script running the compiler 139 under test on individual test files grouped in the directories under the 140 test directory. The individual test files include comments at the 141 beginning indicating the Clang compile options to use, to be read 142 by the test runner. Embedded comments also can do things like telling 143 the test runner that an error is expected at the current line. 144 Any output files produced by the test will be placed under 145 a created Output directory.</p> 146 147 <p>During the run of <tt>make test</tt>, the terminal output will 148 display a line similar to the following:</p> 149 150 <pre>--- Running clang tests for i686-pc-linux-gnu ---</pre> 151 152 <p>followed by a line continually overwritten with the current test 153 file being compiled, and an overall completion percentage.</p> 154 155 <p>After the <tt>make test</tt> run completes, the absence of any 156 <tt>Failing Tests (count):</tt> message indicates that no tests 157 failed unexpectedly. If any tests did fail, the 158 <tt>Failing Tests (count):</tt> message will be followed by a list 159 of the test source file paths that failed. For example:</p> 160 161 <pre> 162 Failing Tests (3): 163 /home/john/llvm/tools/clang/test/SemaCXX/member-name-lookup.cpp 164 /home/john/llvm/tools/clang/test/SemaCXX/namespace-alias.cpp 165 /home/john/llvm/tools/clang/test/SemaCXX/using-directive.cpp 166</pre> 167 168 <p>If you used the <tt>make VERBOSE=1</tt> option, the terminal 169 output will reflect the error messages from the compiler and 170 test runner.</p> 171 172 <p>The regression suite can also be run with Valgrind by running 173 <tt>make test VG=1</tt> in the top-level clang directory.</p> 174 175 <p>For more intensive changes, running 176 the <a href="http://llvm.org/docs/TestingGuide.html#testsuiterun">LLVM 177 Test Suite</a> with clang is recommended. Currently the best way to 178 override LLVMGCC, as in: <tt>make LLVMGCC="clang -std=gnu89" 179 TEST=nightly report</tt> (make sure <tt>clang</tt> is in your PATH or use the 180 full path).</p> 181 182 <!--=====================================================================--> 183 <h3 id="testingWindows">Testing using Visual Studio on Windows</h3> 184 <!--=====================================================================--> 185 186 <p>The Clang test suite can be run from either Visual Studio or 187 the command line.</p> 188 189 <p>Note that the test runner is based on 190 Python, which must be installed. Find Python at: 191 <a href="http://www.python.org/download/">http://www.python.org/download/</a>. 192 Download the latest stable version (2.6.2 at the time of this writing).</p> 193 194 <p>The GnuWin32 tools are also necessary for running the tests. 195 Get them from <a href="http://getgnuwin32.sourceforge.net/"> 196 http://getgnuwin32.sourceforge.net/</a>. 197 If the environment variable <tt>%PATH%</tt> does not have GnuWin32, 198 or if other grep(s) supercedes GnuWin32 on <tt>%PATH%,</tt> 199 you should specify <tt>LLVM_LIT_TOOLS_DIR</tt> 200 to CMake explicitly.</p> 201 202 <p>The cmake build tool is set up to create Visual Studio project files 203 for running the tests, "clang-test" being the root. Therefore, to 204 run the test from Visual Studio, right-click the clang-test project 205 and select "Build".</p> 206 207 <p> 208 Please see also 209 <a href="http://llvm.org/docs/GettingStartedVS.html">Getting Started 210 with the LLVM System using Microsoft Visual Studio</a> and 211 <a href="http://llvm.org/docs/CMake.html">Building LLVM with CMake</a>. 212 </p> 213 214 <!--=====================================================================--> 215 <h3 id="testingCommands">Testing on the Command Line</h3> 216 <!--=====================================================================--> 217 218 <p>If you want more control over how the tests are run, it may 219 be convenient to run the test harness on the command-line directly. Before 220 running tests from the command line, you will need to ensure that 221 <tt>lit.site.cfg</tt> files have been created for your build. You can do 222 this by running the tests as described in the previous sections. Once the 223 tests have started running, you can stop them with control+C, as the 224 files are generated before running any tests.</p> 225 226 <p>Once that is done, to run all the tests from the command line, 227 execute a command like the following:</p> 228 229 <pre> 230 python (path to llvm)\llvm\utils\lit\lit.py -sv 231 --param=build_mode=Win32 --param=build_config=Debug 232 --param=clang_site_config=(build dir)\tools\clang\test\lit.site.cfg 233 (path to llvm)\llvm\tools\clang\test 234</pre> 235 236 <p>For CMake builds e.g. on Windows with Visual Studio, you will need 237 to specify your build configuration (Debug, Release, etc.) via 238 <tt>--param=build_config=(build config)</tt>. You may also need to specify 239 the build mode (Win32, etc) via <tt>--param=build_mode=(build mode)</tt>.</p> 240 241 <p>Additionally, you will need to specify the lit site configuration which 242 lives in (build dir)\tools\clang\test, via 243 <tt>--param=clang_site_config=(build dir)\tools\clang\test\lit.site.cfg</tt>. 244 </p> 245 246 <p>To run a single test:</p> 247 248 <pre> 249 python (path to llvm)\llvm\utils\lit\lit.py -sv 250 --param=build_mode=Win32 --param=build_config=Debug 251 --param=clang_site_config=(build dir)\tools\clang\test\lit.site.cfg 252 (path to llvm)\llvm\tools\clang\test\(dir)\(test) 253</pre> 254 255 <p>For example:</p> 256 257 <pre> 258 python C:\Tool\llvm\utils\lit\lit.py -sv 259 --param=build_mode=Win32 --param=build_config=Debug 260 --param=clang_site_config=c:\Tools\build\tools\clang\test\lit.site.cfg 261 C:\Tools\llvm\tools\clang\test\Sema\wchar.c 262</pre> 263 264 <p>The -sv option above tells the runner to show the test output if 265 any tests failed, to help you determine the cause of failure.</p> 266 267 <p>You can also pass in the --no-progress-bar option if you wish to disable 268 progress indications while the tests are running.</p> 269 270 <p>Your output might look something like this:</p> 271 272 <pre>lit.py: lit.cfg:152: note: using clang: 'C:\Tools\llvm\bin\Release\clang.EXE' 273-- Testing: Testing: 2534 tests, 4 threads -- 274Testing: 0 .. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80.. 90.. 275Testing Time: 81.52s 276 Expected Passes : 2503 277 Expected Failures : 28 278 Unsupported Tests : 3 279</pre> 280 281 <p>The statistic, "Unexpected Failures" (not shown if all tests pass), is the important one.</p> 282 283 <!--=====================================================================--> 284 <h2 id="patches">Creating Patch Files</h2> 285 <!--=====================================================================--> 286 287 <p>To return changes to the Clang team, unless you have checkin 288 privileges, the preferred way is to send patch files to the 289 cfe-commits mailing list, with an explanation of what the patch is 290 for. If your patch requires a wider discussion (for example, 291 because it is an architectural change), you can use the cfe-dev 292 mailing list. </p> 293 294 <p>To create these patch files, change directory 295 to the llvm/tools/clang root and run:</p> 296 297 <pre>svn diff (relative path) >(patch file name)</pre> 298 299 <p>For example, for getting the diffs of all of clang:</p> 300 301 <pre>svn diff . >~/mypatchfile.patch</pre> 302 303 <p>For example, for getting the diffs of a single file:</p> 304 305 <pre>svn diff lib/Parse/ParseDeclCXX.cpp >~/ParseDeclCXX.patch</pre> 306 307 <p>Note that the paths embedded in the patch depend on where you run it, 308 so changing directory to the llvm/tools/clang directory is recommended.</p> 309 310 <!--=====================================================================--> 311 <h2 id="irgen">LLVM IR Generation</h2> 312 <!--=====================================================================--> 313 314 <p>The LLVM IR generation part of clang handles conversion of the 315 AST nodes output by the Sema module to the LLVM Intermediate 316 Representation (IR). Historically, this was referred to as 317 "codegen", and the Clang code for this lives 318 in <tt>lib/CodeGen</tt>.</p> 319 320 <p>The output is most easily inspected using the <tt>-emit-llvm</tt> 321 option to clang (possibly in conjunction with <tt>-o -</tt>). You 322 can also use <tt>-emit-llvm-bc</tt> to write an LLVM bitcode file 323 which can be processed by the suite of LLVM tools 324 like <tt>llvm-dis</tt>, <tt>llvm-nm</tt>, etc. See the LLVM 325 <a href="http://llvm.org/docs/CommandGuide/">Command Guide</a> 326 for more information.</p> 327 328</div> 329</body> 330</html> 331