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 files 101 <a href="http://llvm.org/svn/llvm-project/llvm/trunk/utils/LLVMVisualizers/llvm.natvis"> 102 <tt>utils/LLVMVisualizers/llvm.natvis</tt></a> and 103 <a href="http://llvm.org/svn/llvm-project/cfe/trunk/utils/ClangVisualizers/clang.natvis"> 104 <tt>utils/ClangVisualizers/clang.natvis</tt></a> provide debugger visualizers 105 that make debugging of more complex data types much easier.</p> 106 <p>For Visual Studio 2013 only, put the files into 107 <tt>%USERPROFILE%\Documents\Visual Studio 2013\Visualizers</tt> or 108 create a symbolic link so they update automatically.</p> 109 <p>For later versions of Visual Studio, no installation is required. 110 Note also that later versions of Visual Studio also display better visualizations.</p> 111 112 <!--=====================================================================--> 113 <h2 id="testing">Testing</h2> 114 <!--=====================================================================--> 115 116 <!--=====================================================================--> 117 <h3 id="testingNonWindows">Testing on Unix-like Systems</h3> 118 <!--=====================================================================--> 119 120 <p>Clang includes a basic regression suite in the tree which can be 121 run with <tt>make test</tt> from the top-level clang directory, or 122 just <tt>make</tt> in the <em>test</em> sub-directory. 123 <tt>make VERBOSE=1</tt> can be used to show more detail 124 about what is being run.</p> 125 126 <p>If you built LLVM and Clang using CMake, the test suite can be run 127 with <tt>make clang-test</tt> from the top-level LLVM directory.</p> 128 129 <p>The tests primarily consist of a test runner script running the compiler 130 under test on individual test files grouped in the directories under the 131 test directory. The individual test files include comments at the 132 beginning indicating the Clang compile options to use, to be read 133 by the test runner. Embedded comments also can do things like telling 134 the test runner that an error is expected at the current line. 135 Any output files produced by the test will be placed under 136 a created Output directory.</p> 137 138 <p>During the run of <tt>make test</tt>, the terminal output will 139 display a line similar to the following:</p> 140 141 <pre>--- Running clang tests for i686-pc-linux-gnu ---</pre> 142 143 <p>followed by a line continually overwritten with the current test 144 file being compiled, and an overall completion percentage.</p> 145 146 <p>After the <tt>make test</tt> run completes, the absence of any 147 <tt>Failing Tests (count):</tt> message indicates that no tests 148 failed unexpectedly. If any tests did fail, the 149 <tt>Failing Tests (count):</tt> message will be followed by a list 150 of the test source file paths that failed. For example:</p> 151 152 <pre> 153 Failing Tests (3): 154 /home/john/llvm/tools/clang/test/SemaCXX/member-name-lookup.cpp 155 /home/john/llvm/tools/clang/test/SemaCXX/namespace-alias.cpp 156 /home/john/llvm/tools/clang/test/SemaCXX/using-directive.cpp 157</pre> 158 159 <p>If you used the <tt>make VERBOSE=1</tt> option, the terminal 160 output will reflect the error messages from the compiler and 161 test runner.</p> 162 163 <p>The regression suite can also be run with Valgrind by running 164 <tt>make test VG=1</tt> in the top-level clang directory.</p> 165 166 <p>For more intensive changes, running 167 the <a href="http://llvm.org/docs/TestingGuide.html#testsuiterun">LLVM 168 Test Suite</a> with clang is recommended. Currently the best way to 169 override LLVMGCC, as in: <tt>make LLVMGCC="clang -std=gnu89" 170 TEST=nightly report</tt> (make sure <tt>clang</tt> is in your PATH or use the 171 full path).</p> 172 173 <!--=====================================================================--> 174 <h3 id="testingWindows">Testing using Visual Studio on Windows</h3> 175 <!--=====================================================================--> 176 177 <p>The Clang test suite can be run from either Visual Studio or 178 the command line.</p> 179 180 <p>Note that the test runner is based on 181 Python, which must be installed. Find Python at: 182 <a href="http://www.python.org/download/">http://www.python.org/download/</a>. 183 Download the latest stable version (2.6.2 at the time of this writing).</p> 184 185 <p>The GnuWin32 tools are also necessary for running the tests. 186 Get them from <a href="http://getgnuwin32.sourceforge.net/"> 187 http://getgnuwin32.sourceforge.net/</a>. 188 If the environment variable <tt>%PATH%</tt> does not have GnuWin32, 189 or if other grep(s) supercedes GnuWin32 on <tt>%PATH%,</tt> 190 you should specify <tt>LLVM_LIT_TOOLS_DIR</tt> 191 to CMake explicitly.</p> 192 193 <p>The cmake build tool is set up to create Visual Studio project files 194 for running the tests, "clang-test" being the root. Therefore, to 195 run the test from Visual Studio, right-click the clang-test project 196 and select "Build".</p> 197 198 <p> 199 Please see also 200 <a href="http://llvm.org/docs/GettingStartedVS.html">Getting Started 201 with the LLVM System using Microsoft Visual Studio</a> and 202 <a href="http://llvm.org/docs/CMake.html">Building LLVM with CMake</a>. 203 </p> 204 205 <!--=====================================================================--> 206 <h3 id="testingCommands">Testing on the Command Line</h3> 207 <!--=====================================================================--> 208 209 <p>If you want more control over how the tests are run, it may 210 be convenient to run the test harness on the command-line directly. Before 211 running tests from the command line, you will need to ensure that 212 <tt>lit.site.cfg</tt> files have been created for your build. You can do 213 this by running the tests as described in the previous sections. Once the 214 tests have started running, you can stop them with control+C, as the 215 files are generated before running any tests.</p> 216 217 <p>Once that is done, to run all the tests from the command line, 218 execute a command like the following:</p> 219 220 <pre> 221 python (path to llvm)\llvm\utils\lit\lit.py -sv 222 --param=build_mode=Win32 --param=build_config=Debug 223 --param=clang_site_config=(build dir)\tools\clang\test\lit.site.cfg 224 (path to llvm)\llvm\tools\clang\test 225</pre> 226 227 <p>For CMake builds e.g. on Windows with Visual Studio, you will need 228 to specify your build configuration (Debug, Release, etc.) via 229 <tt>--param=build_config=(build config)</tt>. You may also need to specify 230 the build mode (Win32, etc) via <tt>--param=build_mode=(build mode)</tt>.</p> 231 232 <p>Additionally, you will need to specify the lit site configuration which 233 lives in (build dir)\tools\clang\test, via 234 <tt>--param=clang_site_config=(build dir)\tools\clang\test\lit.site.cfg</tt>. 235 </p> 236 237 <p>To run a single test:</p> 238 239 <pre> 240 python (path to llvm)\llvm\utils\lit\lit.py -sv 241 --param=build_mode=Win32 --param=build_config=Debug 242 --param=clang_site_config=(build dir)\tools\clang\test\lit.site.cfg 243 (path to llvm)\llvm\tools\clang\test\(dir)\(test) 244</pre> 245 246 <p>For example:</p> 247 248 <pre> 249 python C:\Tool\llvm\utils\lit\lit.py -sv 250 --param=build_mode=Win32 --param=build_config=Debug 251 --param=clang_site_config=c:\Tools\build\tools\clang\test\lit.site.cfg 252 C:\Tools\llvm\tools\clang\test\Sema\wchar.c 253</pre> 254 255 <p>The -sv option above tells the runner to show the test output if 256 any tests failed, to help you determine the cause of failure.</p> 257 258 <p>You can also pass in the --no-progress-bar option if you wish to disable 259 progress indications while the tests are running.</p> 260 261 <p>Your output might look something like this:</p> 262 263 <pre>lit.py: lit.cfg:152: note: using clang: 'C:\Tools\llvm\bin\Release\clang.EXE' 264-- Testing: Testing: 2534 tests, 4 threads -- 265Testing: 0 .. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80.. 90.. 266Testing Time: 81.52s 267 Expected Passes : 2503 268 Expected Failures : 28 269 Unsupported Tests : 3 270</pre> 271 272 <p>The statistic, "Unexpected Failures" (not shown if all tests pass), is the important one.</p> 273 274 <!--=====================================================================--> 275 <h2 id="patches">Creating Patch Files</h2> 276 <!--=====================================================================--> 277 278 <p>To return changes to the Clang team, unless you have checkin 279 privileges, the preferred way is to send patch files to the 280 cfe-commits mailing list, with an explanation of what the patch is 281 for. clang follows <a 282 href="http://llvm.org/docs/DeveloperPolicy.html">LLVM's developer policy</a>. 283 If your patch requires a wider discussion (for example, because it is an 284 architectural change), you can use the cfe-dev mailing list.</p> 285 286 <p>To create these patch files, change directory 287 to the llvm/tools/clang root and run:</p> 288 289 <pre>svn diff (relative path) >(patch file name)</pre> 290 291 <p>For example, for getting the diffs of all of clang:</p> 292 293 <pre>svn diff . >~/mypatchfile.patch</pre> 294 295 <p>For example, for getting the diffs of a single file:</p> 296 297 <pre>svn diff lib/Parse/ParseDeclCXX.cpp >~/ParseDeclCXX.patch</pre> 298 299 <p>Note that the paths embedded in the patch depend on where you run it, 300 so changing directory to the llvm/tools/clang directory is recommended.</p> 301 302 <!--=====================================================================--> 303 <h2 id="irgen">LLVM IR Generation</h2> 304 <!--=====================================================================--> 305 306 <p>The LLVM IR generation part of clang handles conversion of the 307 AST nodes output by the Sema module to the LLVM Intermediate 308 Representation (IR). Historically, this was referred to as 309 "codegen", and the Clang code for this lives 310 in <tt>lib/CodeGen</tt>.</p> 311 312 <p>The output is most easily inspected using the <tt>-emit-llvm</tt> 313 option to clang (possibly in conjunction with <tt>-o -</tt>). You 314 can also use <tt>-emit-llvm-bc</tt> to write an LLVM bitcode file 315 which can be processed by the suite of LLVM tools 316 like <tt>llvm-dis</tt>, <tt>llvm-nm</tt>, etc. See the LLVM 317 <a href="http://llvm.org/docs/CommandGuide/">Command Guide</a> 318 for more information.</p> 319 320</div> 321</body> 322</html> 323