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/llvm.natvis"> 102 <tt>utils/llvm.natvis</tt></a> and 103 <a href="http://llvm.org/svn/llvm-project/cfe/trunk/utils/clang.natvis"> 104 <tt>utils/clang.natvis</tt></a> provide debugger visualizers 105 that make debugging of more complex data types much easier.</p> 106 <p>Put the files into 107 <tt>%USERPROFILE%\Documents\Visual Studio 2012\Visualizers</tt> or 108 create a symbolic link so they update automatically.</p> 109 110 <!--=====================================================================--> 111 <h2 id="testing">Testing</h2> 112 <!--=====================================================================--> 113 114 <!--=====================================================================--> 115 <h3 id="testingNonWindows">Testing on Unix-like Systems</h3> 116 <!--=====================================================================--> 117 118 <p>Clang includes a basic regression suite in the tree which can be 119 run with <tt>make test</tt> from the top-level clang directory, or 120 just <tt>make</tt> in the <em>test</em> sub-directory. 121 <tt>make VERBOSE=1</tt> can be used to show more detail 122 about what is being run.</p> 123 124 <p>If you built LLVM and Clang using CMake, the test suite can be run 125 with <tt>make clang-test</tt> from the top-level LLVM directory.</p> 126 127 <p>The tests primarily consist of a test runner script running the compiler 128 under test on individual test files grouped in the directories under the 129 test directory. The individual test files include comments at the 130 beginning indicating the Clang compile options to use, to be read 131 by the test runner. Embedded comments also can do things like telling 132 the test runner that an error is expected at the current line. 133 Any output files produced by the test will be placed under 134 a created Output directory.</p> 135 136 <p>During the run of <tt>make test</tt>, the terminal output will 137 display a line similar to the following:</p> 138 139 <pre>--- Running clang tests for i686-pc-linux-gnu ---</pre> 140 141 <p>followed by a line continually overwritten with the current test 142 file being compiled, and an overall completion percentage.</p> 143 144 <p>After the <tt>make test</tt> run completes, the absence of any 145 <tt>Failing Tests (count):</tt> message indicates that no tests 146 failed unexpectedly. If any tests did fail, the 147 <tt>Failing Tests (count):</tt> message will be followed by a list 148 of the test source file paths that failed. For example:</p> 149 150 <pre> 151 Failing Tests (3): 152 /home/john/llvm/tools/clang/test/SemaCXX/member-name-lookup.cpp 153 /home/john/llvm/tools/clang/test/SemaCXX/namespace-alias.cpp 154 /home/john/llvm/tools/clang/test/SemaCXX/using-directive.cpp 155</pre> 156 157 <p>If you used the <tt>make VERBOSE=1</tt> option, the terminal 158 output will reflect the error messages from the compiler and 159 test runner.</p> 160 161 <p>The regression suite can also be run with Valgrind by running 162 <tt>make test VG=1</tt> in the top-level clang directory.</p> 163 164 <p>For more intensive changes, running 165 the <a href="http://llvm.org/docs/TestingGuide.html#testsuiterun">LLVM 166 Test Suite</a> with clang is recommended. Currently the best way to 167 override LLVMGCC, as in: <tt>make LLVMGCC="clang -std=gnu89" 168 TEST=nightly report</tt> (make sure <tt>clang</tt> is in your PATH or use the 169 full path).</p> 170 171 <!--=====================================================================--> 172 <h3 id="testingWindows">Testing using Visual Studio on Windows</h3> 173 <!--=====================================================================--> 174 175 <p>The Clang test suite can be run from either Visual Studio or 176 the command line.</p> 177 178 <p>Note that the test runner is based on 179 Python, which must be installed. Find Python at: 180 <a href="http://www.python.org/download/">http://www.python.org/download/</a>. 181 Download the latest stable version (2.6.2 at the time of this writing).</p> 182 183 <p>The GnuWin32 tools are also necessary for running the tests. 184 Get them from <a href="http://getgnuwin32.sourceforge.net/"> 185 http://getgnuwin32.sourceforge.net/</a>. 186 If the environment variable <tt>%PATH%</tt> does not have GnuWin32, 187 or if other grep(s) supercedes GnuWin32 on <tt>%PATH%,</tt> 188 you should specify <tt>LLVM_LIT_TOOLS_DIR</tt> 189 to CMake explicitly.</p> 190 191 <p>The cmake build tool is set up to create Visual Studio project files 192 for running the tests, "clang-test" being the root. Therefore, to 193 run the test from Visual Studio, right-click the clang-test project 194 and select "Build".</p> 195 196 <p> 197 Please see also 198 <a href="http://llvm.org/docs/GettingStartedVS.html">Getting Started 199 with the LLVM System using Microsoft Visual Studio</a> and 200 <a href="http://llvm.org/docs/CMake.html">Building LLVM with CMake</a>. 201 </p> 202 203 <!--=====================================================================--> 204 <h3 id="testingCommands">Testing on the Command Line</h3> 205 <!--=====================================================================--> 206 207 <p>If you want more control over how the tests are run, it may 208 be convenient to run the test harness on the command-line directly. Before 209 running tests from the command line, you will need to ensure that 210 <tt>lit.site.cfg</tt> files have been created for your build. You can do 211 this by running the tests as described in the previous sections. Once the 212 tests have started running, you can stop them with control+C, as the 213 files are generated before running any tests.</p> 214 215 <p>Once that is done, to run all the tests from the command line, 216 execute a command like the following:</p> 217 218 <pre> 219 python (path to llvm)\llvm\utils\lit\lit.py -sv 220 --param=build_mode=Win32 --param=build_config=Debug 221 --param=clang_site_config=(build dir)\tools\clang\test\lit.site.cfg 222 (path to llvm)\llvm\tools\clang\test 223</pre> 224 225 <p>For CMake builds e.g. on Windows with Visual Studio, you will need 226 to specify your build configuration (Debug, Release, etc.) via 227 <tt>--param=build_config=(build config)</tt>. You may also need to specify 228 the build mode (Win32, etc) via <tt>--param=build_mode=(build mode)</tt>.</p> 229 230 <p>Additionally, you will need to specify the lit site configuration which 231 lives in (build dir)\tools\clang\test, via 232 <tt>--param=clang_site_config=(build dir)\tools\clang\test\lit.site.cfg</tt>. 233 </p> 234 235 <p>To run a single test:</p> 236 237 <pre> 238 python (path to llvm)\llvm\utils\lit\lit.py -sv 239 --param=build_mode=Win32 --param=build_config=Debug 240 --param=clang_site_config=(build dir)\tools\clang\test\lit.site.cfg 241 (path to llvm)\llvm\tools\clang\test\(dir)\(test) 242</pre> 243 244 <p>For example:</p> 245 246 <pre> 247 python C:\Tool\llvm\utils\lit\lit.py -sv 248 --param=build_mode=Win32 --param=build_config=Debug 249 --param=clang_site_config=c:\Tools\build\tools\clang\test\lit.site.cfg 250 C:\Tools\llvm\tools\clang\test\Sema\wchar.c 251</pre> 252 253 <p>The -sv option above tells the runner to show the test output if 254 any tests failed, to help you determine the cause of failure.</p> 255 256 <p>You can also pass in the --no-progress-bar option if you wish to disable 257 progress indications while the tests are running.</p> 258 259 <p>Your output might look something like this:</p> 260 261 <pre>lit.py: lit.cfg:152: note: using clang: 'C:\Tools\llvm\bin\Release\clang.EXE' 262-- Testing: Testing: 2534 tests, 4 threads -- 263Testing: 0 .. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80.. 90.. 264Testing Time: 81.52s 265 Expected Passes : 2503 266 Expected Failures : 28 267 Unsupported Tests : 3 268</pre> 269 270 <p>The statistic, "Unexpected Failures" (not shown if all tests pass), is the important one.</p> 271 272 <!--=====================================================================--> 273 <h2 id="patches">Creating Patch Files</h2> 274 <!--=====================================================================--> 275 276 <p>To return changes to the Clang team, unless you have checkin 277 privileges, the preferred way is to send patch files to the 278 cfe-commits mailing list, with an explanation of what the patch is 279 for. clang follows <a 280 href="http://llvm.org/docs/DeveloperPolicy.html">LLVM's developer policy</a>. 281 If your patch requires a wider discussion (for example, because it is an 282 architectural change), you can use the cfe-dev mailing list.</p> 283 284 <p>To create these patch files, change directory 285 to the llvm/tools/clang root and run:</p> 286 287 <pre>svn diff (relative path) >(patch file name)</pre> 288 289 <p>For example, for getting the diffs of all of clang:</p> 290 291 <pre>svn diff . >~/mypatchfile.patch</pre> 292 293 <p>For example, for getting the diffs of a single file:</p> 294 295 <pre>svn diff lib/Parse/ParseDeclCXX.cpp >~/ParseDeclCXX.patch</pre> 296 297 <p>Note that the paths embedded in the patch depend on where you run it, 298 so changing directory to the llvm/tools/clang directory is recommended.</p> 299 300 <!--=====================================================================--> 301 <h2 id="irgen">LLVM IR Generation</h2> 302 <!--=====================================================================--> 303 304 <p>The LLVM IR generation part of clang handles conversion of the 305 AST nodes output by the Sema module to the LLVM Intermediate 306 Representation (IR). Historically, this was referred to as 307 "codegen", and the Clang code for this lives 308 in <tt>lib/CodeGen</tt>.</p> 309 310 <p>The output is most easily inspected using the <tt>-emit-llvm</tt> 311 option to clang (possibly in conjunction with <tt>-o -</tt>). You 312 can also use <tt>-emit-llvm-bc</tt> to write an LLVM bitcode file 313 which can be processed by the suite of LLVM tools 314 like <tt>llvm-dis</tt>, <tt>llvm-nm</tt>, etc. See the LLVM 315 <a href="http://llvm.org/docs/CommandGuide/">Command Guide</a> 316 for more information.</p> 317 318</div> 319</body> 320</html> 321