1======================== 2Creating an LLVM Project 3======================== 4 5.. contents:: 6 :local: 7 8Overview 9======== 10 11The LLVM build system is designed to facilitate the building of third party 12projects that use LLVM header files, libraries, and tools. In order to use 13these facilities, a ``Makefile`` from a project must do the following things: 14 15* Set ``make`` variables. There are several variables that a ``Makefile`` needs 16 to set to use the LLVM build system: 17 18 * ``PROJECT_NAME`` - The name by which your project is known. 19 * ``LLVM_SRC_ROOT`` - The root of the LLVM source tree. 20 * ``LLVM_OBJ_ROOT`` - The root of the LLVM object tree. 21 * ``PROJ_SRC_ROOT`` - The root of the project's source tree. 22 * ``PROJ_OBJ_ROOT`` - The root of the project's object tree. 23 * ``PROJ_INSTALL_ROOT`` - The root installation directory. 24 * ``LEVEL`` - The relative path from the current directory to the 25 project's root ``($PROJ_OBJ_ROOT)``. 26 27* Include ``Makefile.config`` from ``$(LLVM_OBJ_ROOT)``. 28 29* Include ``Makefile.rules`` from ``$(LLVM_SRC_ROOT)``. 30 31There are two ways that you can set all of these variables: 32 33* You can write your own ``Makefiles`` which hard-code these values. 34 35* You can use the pre-made LLVM sample project. This sample project includes 36 ``Makefiles``, a configure script that can be used to configure the location 37 of LLVM, and the ability to support multiple object directories from a single 38 source directory. 39 40If you want to devise your own build system, studying other projects and LLVM 41``Makefiles`` will probably provide enough information on how to write your own 42``Makefiles``. 43 44Source Tree Layout 45================== 46 47In order to use the LLVM build system, you will want to organize your source 48code so that it can benefit from the build system's features. Mainly, you want 49your source tree layout to look similar to the LLVM source tree layout. 50 51Underneath your top level directory, you should have the following directories: 52 53**lib** 54 55 This subdirectory should contain all of your library source code. For each 56 library that you build, you will have one directory in **lib** that will 57 contain that library's source code. 58 59 Libraries can be object files, archives, or dynamic libraries. The **lib** 60 directory is just a convenient place for libraries as it places them all in 61 a directory from which they can be linked later. 62 63**include** 64 65 This subdirectory should contain any header files that are global to your 66 project. By global, we mean that they are used by more than one library or 67 executable of your project. 68 69 By placing your header files in **include**, they will be found 70 automatically by the LLVM build system. For example, if you have a file 71 **include/jazz/note.h**, then your source files can include it simply with 72 **#include "jazz/note.h"**. 73 74**tools** 75 76 This subdirectory should contain all of your source code for executables. 77 For each program that you build, you will have one directory in **tools** 78 that will contain that program's source code. 79 80**test** 81 82 This subdirectory should contain tests that verify that your code works 83 correctly. Automated tests are especially useful. 84 85 Currently, the LLVM build system provides basic support for tests. The LLVM 86 system provides the following: 87 88* LLVM contains regression tests in ``llvm/test``. These tests are run by the 89 :doc:`Lit <CommandGuide/lit>` testing tool. This test procedure uses ``RUN`` 90 lines in the actual test case to determine how to run the test. See the 91 :doc:`TestingGuide` for more details. 92 93* LLVM contains an optional package called ``llvm-test``, which provides 94 benchmarks and programs that are known to compile with the Clang front 95 end. You can use these programs to test your code, gather statistical 96 information, and compare it to the current LLVM performance statistics. 97 98 Currently, there is no way to hook your tests directly into the ``llvm/test`` 99 testing harness. You will simply need to find a way to use the source 100 provided within that directory on your own. 101 102Typically, you will want to build your **lib** directory first followed by your 103**tools** directory. 104 105Writing LLVM Style Makefiles 106============================ 107 108The LLVM build system provides a convenient way to build libraries and 109executables. Most of your project Makefiles will only need to define a few 110variables. Below is a list of the variables one can set and what they can 111do: 112 113Required Variables 114------------------ 115 116``LEVEL`` 117 118 This variable is the relative path from this ``Makefile`` to the top 119 directory of your project's source code. For example, if your source code 120 is in ``/tmp/src``, then the ``Makefile`` in ``/tmp/src/jump/high`` 121 would set ``LEVEL`` to ``"../.."``. 122 123Variables for Building Subdirectories 124------------------------------------- 125 126``DIRS`` 127 128 This is a space separated list of subdirectories that should be built. They 129 will be built, one at a time, in the order specified. 130 131``PARALLEL_DIRS`` 132 133 This is a list of directories that can be built in parallel. These will be 134 built after the directories in DIRS have been built. 135 136``OPTIONAL_DIRS`` 137 138 This is a list of directories that can be built if they exist, but will not 139 cause an error if they do not exist. They are built serially in the order 140 in which they are listed. 141 142Variables for Building Libraries 143-------------------------------- 144 145``LIBRARYNAME`` 146 147 This variable contains the base name of the library that will be built. For 148 example, to build a library named ``libsample.a``, ``LIBRARYNAME`` should 149 be set to ``sample``. 150 151``BUILD_ARCHIVE`` 152 153 By default, a library is a ``.o`` file that is linked directly into a 154 program. To build an archive (also known as a static library), set the 155 ``BUILD_ARCHIVE`` variable. 156 157``SHARED_LIBRARY`` 158 159 If ``SHARED_LIBRARY`` is defined in your Makefile, a shared (or dynamic) 160 library will be built. 161 162Variables for Building Programs 163------------------------------- 164 165``TOOLNAME`` 166 167 This variable contains the name of the program that will be built. For 168 example, to build an executable named ``sample``, ``TOOLNAME`` should be set 169 to ``sample``. 170 171``USEDLIBS`` 172 173 This variable holds a space separated list of libraries that should be 174 linked into the program. These libraries must be libraries that come from 175 your **lib** directory. The libraries must be specified without their 176 ``lib`` prefix. For example, to link ``libsample.a``, you would set 177 ``USEDLIBS`` to ``sample.a``. 178 179 Note that this works only for statically linked libraries. 180 181``LLVMLIBS`` 182 183 This variable holds a space separated list of libraries that should be 184 linked into the program. These libraries must be LLVM libraries. The 185 libraries must be specified without their ``lib`` prefix. For example, to 186 link with a driver that performs an IR transformation you might set 187 ``LLVMLIBS`` to this minimal set of libraries ``LLVMSupport.a LLVMCore.a 188 LLVMBitReader.a LLVMAsmParser.a LLVMAnalysis.a LLVMTransformUtils.a 189 LLVMScalarOpts.a LLVMTarget.a``. 190 191 Note that this works only for statically linked libraries. LLVM is split 192 into a large number of static libraries, and the list of libraries you 193 require may be much longer than the list above. To see a full list of 194 libraries use: ``llvm-config --libs all``. Using ``LINK_COMPONENTS`` as 195 described below, obviates the need to set ``LLVMLIBS``. 196 197``LINK_COMPONENTS`` 198 199 This variable holds a space separated list of components that the LLVM 200 ``Makefiles`` pass to the ``llvm-config`` tool to generate a link line for 201 the program. For example, to link with all LLVM libraries use 202 ``LINK_COMPONENTS = all``. 203 204``LIBS`` 205 206 To link dynamic libraries, add ``-l<library base name>`` to the ``LIBS`` 207 variable. The LLVM build system will look in the same places for dynamic 208 libraries as it does for static libraries. 209 210 For example, to link ``libsample.so``, you would have the following line in 211 your ``Makefile``: 212 213 .. code-block:: makefile 214 215 LIBS += -lsample 216 217Note that ``LIBS`` must occur in the Makefile after the inclusion of 218``Makefile.common``. 219 220Miscellaneous Variables 221----------------------- 222 223``CFLAGS`` & ``CPPFLAGS`` 224 225 This variable can be used to add options to the C and C++ compiler, 226 respectively. It is typically used to add options that tell the compiler 227 the location of additional directories to search for header files. 228 229 It is highly suggested that you append to ``CFLAGS`` and ``CPPFLAGS`` as 230 opposed to overwriting them. The master ``Makefiles`` may already have 231 useful options in them that you may not want to overwrite. 232 233Placement of Object Code 234======================== 235 236The final location of built libraries and executables will depend upon whether 237you do a ``Debug``, ``Release``, or ``Profile`` build. 238 239Libraries 240 241 All libraries (static and dynamic) will be stored in 242 ``PROJ_OBJ_ROOT/<type>/lib``, where *type* is ``Debug``, ``Release``, or 243 ``Profile`` for a debug, optimized, or profiled build, respectively. 244 245Executables 246 247 All executables will be stored in ``PROJ_OBJ_ROOT/<type>/bin``, where *type* 248 is ``Debug``, ``Release``, or ``Profile`` for a debug, optimized, or 249 profiled build, respectively. 250 251Further Help 252============ 253 254If you have any questions or need any help creating an LLVM project, the LLVM 255team would be more than happy to help. You can always post your questions to 256the `LLVM Developers Mailing List 257<http://lists.cs.uiuc.edu/pipermail/llvmdev/>`_. 258