This document provides usage information about the LLVM makefile system. While loosely patterned after the BSD makefile system, LLVM has taken a departure from BSD in order to implement additional features needed by LLVM. Although makefile systems such as automake were attempted at one point, it has become clear that the features needed by LLVM and the Makefile norm are too great to use a more limited tool. Consequently, LLVM requires simply GNU Make 3.79, a widely portable makefile processor. LLVM unabashedly makes heavy use of the features of GNU Make so the dependency on GNU Make is firm. If you're not familiar with make, it is recommended that you read the GNU Makefile Manual .
While this document is rightly part of the LLVM Programmer's Manual, it is treated separately here because of the volume of content and because it is often an early source of bewilderment for new developers.
The LLVM Makefile System is the component of LLVM that is responsible for building the software, testing it, generating distributions, checking those distributions, installing and uninstalling, etc. It consists of a several files throughout the source tree. These files and other general concepts are described in this section.
The LLVM Makefile System is quite generous. It not only builds its own software, but it can build yours too. Built into the system is knowledge of the llvm/projects directory. Any directory under projects that has both a configure script and a Makefile is assumed to be a project that uses the LLVM Makefile system. This allows your project to get up and running quickly by utilizing the built-in features that are used to compile LLVM. LLVM compiles itself using the same features of the makefile system as used for projects.
To use the makefile system, you simply create a file named Makefile in your directory and declare values for certain variables. The variables and values that you select determine what the makefile system will do. These variables enable rules and processing in the makefile system that automatically Do The Right Thing™.
Setting variables alone is not enough. You must include into your Makefile additional files that provide the rules of the LLVM Makefile system. The various files involved are described in the sections that follow.
Each directory to participate in the build needs to have a file named Makefile. This is the file first read by make. It has three sections:
Every project must have a Makefile.common file at its top source directory. This file serves three purposes:
Every project must have a Makefile.config at the top of its build directory. This file is generated by the configure script from the pattern provided by the Makefile.config.in file located at the top of the project's source directory. The contents of this file depend largely on what configuration items the project uses, however most projects can get what they need by just relying on LLVM's configuration found in $(LLVM_OBJ_ROOT)/Makefile.config.
This file, located at $(LLVM_SRC_ROOT)/Makefile.rules is the heart of the LLVM Makefile System. It provides all the logic, dependencies, and rules for building the targets supported by the system. What it does largely depends on the values of make variables that have been set before Makefile.rules is included.
User Makefiles need not have comments in them unless the construction is unusual or it doesn't strictly follow the rules and patterns of the LLVM makefile system. Makefile comments are invoked with the pound (#) character. The # character and any text following it, to the end of the line, are ignored by make.
This section provides some examples of the different kinds of modules you can build with the LLVM makefile system. In general, each directory you provide will build a single object although that object may be composed of additionally compiled components.
Only a few variable definitions are needed to build a regular library. Normally, the makefile system will build all the software into a single libname.o (pre-linked) object. This means the library is not searchable and that the distinction between compilation units has been dissolved. Optionally, you can ask for a shared library (.so), archive library (.a) or to not have the default (relinked) library built. For example:
LIBRARYNAME = mylib
SHARED_LIBRARY = 1
ARCHIVE_LIBRARY = 1
DONT_BUILT_RELINKED = 1
says to build a library named "mylib" with both a shared library (mylib.so) and an archive library (mylib.a) version but not to build the relinked object (mylib.o). The contents of all the libraries produced will be the same, they are just constructed differently. Note that you normally do not need to specify the sources involved. The LLVM Makefile system will infer the source files from the contents of the source directory.
For building executable programs (tools), you must provide the name of the tool and the names of the libraries you wish to link with the tool. For example:
TOOLNAME = mytool
USEDLIBS = mylib
LLVMLIBS = LLVMSupport.a LLVMSystem.a
says that we are to build a tool name mytool and that it requires three libraries: mylib, LLVMSupport.a and LLVMSystem.a.
Note that two different variables are use to indicate which libraries are linked: USEDLIBS and LLVMLIBS. This distinction is necessary to support projects. LLVMLIBS refers to the LLVM libraries found in the LLVM object directory. USEDLIBS refers to the libraries built by your project. In the case of building LLVM tools, USEDLIBS and LLVMLIBS can be used interchangeably since the "project" is LLVM itself and USEDLIBS refers to the same place as LLVMLIBS.
Also note that there are two different ways of specifying a library: with a .a suffix and without. Without the suffix, the entry refers to the re-linked (.o) file which will include all symbols of the library. This is useful, for example, to include all passes from a library of passes. If the .a suffix is used then the library is linked as a searchable library (with the -l option). In this case, only the symbols that are unresolved at that point will be resolved from the library, if they exist. Other (unreferenced) symbols will not be included when the .a syntax is used. Note that in order to use the .a suffix, the library in question must have been built with the ARCHIVE_LIBRARY option set.
Many tools will want to use the JIT features of LLVM. However, getting the right set of libraries to link with is tedious, platform specific, and error prone. Additionally, the JIT has special linker switch options that it needs. Consequently, to make it easier to build tools that use the JIT, you can use a special value for the LLVMLIBS variable:
TOOLNAME = my_jit_tool
USEDLIBS = mylib
LLVMLIBS = JIT
Using a value of JIT for LLVMLIBS tells the makefile system to construct a special value for LLVMLIBS that gives the program all the LLVM libraries needed to run the JIT. Any additional libraries needed can still be specified with USEDLIBS. To get a full understanding of how this changes the linker command, it is recommended that you:
cd examples/Fibonacci
make VERBOSE=1
By default, using LLVMLIBS=JIT will link in enough to support JIT code generation for the architecture on which the tool is linked. If you need additional target architectures linked in, you may specify them on the command line or in your Makefile. For example:
ENABLE_X86_JIT=1
ENABLE_SPARCV9_JIT=1
ENALBE_PPC_JIT=1
will cause the tool to be able to generate code for all three platforms.
This section describes each of the targets that can be built using the LLVM Makefile system. Any target can be invoked from any directory but not all are applicable to a given directory (e.g. "check", "dist", and "install" will always operate as if invoked from the top level directory).
| Target Name | Implied Targets | Target Description |
|---|---|---|
| all | Compile the software recursively. Default target. | |
| all-local | Compile the software in the local directory only. | |
| check | Change to the llvm/test directory and run regression tests. | |
| clean | Remove built objects recursively. | |
| clean-local | Remove built objects from the local directory only. | |
| dist | all | Prepare a source distribution tarball. |
| dist-check | all check | Prepare a source distribution tarball and check that it builds. |
| dist-clean | clean | Clean source distribution tarball temporary files. |
| install | all | Copy built objects to installation directory. |
| preconditions | all | Check to make sure configuration and makefiles are up to date. |
| printvars | all | Prints variables defined by the makefile system (for debugging). |
| tags | Make C and C++ tags files for emacs and vi. | |
| uninstall | Remove built objects from installation directory. |
When you invoke make with no arguments, you are implicitly instructing it to seek the "all" target (goal). This target is used for building the software recursively and will do different things in different directories. For example, in a lib directory, the "all" target will compile source files and generate libraries. But, in a tools directory, it will link libraries and generate executables.
This target is the same as all but it operates only on the current directory instead of recursively.
This target cleans the build directory, recursively removing all things that the Makefile builds. Despite once or twice attempting to remove /*, the cleaning rules have been made guarded so they shouldn't go awry.
This target does the same thing as clean but only for the current (local) directory.
This target builds a distribution tarball. It first builds the entire project using the all target and then tars up the necessary files and compresses it. The generated tarball is sufficient for a casual source distribution, but probably not for a release (see dist-check).
This target does the same thing as the dist target but also checks the distribution tarball. The check is made by unpacking the tarball to a new directory, configuring it, building it, installing it, and then verifying that the installation results are correct (by comparing to the original build). This target can take a long time to run but should be done before a release goes out to make sure that the distributed tarball can actually be built into a working release.
This is a special form of the clean clean target. It performs a normal clean but also removes things pertaining to building the distribution.
This target finalizes shared objects and executables and copies all libraries, headers, executables and documentation to the directory given with the --prefix option to configure. When completed, the prefix directory will have everything needed to use LLVM.
The LLVM makefiles can generate complete internal documentation for all the classes by using doxygen. By default, this feature is not enabled because it takes a long time and generates a massive amount of data (>100MB). If you want this feature, you must configure LLVM with the --enable-doxygen switch and ensure that a modern version of doxygen (1.3.7 or later) is available in your PATH. You can download doxygen from here.
This utility target checks to see if the Makefile in the object directory is older than the Makefile in the source directory and copies it if so. It also reruns the configure script if that needs to be done and rebuilds the Makefile.config file similarly. Users may overload this target to ensure that sanity checks are run before any building of targets as all the targets depend on preconditions.
This utility target just causes LLVM to print out some of its variables so that you can double check how things are set.
This target will generate a TAGS file in the top-level source directory. It is meant for use with emacs, XEmacs, or ViM. The TAGS file provides an index of symbol definitions so that the editor can jump you to the definition quickly.
This target is the opposite of the install target. It removes the header, library and executable files from the installation directories. Note that the directories themselves are not removed because it is not guaranteed that LLVM is the only thing installing there (e.g. --prefix=/usr).
Variables are used to tell the LLVM Makefile System what to do and to obtain information from it. Variables are also used internally by the LLVM Makefile System. Variable names that contain only the upper case alphabetic letters and underscore are intended for use by the end user. All other variables are internal to the LLVM Makefile System and should not be relied upon nor modified. The sections below describe how to use the LLVM Makefile variables.
Variables listed in the table below should be set before the inclusion of $(LEVEL)/Makefile.common. These variables provide input to the LLVM make system that tell it what to do for the current directory.
Override variables can be used to override the default values provided by the LLVM makefile system. These variables can be set in several ways:
The overridable variables are given below:
Variables listed in the table below can be used by the user's Makefile but should not be changed. Changing the value will generally cause the build to go wrong, so don't do it.
Variables listed below are used by the LLVM Makefile System and considered internal. You should not use these variables under any circumstances.