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 variations required by LLVM from any Makefile norm are too many to strictly use a more limited tool. Consequently, LLVM requires simply GNU Make 3.79, a widely portably 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, rpms and other packages, installing and uninstalling, etc.

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.

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:

1. Settable Variables - Required that must be set first.
2. include $(LEVEL)/Makefile.common - include the LLVM Makefile system.
3. Overridable Variables - Override variables set by the LLVM Makefile system.

Every project must have a Makefile.common file at its top source directory. This file serves three purposes:

1. It includes the project's configuration makefile to obtain values determined by the configure script. This is done by including the $(LEVEL)/Makefile.config file.
2. It specifies any other (static) values that are needed throughout the project. Only values that are used in all or a large proportion of the project's directories should be placed here.
3. It include's the standard rules for the LLVM Makefile system, $(LLVM_SRC_ROOT)/Makefile.rules. This file is the "guts" of the LLVM Makefile system.

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 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. "dist" and "install" will always operate as if invoked from the top level 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 is used to perform any functional, unit or sanity tests as the software is being built. The check target depends on the all target so the software is built in each directory first and then the "check" is applied.

The definition of "check" is pretty general. It depends on the value of the TESTS variable. This variable should be set to a list of executables to run in order to test the software. If they all return 0 then the check succeeds, otherwise not. The programs run can be anything but they should either be local to the directory or in your path.

This target does the same thing as check but only for the current (local) directory.

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 and executables to the directory given with the --prefix option to configure. When completed, the prefix directory will have everything needed to use LLVM.

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. The sections below describe the three kinds of 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.

Variables listed in the table below can be used to override the default values provided by the LLVM makefile system. These variables should be set after the inclusion of $(LEVEL)/Makefile.common.

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.