LLVM Makefile Guide

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 differences between the LLVM way of doing things and the Makefile norm are too great to 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:

Settable Variables - Required that must be set first.
include $(LEVEL)/Makefile.common - include the LLVM Makefile system.
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:

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.
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.
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).

Target Name	Implied Targets	Target Description
`all`		Compile the software recursively. Default target.
`all-local`		Compile the software in the local directory only.
`check`	all	Test the software recursively.
`check-local`	all-local	Test the software in the local directory only.
`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.
`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 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. 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.

BUILD_ARCHIVE: If set to any value, causes an archive (.a) library to be built.
BUILT_SOURCES: Specifies a set of source files that are generated from other source files. These sources will be built before any other target processing to ensure they are present.
BYTECODE_LIBRARY: If set to any value, causes a bytecode library (.bc) to be built.
CONFIG_FILES: Specifies a set of configuration files to be installed.
DIRS: Specifies a set of directories, usually children of the current directory, that should also be made using the same goal. These directories will be built serially.
DISABLE_AUTO_DEPENDENCIES: If set to any value, causes the makefiles to not automatically generate dependencies when running the compiler. Use of this feature is discouraged and it may be removed at a later date.
DONT_BUILD_RELINKED: If set to any value, causes a relinked library (.o) not to be built. By default, libraries are built as re-linked since most LLVM libraries are needed in their entirety and re-linked libraries will be linked more quickly than equival archive libraries.
ENABLE_OPTIMIZED: If set to any value, causes the build to generate optimized objects, libraries and executables. This alters the flags specified to the compilers and linkers. Generally debugging won't be a fun experience with an optimized build.
ENABLE_PROFILING: If set to any value, causes the build to generate both optimized and profiled objects, libraries and executables. This alters the flags specified to the compilers and linkers to ensure that profile data can be collected from the tools built. Use the gprof tool to analyze the output from the profiled tools (gmon.out).
EXPERIMENTAL_DIRS: Specify a set of directories that should be built, but if they fail, it should not cause the build to fail. Note that this should only be used temporarily while code is being written.
EXPORTED_SYMBOL_FILE: Specifies the name of a single file that contains a list of the symbols to be exported by the linker. One symbol per line.
EXPORTED_SYMBOL_LIST: Specifies a set of symbols to be exported by the linker.
EXTRA_DIST: Specifies additional files that should be distributed with LLVM. All source files, all built sources, all Makefiles, and most documentation files will be automatically distributed. Use this variable to distribute any files that are not automatically distributed.
KEEP_SYMBOLS: If set to any value, specifies that when linking executables the makefiles should retain debug symbols in the executable. Normally, symbols are stripped from the executable.
LEVEL(required): Specify the level of nesting from the top level. This variable must be set in each makefile as it is used to find the top level and thus the other makefiles.
LIBRARYNAME: Specify the name of the library to be built. (Required For Libraries)
LLVMLIBS: Specifies the set of libraries from the LLVM $(ObjDir) that will be linked into the tool or library.
OPTIONAL_DIRS: Specify a set of directories that may be built, if they exist, but its not an error for them not to exist.
PARALLEL_DIRS: Specify a set of directories to build recursively and in parallel if the -j option was used with make.
SHARED_LIBRARY: If set to any value, causes a shared library (.so) to be built in addition to any other kinds of libraries. Note that this option will cause all source files to be built twice: once with options for position independent code and once without. Use it only where you really need a shared library.
SOURCES(optional): Specifies the list of source files in the current directory to be built. Source files of any type may be specified (programs, documentation, config files, etc.). If not specified, the makefile system will infer the set of source files from the files present in the current directory.
SUFFIXES: Specifies a set of filename suffixes that occur in suffix match rules. Only set this if your local Makefile specifies additional suffix match rules.
TARGET: Specifies the name of the LLVM code generation target that the current directory builds. Setting this variable enables additional rules to build .inc files from .td files.
TOOLNAME: Specifies the name of the tool that the current directory should build.
USEDLIBS: Specifies the list of project libraries that will be linked into the tool or library.
VERBOSE: Tells the Makefile system to produce detailed output of what it is doing instead of just summary comments. This will generate a LOT of output.

Overridable variables can be used to override the default values provided by the LLVM makefile system. These variables can be set in several ways:

In the environment (e.g. setenv, export) -- not recommended.
On the make command line -- recommended.
On the configure command line
In the Makefile (only after the inclusion of $(LEVEL)/Makefile.common.

The overridable variables are given below:

AR (defaulted): Specifies the path to the ar tool.
BISON(configured): Specifies the path to the bison tool.
BUILD_OBJ_DIR: The directory into which the products of build rules will be placed. This might be the same as BUILD_SRC_DIR but typically is not.
BUILD_SRC_DIR: The directory which contains the source files to be built.
BURG: Specifies the path to the burg tool.
BZIP2(configured): The path to the bzip2 tool.
CC(configured): The path to the 'C' compiler.
CFLAGS: Additional flags to be passed to the 'C' compiler.
CXX: Specifies the path to the C++ compiler.
CXXFLAGS: Additional flags to be passed to the C++ compiler.
DATE(configured): Specifies the path to the date program or any program that can generate the current date and time on its standard output
DOT(configured): Specifies the path to the dot tool or false if there isn't one.
ECHO(configured): Specifies the path to the echo tool for printing output.
ETAGS(configured): Specifies the path to the etags tool.
ETAGSFLAGS(configured): Provides flags to be passed to the etags tool.
EXEEXT(configured): Provides the extension to be used on executables built by the makefiles. The value may be empty on platforms that do not use file extensions for executables (e.g. Unix).
FLEX(configured): Specifies the path to the flex tool.
GCCLD(defaulted): Specifies the path to the gccld tool.
HAVE_BZIP2(configured): This variable is set automatically if the configure script could find the bzip2 library.
HAVE_ZLIB(configured): This variable is set automatically if the configure script could find the zlib library.
INSTALL(configured): Specifies the path to the install tool.
LDFLAGS(configured): Allows users to specify additional flags to pass to the linker.
LIBS(configured): The list of libraries that should be linked with each tool.
LIBTOOL(configured): Specifies the path to the libtool tool. This tool is renamed mklib by the configure script and always located in the
LLVMAS(defaulted): Specifies the path to the llvm-as tool.
LLVMGCC(defaulted): Specifies the path to the LLVM version of the GCC 'C' Compiler
LLVMGXX(defaulted): Specifies the path to the LLVM version of the GCC C++ Compiler
LLVM_OBJ_ROOT(configured): Specifies the top directory into which the output of the build is placed.
LLVM_SRC_ROOT(configured): Specifies the top directory in which the sources are found.
LLVM_TARBALL_NAME(configured): Specifies the name of the distribution tarball to create. This is configured from the name of the project and its version number.
MKDIR(defaulted): Specifies the path to the mkdir tool that creates directories.
PLATFORMSTRIPOPTS: The options to provide to the linker to specify that a stripped (no symbols) executable should be built.
RANLIB(defaulted): Specifies the path to the ranlib tool.
RM(defaulted): Specifies the path to the rm tool.
SED(defaulted): Specifies the path to the sed tool.
SHLIBEXT(configured): Provides the filename extension to use for shared libraries.
TBLGEN(defaulted): Specifies the path to the tblgen tool.
TAR(defaulted): Specifies the path to the tar tool.
ZIP(defaulted): Specifies the path to the zip tool.

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.

bindir: The directory into which executables will ultimately be installed. This value is derived from the --prefix option given to configure.
bytecode_libdir: The directory into which bytecode libraries will ultimately be installed. This value is derived from the --prefix option given to configure.
ConfigureScriptFLAGS: Additional flags given to the configure script when reconfiguring.
DistDir: The current directory for which a distribution copy is being made.
Echo: The LLVM Makefile System output command. This provides the llvm[n] prefix and starts with @ so the command itself is not printed by make.
EchoCmd: Same as Echo but without the leading @.
includedir: The directory into which include files will ultimately be installed. This value is derived from the --prefix option given to configure.
libdir: The directory into which native libraries will ultimately be installed. This value is derived from the --prefix option given to configure.
LibDir: The configuration specific directory into which libraries are placed before installation.
MakefileConfig: Full path of the Makefile.config file.
MakefileConfigIn: Full path of the Makefile.config.in file.
ObjDir: The configuration and directory specific directory where build objects (compilation results) are placed.
SubDirs: The complete list of sub-directories of the current directory as specified by other variables.
Sources: The complete list of source files.
sysconfdir: The directory into which configuration files will ulitmately be installed. This value is derived from the --prefix option given to configure.
ToolDir: The configuration specific directory into which executables are placed before they are installed.
TopDistDir: The top most directory into which the distribution files are copied.
Verb: Use this as the first thing on your build script lines to enable or disable verbose mode. It expands to either an @ (quiet mode) or nothing (verbose mode).