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. Building software that uses LLVM does not require the LLVM Makefile System nor even placement in the llvm/projects directory. However, doing so will allow 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.
For further details, consult the Projects page.
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 (C).
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 does not 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) or archive library (.a) built. Archive libraries are the default. For example:
LIBRARYNAME = mylib
SHARED_LIBRARY = 1
BUILD_ARCHIVE = 1
says to build a library named mylib with both a shared library (mylib.so) and an archive library (mylib.a) version. 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.
The LOADABLE_MODULE=1 directive can be used in conjunction with SHARED_LIBRARY=1 to indicate that the resulting shared library should be openable with the dlopen function and searchable with the dlsym function (or your operating system’s equivalents). While this isn’t strictly necessary on Linux and a few other platforms, it is required on systems like HP-UX and Darwin. You should use LOADABLE_MODULE for any shared library that you intend to be loaded into an tool via the -load option. Pass documentation has an example of why you might want to do this.
In some situations, you need to create a loadable module. Loadable modules can be loaded into programs like opt or llc to specify additional passes to run or targets to support. Loadable modules are also useful for debugging a pass or providing a pass with another package if that pass can’t be included in LLVM.
LLVM provides complete support for building such a module. All you need to do is use the LOADABLE_MODULE variable in your Makefile. For example, to build a loadable module named MyMod that uses the LLVM libraries LLVMSupport.a and LLVMSystem.a, you would specify:
LIBRARYNAME := MyMod
LOADABLE_MODULE := 1
LINK_COMPONENTS := support system
Use of the LOADABLE_MODULE facility implies several things:
a standard shared library of the same name.
The SHARED_LIBRARY variable is turned on.
The LINK_LIBS_IN_SHARED variable is turned on.
A loadable module is loaded by LLVM via the facilities of libtool’s libltdl library which is part of lib/System implementation.
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
LINK_COMPONENTS = support system
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 used 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 BUILD_ARCHIVE option set.
Many tools will want to use the JIT features of LLVM. To do this, you simply specify that you want an execution ‘engine’, and the makefiles will automatically link in the appropriate JIT for the host or an interpreter if none is available:
TOOLNAME = my_jit_tool
USEDLIBS = mylib
LINK_COMPONENTS = engine
Of course, any additional libraries may be listed as other components. To get a full understanding of how this changes the linker command, it is recommended that you:
% cd examples/Fibonacci
% make VERBOSE=1
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 test directory in a project and run the test suite there. | |
| check-local | Run a local test suite. Generally this is only defined in the Makefile of the project’s test directory. | |
| 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 | 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 can be invoked from anywhere within a project’s directories but always invokes the check-local target in the project’s test directory, if it exists and has a Makefile. A warning is produced otherwise. If TESTSUITE is defined on the make command line, it will be passed down to the invocation of make check-local in the test directory. The intended usage for this is to assist in running specific suites of tests. If TESTSUITE is not set, the implementation of check-local should run all normal tests. It is up to the project to define what different values for TESTSUTE will do. See the Testing Guide for further details.
This target should be implemented by the Makefile in the project’s test directory. It is invoked by the check target elsewhere. Each project is free to define the actions of check-local as appropriate for that project. The LLVM project itself uses the Lit testing tool to run a suite of feature and regression tests. Other projects may choose to use lit or any other testing mechanism.
This target cleans the build directory, recursively removing all things that the Makefile builds. The cleaning rules have been made guarded so they shouldn’t go awry (via rm -f $(UNSET_VARIABLE)/* which will attempt to erase the entire directory structure).
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 the LLVM makefiles to print out some of the makefile variables so that you can double check how things are set.
This utility target will force a reconfigure of LLVM or your project. It simply runs $(PROJ_OBJ_ROOT)/config.status --recheck to rerun the configuration tests and rebuild the configured files. This isn’t generally useful as the makefiles will reconfigure themselves whenever its necessary.
Warning
Use with caution!
This utility target, only available when $(PROJ_OBJ_ROOT) is not the same as $(PROJ_SRC_ROOT), will completely clean the $(PROJ_OBJ_ROOT) directory by removing its content entirely and reconfiguring the directory. This returns the $(PROJ_OBJ_ROOT) directory to a completely fresh state. All content in the directory except configured files and top-level makefiles will be lost.
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 override 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.
Archive
AR.Flags
BaseNameSources
BCLinkLib
C.Flags
Compile.C
CompileCommonOpts
Compile.CXX
ConfigStatusScript
ConfigureScript
CPP.Flags
CPP.Flags
CXX.Flags
DependFiles
DestArchiveLib
DestBitcodeLib
DestModule
DestSharedLib
DestTool
DistAlways
DistCheckDir
DistCheckTop
DistFiles
DistName
DistOther
DistSources
DistSubDirs
DistTarBZ2
DistTarGZip
DistZip
ExtraLibs
FakeSources
INCFiles
InternalTargets
LD.Flags
LibName.A
LibName.BC
LibName.LA
LibName.O
LibTool.Flags
Link
LinkModule
LLVMLibDir
LLVMLibsOptions
LLVMLibsPaths
LLVMToolDir
LLVMUsedLibs
LocalTargets
Module
ObjectsLO
ObjectsO
ObjMakefiles
ParallelTargets
PreConditions
ProjLibsOptions
ProjLibsPaths
ProjUsedLibs
Ranlib
RecursiveTargets
SrcMakefiles
Strip
StripWarnMsg
TableGen
TDFiles
ToolBuildPath
TopLevelTargets
UserTargets