LLVM Makefile Guide

1. Introduction
2. General Concepts
   1. Projects
   2. Makefile
   3. Makefile.common
   4. Makefile.config
   5. Makefil.rules
   6. Comments
3. Targets Supported
   1. all
   2. all-local
   3. check
   4. check-local
   5. clean
   6. clean-local
   7. dist
   8. dist-check
   9. dist-clean
   10. install
   11. printvars
   12. tags
   13. uninstall
4. Using Variables
   1. Control Variables
   2. Override Variables
   3. Readable Variables

Written by Reid Spencer

WARNING: This document is a work in progress!

Introduction

This document provides usage information about the LLVM makefile system. While loosely patterned after the BSD makefile system, LLVM has taken a deparature 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 requried by LLVM from any Makefle 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.

General Concepts

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.

Projects

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.

Makefile

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.

Makefile.common

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.

Makefile.config

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`.

Makefile.rules

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.

Comments

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`.

Targets Supported

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 applicabe 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.
`tags` |  | Make C and C++ tags files for emacs and vi.
`uninstall` |  | Remove built objects from installation directory.

all (default)

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.

all-local

This target is the same as all but it operates only on the current directory instead of recursively.

check

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.

Not implemented yet!

check-local

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

Not implemented yet!

clean

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 gaurded so they shouldn't go awry.

clean-local

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

dist

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`).

Not implemented yet!

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.

Not implemented yet!

dist-clean

This is a special form of the `clean` clean target. It performs a normal `clean` but also removes things pertaining to building the distribution.

Not implemented yet!

install

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.

printvars

This utility target just causes LLVM to print out some of its variables so that you can double check how things are set.

tags

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.

uninstall

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 gauranteed that LLVM is the only thing installing there (e.g. --prefix=/usr).

Variables

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.

Control 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.

Variable Name | Variable Description
--- | ---
`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. These will be built before any other target processing to ensure they are present.
`BUILT_SOURCES` | If set to any value, causes a bytecode library (.bc) to be built.
`BUILT_SOURCES` | Specivies a set of configuration files to be installed.
`DIRS` | Specifies a set of directories that should also be made using the same goal. These directories will be built serially.
`DONT_BUILD_RELINKED` | If set to any value, causes a relinked library (.o) not to be built.
`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.
`LEVEL` | Specify the level of nesting from the top level. (Required)
`LIBRARYNAME` | Specify the name of the library to be built. (Required For Libraries)
`LLVMLIBS` | Specify the set of libraries from the LLVM $(OBJDIR) that will be linked into the tool or library.
`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.
`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. (Optional)
`SOURCES` | Specifies the list of source files in the current directory to be acted upon. Source files of any type may be specified (programs, documentation, config files, etc.)
`TARGET` | Specifies the name of the LLVM code generation target that the current directory builds.
`TOOLNAME` | Specifies the name of the tool to build. (Required For Tools)
`USEDLIBS` | Specifies the list of project libraries that will be linked into the tool or library.

Overridable Variables

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`.

Variable Name | Variable Description
--- | ---
`C` | The name (and optional path) of the 'C' compiler (gcc normally).
`CFLAGS` | The set of options to be passed to the 'C' compiler on every compile.
`CPP` | The name (and optional path) of the 'C' pre-processor (cpp normally).
`CXX` | The name (and optional path) of the C++ compiler (g++ normally).
`LD` | The name (and optional path) of the system linker (gcc normally).
`LIBTOOL` | The name (and optional path) of the libtool tool (libtool normally).

Readable Variables

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.

Variable Name | Variable Description
--- | ---
`BUILD_SRC_DIR` | The project directory contaning the directories source files.
`BUILD_OBJ_DIR` | The project directory that will receive the object files.
`CONFIGURATION` | The name of the configuration being built.
`DESTDIR` | The top level directory into which files are installed.
`LLVM_SRC_ROOT` | The top level directory of the LLVM source.
`LLVM_OBJ_ROOT` | The top level directory of the LLVM objects.
`OBJDIR` | The directory in which the project's object files should be placed.
`LIBDIR` | The directory in which the project's library files should be placed.
`TOOLDIR` | The directory in which the project's executable tools should be placed.