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+.. _defining_binaries:
+
+======================================
+Defining Binaries for the Build System
+======================================
+
+One part of what the build system does is compile C/C++ and link the resulting
+objects to produce executables and/or libraries. This document describes the
+basics of defining what is going to be built and how. All the following
+describes constructs to use in moz.build files.
+
+
+Source files
+============
+
+Source files to be used in a given directory are registered in the ``SOURCES``
+and ``UNIFIED_SOURCES`` variables. ``UNIFIED_SOURCES`` have a special behavior
+in that they are aggregated by batches of 16, requiring, for example, that there
+are no conflicting variables in those source files.
+
+``SOURCES`` and ``UNIFIED_SOURCES`` are lists which must be appended to, and
+each append requires the given list to be alphanumerically ordered.
+
+.. code-block:: python
+
+   UNIFIED_SOURCES += [
+       'FirstSource.cpp',
+       'SecondSource.cpp',
+       'ThirdSource.cpp',
+   ]
+
+   SOURCES += [
+       'OtherSource.cpp',
+   ]
+
+``SOURCES`` and ``UNIFIED_SOURCES`` can contain a mix of different file types,
+for C, C++, and Objective C.
+
+
+Static Libraries
+================
+
+To build a static library, other than defining the source files (see above), one
+just needs to define a library name with the ``Library`` template.
+
+.. code-block:: python
+
+   Library('foo')
+
+The library file name will be ``libfoo.a`` on UNIX systems and ``foo.lib`` on
+Windows.
+
+If the static library needs to aggregate other static libraries, a list of
+``Library`` names can be added to the ``USE_LIBS`` variable. Like ``SOURCES``, it
+requires the appended list to be alphanumerically ordered.
+
+.. code-block:: python
+
+   USE_LIBS += ['bar', 'baz']
+
+If there are multiple directories containing the same ``Library`` name, it is
+possible to disambiguate by prefixing with the path to the wanted one (relative
+or absolute):
+
+.. code-block:: python
+
+   USE_LIBS += [
+       '/path/from/topsrcdir/to/bar',
+       '../relative/baz',
+   ]
+
+Note that the leaf name in those paths is the ``Library`` name, not an actual
+file name.
+
+Note that currently, the build system may not create an actual library for
+static libraries. It is an implementation detail that shouldn't need to be
+worried about.
+
+As a special rule, ``USE_LIBS`` is allowed to contain references to shared
+libraries. In such cases, programs and shared libraries linking this static
+library will inherit those shared library dependencies.
+
+
+Intermediate (Static) Libraries
+===============================
+
+In many cases in the tree, static libraries are built with the only purpose
+of being linked into another, bigger one (like libxul). Instead of adding all
+required libraries to ``USE_LIBS`` for the bigger one, it is possible to tell
+the build system that the library built in the current directory is meant to
+be linked to that bigger library, with the ``FINAL_LIBRARY`` variable.
+
+.. code-block:: python
+
+   FINAL_LIBRARY = 'xul'
+
+The ``FINAL_LIBRARY`` value must match a unique ``Library`` name somewhere
+in the tree.
+
+As a special rule, those intermediate libraries don't need a ``Library`` name
+for themselves.
+
+
+Shared Libraries
+================
+
+Sometimes, we want shared libraries, a.k.a. dynamic libraries. Such libraries
+are defined similarly to static libraries, using the ``SharedLibrary`` template
+instead of ``Library``.
+
+.. code-block:: python
+
+   SharedLibrary('foo')
+
+When this template is used, no static library is built. See further below to
+build both types of libraries.
+
+With a ``SharedLibrary`` name of ``foo``, the library file name will be
+``libfoo.dylib`` on OSX, ``libfoo.so`` on ELF systems (Linux, etc.), and
+``foo.dll`` on Windows. On Windows, there is also an import library named
+``foo.lib``, used on the linker command line. ``libfoo.dylib`` and
+``libfoo.so`` are considered the import library name for, resp. OSX and ELF
+systems.
+
+On OSX, one may want to create a special kind of dynamic library: frameworks.
+This is done with the ``Framework`` template.
+
+.. code-block:: python
+
+   Framework('foo')
+
+With a ``Framework`` name of ``foo``, the framework file name will be ``foo``.
+This template however affects the behavior on all platforms, so it needs to
+be set only on OSX.
+
+
+Executables
+===========
+
+Executables, a.k.a. programs, are, in the simplest form, defined with the
+``Program`` template.
+
+.. code-block:: python
+
+   Program('foobar')
+
+On UNIX systems, the executable file name will be ``foobar``, while on Windows,
+it will be ``foobar.exe``.
+
+Like static and shared libraries, the build system can be instructed to link
+libraries to the executable with ``USE_LIBS``, listing various ``Library``
+names.
+
+In some cases, we want to create an executable per source file in the current
+directory, in which case we can use the ``SimplePrograms`` template
+
+.. code-block:: python
+
+   SimplePrograms([
+       'FirstProgram',
+       'SecondProgram',
+   ])
+
+Contrary to ``Program``, which requires corresponding ``SOURCES``, when using
+``SimplePrograms``, the corresponding ``SOURCES`` are implied. If the
+corresponding ``sources`` have an extension different from ``.cpp``, it is
+possible to specify the proper extension:
+
+.. code-block:: python
+
+   SimplePrograms([
+       'ThirdProgram',
+       'FourthProgram',
+   ], ext='.c')
+
+Please note this construct was added for compatibility with what already lives
+in the mozilla tree ; it is recommended not to add new simple programs with
+sources with a different extension than ``.cpp``.
+
+Similar to ``SimplePrograms``, is the ``CppUnitTests`` template, which defines,
+with the same rules, C++ unit tests programs. Like ``SimplePrograms``, it takes
+an ``ext`` argument to specify the extension for the corresponding ``SOURCES``,
+if it's different from ``.cpp``.
+
+
+Linking with system libraries
+=============================
+
+Programs and libraries usually need to link with system libraries, such as a
+widget toolkit, etc. Those required dependencies can be given with the
+``OS_LIBS`` variable.
+
+.. code-block:: python
+
+   OS_LIBS += [
+       'foo',
+       'bar',
+   ]
+
+This expands to ``foo.lib bar.lib`` when building with MSVC, and
+``-lfoo -lbar`` otherwise.
+
+For convenience with ``pkg-config``, ``OS_LIBS`` can also take linker flags
+such as ``-L/some/path`` and ``-llib``, such that it is possible to directly
+assign ``LIBS`` variables from ``CONFIG``, such as:
+
+.. code-block:: python
+
+   OS_LIBS += CONFIG['MOZ_PANGO_LIBS']
+
+(assuming ``CONFIG['MOZ_PANGO_LIBS']`` is a list, not a string)
+
+Like ``USE_LIBS``, this variable applies to static and shared libraries, as
+well as programs.
+
+
+Libraries from third party build system
+=======================================
+
+Some libraries in the tree are not built by the moz.build-governed build
+system, and there is no ``Library`` corresponding to them.
+
+However, ``USE_LIBS`` allows to reference such libraries by giving a full
+path (like when disambiguating identical ``Library`` names). The same naming
+rules apply as other uses of ``USE_LIBS``, so only the library name without
+prefix and suffix shall be given.
+
+.. code-block:: python
+
+   USE_LIBS += [
+       '/path/from/topsrcdir/to/third-party/bar',
+       '../relative/third-party/baz',
+   ]
+
+Note that ``/path/from/topsrcdir/to/third-party`` and
+``../relative/third-party/baz`` must lead under a subconfigured directory (a
+directory with an AC_OUTPUT_SUBDIRS in configure.in), or ``security/nss``.
+
+
+Building both static and shared libraries
+=========================================
+
+When both types of libraries are required, one needs to set both
+``FORCE_SHARED_LIB`` and ``FORCE_STATIC_LIB`` boolean variables.
+
+.. code-block:: python
+
+   FORCE_SHARED_LIB = True
+   FORCE_STATIC_LIB = True
+
+But because static libraries and Windows import libraries have the same file
+names, either the static or the shared library name needs to be different
+than the name given to the ``Library`` template.
+
+The ``STATIC_LIBRARY_NAME`` and ``SHARED_LIBRARY_NAME`` variables can be used
+to change either the static or the shared library name.
+
+.. code-block:: python
+
+  Library('foo')
+  STATIC_LIBRARY_NAME = 'foo_s'
+
+With the above, on Windows, ``foo_s.lib`` will be the static library,
+``foo.dll`` the shared library, and ``foo.lib`` the import library.
+
+In some cases, for convenience, it is possible to set both
+``STATIC_LIBRARY_NAME`` and ``SHARED_LIBRARY_NAME``. For example:
+
+.. code-block:: python
+
+  Library('mylib')
+  STATIC_LIBRARY_NAME = 'mylib_s'
+  SHARED_LIBRARY_NAME = CONFIG['SHARED_NAME']
+
+This allows to use ``mylib`` in the ``USE_LIBS`` of another library or
+executable.
+
+When refering to a ``Library`` name building both types of libraries in
+``USE_LIBS``, the shared library is chosen to be linked. But sometimes,
+it is wanted to link the static version, in which case the ``Library`` name
+needs to be prefixed with ``static:`` in ``USE_LIBS``
+
+::
+
+   a/moz.build:
+      Library('mylib')
+      FORCE_SHARED_LIB = True
+      FORCE_STATIC_LIB = True
+      STATIC_LIBRARY_NAME = 'mylib_s'
+   b/moz.build:
+      Program('myprog')
+      USE_LIBS += [
+          'static:mylib',
+      ]
+
+
+Miscellaneous
+=============
+
+The ``SDK_LIBRARY`` boolean variable defines whether the library in the current
+directory is going to be installed in the SDK.
+
+The ``SONAME`` variable declares a "shared object name" for the library. It
+defaults to the ``Library`` name or the ``SHARED_LIBRARY_NAME`` if set. When
+linking to a library with a ``SONAME``, the resulting library or program will
+have a dependency on the library with the name corresponding to the ``SONAME``
+instead of the ``Library`` name. This only impacts ELF systems.
+
+::
+
+   a/moz.build:
+      Library('mylib')
+   b/moz.build:
+      Library('otherlib')
+      SONAME = 'foo'
+   c/moz.build:
+      Program('myprog')
+      USE_LIBS += [
+          'mylib',
+          'otherlib',
+      ]
+
+On e.g. Linux, the above ``myprog`` will have DT_NEEDED markers for
+``libmylib.so`` and ``libfoo.so`` instead of ``libmylib.so`` and
+``libotherlib.so`` if there weren't a ``SONAME``. This means the runtime
+requirement for ``myprog`` is ``libfoo.so`` instead of ``libotherlib.so``.
+
+
+Gecko-related binaries
+======================
+
+Some programs or libraries are totally independent of Gecko, and can use the
+above mentioned templates. Others are Gecko-related in some way, and may
+need XPCOM linkage, mozglue. These things are tedious. A set of additional
+templates exists to ease defining such programs and libraries. They are
+essentially the same as the above mentioned templates, prefixed with "Gecko":
+
+  - ``GeckoProgram``
+  - ``GeckoSimplePrograms``
+  - ``GeckoCppUnitTests``
+  - ``GeckoSharedLibrary``
+  - ``GeckoFramework``
+
+There is also ``XPCOMBinaryComponent`` for XPCOM components, which is a
+special kind of library.
+
+All the Gecko-prefixed templates take the same arguments as their
+non-Gecko-prefixed counterparts, and can take a few more arguments
+for non-standard cases. See the definition of ``GeckoBinary`` in
+build/gecko_templates.mozbuild for more details, but most usecases
+should not require these additional arguments.