.. _conan_tools_gnu_build_helper:

Autotools
=========


The ``Autotools`` build helper is a wrapper around the command line invocation of autotools. It will abstract the
calls like ``./configure`` or ``make`` into Python method calls.

Usage:

.. code:: python

    from conan import ConanFile
    from conan.tools.gnu import Autotools

    class App(ConanFile):
        settings = "os", "arch", "compiler", "build_type"

        def build(self):
            autotools = Autotools(self)
            autotools.configure()
            autotools.make()

It will read the ``conanbuild.conf`` file generated by the :ref:`AutotoolsToolchain<conan_tools_gnu_autotoolstoolchain>`
to know read the arguments for calling the configure and make scripts:

- **configure_args**: Arguments to call the ``configure`` script.
- **make_args**: Arguments to call the ``make`` script.


Reference
---------

.. currentmodule:: conan.tools.gnu.autotools

.. autoclass:: Autotools
    :members:



conf
----

The ``Autotools`` build helper is affected by these ``[conf]`` variables:

- ``tools.gnu:make_program`` allows to define which ``make`` executable is being used. This will default for ``mingw32-make`` for MinGW builds or to ``make`` for any other build.

- ``tools.build:install_strip`` (Since Conan 2.20.0) will define in the ``Autotools.install()`` method the ``make install-strip`` target if set to ``True``, otherwise it will use the ``make install`` target.



A note about relocatable shared libraries in macOS built the  Autotools build helper
------------------------------------------------------------------------------------

When building a shared library with Autotools in macOS a section ``LC_ID_DYLIB`` and
another ``LC_LOAD_DYLIB`` are added to the ``.dylib``. These sections store
``install_name`` information, which is the location of the folder where the library or its
dependencies are installed. You can check the install_name of your shared libraries using
the otool command:

.. code-block:: text

    $ otool -l path/to/libMyLib.dylib 
    ...
    cmd LC_ID_DYLIB
        cmdsize 48
            name path/to/libMyLib.dylib (offset 24)
    time stamp 1 Thu Jan  1 01:00:01 1970
        current version 1.0.0
    compatibility version 1.0.0
    ...
    Load command 11
            cmd LC_LOAD_DYLIB
        cmdsize 48
            name path/to/dependency.dylib (offset 24)
    time stamp 2 Thu Jan  1 01:00:02 1970
        current version 1.0.0
    compatibility version 1.0.0
    ...

Why is this a problem when using Conan?
+++++++++++++++++++++++++++++++++++++++

When using Conan the library will be built in the local cache and this means that this
location will point to Conan's local cache folder where the library was installed. This
location is where the library tells any other binaries using it where to load it at
runtime. This is a problem since you can build the shared library in one machine, then
upload it to a server and install it in another machine to use it. In this case, as
Autotools behaves by default, you would have a library storing an ``install_name``
pointing to a folder that does not exist in your current machine so you would get linker
errors when building. 


How to address this problem in Conan
++++++++++++++++++++++++++++++++++++

The only thing Conan can do to make these shared libraries relocatable is to patch the
built binaries after installation. To do this, when using the ``Autotools`` build helper
and after running the Makefile's ``install()`` step, you can use the
:ref:`fix_apple_shared_install_name() <conan_tools_apple_fix_apple_shared_install_name>`
tool to search for the built ``.dylib`` files and patch them by running the
``install_name_tool`` macOS utility, like this:

.. code-block:: python

    from conan.tools.apple import fix_apple_shared_install_name
    class HelloConan(ConanFile):
      ...
      def package(self):
          autotools = Autotools(self)
          autotools.install()
          fix_apple_shared_install_name(self)


This will change the value of the ``LC_ID_DYLIB`` and ``LC_LOAD_DYLIB`` sections in the
``.dylib`` file to:

.. code-block:: text

    $ otool -l path/to/libMyLib.dylib 
    ...
    cmd LC_ID_DYLIB
        cmdsize 48
            name @rpath/libMyLib.dylib (offset 24)
    time stamp 1 Thu Jan  1 01:00:01 1970
        current version 1.0.0
    compatibility version 1.0.0
    ...
    Load command 11
            cmd LC_LOAD_DYLIB
        cmdsize 48
            name @rpath/dependency.dylib (offset 24)
    time stamp 2 Thu Jan  1 01:00:02 1970
        current version 1.0.0
    compatibility version 1.0.0

The ``@rpath`` special keyword will tell the loader to search a list of paths to find the
library. These paths can be defined by the consumer of that library by defining the
``LC_RPATH`` field. This is done by passing the ``-Wl,-rpath -Wl,/path/to/libMyLib.dylib``
linker flag when building the consumer of the library. Then if Conan builds an executable
that consumes the ``libMyLib.dylib`` library, it will automatically add the ``-Wl,-rpath
-Wl,/path/to/libMyLib.dylib`` flag so that the library is correctly found
when building.