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diff --git a/documentation/dev-manual/prebuilt-libraries.rst b/documentation/dev-manual/prebuilt-libraries.rst new file mode 100644 index 0000000000..a05f39ca1e --- /dev/null +++ b/documentation/dev-manual/prebuilt-libraries.rst @@ -0,0 +1,209 @@ +.. SPDX-License-Identifier: CC-BY-SA-2.0-UK + +Working with Pre-Built Libraries +******************************** + +Introduction +============ + +Some library vendors do not release source code for their software but do +release pre-built binaries. When shared libraries are built, they should +be versioned (see `this article +<https://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html>`__ +for some background), but sometimes this is not done. + +To summarize, a versioned library must meet two conditions: + +#. The filename must have the version appended, for example: ``libfoo.so.1.2.3``. +#. The library must have the ELF tag ``SONAME`` set to the major version + of the library, for example: ``libfoo.so.1``. You can check this by + running ``readelf -d filename | grep SONAME``. + +This section shows how to deal with both versioned and unversioned +pre-built libraries. + +Versioned Libraries +=================== + +In this example we work with pre-built libraries for the FT4222H USB I/O chip. +Libraries are built for several target architecture variants and packaged in +an archive as follows:: + + ├── build-arm-hisiv300 + │ └── libft4222.so.1.4.4.44 + ├── build-arm-v5-sf + │ └── libft4222.so.1.4.4.44 + ├── build-arm-v6-hf + │ └── libft4222.so.1.4.4.44 + ├── build-arm-v7-hf + │ └── libft4222.so.1.4.4.44 + ├── build-arm-v8 + │ └── libft4222.so.1.4.4.44 + ├── build-i386 + │ └── libft4222.so.1.4.4.44 + ├── build-i486 + │ └── libft4222.so.1.4.4.44 + ├── build-mips-eglibc-hf + │ └── libft4222.so.1.4.4.44 + ├── build-pentium + │ └── libft4222.so.1.4.4.44 + ├── build-x86_64 + │ └── libft4222.so.1.4.4.44 + ├── examples + │ ├── get-version.c + │ ├── i2cm.c + │ ├── spim.c + │ └── spis.c + ├── ftd2xx.h + ├── install4222.sh + ├── libft4222.h + ├── ReadMe.txt + └── WinTypes.h + +To write a recipe to use such a library in your system: + +- The vendor will probably have a proprietary licence, so set + :term:`LICENSE_FLAGS` in your recipe. +- The vendor provides a tarball containing libraries so set :term:`SRC_URI` + appropriately. +- Set :term:`COMPATIBLE_HOST` so that the recipe cannot be used with an + unsupported architecture. In the following example, we only support the 32 + and 64 bit variants of the ``x86`` architecture. +- As the vendor provides versioned libraries, we can use ``oe_soinstall`` + from :ref:`ref-classes-utils` to install the shared library and create + symbolic links. If the vendor does not do this, we need to follow the + non-versioned library guidelines in the next section. +- As the vendor likely used :term:`LDFLAGS` different from those in your Yocto + Project build, disable the corresponding checks by adding ``ldflags`` + to :term:`INSANE_SKIP`. +- The vendor will typically ship release builds without debugging symbols. + Avoid errors by preventing the packaging task from stripping out the symbols + and adding them to a separate debug package. This is done by setting the + ``INHIBIT_`` flags shown below. + +The complete recipe would look like this:: + + SUMMARY = "FTDI FT4222H Library" + SECTION = "libs" + LICENSE_FLAGS = "ftdi" + LICENSE = "CLOSED" + + COMPATIBLE_HOST = "(i.86|x86_64).*-linux" + + # Sources available in a .tgz file in .zip archive + # at https://ftdichip.com/wp-content/uploads/2021/01/libft4222-linux-1.4.4.44.zip + # Found on https://ftdichip.com/software-examples/ft4222h-software-examples/ + # Since dealing with this particular type of archive is out of topic here, + # we use a local link. + SRC_URI = "file://libft4222-linux-${PV}.tgz" + + S = "${WORKDIR}" + + ARCH_DIR:x86-64 = "build-x86_64" + ARCH_DIR:i586 = "build-i386" + ARCH_DIR:i686 = "build-i386" + + INSANE_SKIP:${PN} = "ldflags" + INHIBIT_PACKAGE_STRIP = "1" + INHIBIT_SYSROOT_STRIP = "1" + INHIBIT_PACKAGE_DEBUG_SPLIT = "1" + + do_install () { + install -m 0755 -d ${D}${libdir} + oe_soinstall ${S}/${ARCH_DIR}/libft4222.so.${PV} ${D}${libdir} + install -d ${D}${includedir} + install -m 0755 ${S}/*.h ${D}${includedir} + } + +If the precompiled binaries are not statically linked and have dependencies on +other libraries, then by adding those libraries to :term:`DEPENDS`, the linking +can be examined and the appropriate :term:`RDEPENDS` automatically added. + +Non-Versioned Libraries +======================= + +Some Background +--------------- + +Libraries in Linux systems are generally versioned so that it is possible +to have multiple versions of the same library installed, which eases upgrades +and support for older software. For example, suppose that in a versioned +library, an actual library is called ``libfoo.so.1.2``, a symbolic link named +``libfoo.so.1`` points to ``libfoo.so.1.2``, and a symbolic link named +``libfoo.so`` points to ``libfoo.so.1.2``. Given these conditions, when you +link a binary against a library, you typically provide the unversioned file +name (i.e. ``-lfoo`` to the linker). However, the linker follows the symbolic +link and actually links against the versioned filename. The unversioned symbolic +link is only used at development time. Consequently, the library is packaged +along with the headers in the development package ``${PN}-dev`` along with the +actual library and versioned symbolic links in ``${PN}``. Because versioned +libraries are far more common than unversioned libraries, the default packaging +rules assume versioned libraries. + +Yocto Library Packaging Overview +-------------------------------- + +It follows that packaging an unversioned library requires a bit of work in the +recipe. By default, ``libfoo.so`` gets packaged into ``${PN}-dev``, which +triggers a QA warning that a non-symlink library is in a ``-dev`` package, +and binaries in the same recipe link to the library in ``${PN}-dev``, +which triggers more QA warnings. To solve this problem, you need to package the +unversioned library into ``${PN}`` where it belongs. The abridged +default :term:`FILES` variables in ``bitbake.conf`` are:: + + SOLIBS = ".so.*" + SOLIBSDEV = ".so" + FILES:${PN} = "... ${libdir}/lib*${SOLIBS} ..." + FILES_SOLIBSDEV ?= "... ${libdir}/lib*${SOLIBSDEV} ..." + FILES:${PN}-dev = "... ${FILES_SOLIBSDEV} ..." + +:term:`SOLIBS` defines a pattern that matches real shared object libraries. +:term:`SOLIBSDEV` matches the development form (unversioned symlink). These two +variables are then used in ``FILES:${PN}`` and ``FILES:${PN}-dev``, which puts +the real libraries into ``${PN}`` and the unversioned symbolic link into ``${PN}-dev``. +To package unversioned libraries, you need to modify the variables in the recipe +as follows:: + + SOLIBS = ".so" + FILES_SOLIBSDEV = "" + +The modifications cause the ``.so`` file to be the real library +and unset :term:`FILES_SOLIBSDEV` so that no libraries get packaged into +``${PN}-dev``. The changes are required because unless :term:`PACKAGES` is changed, +``${PN}-dev`` collects files before `${PN}`. ``${PN}-dev`` must not collect any of +the files you want in ``${PN}``. + +Finally, loadable modules, essentially unversioned libraries that are linked +at runtime using ``dlopen()`` instead of at build time, should generally be +installed in a private directory. However, if they are installed in ``${libdir}``, +then the modules can be treated as unversioned libraries. + +Example +------- + +The example below installs an unversioned x86-64 pre-built library named +``libfoo.so``. The :term:`COMPATIBLE_HOST` variable limits recipes to the +x86-64 architecture while the :term:`INSANE_SKIP`, :term:`INHIBIT_PACKAGE_STRIP` +and :term:`INHIBIT_SYSROOT_STRIP` variables are all set as in the above +versioned library example. The "magic" is setting the :term:`SOLIBS` and +:term:`FILES_SOLIBSDEV` variables as explained above:: + + SUMMARY = "libfoo sample recipe" + SECTION = "libs" + LICENSE = "CLOSED" + + SRC_URI = "file://libfoo.so" + + COMPATIBLE_HOST = "x86_64.*-linux" + + INSANE_SKIP:${PN} = "ldflags" + INHIBIT_PACKAGE_STRIP = "1" + INHIBIT_SYSROOT_STRIP = "1" + SOLIBS = ".so" + FILES_SOLIBSDEV = "" + + do_install () { + install -d ${D}${libdir} + install -m 0755 ${WORKDIR}/libfoo.so ${D}${libdir} + } + |