mirror of
https://github.com/AsahiLinux/u-boot
synced 2024-12-18 09:13:06 +00:00
a55014d09b
LTO (Link-Time Optimisation) is an very useful feature which can significantly reduce the size of U-Boot binaries. So far it has been made available for selected ARM boards and sandbox. However, incremental builds are much slower when LTO is used. For example, an incremental build of sandbox takes 2.1 seconds on my machine, but 6.7 seconds with LTO enabled. Add a NO_LTO parameter to the build, similar to NO_SDL, so it can be disabled during development if needed, for faster builds. Add some documentation about LTO while we are here. Signed-off-by: Simon Glass <sjg@chromium.org>
190 lines
5.3 KiB
ReStructuredText
190 lines
5.3 KiB
ReStructuredText
Building with GCC
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=================
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Dependencies
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------------
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For building U-Boot you need a GCC compiler for your host platform. If you
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are not building on the target platform you further need a GCC cross compiler.
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Debian based
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~~~~~~~~~~~~
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On Debian based systems the cross compiler packages are named
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gcc-<architecture>-linux-gnu.
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You could install GCC and the GCC cross compiler for the ARMv8 architecture with
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.. code-block:: bash
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sudo apt-get install gcc gcc-aarch64-linux-gnu
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Depending on the build targets further packages maybe needed
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.. code-block:: bash
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sudo apt-get install bc bison build-essential coccinelle \
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device-tree-compiler dfu-util efitools flex gdisk graphviz imagemagick \
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liblz4-tool libgnutls28-dev libguestfs-tools libncurses-dev \
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libpython3-dev libsdl2-dev libssl-dev lz4 lzma lzma-alone openssl \
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pkg-config python3 python3-asteval python3-coverage \
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python3-pkg-resources python3-pycryptodome python3-pyelftools \
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python3-pytest python3-sphinxcontrib.apidoc python3-sphinx-rtd-theme \
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python3-subunit python3-testtools python3-virtualenv swig uuid-dev
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SUSE based
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~~~~~~~~~~
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On suse based systems the cross compiler packages are named
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cross-<architecture>-gcc<version>.
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You could install GCC and the GCC 10 cross compiler for the ARMv8 architecture
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with
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.. code-block:: bash
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sudo zypper install gcc cross-aarch64-gcc10
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Depending on the build targets further packages maybe needed.
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.. code-block:: bash
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zypper install bc bison flex gcc libopenssl-devel libSDL2-devel make \
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ncurses-devel python3-devel python3-pytest swig
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Alpine Linux
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~~~~~~~~~~~~
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For building U-Boot on Alpine Linux at least the following packages are needed:
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.. code-block:: bash
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apk add alpine-sdk bc bison dtc flex linux-headers ncurses-dev \
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openssl-dev perl python3 py3-setuptools python3-dev sdl2-dev
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Prerequisites
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-------------
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For some boards you have to build prerequisite files before you can build
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U-Boot, e.g. for the some boards you will need to build the ARM Trusted Firmware
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beforehand. Please, refer to the board specific documentation
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:doc:`../board/index`.
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Configuration
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-------------
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Directory configs/ contains the template configuration files for the maintained
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boards following the naming scheme::
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<board name>_defconfig
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These files have been stripped of default settings. So you cannot use them
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directly. Instead their name serves as a make target to generate the actual
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configuration file .config. For instance the configuration template for the
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Odroid C2 board is called odroid-c2_defconfig. The corresponding .config file
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is generated by
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.. code-block:: bash
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make odroid-c2_defconfig
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You can adjust the configuration using
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.. code-block:: bash
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make menuconfig
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Building
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--------
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When cross compiling you will have to specify the prefix of the cross-compiler.
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You can either specify the value of the CROSS_COMPILE variable on the make
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command line or export it beforehand.
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.. code-block:: bash
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CROSS_COMPILE=<compiler-prefix> make
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Assuming cross compiling on Debian for ARMv8 this would be
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.. code-block:: bash
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CROSS_COMPILE=aarch64-linux-gnu- make
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Build parameters
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~~~~~~~~~~~~~~~~
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A list of available parameters for the make command can be obtained via
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.. code-block:: bash
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make help
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You can speed up compilation by parallelization using the -j parameter, e.g.
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.. code-block:: bash
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CROSS_COMPILE=aarch64-linux-gnu- make -j$(nproc)
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Further important build parameters are
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* O=<dir> - generate all output files in directory <dir>, including .config
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* V=1 - verbose build
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Devicetree compiler
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~~~~~~~~~~~~~~~~~~~
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Boards that use `CONFIG_OF_CONTROL` (i.e. almost all of them) need the
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devicetree compiler (dtc). Those with `CONFIG_PYLIBFDT` need pylibfdt, a Python
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library for accessing devicetree data. Suitable versions of these are included
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in the U-Boot tree in `scripts/dtc` and built automatically as needed.
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To use the system versions of these, use the DTC parameter, for example
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.. code-block:: bash
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DTC=/usr/bin/dtc make
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In this case, dtc and pylibfdt are not built. The build checks that the version
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of dtc is new enough. It also makes sure that pylibfdt is present, if needed
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(see `scripts_dtc` in the Makefile).
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Note that the :doc:`tools` are always built with the included version of libfdt
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so it is not possible to build U-Boot tools with a system libfdt, at present.
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Link-time optimisation (LTO)
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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U-Boot supports link-time optimisation which can reduce the size of the final
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U-Boot binaries, particularly with SPL.
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At present this can be enabled by ARM boards by adding `CONFIG_LTO=y` into the
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defconfig file. Other architectures are not supported. LTO is enabled by default
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for sandbox.
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This does incur a link-time penalty of several seconds. For faster incremental
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builds during development, you can disable it by setting `NO_LTO` to `1`.
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.. code-block:: bash
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NO_LTO=1 make
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Other build targets
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~~~~~~~~~~~~~~~~~~~
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A list of all make targets can be obtained via
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.. code-block:: bash
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make help
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Important ones are
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* clean - remove most generated files but keep the configuration
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* mrproper - remove all generated files + config + various backup files
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Installation
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------------
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The process for installing U-Boot on the target device is device specific.
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Please, refer to the board specific documentation :doc:`../board/index`.
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