32cec3be97
by using this standard extension `adoc`, these files are rendered on gitlab & github Signed-off-by: Francois Perrad <francois.perrad@gadz.org> Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
70 lines
2.6 KiB
Plaintext
70 lines
2.6 KiB
Plaintext
// -*- mode:doc; -*-
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// vim: set syntax=asciidoc:
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== How Buildroot works
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As mentioned above, Buildroot is basically a set of Makefiles that
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download, configure, and compile software with the correct options. It
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also includes patches for various software packages - mainly the ones
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involved in the cross-compilation toolchain (+gcc+, +binutils+ and
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+uClibc+).
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There is basically one Makefile per software package, and they are
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named with the +.mk+ extension. Makefiles are split into many different
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parts.
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* The +toolchain/+ directory contains the Makefiles
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and associated files for all software related to the
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cross-compilation toolchain: +binutils+, +gcc+, +gdb+,
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+kernel-headers+ and +uClibc+.
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* The +arch/+ directory contains the definitions for all the processor
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architectures that are supported by Buildroot.
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* The +package/+ directory contains the Makefiles and
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associated files for all user-space tools and libraries that Buildroot
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can compile and add to the target root filesystem. There is one
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sub-directory per package.
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* The +linux/+ directory contains the Makefiles and associated files for
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the Linux kernel.
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* The +boot/+ directory contains the Makefiles and associated files for
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the bootloaders supported by Buildroot.
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* The +system/+ directory contains support for system integration, e.g.
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the target filesystem skeleton and the selection of an init system.
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* The +fs/+ directory contains the Makefiles and
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associated files for software related to the generation of the
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target root filesystem image.
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Each directory contains at least 2 files:
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* +something.mk+ is the Makefile that downloads, configures,
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compiles and installs the package +something+.
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* +Config.in+ is a part of the configuration tool
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description file. It describes the options related to the
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package.
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The main Makefile performs the following steps (once the
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configuration is done):
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* Create all the output directories: +staging+, +target+, +build+,
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etc. in the output directory (+output/+ by default,
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another value can be specified using +O=+)
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* Generate the toolchain target. When an internal toolchain is used, this
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means generating the cross-compilation toolchain. When an external
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toolchain is used, this means checking the features of the external
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toolchain and importing it into the Buildroot environment.
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* Generate all the targets listed in the +TARGETS+ variable. This
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variable is filled by all the individual components'
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Makefiles. Generating these targets will trigger the compilation of
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the userspace packages (libraries, programs), the kernel, the
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bootloader and the generation of the root filesystem images,
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depending on the configuration.
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