60 lines
2.4 KiB
Plaintext
60 lines
2.4 KiB
Plaintext
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How Buildroot works
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===================
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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 tool chain (+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 three main
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sections:
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* *toolchain* (in 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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* *package* (in the +package/+ directory) contains the Makefiles and
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associated files for all user-space tools that Buildroot can compile
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and add to the target root filesystem. There is one sub-directory
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per tool.
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* *target* (in the +target+ 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. Four types of filesystems are
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supported: ext2, jffs2, cramfs and squashfs. For each of them there
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is a sub-directory with the required files. There is also a
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+default/+ directory that contains the target filesystem skeleton.
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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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+stamps+, etc. in the output directory (+output/+ by default,
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another value can be specified using +O=+)
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* Generate all the targets listed in the +BASE_TARGETS+ variable. When
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an internal toolchain is used, this means generating the
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cross-compilation toolchain. When an external toolchain is used,
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this means checking the features of the external toolchain and
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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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