Source of how-buildroot-works.txt - buildroot

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== How Buildroot works

As mentioned above, Buildroot is basically a set of Makefiles that

download, configure, and compile software with the correct options. It

also includes patches for various software packages - mainly the ones

involved in the cross-compilation toolchain (+gcc+, +binutils+ and

+uClibc+).

There is basically one Makefile per software package, and they are

named with the +.mk+ extension. Makefiles are split into many different

parts.

* The +toolchain/+ directory contains the Makefiles

  and associated files for all software related to the

  cross-compilation toolchain: +binutils+, +gcc+, +gdb+,

  +kernel-headers+ and +uClibc+.

* The +arch/+ directory contains the definitions for all the processor

  architectures that are supported by Buildroot.

* The +package/+ directory contains the Makefiles and

  associated files for all user-space tools and libraries that Buildroot

  can compile and add to the target root filesystem. There is one

  sub-directory per package.

* The +linux/+ directory contains the Makefiles and associated files for

  the Linux kernel.

* The +boot/+ directory contains the Makefiles and associated files for

  the bootloaders supported by Buildroot.

* The +system/+ directory contains support for system integration, e.g.

  the target filesystem skeleton and the selection of an init system.

* The +fs/+ directory contains the Makefiles and

  associated files for software related to the generation of the

  target root filesystem image.

Each directory contains at least 2 files:

* +something.mk+ is the Makefile that downloads, configures,

  compiles and installs the package +something+.

* +Config.in+ is a part of the configuration tool

  description file. It describes the options related to the

  package.

The main Makefile performs the following steps (once the

configuration is done):

* Create all the output directories: +staging+, +target+, +build+,

  etc. in the output directory (+output/+ by default,

  another value can be specified using +O=+)

* Generate the toolchain target. When an internal toolchain is used, this

  means generating the cross-compilation toolchain. When an external

  toolchain is used, this means checking the features of the external

  toolchain and importing it into the Buildroot environment.

* Generate all the targets listed in the +TARGETS+ variable. This