• Masahiro Yamada's avatar
    kbuild: change out-of-tree build · 9e414032
    Masahiro Yamada authored
    This commit changes the working directory
    where the build process occurs.
    Before this commit, build process occurred under the source
    tree for both in-tree and out-of-tree build.
    That's why we needed to add $(obj) prefix to all generated
    files in makefiles like follows:
      $(obj)u-boot.bin:  $(obj)u-boot
    Here, $(obj) is empty for in-tree build, whereas it points
    to the output directory for out-of-tree build.
    And our old build system changes the current working directory
    with "make -C <sub-dir>" syntax when descending into the
    On the other hand, Kbuild uses a different idea
    to handle out-of-tree build and directory descending.
    The build process of Kbuild always occurs under the output tree.
    When "O=dir/to/store/output/files" is given, the build system
    changes the current working directory to that directory and
    restarts the make.
    Kbuild uses "make -f $(srctree)/scripts/Makefile.build obj=<sub-dir>"
    syntax for descending into sub-directories.
    (We can write it like "make $(obj)=<sub-dir>" with a shorthand.)
    This means the current working directory is always the top
    of the output directory.
    Signed-off-by: default avatarMasahiro Yamada <yamada.m@jp.panasonic.com>
    Tested-by: default avatarGerhard Sittig <gsi@denx.de>
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