• Masahiro Yamada's avatar
    kbuild: let fixdep directly write to .*.cmd files · a41c9b57
    Masahiro Yamada authored
    [ Upstream commit 392885ee ]
    
    Currently, fixdep writes dependencies to .*.tmp, which is renamed to
    .*.cmd after everything succeeds. This is a very safe way to avoid
    corrupted .*.cmd files. The if_changed_dep has carried this safety
    mechanism since it was added in 2002.
    
    If fixdep fails for some reasons or a user terminates the build while
    fixdep is running, the incomplete output from the fixdep could be
    troublesome.
    
    This is my insight about some bad scenarios:
    
    [1] If the compiler succeeds to generate *.o file, but fixdep fails
        to write necessary dependencies to .*.cmd file, Make will miss
        to rebuild the object when headers or CONFIG options are changed.
        In this case, fixdep should not generate .*.cmd file at all so
        that 'arg-check' will surely trigger the rebuild of the object.
    
    [2] A partially constructed .*.cmd file may not be a syntactically
        correct makefile. The next time Make runs, it would include it,
        then fail to parse it. Once this happens, 'make clean' is be the
        only way to fix it.
    
    In fact, [1] is no longer a problem since commit 9c2af1c7 ("kbuild:
    add .DELETE_ON_ERROR special target"). Make deletes a target file on
    any failure in its recipe. Because fixdep is a part of the recipe of
    *.o target, if it fails, the *.o is deleted anyway. However, I am a
    bit worried about the slight possibility of [2].
    
    So, here is a solution. Let fixdep directly write to a .*.cmd file,
    but allow makefiles to include it only when its corresponding target
    exists.
    
    This effectively reverts commit 2982c953 ("kbuild: remove redundant
    $(wildcard ...) for cmd_files calculation"), and commit 00d78ab2
    ("kbuild: remove dead code in cmd_files calculation in top Makefile")
    because now we must check the presence of targets.
    Signed-off-by: 's avatarMasahiro Yamada <yamada.masahiro@socionext.com>
    Signed-off-by: 's avatarSasha Levin <sashal@kernel.org>
    a41c9b57
Makefile.build 18 KB