• Masahiro Yamada's avatar
    kbuild: create *.mod with full directory path and remove MODVERDIR · b7dca6dd
    Masahiro Yamada authored
    While descending directories, Kbuild produces objects for modules,
    but do not link final *.ko files; it is done in the modpost.
    
    To keep track of modules, Kbuild creates a *.mod file in $(MODVERDIR)
    for every module it is building. Some post-processing steps read the
    necessary information from *.mod files. This avoids descending into
    directories again. This mechanism was introduced in 2003 or so.
    
    Later, commit 551559e1 ("kbuild: implement modules.order") added
    modules.order. So, we can simply read it out to know all the modules
    with directory paths. This is easier than parsing the first line of
    *.mod files.
    
    $(MODVERDIR) has a flat directory structure, that is, *.mod files
    are named only with base names. This is based on the assumption that
    the module name is unique across the tree. This assumption is really
    fragile.
    
    Stephen Rothwell reported a race condition caused by a module name
    conflict:
    
      https://lkml.org/lkml/2019/5/13/991
    
    In parallel building, two different threads could write to the same
    $(MODVERDIR)/*.mod simultaneously.
    
    Non-unique module names are the source of all kind of troubles, hence
    commit 3a48a919 ("kbuild: check uniqueness of module names")
    introduced a new checker script.
    
    However, it is still fragile in the build system point of view because
    this race happens before scripts/modules-check.sh is invoked. If it
    happens again, the modpost will emit unclear error messages.
    
    To fix this issue completely, create *.mod with full directory path
    so that two threads never attempt to write to the same file.
    
    $(MODVERDIR) is no longer needed.
    
    Since modules with directory paths are listed in modules.order, Kbuild
    is still able to find *.mod files without additional descending.
    
    I also killed cmd_secanalysis; scripts/mod/sumversion.c computes MD4 hash
    for modules with MODULE_VERSION(). When CONFIG_DEBUG_SECTION_MISMATCH=y,
    it occurs not only in the modpost stage, but also during directory
    descending, where sumversion.c may parse stale *.mod files. It would emit
    'No such file or directory' warning when an object consisting a module is
    renamed, or when a single-obj module is turned into a multi-obj module or
    vice versa.
    Signed-off-by: 's avatarMasahiro Yamada <yamada.masahiro@socionext.com>
    Acked-by: 's avatarNicolas Pitre <nico@fluxnic.net>
    b7dca6dd