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  1. Jul 17, 2019
    • 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: default avatarMasahiro Yamada <yamada.masahiro@socionext.com>
      Acked-by: default avatarNicolas Pitre <nico@fluxnic.net>
      b7dca6dd
  2. Jul 12, 2019
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