• Masahiro Yamada's avatar
    kbuild: add .SECONDARY special target to scripts/Kbuild.include · c16b137e
    Masahiro Yamada authored
    Based on the following Linux commits:
    
     - 54a702f70589 ("kbuild: mark $(targets) as .SECONDARY and remove
       .PRECIOUS markers")
    
     - 8e9b61b293d9 ("kbuild: move .SECONDARY special target to
       Kbuild.include")
    
    GNU Make automatically deletes intermediate files that are updated
    in a chain of pattern rules.
    
    Example 1) %.dtb.o <- %.dtb.S <- %.dtb <- %.dts
    Example 2) %.o <- %.c <- %.c_shipped
    
    A couple of makefiles mark such targets as .PRECIOUS to prevent Make
    from deleting them, but the correct way is to use .SECONDARY.
    
      .SECONDARY
        Prerequisites of this special target are treated as intermediate
        files but are never automatically deleted.
    
      .PRECIOUS
        When make is interrupted during execution, it may delete the target
        file it is updating if the file was modified since make started.
        If you mark the file as precious, make will never delete the file
        if interrupted.
    
    Both can avoid deletion of intermediate files, but the difference is
    the behavior when Make is interrupted; .SECONDARY deletes the target,
    but .PRECIOUS does not.
    
    The use of .PRECIOUS is relatively rare since we do not want to keep
    partially constructed (possibly corrupted) targets.
    
    .SECONDARY with no prerequisites causes all targets to be treated as
    secondary. This agrees the policy of Kbuild.
    
    scripts/Kbuild.include seems a suitable place to add it because it is
    included from almost all sub-makes.
    Signed-off-by: 's avatarMasahiro Yamada <yamada.masahiro@socionext.com>
    c16b137e
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