• Masahiro Yamada's avatar
    kbuild: mark $(targets) as .SECONDARY and remove .PRECIOUS markers · 54a702f7
    Masahiro Yamada authored
    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.
    
    Another difference is that .PRECIOUS works with pattern rules whereas
    .SECONDARY does not.
    
      .PRECIOUS: $(obj)/%.lex.c
    
    works, but
    
      .SECONDARY: $(obj)/%.lex.c
    
    has no effect.  However, for the reason above, I do not want to use
    .PRECIOUS which could cause obscure build breakage.
    
    The targets specified as .SECONDARY must be explicit.  $(targets)
    contains all targets that need to include .*.cmd files.  So, the
    intermediates you want to keep are mostly in there.  Therefore, mark
    $(targets) as .SECONDARY.  It means primary targets are also marked
    as .SECONDARY, but I do not see any drawback for this.
    
    I replaced some .SECONDARY / .PRECIOUS markers with 'targets'.  This
    will make Kbuild search for non-existing .*.cmd files, but this is
    not a noticeable performance issue.
    Signed-off-by: default avatarMasahiro Yamada <yamada.masahiro@socionext.com>
    Acked-by: default avatarFrank Rowand <frowand.list@gmail.com>
    Acked-by: default avatarIngo Molnar <mingo@kernel.org>
    54a702f7
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