kbuild: mark $(targets) as .SECONDARY and remove .PRECIOUS markers

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: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Frank Rowand <frowand.list@gmail.com>
Acked-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 7 insertions, 6 deletions

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 8c3ca611b978..8bdb1dc4072c 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -430,8 +430,6 @@ quiet_cmd_asn1_compiler = ASN.1   $@
       cmd_asn1_compiler = $(objtree)/scripts/asn1_compiler $< \
 				$(subst .h,.c,$@) $(subst .c,.h,$@)
 
-.PRECIOUS: $(objtree)/$(obj)/%.asn1.c $(objtree)/$(obj)/%.asn1.h
-
 $(obj)/%.asn1.c $(obj)/%.asn1.h: $(src)/%.asn1 $(objtree)/scripts/asn1_compiler
 	$(call cmd,asn1_compiler)
 
@@ -544,10 +542,12 @@ targets := $(filter-out $(PHONY), $(targets))
 intermediate_targets = $(foreach sfx, $(2), \
 				$(patsubst %$(strip $(1)),%$(sfx), \
 					$(filter %$(strip $(1)), $(targets))))
+# %.asn1.o <- %.asn1.[ch] <- %.asn1
 # %.dtb.o <- %.dtb.S <- %.dtb <- %.dts
 # %.lex.o <- %.lex.c <- %.l
 # %.tab.o <- %.tab.[ch] <- %.y
-targets += $(call intermediate_targets, .dtb.o, .dtb.S .dtb) \
+targets += $(call intermediate_targets, .asn1.o, .asn1.c .asn1.h) \
+	   $(call intermediate_targets, .dtb.o, .dtb.S .dtb) \
 	   $(call intermediate_targets, .lex.o, .lex.c) \
 	   $(call intermediate_targets, .tab.o, .tab.c .tab.h)
 
@@ -587,6 +587,10 @@ $(shell mkdir -p $(obj-dirs))
 endif
 endif
 
+# Some files contained in $(targets) are intermediate artifacts.
+# We never want them to be removed automatically.
+.SECONDARY: $(targets)
+
 # Declare the contents of the .PHONY variable as phony.  We keep that
 # information in a variable se we can use it in if_changed and friends.
 
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 7f5bca0c3b7b..07d07409f16f 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -184,7 +184,6 @@ endef
 quiet_cmd_flex = LEX     $@
       cmd_flex = $(LEX) -o$@ -L $<
 
-.PRECIOUS: $(obj)/%.lex.c
 $(obj)/%.lex.c: $(src)/%.l FORCE
 	$(call if_changed,flex)
 
@@ -193,14 +192,12 @@ $(obj)/%.lex.c: $(src)/%.l FORCE
 quiet_cmd_bison = YACC    $@
       cmd_bison = $(YACC) -o$@ -t -l $<
 
-.PRECIOUS: $(obj)/%.tab.c
 $(obj)/%.tab.c: $(src)/%.y FORCE
 	$(call if_changed,bison)
 
 quiet_cmd_bison_h = YACC    $@
       cmd_bison_h = bison -o/dev/null --defines=$@ -t -l $<
 
-.PRECIOUS: $(obj)/%.tab.h
 $(obj)/%.tab.h: $(src)/%.y FORCE
 	$(call if_changed,bison_h)