[PATCH 10/10] kbuild: mark $(targets) as .SECONDARY and remove .PRECIOUS specifier

[Masahiro Yamada]

GNU Make automatically deletes intermediate files that are updated
in a chain of pattern rules.

Example 1) %.dtb.o <- %.dtb.S <- %.dtb.S <- %.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 to avoid 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 likely to be contained in
$(targets).  So, mark it as .SECONDARY.  The exception is when they
are created by $(call cmd,...) instead of $(call if_changed,...)
since the former does not need to include .*.cmd file.  In this
case, makefiles need to mark them .SECONDARY by themselves, like
arch/arm(64)/crypto/Makefile.

Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
---

 arch/arc/boot/dts/Makefile        | 2 --
 arch/arm/crypto/Makefile          | 2 +-
 arch/arm64/crypto/Makefile        | 2 +-
 arch/metag/boot/dts/Makefile      | 2 --
 drivers/of/unittest-data/Makefile | 4 ----
 scripts/Makefile.build            | 6 ++++--
 scripts/Makefile.lib              | 3 ---
 7 files changed, 6 insertions(+), 15 deletions(-)

diff --git a/arch/arc/boot/dts/Makefile b/arch/arc/boot/dts/Makefile
index 22a4c5d..a83c4f5 100644
--- a/arch/arc/boot/dts/Makefile
+++ b/arch/arc/boot/dts/Makefile
@@ -9,8 +9,6 @@ endif
 obj-y   += $(builtindtb-y).dtb.o
 dtb-y := $(builtindtb-y).dtb
 
-.SECONDARY: $(obj)/$(builtindtb-y).dtb.S
-
 # for CONFIG_OF_ALL_DTBS test
 dtstree	:= $(srctree)/$(src)
 dtb-	:= $(patsubst $(dtstree)/%.dts,%.dtb, $(wildcard $(dtstree)/*.dts))
diff --git a/arch/arm/crypto/Makefile b/arch/arm/crypto/Makefile
index 30ef8e2..3d59567 100644
--- a/arch/arm/crypto/Makefile
+++ b/arch/arm/crypto/Makefile
@@ -63,4 +63,4 @@ $(src)/sha256-core.S_shipped: $(src)/sha256-armv4.pl
 $(src)/sha512-core.S_shipped: $(src)/sha512-armv4.pl
 	$(call cmd,perl)
 
-.PRECIOUS: $(obj)/sha256-core.S $(obj)/sha512-core.S
+.SECONDARY: $(obj)/sha256-core.S $(obj)/sha512-core.S
diff --git a/arch/arm64/crypto/Makefile b/arch/arm64/crypto/Makefile
index cee9b8d9..fceb638 100644
--- a/arch/arm64/crypto/Makefile
+++ b/arch/arm64/crypto/Makefile
@@ -76,4 +76,4 @@ $(src)/sha256-core.S_shipped: $(src)/sha512-armv8.pl
 $(src)/sha512-core.S_shipped: $(src)/sha512-armv8.pl
 	$(call cmd,perlasm)
 
-.PRECIOUS: $(obj)/sha256-core.S $(obj)/sha512-core.S
+.SECONDARY: $(obj)/sha256-core.S $(obj)/sha512-core.S
diff --git a/arch/metag/boot/dts/Makefile b/arch/metag/boot/dts/Makefile
index f0a180f..16505aa 100644
--- a/arch/metag/boot/dts/Makefile
+++ b/arch/metag/boot/dts/Makefile
@@ -12,5 +12,3 @@ endif
 
 dtb-$(CONFIG_METAG_BUILTIN_DTB)	+= $(builtindtb-y).dtb
 obj-$(CONFIG_METAG_BUILTIN_DTB)	+= $(builtindtb-y).dtb.o
-
-.SECONDARY: $(obj)/$(builtindtb-y).dtb.S
diff --git a/drivers/of/unittest-data/Makefile b/drivers/of/unittest-data/Makefile
index 333bc4c..0fb87cb 100644
--- a/drivers/of/unittest-data/Makefile
+++ b/drivers/of/unittest-data/Makefile
@@ -12,7 +12,3 @@ DTC_FLAGS_overlay := -@
 DTC_FLAGS_overlay_bad_phandle := -@
 DTC_FLAGS_overlay_bad_symbol := -@
 DTC_FLAGS_overlay_base := -@
-
-.PRECIOUS: \
-	$(obj)/%.dtb.S \
-	$(obj)/%.dtb
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index cc081af..4397adb 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 FORCE
 	$(call if_changed,asn1_compiler)
@@ -590,6 +588,10 @@ $(shell mkdir -p $(obj-dirs))
 endif
 endif
 
+# Some 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 7a1fa92..c114ce5 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -183,7 +183,6 @@ endef
 quiet_cmd_flex = LEX     $@
       cmd_flex = $(LEX) -o$@ -L $<
 
-.PRECIOUS: $(obj)/%.lex.c
 $(obj)/%.lex.c: $(src)/%.l FORCE
 	$(call if_changed,flex)
 
@@ -192,14 +191,12 @@ $(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)
 
-- 
2.7.4