kbuild: remove incremental linking option

This removes the old `ld -r` incremental link option, which has not
been selected by any architecture since June 2017.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Documentation/kbuild/makefiles.txt

@@ -153,8 +153,14 @@ more details, with real examples.
 	configuration.
 
 	Kbuild compiles all the $(obj-y) files.  It then calls
-	"$(LD) -r" to merge these files into one built-in.o file.
-	built-in.o is later linked into vmlinux by the parent Makefile.
+	"$(AR) rcSTP" to merge these files into one built-in.o file.
+	This is a thin archive without a symbol table, which makes it
+	unsuitable as a linker input.
+
+	The scripts/link-vmlinux.sh script later makes an aggregate
+	built-in.o with "${AR} rcsTP", which creates the thin archive
+	with a symbol table and an index, making it a valid input for
+	the final vmlinux link passes.
 
 	The order of files in $(obj-y) is significant.  Duplicates in
 	the lists are allowed: the first instance will be linked into

arch/Kconfig

@@ -596,12 +596,6 @@ config CC_STACKPROTECTOR_AUTO
 
 endchoice
 
-config THIN_ARCHIVES
-	def_bool y
-	help
-	  Select this if the architecture wants to use thin archives
-	  instead of ld -r to create the built-in.o files.
-
 config LD_DEAD_CODE_DATA_ELIMINATION
 	bool
 	help

scripts/Makefile.build

@@ -458,15 +458,13 @@ $(sort $(subdir-obj-y)): $(subdir-ym) ;
 #
 ifdef builtin-target
 
-ifdef CONFIG_THIN_ARCHIVES
-  cmd_make_builtin = rm -f $@; $(AR) rcSTP$(KBUILD_ARFLAGS)
-  cmd_make_empty_builtin = rm -f $@; $(AR) rcSTP$(KBUILD_ARFLAGS)
-  quiet_cmd_link_o_target = AR      $@
-else
-  cmd_make_builtin = $(LD) $(ld_flags) -r -o
-  cmd_make_empty_builtin = rm -f $@; $(AR) rcs$(KBUILD_ARFLAGS)
-  quiet_cmd_link_o_target = LD      $@
-endif
+# built-in.o archives are made with no symbol table or index which
+# makes them small and fast, but unable to be used by the linker.
+# scripts/link-vmlinux.sh builds an aggregate built-in.o with a symbol
+# table and index.
+cmd_make_builtin = rm -f $@; $(AR) rcSTP$(KBUILD_ARFLAGS)
+cmd_make_empty_builtin = rm -f $@; $(AR) rcSTP$(KBUILD_ARFLAGS)
+quiet_cmd_link_o_target = AR      $@
 
 # If the list of objects to link is empty, just create an empty built-in.o
 cmd_link_o_target = $(if $(strip $(obj-y)),\
@@ -499,11 +497,8 @@ $(modorder-target): $(subdir-ym) FORCE
 ifdef lib-target
 quiet_cmd_link_l_target = AR      $@
 
-ifdef CONFIG_THIN_ARCHIVES
-  cmd_link_l_target = rm -f $@; $(AR) rcsTP$(KBUILD_ARFLAGS) $@ $(lib-y)
-else
-  cmd_link_l_target = rm -f $@; $(AR) rcs$(KBUILD_ARFLAGS) $@ $(lib-y)
-endif
+# lib target archives do get a symbol table and index
+cmd_link_l_target = rm -f $@; $(AR) rcsTP$(KBUILD_ARFLAGS) $@ $(lib-y)
 
 $(lib-target): $(lib-y) FORCE
 	$(call if_changed,link_l_target)
@@ -551,13 +546,8 @@ $($(subst $(obj)/,,$(@:.o=-m)))), $^)
 
 cmd_link_multi-link = $(LD) $(ld_flags) -r -o $@ $(link_multi_deps) $(cmd_secanalysis)
 
-ifdef CONFIG_THIN_ARCHIVES
-  quiet_cmd_link_multi-y = AR      $@
-  cmd_link_multi-y = rm -f $@; $(AR) rcSTP$(KBUILD_ARFLAGS) $@ $(link_multi_deps)
-else
-  quiet_cmd_link_multi-y = LD      $@
-  cmd_link_multi-y = $(cmd_link_multi-link)
-endif
+quiet_cmd_link_multi-y = AR      $@
+cmd_link_multi-y = rm -f $@; $(AR) rcSTP$(KBUILD_ARFLAGS) $@ $(link_multi_deps)
 
 quiet_cmd_link_multi-m = LD [M]  $@
 cmd_link_multi-m = $(cmd_link_multi-link)

scripts/link-vmlinux.sh

@@ -55,13 +55,11 @@ info()
 #
 archive_builtin()
 {
-	if [ -n "${CONFIG_THIN_ARCHIVES}" ]; then
 	info AR built-in.o
 	rm -f built-in.o;
 	${AR} rcsTP${KBUILD_ARFLAGS} built-in.o			\
 				${KBUILD_VMLINUX_INIT}		\
 				${KBUILD_VMLINUX_MAIN}
-	fi
 }
 
 # Link of vmlinux.o used for section mismatch analysis
@@ -70,20 +68,13 @@ modpost_link()
 {
 	local objects
 
-	if [ -n "${CONFIG_THIN_ARCHIVES}" ]; then
 	objects="--whole-archive				\
 		built-in.o					\
 		--no-whole-archive				\
 		--start-group					\
 		${KBUILD_VMLINUX_LIBS}				\
 		--end-group"
-	else
-		objects="${KBUILD_VMLINUX_INIT}				\
-			--start-group					\
-			${KBUILD_VMLINUX_MAIN}				\
-			${KBUILD_VMLINUX_LIBS}				\
-			--end-group"
-	fi
+
 	${LD} ${LDFLAGS} -r -o ${1} ${objects}
 }
 
@@ -96,7 +87,6 @@ vmlinux_link()
 	local objects
 
 	if [ "${SRCARCH}" != "um" ]; then
-		if [ -n "${CONFIG_THIN_ARCHIVES}" ]; then
 		objects="--whole-archive			\
 			built-in.o				\
 			--no-whole-archive			\
@@ -104,19 +94,10 @@ vmlinux_link()
 			${KBUILD_VMLINUX_LIBS}			\
 			--end-group				\
 			${1}"
-		else
-			objects="${KBUILD_VMLINUX_INIT}			\
-				--start-group				\
-				${KBUILD_VMLINUX_MAIN}			\
-				${KBUILD_VMLINUX_LIBS}			\
-				--end-group				\
-				${1}"
-		fi
 
 		${LD} ${LDFLAGS} ${LDFLAGS_vmlinux} -o ${2}	\
 			-T ${lds} ${objects}
 	else
-		if [ -n "${CONFIG_THIN_ARCHIVES}" ]; then
 		objects="-Wl,--whole-archive			\
 			built-in.o				\
 			-Wl,--no-whole-archive			\
@@ -124,14 +105,6 @@ vmlinux_link()
 			${KBUILD_VMLINUX_LIBS}			\
 			-Wl,--end-group				\
 			${1}"
-		else
-			objects="${KBUILD_VMLINUX_INIT}			\
-				-Wl,--start-group			\
-				${KBUILD_VMLINUX_MAIN}			\
-				${KBUILD_VMLINUX_LIBS}			\
-				-Wl,--end-group				\
-				${1}"
-		fi
 
 		${CC} ${CFLAGS_vmlinux} -o ${2}			\
 			-Wl,-T,${lds}				\