kbuild: link of vmlinux moved to a script

Move the final link of vmlinux to a script to improve
readability and maintainability of the code.

The Makefile fragments used to link vmlinux has over the
years seen far too many changes and the logic had become
hard to follow.

As the process by nature is serialized there was
nothing gained including this in the Makefile.

"um" has special link requirments - and the
only way to handle this was to hard-code the linking
of "um" in the script.
This was better than trying to modularize it only for the
benefit of "um" anyway.

The shell script has been improved after input from:
Arnaud Lacombe <lacombar@gmail.com>
Nick Bowler <nbowler@elliptictech.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Arnaud Lacombe <lacombar@gmail.com>
Cc: Nick Bowler <nbowler@elliptictech.com>
Cc: Richard Weinberger <richard@nod.at>
Signed-off-by: Michal Marek <mmarek@suse.cz>

Makefile

@@ -337,7 +337,6 @@ AWK		= awk
 GENKSYMS	= scripts/genksyms/genksyms
 INSTALLKERNEL  := installkernel
 DEPMOD		= /sbin/depmod
-KALLSYMS	= scripts/kallsyms
 PERL		= perl
 CHECK		= sparse
 
@@ -723,191 +722,21 @@ libs-y1		:= $(patsubst %/, %/lib.a, $(libs-y))
 libs-y2		:= $(patsubst %/, %/built-in.o, $(libs-y))
 libs-y		:= $(libs-y1) $(libs-y2)
 
-# externally visible symbols
+# Externally visible symbols (used by link-vmlinux.sh)
 export KBUILD_VMLINUX_INIT := $(head-y) $(init-y)
 export KBUILD_VMLINUX_MAIN := $(core-y) $(libs-y) $(drivers-y) $(net-y)
 export KBUILD_LDS          := arch/$(SRCARCH)/kernel/vmlinux.lds
+export LDFLAGS_vmlinux
 
-# Build vmlinux
-# ---------------------------------------------------------------------------
-# vmlinux is built from the objects selected by $(vmlinux-init) and
-# $(vmlinux-main). Most are built-in.o files from top-level directories
-# in the kernel tree, others are specified in arch/$(ARCH)/Makefile.
-# Ordering when linking is important, and $(vmlinux-init) must be first.
-#
-# vmlinux
-#   ^
-#   |
-#   +-< $(vmlinux-init)
-#   |   +--< init/version.o + more
-#   |
-#   +--< $(vmlinux-main)
-#   |    +--< driver/built-in.o mm/built-in.o + more
-#   |
-#   +-< kallsyms.o (see description in CONFIG_KALLSYMS section)
-#
-# vmlinux version (uname -v) cannot be updated during normal
-# descending-into-subdirs phase since we do not yet know if we need to
-# update vmlinux.
-# Therefore this step is delayed until just before final link of vmlinux -
-# except in the kallsyms case where it is done just before adding the
-# symbols to the kernel.
-#
-# System.map is generated to document addresses of all kernel symbols
-
-vmlinux-init := $(head-y) $(init-y)
-vmlinux-main := $(core-y) $(libs-y) $(drivers-y) $(net-y)
-vmlinux-all  := $(vmlinux-init) $(vmlinux-main)
-vmlinux-lds  := arch/$(SRCARCH)/kernel/vmlinux.lds
-
-# Rule to link vmlinux - also used during CONFIG_KALLSYMS
-# May be overridden by arch/$(ARCH)/Makefile
-quiet_cmd_vmlinux__ ?= LD      $@
-      cmd_vmlinux__ ?= $(LD) $(LDFLAGS) $(LDFLAGS_vmlinux) -o $@ \
-      -T $(vmlinux-lds) $(vmlinux-init)                          \
-      --start-group $(vmlinux-main) --end-group                  \
-      $(filter-out $(vmlinux-lds) $(vmlinux-init) $(vmlinux-main) vmlinux.o FORCE ,$^)
-
-# Generate new vmlinux version
-quiet_cmd_vmlinux_version = GEN     .version
-      cmd_vmlinux_version = set -e;                     \
-	if [ ! -r .version ]; then			\
-	  rm -f .version;				\
-	  echo 1 >.version;				\
-	else						\
-	  mv .version .old_version;			\
-	  expr 0$$(cat .old_version) + 1 >.version;	\
-	fi;						\
-	$(MAKE) $(build)=init
-
-# Generate System.map
-quiet_cmd_sysmap = SYSMAP
-      cmd_sysmap = $(CONFIG_SHELL) $(srctree)/scripts/mksysmap
-
-# Link of vmlinux
-# If CONFIG_KALLSYMS is set .version is already updated
-# Generate System.map and verify that the content is consistent
-# Use + in front of the vmlinux_version rule to silent warning with make -j2
-# First command is ':' to allow us to use + in front of the rule
-define rule_vmlinux__
-	:
-	$(if $(CONFIG_KALLSYMS),,+$(call cmd,vmlinux_version))
-
-	$(call cmd,vmlinux__)
-	$(Q)echo 'cmd_$@ := $(cmd_vmlinux__)' > $(@D)/.$(@F).cmd
-
-	$(Q)$(if $($(quiet)cmd_sysmap),                                      \
-	  echo '  $($(quiet)cmd_sysmap)  System.map' &&)                     \
-	$(cmd_sysmap) $@ System.map;                                         \
-	if [ $$? -ne 0 ]; then                                               \
-		rm -f $@;                                                    \
-		/bin/false;                                                  \
-	fi;
-	$(verify_kallsyms)
-endef
-
-
-ifdef CONFIG_KALLSYMS
-# Generate section listing all symbols and add it into vmlinux $(kallsyms.o)
-# It's a three stage process:
-# o .tmp_vmlinux1 has all symbols and sections, but __kallsyms is
-#   empty
-#   Running kallsyms on that gives us .tmp_kallsyms1.o with
-#   the right size - vmlinux version (uname -v) is updated during this step
-# o .tmp_vmlinux2 now has a __kallsyms section of the right size,
-#   but due to the added section, some addresses have shifted.
-#   From here, we generate a correct .tmp_kallsyms2.o
-# o The correct .tmp_kallsyms2.o is linked into the final vmlinux.
-# o Verify that the System.map from vmlinux matches the map from
-#   .tmp_vmlinux2, just in case we did not generate kallsyms correctly.
-# o If 'make KALLSYMS_EXTRA_PASS=1" was used, do an extra pass using
-#   .tmp_vmlinux3 and .tmp_kallsyms3.o.  This is only meant as a
-#   temporary bypass to allow the kernel to be built while the
-#   maintainers work out what went wrong with kallsyms.
-
-last_kallsyms := 2
-
-ifdef KALLSYMS_EXTRA_PASS
-ifneq ($(KALLSYMS_EXTRA_PASS),0)
-last_kallsyms := 3
-endif
-endif
-
-kallsyms.o := .tmp_kallsyms$(last_kallsyms).o
-
-define verify_kallsyms
-	$(Q)$(if $($(quiet)cmd_sysmap),                                      \
-	  echo '  $($(quiet)cmd_sysmap)  .tmp_System.map' &&)                \
-	  $(cmd_sysmap) .tmp_vmlinux$(last_kallsyms) .tmp_System.map
-	$(Q)cmp -s System.map .tmp_System.map ||                             \
-		(echo Inconsistent kallsyms data;                            \
-		 echo This is a bug - please report about it;                \
-		 echo Try "make KALLSYMS_EXTRA_PASS=1" as a workaround;      \
-		 rm .tmp_kallsyms* ; /bin/false )
-endef
-
-# Update vmlinux version before link
-# Use + in front of this rule to silent warning about make -j1
-# First command is ':' to allow us to use + in front of this rule
-cmd_ksym_ld = $(cmd_vmlinux__)
-define rule_ksym_ld
-	: 
-	+$(call cmd,vmlinux_version)
-	$(call cmd,vmlinux__)
-	$(Q)echo 'cmd_$@ := $(cmd_vmlinux__)' > $(@D)/.$(@F).cmd
-endef
-
-# Generate .S file with all kernel symbols
-quiet_cmd_kallsyms = KSYM    $@
-      cmd_kallsyms = $(NM) -n $< | $(KALLSYMS) \
-                     $(if $(CONFIG_KALLSYMS_ALL),--all-symbols) > $@
-
-.tmp_kallsyms1.o .tmp_kallsyms2.o .tmp_kallsyms3.o: %.o: %.S scripts FORCE
-	$(call if_changed_dep,as_o_S)
+vmlinux-deps := $(KBUILD_LDS) $(KBUILD_VMLINUX_INIT) $(KBUILD_VMLINUX_MAIN)
 
-.tmp_kallsyms%.S: .tmp_vmlinux% $(KALLSYMS)
-	$(call cmd,kallsyms)
+# Final link of vmlinux
+      cmd_link-vmlinux = $(CONFIG_SHELL) $< $(LD) $(LDFLAGS) $(LDFLAGS_vmlinux)
+quiet_cmd_link-vmlinux = LINK    $@
 
-# .tmp_vmlinux1 must be complete except kallsyms, so update vmlinux version
-.tmp_vmlinux1: $(vmlinux-lds) $(vmlinux-all) FORCE
-	$(call if_changed_rule,ksym_ld)
-
-.tmp_vmlinux2: $(vmlinux-lds) $(vmlinux-all) .tmp_kallsyms1.o FORCE
-	$(call if_changed,vmlinux__)
-
-.tmp_vmlinux3: $(vmlinux-lds) $(vmlinux-all) .tmp_kallsyms2.o FORCE
-	$(call if_changed,vmlinux__)
-
-# Needs to visit scripts/ before $(KALLSYMS) can be used.
-$(KALLSYMS): scripts ;
-
-# Generate some data for debugging strange kallsyms problems
-debug_kallsyms: .tmp_map$(last_kallsyms)
-
-.tmp_map%: .tmp_vmlinux% FORCE
-	($(OBJDUMP) -h $< | $(AWK) '/^ +[0-9]/{print $$4 " 0 " $$2}'; $(NM) $<) | sort > $@
-
-.tmp_map3: .tmp_map2
-
-.tmp_map2: .tmp_map1
-
-endif # ifdef CONFIG_KALLSYMS
-
-# Do modpost on a prelinked vmlinux. The finally linked vmlinux has
-# relevant sections renamed as per the linker script.
-quiet_cmd_vmlinux-modpost = LD      $@
-      cmd_vmlinux-modpost = $(LD) $(LDFLAGS) -r -o $@                          \
-	 $(vmlinux-init) --start-group $(vmlinux-main) --end-group             \
-	 $(filter-out $(vmlinux-init) $(vmlinux-main) FORCE ,$^)
-define rule_vmlinux-modpost
-	:
-	+$(call cmd,vmlinux-modpost)
-	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost $@
-	$(Q)echo 'cmd_$@ := $(cmd_vmlinux-modpost)' > $(dot-target).cmd
-endef
-
-# vmlinux image - including updated kernel symbols
-vmlinux: $(vmlinux-lds) $(vmlinux-init) $(vmlinux-main) vmlinux.o $(kallsyms.o) FORCE
+# Include targets which we want to
+# execute if the rest of the kernel build went well.
+vmlinux: scripts/link-vmlinux.sh $(vmlinux-deps) FORCE
 ifdef CONFIG_HEADERS_CHECK
 	$(Q)$(MAKE) -f $(srctree)/Makefile headers_check
 endif
@@ -917,22 +746,11 @@ endif
 ifdef CONFIG_BUILD_DOCSRC
 	$(Q)$(MAKE) $(build)=Documentation
 endif
-	$(call vmlinux-modpost)
-	$(call if_changed_rule,vmlinux__)
-	$(Q)rm -f .old_version
-
-# build vmlinux.o first to catch section mismatch errors early
-ifdef CONFIG_KALLSYMS
-.tmp_vmlinux1: vmlinux.o
-endif
-
-modpost-init := $(filter-out init/built-in.o, $(vmlinux-init))
-vmlinux.o: $(modpost-init) $(vmlinux-main) FORCE
-	$(call if_changed_rule,vmlinux-modpost)
+	+$(call if_changed,link-vmlinux)
 
 # The actual objects are generated when descending, 
 # make sure no implicit rule kicks in
-$(sort $(vmlinux-init) $(vmlinux-main)) $(vmlinux-lds): $(vmlinux-dirs) ;
+$(sort $(vmlinux-deps)): $(vmlinux-dirs) ;
 
 # Handle descending into subdirectories listed in $(vmlinux-dirs)
 # Preset locale variables to speed up the build process. Limit locale
@@ -1156,8 +974,6 @@ endif # CONFIG_MODULES
 
 # Directories & files removed with 'make clean'
 CLEAN_DIRS  += $(MODVERDIR)
-CLEAN_FILES +=	vmlinux System.map \
-                .tmp_kallsyms* .tmp_version .tmp_vmlinux* .tmp_System.map
 
 # Directories & files removed with 'make mrproper'
 MRPROPER_DIRS  += include/config usr/include include/generated          \
@@ -1403,6 +1219,7 @@ scripts: ;
 endif # KBUILD_EXTMOD
 
 clean: $(clean-dirs)
+	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/link-vmlinux.sh clean
 	$(call cmd,rmdirs)
 	$(call cmd,rmfiles)
 	@find $(if $(KBUILD_EXTMOD), $(KBUILD_EXTMOD), .) $(RCS_FIND_IGNORE) \
@@ -1536,14 +1353,6 @@ quiet_cmd_depmod = DEPMOD  $(KERNELRELEASE)
 cmd_crmodverdir = $(Q)mkdir -p $(MODVERDIR) \
                   $(if $(KBUILD_MODULES),; rm -f $(MODVERDIR)/*)
 
-a_flags = -Wp,-MD,$(depfile) $(KBUILD_AFLAGS) $(AFLAGS_KERNEL) \
-	  $(KBUILD_AFLAGS_KERNEL)                              \
-	  $(NOSTDINC_FLAGS) $(LINUXINCLUDE) $(KBUILD_CPPFLAGS) \
-	  $(modkern_aflags) $(EXTRA_AFLAGS) $(AFLAGS_$(basetarget).o)
-
-quiet_cmd_as_o_S = AS      $@
-cmd_as_o_S       = $(CC) $(a_flags) -c -o $@ $<
-
 # read all saved command lines
 
 targets := $(wildcard $(sort $(targets)))

arch/um/Makefile

@@ -121,15 +121,8 @@ LINK_WRAPS = -Wl,--wrap,malloc -Wl,--wrap,free -Wl,--wrap,calloc
 
 LD_FLAGS_CMDLINE = $(foreach opt,$(LDFLAGS),-Wl,$(opt))
 
-CFLAGS_vmlinux := $(LINK-y) $(LINK_WRAPS) $(LD_FLAGS_CMDLINE)
-define cmd_vmlinux__
-	$(CC) $(CFLAGS_vmlinux) -o $@ \
-	-Wl,-T,$(vmlinux-lds) $(vmlinux-init) \
-	-Wl,--start-group $(vmlinux-main) -Wl,--end-group \
-	-lutil \
-	$(filter-out $(vmlinux-lds) $(vmlinux-init) $(vmlinux-main) vmlinux.o \
-	FORCE ,$^) ; rm -f linux
-endef
+# Used by link-vmlinux.sh which has special support for um link
+export CFLAGS_vmlinux := $(LINK-y) $(LINK_WRAPS) $(LD_FLAGS_CMDLINE)
 
 # When cleaning we don't include .config, so we don't include
 # TT or skas makefiles and don't clean skas_ptregs.h.

scripts/link-vmlinux.sh

+#!/bin/sh
+#
+# link vmlinux
+#
+# vmlinux is linked from the objects selected by $(KBUILD_VMLINUX_INIT) and
+# $(KBUILD_VMLINUX_MAIN). Most are built-in.o files from top-level directories
+# in the kernel tree, others are specified in arch/$(ARCH)/Makefile.
+# Ordering when linking is important, and $(KBUILD_VMLINUX_INIT) must be first.
+#
+# vmlinux
+#   ^
+#   |
+#   +-< $(KBUILD_VMLINUX_INIT)
+#   |   +--< init/version.o + more
+#   |
+#   +--< $(KBUILD_VMLINUX_MAIN)
+#   |    +--< drivers/built-in.o mm/built-in.o + more
+#   |
+#   +-< ${kallsymso} (see description in KALLSYMS section)
+#
+# vmlinux version (uname -v) cannot be updated during normal
+# descending-into-subdirs phase since we do not yet know if we need to
+# update vmlinux.
+# Therefore this step is delayed until just before final link of vmlinux.
+#
+# System.map is generated to document addresses of all kernel symbols
+
+# Error out on error
+set -e
+
+# Nice output in kbuild format
+# Will be supressed by "make -s"
+info()
+{
+	if [ "${quiet}" != "silent_" ]; then
+		printf "  %-7s %s\n" ${1} ${2}
+	fi
+}
+
+# Link of vmlinux.o used for section mismatch analysis
+# ${1} output file
+modpost_link()
+{
+	${LD} ${LDFLAGS} -r -o ${1} ${KBUILD_VMLINUX_INIT}                   \
+		--start-group ${KBUILD_VMLINUX_MAIN} --end-group
+}
+
+# Link of vmlinux
+# ${1} - optional extra .o files
+# ${2} - output file
+vmlinux_link()
+{
+	local lds="${objtree}/${KBUILD_LDS}"
+
+	if [ "${SRCARCH}" != "um" ]; then
+		${LD} ${LDFLAGS} ${LDFLAGS_vmlinux} -o ${2}                  \
+			-T ${lds} ${KBUILD_VMLINUX_INIT}                     \
+			--start-group ${KBUILD_VMLINUX_MAIN} --end-group ${1}
+	else
+		${CC} ${CFLAGS_vmlinux} -o ${2}                              \
+			-Wl,-T,${lds} ${KBUILD_VMLINUX_INIT}                 \
+			-Wl,--start-group                                    \
+				 ${KBUILD_VMLINUX_MAIN}                      \
+			-Wl,--end-group                                      \
+			-lutil ${1}
+		rm -f linux
+	fi
+}
+
+
+# Create ${2} .o file with all symbols from the ${1} object file
+kallsyms()
+{
+	info KSYM ${2}
+	local kallsymopt;
+
+	if [ -n "${CONFIG_KALLSYMS_ALL}" ]; then
+		kallsymopt=--all-symbols
+	fi
+
+	local aflags="${KBUILD_AFLAGS} ${NOSTDINC_FLAGS}                     \
+		      ${LINUXINCLUDE} ${KBUILD_CPPFLAGS}"
+
+	${NM} -n ${1} | \
+		scripts/kallsyms ${kallsymopt} | \
+		${CC} ${aflags} -c -o ${2} -x assembler-with-cpp -
+}
+
+# Create map file with all symbols from ${1}
+# See mksymap for additional details
+mksysmap()
+{
+	${CONFIG_SHELL} "${srctree}/scripts/mksysmap" ${1} ${2}
+}
+
+# Delete output files in case of error
+trap cleanup SIGHUP SIGINT SIGQUIT SIGTERM ERR
+cleanup()
+{
+	rm -f .old_version
+	rm -f .tmp_System.map
+	rm -f .tmp_kallsyms*
+	rm -f .tmp_version
+	rm -f .tmp_vmlinux*
+	rm -f System.map
+	rm -f vmlinux
+	rm -f vmlinux.o
+}
+
+#
+#
+# Use "make V=1" to debug this script
+case "${KBUILD_VERBOSE}" in
+*1*)
+	set -x
+	;;
+esac
+
+if [ "$1" = "clean" ]; then
+	cleanup
+	exit 0
+fi
+
+# We need access to CONFIG_ symbols
+. ./.config
+
+#link vmlinux.o
+info LD vmlinux.o
+modpost_link vmlinux.o
+
+# modpost vmlinux.o to check for section mismatches
+${MAKE} -f "${srctree}/scripts/Makefile.modpost" vmlinux.o
+
+# Update version
+info GEN .version
+if [ ! -r .version ]; then
+	rm -f .version;
+	echo 1 >.version;
+else
+	mv .version .old_version;
+	expr 0$(cat .old_version) + 1 >.version;
+fi;
+
+# final build of init/
+${MAKE} -f "${srctree}/scripts/Makefile.build" obj=init
+
+kallsymso=""
+kallsyms_vmlinux=""
+if [ -n "${CONFIG_KALLSYMS}" ]; then
+
+	# kallsyms support
+	# Generate section listing all symbols and add it into vmlinux
+	# It's a three step process:
+	# 1)  Link .tmp_vmlinux1 so it has all symbols and sections,
+	#     but __kallsyms is empty.
+	#     Running kallsyms on that gives us .tmp_kallsyms1.o with
+	#     the right size
+	# 2)  Link .tmp_vmlinux2 so it now has a __kallsyms section of
+	#     the right size, but due to the added section, some
+	#     addresses have shifted.
+	#     From here, we generate a correct .tmp_kallsyms2.o
+	# 2a) We may use an extra pass as this has been necessary to
+	#     woraround some alignment related bugs.
+	#     KALLSYMS_EXTRA_PASS=1 is used to trigger this.
+	# 3)  The correct ${kallsymso} is linked into the final vmlinux.
+	#
+	# a)  Verify that the System.map from vmlinux matches the map from
+	#     ${kallsymso}.
+
+	kallsymso=.tmp_kallsyms2.o
+	kallsyms_vmlinux=.tmp_vmlinux2
+
+	# step 1
+	vmlinux_link "" .tmp_vmlinux1
+	kallsyms .tmp_vmlinux1 .tmp_kallsyms1.o
+
+	# step 2
+	vmlinux_link .tmp_kallsyms1.o .tmp_vmlinux2
+	kallsyms .tmp_vmlinux2 .tmp_kallsyms2.o
+
+	# step 2a
+	if [ -n "${KALLSYMS_EXTRA_PASS}" ]; then
+		kallsymso=.tmp_kallsyms3.o
+		kallsyms_vmlinux=.tmp_vmlinux3
+
+		vmlinux_link .tmp_kallsyms2.o .tmp_vmlinux3
+
+		kallsyms .tmp_vmlinux3 .tmp_kallsyms3.o
+	fi
+fi
+
+info LD vmlinux
+vmlinux_link "${kallsymso}" vmlinux
+
+info SYSMAP System.map
+mksysmap vmlinux System.map
+
+# step a (see comment above)
+if [ -n "${CONFIG_KALLSYMS}" ]; then
+	mksysmap ${kallsyms_vmlinux} .tmp_System.map
+
+	if ! cmp -s System.map .tmp_System.map; then
+		echo Inconsistent kallsyms data
+		echo echo Try "make KALLSYMS_EXTRA_PASS=1" as a workaround
+		cleanup
+		exit 1
+	fi
+fi
+
+# We made a new kernel - delete old version file
+rm -f .old_version