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Subject[PATCH 7/7] kbuild: link vmlinux just once for CONFIG_TRIM_UNUSED_KSYMS
Date
If CONFIG_TRIM_UNUSED_KSYMS is enabled and the kernel is built from
a pristine state, the vmlinux is linked twice.

[1] A user runs "make"

[2] First build with empty autoksyms.h

[3] adjust_autoksyms.sh updates autoksyms.h and recurses "make vmlinux"

--------(begin sub-make)--------
[4] Second build with new autoksyms.h

[5] link-vmlinux.sh is invoked because "vmlinux" is missing
---------(end sub-make)---------

[6] link-vmlinux.sh is invoked again despite "vmlinux" is up-to-date.

The reason of [6] is probably because Make already decided to update
"vmlinux" at the time of [2] because "vmlinux" was missing when Make
generated the dependency list.

link-vmlinus.sh is costly, so it is better to not run it when unneeded.
Split CONFIG_TRIM_UNUSED_KSYMS handling to a dedicated target.

The reason of commit 2441e78b1919 ("kbuild: better abstract vmlinux
sequential prerequisites") was to cater to CONFIG_BUILD_DOCSRC, but
it was later removed by commit 184892925118 ("samples: move blackfin
gptimers-example from Documentation").

I also changed adjust_autoksyms.sh to simply exit with 1 or 0 to make
it look straightforward.

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

Makefile | 28 ++++++++++++----------------
scripts/adjust_autoksyms.sh | 3 +--
2 files changed, 13 insertions(+), 18 deletions(-)

diff --git a/Makefile b/Makefile
index 1dab647..0a7bab6 100644
--- a/Makefile
+++ b/Makefile
@@ -987,21 +987,11 @@ export KBUILD_ALLDIRS := $(sort $(filter-out arch/%,$(vmlinux-alldirs)) arch Doc

vmlinux-deps := $(KBUILD_LDS) $(KBUILD_VMLINUX_INIT) $(KBUILD_VMLINUX_MAIN) $(KBUILD_VMLINUX_LIBS)

-# Include targets which we want to execute sequentially if the rest of the
-# kernel build went well. If CONFIG_TRIM_UNUSED_KSYMS is set, this might be
-# evaluated more than once.
-PHONY += vmlinux_prereq
-vmlinux_prereq: $(vmlinux-deps) FORCE
-ifdef CONFIG_HEADERS_CHECK
- $(Q)$(MAKE) -f $(srctree)/Makefile headers_check
-endif
-ifdef CONFIG_GDB_SCRIPTS
- $(Q)ln -fsn $(abspath $(srctree)/scripts/gdb/vmlinux-gdb.py)
-endif
-ifdef CONFIG_TRIM_UNUSED_KSYMS
- $(Q)$(CONFIG_SHELL) $(srctree)/scripts/adjust_autoksyms.sh \
- "$(MAKE) -f $(srctree)/Makefile vmlinux"
-endif
+# Recurse until adjust_autoksyms.sh is satisfied
+PHONY += autoksyms_recursive
+autoksyms_recursive: $(vmlinux-deps)
+ $(Q)$(CONFIG_SHELL) $(srctree)/scripts/adjust_autoksyms.sh || \
+ $(MAKE) -f $(srctree)/Makefile autoksyms_recursive

# For the kernel to actually contain only the needed exported symbols,
# we have to build modules as well to determine what those symbols are.
@@ -1023,7 +1013,13 @@ cmd_link-vmlinux = \
$(CONFIG_SHELL) $< $(LD) $(LDFLAGS) $(LDFLAGS_vmlinux) ; \
$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)

-vmlinux: scripts/link-vmlinux.sh vmlinux_prereq $(vmlinux-deps) FORCE
+vmlinux: scripts/link-vmlinux.sh autoksyms_recursive $(vmlinux-deps) FORCE
+ifdef CONFIG_HEADERS_CHECK
+ $(Q)$(MAKE) -f $(srctree)/Makefile headers_check
+endif
+ifdef CONFIG_GDB_SCRIPTS
+ $(Q)ln -fsn $(abspath $(srctree)/scripts/gdb/vmlinux-gdb.py)
+endif
+$(call if_changed,link-vmlinux)

# Build samples along the rest of the kernel
diff --git a/scripts/adjust_autoksyms.sh b/scripts/adjust_autoksyms.sh
index 7bb3618..1377cf8 100755
--- a/scripts/adjust_autoksyms.sh
+++ b/scripts/adjust_autoksyms.sh
@@ -95,8 +95,7 @@ if [ $changed -gt 0 ]; then
info "KSYMS" "symbols: before=$old, after=$new, changed=$changed"
info "UPD" "$cur_ksyms_file"
mv -f "$new_ksyms_file" "$cur_ksyms_file"
- # Then trigger a rebuild of affected source files
- exec $@
+ exit 1
else
rm -f "$new_ksyms_file"
fi
--
2.7.4
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