If CONFIG_TRIM_UNUSED_KSYMS is enabled and the kernel is built from a pristine state, the vmlinux is linked twice.
 A user runs 'make'  First build with empty autoksyms.h  adjust_autoksyms.sh updates autoksyms.h and recurses 'make vmlinux' --------(begin sub-make)--------  Second build with new autoksyms.h  link-vmlinux.sh is invoked because vmlinux is missing ---------(end sub-make)---------  link-vmlinux.sh is invoked again despite vmlinux is up-to-date. The reason of  is probably because Make already decided to update vmlinux at the time of  because vmlinux was missing when Make built up the dependency graph. Because if_changed is implemented based on $?, this issue can be narrowed down to how Make handles $?. You can test it with the following simple code: [Test Makefile] A: B @echo newer prerequisite: $? cp B A B: C cp C B touch A [Result] $ rm -f A B $ touch C $ make cp C B touch A newer prerequisite: B cp B A Here, 'A' has been touched in the recipe of 'B'. So, the dependency 'A: B' has already been met before the recipe of 'A' is executed. However, Make does not notice the fact that the recipe of 'B' also updates 'A' as a side-effect. The situation is similar in this case; the vmlinux has actually been updated in the vmlinux_prereq target. Make cannot predict this, so judges the vmlinux is old. link-vmlinux.sh is costly, so it is better to not run it when unneeded. Split CONFIG_TRIM_UNUSED_KSYMS recursion 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"). Signed-off-by: Masahiro Yamada <yamada.masah...@socionext.com> Acked-by: Nicolas Pitre <n...@linaro.org> --- Changes in v4: - typo fix link-vmlinus.sh -> link-vmlinux.sh Changes in v3: - autoksyms_recursive should be surrounded by ifdef CONFIG_TRIM_UNUSED_KSYMS Changes in v2: - Discard my wrong change to adjust_autoksyms.sh - Add more commit log to explain how Make is working Makefile | 22 ++++++++++------------ 1 file changed, 10 insertions(+), 12 deletions(-) diff --git a/Makefile b/Makefile index 5fee703..ff62b8e 100644 --- a/Makefile +++ b/Makefile @@ -998,17 +998,9 @@ 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 +# Recurse until adjust_autoksyms.sh is satisfied +PHONY += autoksyms_recursive +autoksyms_recursive: $(vmlinux-deps) ifdef CONFIG_TRIM_UNUSED_KSYMS $(Q)$(CONFIG_SHELL) $(srctree)/scripts/adjust_autoksyms.sh \ "$(MAKE) -f $(srctree)/Makefile vmlinux" @@ -1034,7 +1026,13 @@ 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 -- 2.7.4