| Message ID | 1521170449-31194-1-git-send-email-yamada.masahiro@socionext.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | None | expand |
On Fri, 16 Mar 2018, Masahiro Yamada wrote: > 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 > 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; 'vmlinux' has actually been > updated in the 'vmlinux_prereq' target. Make cannot predict this, so > judges 'vmlinux' is old. > > link-vmlinus.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.masahiro@socionext.com> Acked-by: Nicolas Pitre <nico@linaro.org> > --- > > 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 > >
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
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 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; 'vmlinux' has actually been updated in the 'vmlinux_prereq' target. Make cannot predict this, so judges 'vmlinux' is old. link-vmlinus.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.masahiro@socionext.com> --- 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(-) -- 2.7.4