arm64/kernel/{vdso,signal}.c include vdso-offsets.h, as well as any
file that includes asm/vdso.h. Therefore, vdso-offsets.h must be
generated before these files are compiled.
The current rules in arm64/kernel/Makefile do not actually enforce
this, because even though $(obj)/vdso is listed as a prerequisite for
vdso-offsets.h, this does not result in the intended effect of
building the vdso subdirectory (before all the other objects). As a
consequence, depending on the order in which the rules are followed,
vdso-offsets.h is updated or not before arm64/kernel/{vdso,signal}.o
are built. The current rules also impose an unnecessary dependency on
vdso-offsets.h for all arm64/kernel/*.o, resulting in unnecessary
rebuilds. This is made obvious when using make -j:
touch arch/arm64/kernel/vdso/gettimeofday.S && make -j$NCPUS arch/arm64/kernel
will sometimes result in none of arm64/kernel/*.o being
rebuilt, sometimes all of them, or even just some of them.
It is quite difficult to ensure that a header is generated before it
is used with recursive Makefiles by using normal rules. Instead,
arch-specific generated headers are normally built in the archprepare
recipe in the arch Makefile (see for instance arch/ia64/Makefile).
Unfortunately, asm-offsets.h is included in gettimeofday.S, and must
therefore be generated before vdso-offsets.h, which is not the case if
archprepare is used. For this reason, a rule run after archprepare has
to be used.
This commit adds rules in arm64/Makefile to build vdso-offsets.h
during the prepare step, ensuring that vdso-offsets.h is generated
before building anything. It also removes the now-unnecessary
dependencies on vdso-offsets.h in arm64/kernel/Makefile. Finally, it
removes the duplication of asm-offsets.h between arm64/kernel/vdso/
and include/generated/ and makes include/generated/vdso-offsets.h a
target in arm64/kernel/vdso/Makefile.
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Michal Marek <mmarek@xxxxxxxx>
Signed-off-by: Kevin Brodsky <kevin.brodsky@xxxxxxx>
---
Resending with linux-kbuild in cc, hopefully some people there will have
an opinion on this.
I am not completely satisfied with the fix, since it uses a hack with
the prepare and prepare0 rules that should not be used in arch
Makefiles. However, all of my other attempts (including explicit
dependencies on gettimeofday.S, etc. in arm64/kernel/Makefile) failed
in some way. Hopefully, a Makefile wizard will come up with a better
solution.
arch/arm64/Makefile | 10 ++++++++++
arch/arm64/kernel/Makefile | 4 ----
arch/arm64/kernel/vdso/Makefile | 7 +++----
3 files changed, 13 insertions(+), 8 deletions(-)
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 354d75402ace..7bb702a0f1e2 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -119,6 +119,16 @@ archclean:
$(Q)$(MAKE) $(clean)=$(boot)
$(Q)$(MAKE) $(clean)=$(boot)/dts
+# We need to generate vdso-offsets.h before compiling certain files in kernel/.
+# In order to do that, we should use the archprepare target, but we can't since
+# asm-offsets.h is included in some files used to generate vdso-offsets.h, and
+# asm-offsets.h is built in prepare0, for which archprepare is a dependency.
+# Therefore we need to generate the header after prepare0 has been made, hence
+# this hack.
+prepare: vdso_prepare
+vdso_prepare: prepare0
+ $(Q)$(MAKE) $(build)=arch/arm64/kernel/vdso include/generated/vdso-offsets.h
+
define archhelp
echo '* Image.gz - Compressed kernel image (arch/$(ARCH)/boot/Image.gz)'
echo ' Image - Uncompressed kernel image (arch/$(ARCH)/boot/Image)'
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 3793003e16a2..bab85990691d 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -50,7 +50,3 @@ obj-y += $(arm64-obj-y) vdso/
obj-m += $(arm64-obj-m)
head-y := head.o
extra-y += $(head-y) vmlinux.lds
-
-# vDSO - this must be built first to generate the symbol offsets
-$(call objectify,$(arm64-obj-y)): $(obj)/vdso/vdso-offsets.h
-$(obj)/vdso/vdso-offsets.h: $(obj)/vdso
diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
index b467fd0a384b..62c84f7cb01b 100644
--- a/arch/arm64/kernel/vdso/Makefile
+++ b/arch/arm64/kernel/vdso/Makefile
@@ -23,7 +23,7 @@ GCOV_PROFILE := n
ccflags-y += -Wl,-shared
obj-y += vdso.o
-extra-y += vdso.lds vdso-offsets.h
+extra-y += vdso.lds
CPPFLAGS_vdso.lds += -P -C -U$(ARCH)
# Force dependency (incbin is bad)
@@ -42,11 +42,10 @@ $(obj)/%.so: $(obj)/%.so.dbg FORCE
gen-vdsosym := $(srctree)/$(src)/gen_vdso_offsets.sh
quiet_cmd_vdsosym = VDSOSYM $@
define cmd_vdsosym
- $(NM) $< | $(gen-vdsosym) | LC_ALL=C sort > $@ && \
- cp $@ include/generated/
+ $(NM) $< | $(gen-vdsosym) | LC_ALL=C sort > $@
endef
-$(obj)/vdso-offsets.h: $(obj)/vdso.so.dbg FORCE
+include/generated/vdso-offsets.h: $(obj)/vdso.so.dbg FORCE
$(call if_changed,vdsosym)
# Assembly rules for the .S files
--
2.8.0
--
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