Commit a5b8ca97 authored by Masahiro Yamada's avatar Masahiro Yamada Committed by Will Deacon
Browse files

arm64: do not descend to vdso directories twice 

arm64 descends into each vdso directory twice; first in vdso_prepare,
second during the ordinary build process.

PPC mimicked it and uncovered a problem [1]. In the first descend,
Kbuild directly visits the vdso directories, therefore it does not
inherit subdir-ccflags-y from upper directories.

This means the command line parameters may differ between the two.
If it happens, the offset values in the generated headers might be
different from real offsets of vdso.so in the kernel.

This potential danger should be avoided. The vdso directories are
built in the vdso_prepare stage, so the second descend is unneeded.

[1]: https://lore.kernel.org/linux-kbuild/CAK7LNARAkJ3_-4gX0VA2UkapbOftuzfSTVMBbgbw=HD8n7N+7w@mail.gmail.com/T/#ma10dcb961fda13f36d42d58fa6cb2da988b7e73a



Signed-off-by: default avatarMasahiro Yamada <masahiroy@kernel.org>
Link: https://lore.kernel.org/r/20201218024540.1102650-1-masahiroy@kernel.org


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent 19c329f6

arch/arm64/Makefile

+6 −4
Original line number Diff line number Diff line
@@ -188,10 +188,12 @@ ifeq ($(KBUILD_EXTMOD),) 
# this hack.

prepare: vdso_prepare

vdso_prepare: prepare0

	$(Q)$(MAKE) $(build)=arch/arm64/kernel/vdso include/generated/vdso-offsets.h

	$(if $(CONFIG_COMPAT_VDSO),$(Q)$(MAKE) \

		$(build)=arch/arm64/kernel/vdso32  \

		include/generated/vdso32-offsets.h)

	$(Q)$(MAKE) $(build)=arch/arm64/kernel/vdso \

	include/generated/vdso-offsets.h arch/arm64/kernel/vdso/vdso.so

ifdef CONFIG_COMPAT_VDSO

	$(Q)$(MAKE) $(build)=arch/arm64/kernel/vdso32 \

	include/generated/vdso32-offsets.h arch/arm64/kernel/vdso32/vdso.so

endif

endif



define archhelp

arch/arm64/kernel/Makefile

+3 −2
Original line number Diff line number Diff line
@@ -59,9 +59,10 @@ obj-$(CONFIG_CRASH_CORE) += crash_core.o 
obj-$(CONFIG_ARM_SDE_INTERFACE)		+= sdei.o

obj-$(CONFIG_ARM64_PTR_AUTH)		+= pointer_auth.o

obj-$(CONFIG_ARM64_MTE)			+= mte.o

obj-y					+= vdso-wrap.o

obj-$(CONFIG_COMPAT_VDSO)		+= vdso32-wrap.o



obj-y					+= vdso/ probes/

obj-$(CONFIG_COMPAT_VDSO)		+= vdso32/

obj-y					+= probes/

head-y					:= head.o

extra-y					+= $(head-y) vmlinux.lds

arch/arm64/kernel/vdso/Makefile

+0 −1
Original line number Diff line number Diff line
@@ -44,7 +44,6 @@ endif 
# Disable gcov profiling for VDSO code

GCOV_PROFILE := n



obj-y += vdso.o

targets += vdso.lds

CPPFLAGS_vdso.lds += -P -C -U$(ARCH)