On Mon, Dec 21, 2020 at 11:36 PM Vincenzo Frascino <[email protected]> wrote: > > Hi Masahiro, > > On 12/18/20 2:45 AM, Masahiro Yamada wrote: > > 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...@mail.gmail.com/T/#ma10dcb961fda13f36d42d58fa6cb2da988b7e73a > > > > I could not reproduce the problem you are reporting on arm64. Could you please > provide some steps?
As far as I see in arm64 Makefiles, you cannot reproduce it. So, this is a _potential_ problem. When somebody adds subdir-ccflags-y to arch/arm64/Kbuild or arch/arm64/kernel/Makefile, the real issue will suddenly come up. arm64 is the first arch that implemented vdso-offsets.h arch maintainers tend to copy Makefiles from existing ones. Now PPC is the second with almost the same Makefile implementation. This time, powerpc hit the problem because arch/powerpc/Kbuild has subdir-ccflags-y. I do not want to be bothered every time arch maintainers hit this issue. So, I want to fix arm64 first, then powerpc will eventually copy the correct Makefiles. > In my case the vDSO library is not rebuilt as a result of the procedure > reported > in the email you linked at [1]. > > > Signed-off-by: Masahiro Yamada <[email protected]> > > --- > > > > arch/arm64/Makefile | 10 ++++++---- > > arch/arm64/kernel/Makefile | 5 +++-- > > arch/arm64/kernel/{vdso/vdso.S => vdso-wrap.S} | 0 > > arch/arm64/kernel/vdso/Makefile | 1 - > > arch/arm64/kernel/{vdso32/vdso.S => vdso32-wrap.S} | 0 > > arch/arm64/kernel/vdso32/Makefile | 1 - > > 6 files changed, 9 insertions(+), 8 deletions(-) > > rename arch/arm64/kernel/{vdso/vdso.S => vdso-wrap.S} (100%) > > rename arch/arm64/kernel/{vdso32/vdso.S => vdso32-wrap.S} (100%) > > > > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile > > index 6a87d592bd00..f18d20a68170 100644 > > --- a/arch/arm64/Makefile > > +++ b/arch/arm64/Makefile > > @@ -179,10 +179,12 @@ 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) $(build)=arch/arm64/kernel/vdso32 \ > > + include/generated/vdso32-offsets.h arch/arm64/kernel/vdso32/vdso.so > > +endif > > endif > > The reason why it is currently done in two phases (a bit hacky as per comment) > is because vdso-offsets.h is required to be generated before compiling > kernel/. > Please refer to the comment in arch/arm64/Makefile. Yes, I know. > > Could you explain how your change satisfies the dependency? vdso_prepare completes before Kbuild starts ordinary descending. So *.so files and vdso-offsets.h exist when Kbuild builds arch/arm64/kernel/. > > > > define archhelp > > diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile > > index 86364ab6f13f..42f6ad2c7eac 100644 > > --- a/arch/arm64/kernel/Makefile > > +++ b/arch/arm64/kernel/Makefile > > @@ -59,9 +59,10 @@ obj-$(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 += $(head-y) vmlinux.lds > > > > diff --git a/arch/arm64/kernel/vdso/vdso.S b/arch/arm64/kernel/vdso-wrap.S > > similarity index 100% > > rename from arch/arm64/kernel/vdso/vdso.S > > rename to arch/arm64/kernel/vdso-wrap.S > > diff --git a/arch/arm64/kernel/vdso/Makefile > > b/arch/arm64/kernel/vdso/Makefile > > index a8f8e409e2bf..85222f64f394 100644 > > --- a/arch/arm64/kernel/vdso/Makefile > > +++ b/arch/arm64/kernel/vdso/Makefile > > @@ -45,7 +45,6 @@ endif > > # Disable gcov profiling for VDSO code > > GCOV_PROFILE := n > > > > -obj-y += vdso.o > > targets += vdso.lds > > CPPFLAGS_vdso.lds += -P -C -U$(ARCH) > > > > diff --git a/arch/arm64/kernel/vdso32/vdso.S > > b/arch/arm64/kernel/vdso32-wrap.S > > similarity index 100% > > rename from arch/arm64/kernel/vdso32/vdso.S > > rename to arch/arm64/kernel/vdso32-wrap.S > > diff --git a/arch/arm64/kernel/vdso32/Makefile > > b/arch/arm64/kernel/vdso32/Makefile > > index a1e0f91e6cea..789ad420f16b 100644 > > --- a/arch/arm64/kernel/vdso32/Makefile > > +++ b/arch/arm64/kernel/vdso32/Makefile > > @@ -155,7 +155,6 @@ c-obj-vdso-gettimeofday := $(addprefix $(obj)/, > > $(c-obj-vdso-gettimeofday)) > > asm-obj-vdso := $(addprefix $(obj)/, $(asm-obj-vdso)) > > obj-vdso := $(c-obj-vdso) $(c-obj-vdso-gettimeofday) $(asm-obj-vdso) > > > > -obj-y += vdso.o > > targets += vdso.lds > > CPPFLAGS_vdso.lds += -P -C -U$(ARCH) > > > > > > -- > Regards, > Vincenzo -- Best Regards Masahiro Yamada
