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?
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 <masahi...@kernel.org>
> ---
>
> 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) $(build)=arch/arm64/kernel/vdso32 \
> + include/generated/vdso32-offsets.h arch/arm64/kernel/vdso32/vdso.so
> +endif
> endif
The reason why it is currently done in two phases (a bit hacky as per comment)
is because vdso-offsets.h is required to be generated before compiling kernel/.
Please refer to the comment in arch/arm64/Makefile.
Could you explain how your change satisfies the dependency?
>
> define archhelp
> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> index 86364ab6f13f..42f6ad2c7eac 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -59,9 +59,10 @@ obj-$(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
