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SubjectRe: [PATCH 1/2] powerpc/vdso: fix unnecessary rebuilds of vgettimeofday.o
On Thu, Dec 24, 2020 at 2:12 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> vgettimeofday.o is unnecessarily rebuilt. Adding it to 'targets' is not
> enough to fix the issue. Kbuild is correctly rebuilding it because the
> command line is changed.
>
> PowerPC builds each vdso directory twice; first in vdso_prepare to
> generate vdso{32,64}-offsets.h, second as part of the ordinary build
> process to embed vdso{32,64}.so.dbg into the kernel.
>
> The problem shows up when CONFIG_PPC_WERROR=y due to the following line
> in arch/powerpc/Kbuild:
>
> subdir-ccflags-$(CONFIG_PPC_WERROR) := -Werror
>
> In the preparation stage, Kbuild directly visits the vdso directories,
> hence it does not inherit subdir-ccflags-y. In the second descend,
> Kbuild adds -Werror, which results in the command line flipping
> with/without -Werror.
>
> It implies a potential danger; if a more critical flag that would impact
> the resulted vdso, the offsets recorded in the headers might be different
> from real offsets in the embedded vdso images.
>
> Removing the unneeded second descend solves the problem.
>
> Link: https://lore.kernel.org/linuxppc-dev/87tuslxhry.fsf@mpe.ellerman.id.au/
> Reported-by: Michael Ellerman <mpe@ellerman.id.au>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---


Michael, please take a look at this.

The unneeded rebuild problem is still remaining.



>
> arch/powerpc/kernel/Makefile | 4 ++--
> arch/powerpc/kernel/vdso32/Makefile | 5 +----
> arch/powerpc/kernel/{vdso32 => }/vdso32_wrapper.S | 0
> arch/powerpc/kernel/vdso64/Makefile | 6 +-----
> arch/powerpc/kernel/{vdso64 => }/vdso64_wrapper.S | 0
> 5 files changed, 4 insertions(+), 11 deletions(-)
> rename arch/powerpc/kernel/{vdso32 => }/vdso32_wrapper.S (100%)
> rename arch/powerpc/kernel/{vdso64 => }/vdso64_wrapper.S (100%)
>
> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> index fe2ef598e2ea..79ee7750937d 100644
> --- a/arch/powerpc/kernel/Makefile
> +++ b/arch/powerpc/kernel/Makefile
> @@ -51,7 +51,7 @@ obj-y += ptrace/
> obj-$(CONFIG_PPC64) += setup_64.o \
> paca.o nvram_64.o note.o syscall_64.o
> obj-$(CONFIG_COMPAT) += sys_ppc32.o signal_32.o
> -obj-$(CONFIG_VDSO32) += vdso32/
> +obj-$(CONFIG_VDSO32) += vdso32_wrapper.o
> obj-$(CONFIG_PPC_WATCHDOG) += watchdog.o
> obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o
> obj-$(CONFIG_PPC_DAWR) += dawr.o
> @@ -60,7 +60,7 @@ obj-$(CONFIG_PPC_BOOK3S_64) += cpu_setup_power.o
> obj-$(CONFIG_PPC_BOOK3S_64) += mce.o mce_power.o
> obj-$(CONFIG_PPC_BOOK3E_64) += exceptions-64e.o idle_book3e.o
> obj-$(CONFIG_PPC_BARRIER_NOSPEC) += security.o
> -obj-$(CONFIG_PPC64) += vdso64/
> +obj-$(CONFIG_PPC64) += vdso64_wrapper.o
> obj-$(CONFIG_ALTIVEC) += vecemu.o
> obj-$(CONFIG_PPC_BOOK3S_IDLE) += idle_book3s.o
> procfs-y := proc_powerpc.o
> diff --git a/arch/powerpc/kernel/vdso32/Makefile b/arch/powerpc/kernel/vdso32/Makefile
> index 59aa2944ecae..42fc3de89b39 100644
> --- a/arch/powerpc/kernel/vdso32/Makefile
> +++ b/arch/powerpc/kernel/vdso32/Makefile
> @@ -30,7 +30,7 @@ CC32FLAGS += -m32
> KBUILD_CFLAGS := $(filter-out -mcmodel=medium,$(KBUILD_CFLAGS))
> endif
>
> -targets := $(obj-vdso32) vdso32.so.dbg
> +targets := $(obj-vdso32) vdso32.so.dbg vgettimeofday.o
> obj-vdso32 := $(addprefix $(obj)/, $(obj-vdso32))
>
> GCOV_PROFILE := n
> @@ -46,9 +46,6 @@ obj-y += vdso32_wrapper.o
> targets += vdso32.lds
> CPPFLAGS_vdso32.lds += -P -C -Upowerpc
>
> -# Force dependency (incbin is bad)
> -$(obj)/vdso32_wrapper.o : $(obj)/vdso32.so.dbg
> -
> # link rule for the .so file, .lds has to be first
> $(obj)/vdso32.so.dbg: $(src)/vdso32.lds $(obj-vdso32) $(obj)/vgettimeofday.o FORCE
> $(call if_changed,vdso32ld_and_check)
> diff --git a/arch/powerpc/kernel/vdso32/vdso32_wrapper.S b/arch/powerpc/kernel/vdso32_wrapper.S
> similarity index 100%
> rename from arch/powerpc/kernel/vdso32/vdso32_wrapper.S
> rename to arch/powerpc/kernel/vdso32_wrapper.S
> diff --git a/arch/powerpc/kernel/vdso64/Makefile b/arch/powerpc/kernel/vdso64/Makefile
> index d365810a689a..b50b39fedf74 100644
> --- a/arch/powerpc/kernel/vdso64/Makefile
> +++ b/arch/powerpc/kernel/vdso64/Makefile
> @@ -17,7 +17,7 @@ endif
>
> # Build rules
>
> -targets := $(obj-vdso64) vdso64.so.dbg
> +targets := $(obj-vdso64) vdso64.so.dbg vgettimeofday.o
> obj-vdso64 := $(addprefix $(obj)/, $(obj-vdso64))
>
> GCOV_PROFILE := n
> @@ -29,15 +29,11 @@ ccflags-y := -shared -fno-common -fno-builtin -nostdlib \
> -Wl,-soname=linux-vdso64.so.1 -Wl,--hash-style=both
> asflags-y := -D__VDSO64__ -s
>
> -obj-y += vdso64_wrapper.o
> targets += vdso64.lds
> CPPFLAGS_vdso64.lds += -P -C -U$(ARCH)
>
> $(obj)/vgettimeofday.o: %.o: %.c FORCE
>
> -# Force dependency (incbin is bad)
> -$(obj)/vdso64_wrapper.o : $(obj)/vdso64.so.dbg
> -
> # link rule for the .so file, .lds has to be first
> $(obj)/vdso64.so.dbg: $(src)/vdso64.lds $(obj-vdso64) $(obj)/vgettimeofday.o FORCE
> $(call if_changed,vdso64ld_and_check)
> diff --git a/arch/powerpc/kernel/vdso64/vdso64_wrapper.S b/arch/powerpc/kernel/vdso64_wrapper.S
> similarity index 100%
> rename from arch/powerpc/kernel/vdso64/vdso64_wrapper.S
> rename to arch/powerpc/kernel/vdso64_wrapper.S
> --
> 2.27.0
>


--
Best Regards
Masahiro Yamada

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