From: Masahiro Yamada <masahiroy@kernel.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Christophe Leroy <christophe.leroy@csgroup.eu>,
Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>
Subject: Re: powerpc VDSO files being unnecessarily rebuilt
Date: Fri, 18 Dec 2020 01:40:24 +0900 [thread overview]
Message-ID: <CAK7LNARAkJ3_-4gX0VA2UkapbOftuzfSTVMBbgbw=HD8n7N+7w@mail.gmail.com> (raw)
In-Reply-To: <CAK7LNASTXyxhLzH7kRyAKCixe6ksJaKPiuPxWnsYZ6NJVCWDhQ@mail.gmail.com>
On Thu, Dec 17, 2020 at 6:23 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Thu, Dec 17, 2020 at 11:56 AM Michael Ellerman <mpe@ellerman.id.au> wrote:
> >
> > Hi all,
> >
> > Since the merge of the C VDSO I see we are repeatedly rebuilding some
> > files in the VDSO, eg:
> >
> > $ make V=2
> > make[1]: Entering directory '/home/michael/linux/build~'
> > GEN Makefile
> > CALL /home/michael/linux/scripts/checksyscalls.sh - due to target missing
> > CALL /home/michael/linux/scripts/atomic/check-atomics.sh - due to target missing
> > CHK include/generated/compile.h
> > CC arch/powerpc/kernel/vdso64/vgettimeofday.o - due to vgettimeofday.o not in $(targets)
> >
> > This then causes multiple other files to be rebuilt.
> >
> > So the obvious fix is to add it to targets:
> >
> > diff --git a/arch/powerpc/kernel/vdso64/Makefile b/arch/powerpc/kernel/vdso64/Makefile
> > index d365810a689a..5386532866ce 100644
> > --- a/arch/powerpc/kernel/vdso64/Makefile
> > +++ b/arch/powerpc/kernel/vdso64/Makefile
> > @@ -5,6 +5,7 @@ ARCH_REL_TYPE_ABS := R_PPC_JUMP_SLOT|R_PPC_GLOB_DAT|R_PPC_ADDR32|R_PPC_ADDR24|R_
> > include $(srctree)/lib/vdso/Makefile
> >
> > obj-vdso64 = sigtramp.o gettimeofday.o datapage.o cacheflush.o note.o getcpu.o
> > +targets := $(obj-vdso64) vdso64.so.dbg
> >
> > ifneq ($(c-gettimeofday-y),)
> > CFLAGS_vgettimeofday.o += -include $(c-gettimeofday-y)
> > @@ -13,11 +14,11 @@ ifneq ($(c-gettimeofday-y),)
> > CFLAGS_vgettimeofday.o += -DDISABLE_BRANCH_PROFILING
> > CFLAGS_vgettimeofday.o += -ffreestanding -fasynchronous-unwind-tables
> > CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE)
> > + targets += vgettimeofday.o
> > endif
> >
> > # Build rules
> >
> > -targets := $(obj-vdso64) vdso64.so.dbg
> > obj-vdso64 := $(addprefix $(obj)/, $(obj-vdso64))
> >
> > GCOV_PROFILE := n
> >
> >
> > But then I see it still rebuilt:
> >
> > CC arch/powerpc/kernel/vdso64/vgettimeofday.o - due to command line change
> >
> >
> > I'm not changing the command line, and AFAICS the .cmd file is not
> > changing either:
> >
> > $ make V=2
> > ...
> > CC arch/powerpc/kernel/vdso64/vgettimeofday.o - due to command line change
> >
> > $ sha256sum build\~/arch/powerpc/kernel/vdso64/vgettimeofday.o
> > 7f635546bc2768c7b929d3de1724d83285f3cd54394fcd7104f8b1301d689d65 build~/arch/powerpc/kernel/vdso64/vgettimeofday.o
> >
> > $ make V=2
> > ...
> > CC arch/powerpc/kernel/vdso64/vgettimeofday.o - due to command line change
> >
> > $ sha256sum build\~/arch/powerpc/kernel/vdso64/vgettimeofday.o
> > 7f635546bc2768c7b929d3de1724d83285f3cd54394fcd7104f8b1301d689d65 build~/arch/powerpc/kernel/vdso64/vgettimeofday.o
> >
> >
> > So any hints on what I'm missing here?
> >
> > cheers
>
>
> This is because PPC builds the vdso twice
> with different command arguments.
>
>
> First time:
>
> vdso_prepare: prepare0
> $(if $(CONFIG_VDSO32),$(Q)$(MAKE) \
> $(build)=arch/powerpc/kernel/vdso32
> include/generated/vdso32-offsets.h)
> $(if $(CONFIG_PPC64),$(Q)$(MAKE) \
> $(build)=arch/powerpc/kernel/vdso64
> include/generated/vdso64-offsets.h)
>
>
> Second time:
> from arch/powerpc/kernel/Makefile
>
>
>
>
>
> For the first build, -Werror is missing because
> Kbuild directly descends into arch/powerpc/kernel/vdso[32,64]/.
>
>
> For the second build,
>
> arch/powerpc/Kbuild appends the following:
>
> subdir-ccflags-$(CONFIG_PPC_WERROR) := -Werror
>
This is very dangerous because the vdso offsets are wrong.
I think ppc followed arm64 implementation.
Let me figure out how to fix arm64 vdso.
--
Best Regards
Masahiro Yamada
WARNING: multiple messages have this Message-ID (diff)
From: Masahiro Yamada <masahiroy@kernel.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>
Subject: Re: powerpc VDSO files being unnecessarily rebuilt
Date: Fri, 18 Dec 2020 01:40:24 +0900 [thread overview]
Message-ID: <CAK7LNARAkJ3_-4gX0VA2UkapbOftuzfSTVMBbgbw=HD8n7N+7w@mail.gmail.com> (raw)
In-Reply-To: <CAK7LNASTXyxhLzH7kRyAKCixe6ksJaKPiuPxWnsYZ6NJVCWDhQ@mail.gmail.com>
On Thu, Dec 17, 2020 at 6:23 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Thu, Dec 17, 2020 at 11:56 AM Michael Ellerman <mpe@ellerman.id.au> wrote:
> >
> > Hi all,
> >
> > Since the merge of the C VDSO I see we are repeatedly rebuilding some
> > files in the VDSO, eg:
> >
> > $ make V=2
> > make[1]: Entering directory '/home/michael/linux/build~'
> > GEN Makefile
> > CALL /home/michael/linux/scripts/checksyscalls.sh - due to target missing
> > CALL /home/michael/linux/scripts/atomic/check-atomics.sh - due to target missing
> > CHK include/generated/compile.h
> > CC arch/powerpc/kernel/vdso64/vgettimeofday.o - due to vgettimeofday.o not in $(targets)
> >
> > This then causes multiple other files to be rebuilt.
> >
> > So the obvious fix is to add it to targets:
> >
> > diff --git a/arch/powerpc/kernel/vdso64/Makefile b/arch/powerpc/kernel/vdso64/Makefile
> > index d365810a689a..5386532866ce 100644
> > --- a/arch/powerpc/kernel/vdso64/Makefile
> > +++ b/arch/powerpc/kernel/vdso64/Makefile
> > @@ -5,6 +5,7 @@ ARCH_REL_TYPE_ABS := R_PPC_JUMP_SLOT|R_PPC_GLOB_DAT|R_PPC_ADDR32|R_PPC_ADDR24|R_
> > include $(srctree)/lib/vdso/Makefile
> >
> > obj-vdso64 = sigtramp.o gettimeofday.o datapage.o cacheflush.o note.o getcpu.o
> > +targets := $(obj-vdso64) vdso64.so.dbg
> >
> > ifneq ($(c-gettimeofday-y),)
> > CFLAGS_vgettimeofday.o += -include $(c-gettimeofday-y)
> > @@ -13,11 +14,11 @@ ifneq ($(c-gettimeofday-y),)
> > CFLAGS_vgettimeofday.o += -DDISABLE_BRANCH_PROFILING
> > CFLAGS_vgettimeofday.o += -ffreestanding -fasynchronous-unwind-tables
> > CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE)
> > + targets += vgettimeofday.o
> > endif
> >
> > # Build rules
> >
> > -targets := $(obj-vdso64) vdso64.so.dbg
> > obj-vdso64 := $(addprefix $(obj)/, $(obj-vdso64))
> >
> > GCOV_PROFILE := n
> >
> >
> > But then I see it still rebuilt:
> >
> > CC arch/powerpc/kernel/vdso64/vgettimeofday.o - due to command line change
> >
> >
> > I'm not changing the command line, and AFAICS the .cmd file is not
> > changing either:
> >
> > $ make V=2
> > ...
> > CC arch/powerpc/kernel/vdso64/vgettimeofday.o - due to command line change
> >
> > $ sha256sum build\~/arch/powerpc/kernel/vdso64/vgettimeofday.o
> > 7f635546bc2768c7b929d3de1724d83285f3cd54394fcd7104f8b1301d689d65 build~/arch/powerpc/kernel/vdso64/vgettimeofday.o
> >
> > $ make V=2
> > ...
> > CC arch/powerpc/kernel/vdso64/vgettimeofday.o - due to command line change
> >
> > $ sha256sum build\~/arch/powerpc/kernel/vdso64/vgettimeofday.o
> > 7f635546bc2768c7b929d3de1724d83285f3cd54394fcd7104f8b1301d689d65 build~/arch/powerpc/kernel/vdso64/vgettimeofday.o
> >
> >
> > So any hints on what I'm missing here?
> >
> > cheers
>
>
> This is because PPC builds the vdso twice
> with different command arguments.
>
>
> First time:
>
> vdso_prepare: prepare0
> $(if $(CONFIG_VDSO32),$(Q)$(MAKE) \
> $(build)=arch/powerpc/kernel/vdso32
> include/generated/vdso32-offsets.h)
> $(if $(CONFIG_PPC64),$(Q)$(MAKE) \
> $(build)=arch/powerpc/kernel/vdso64
> include/generated/vdso64-offsets.h)
>
>
> Second time:
> from arch/powerpc/kernel/Makefile
>
>
>
>
>
> For the first build, -Werror is missing because
> Kbuild directly descends into arch/powerpc/kernel/vdso[32,64]/.
>
>
> For the second build,
>
> arch/powerpc/Kbuild appends the following:
>
> subdir-ccflags-$(CONFIG_PPC_WERROR) := -Werror
>
This is very dangerous because the vdso offsets are wrong.
I think ppc followed arm64 implementation.
Let me figure out how to fix arm64 vdso.
--
Best Regards
Masahiro Yamada
next prev parent reply other threads:[~2020-12-17 16:42 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-17 2:56 powerpc VDSO files being unnecessarily rebuilt Michael Ellerman
2020-12-17 9:23 ` Masahiro Yamada
2020-12-17 9:23 ` Masahiro Yamada
2020-12-17 16:40 ` Masahiro Yamada [this message]
2020-12-17 16:40 ` Masahiro Yamada
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