diff mbox series

[1/2] kbuild: Hoist '--orphan-handling' into Kconfig

Message ID 20201113195553.1487659-1-natechancellor@gmail.com (mailing list archive)
State New
Headers show
Series [1/2] kbuild: Hoist '--orphan-handling' into Kconfig | expand

Commit Message

Nathan Chancellor Nov. 13, 2020, 7:55 p.m. UTC
Currently, '--orphan-handling=warn' is spread out across four different
architectures in their respective Makefiles, which makes it a little
unruly to deal with in case it needs to be disabled for a specific
linker version (in this case, ld.lld 10.0.1).

To make it easier to control this, hoist this warning into Kconfig and
the main Makefile so that disabling it is simpler, as the warning will
only be enabled in a couple places (main Makefile and a couple of
compressed boot folders that blow away LDFLAGS_vmlinx) and making it
conditional is easier due to Kconfig syntax. One small additional
benefit of this is saving a call to ld-option on incremental builds
because we will have already evaluated it for CONFIG_LD_ORPHAN_WARN.

To keep the list of supported architectures the same, introduce
CONFIG_ARCH_WANT_LD_ORPHAN_WARN, which an architecture can select to
gain this automatically after all of the sections are specified and size
asserted. A special thanks to Kees Cook for the help text on this
config.

Link: https://github.com/ClangBuiltLinux/linux/issues/1187
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
 Makefile                          | 6 ++++++
 arch/Kconfig                      | 9 +++++++++
 arch/arm/Kconfig                  | 1 +
 arch/arm/Makefile                 | 4 ----
 arch/arm/boot/compressed/Makefile | 4 +++-
 arch/arm64/Kconfig                | 1 +
 arch/arm64/Makefile               | 4 ----
 arch/powerpc/Kconfig              | 1 +
 arch/powerpc/Makefile             | 1 -
 arch/x86/Kconfig                  | 1 +
 arch/x86/Makefile                 | 3 ---
 arch/x86/boot/compressed/Makefile | 4 +++-
 init/Kconfig                      | 3 +++
 13 files changed, 28 insertions(+), 14 deletions(-)


base-commit: f8394f232b1eab649ce2df5c5f15b0e528c92091

Comments

Nick Desaulniers Nov. 17, 2020, 1:41 a.m. UTC | #1
On Fri, Nov 13, 2020 at 11:56 AM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> Currently, '--orphan-handling=warn' is spread out across four different
> architectures in their respective Makefiles, which makes it a little
> unruly to deal with in case it needs to be disabled for a specific
> linker version (in this case, ld.lld 10.0.1).

Hi Nathan,
This patch fails to apply for me via b4 on next-20201116 due to a
conflict in arch/Kconfig:1028. Would you mind sending a rebased V2?
Nathan Chancellor Nov. 17, 2020, 1:54 a.m. UTC | #2
On Mon, Nov 16, 2020 at 05:41:58PM -0800, Nick Desaulniers wrote:
> On Fri, Nov 13, 2020 at 11:56 AM Nathan Chancellor
> <natechancellor@gmail.com> wrote:
> >
> > Currently, '--orphan-handling=warn' is spread out across four different
> > architectures in their respective Makefiles, which makes it a little
> > unruly to deal with in case it needs to be disabled for a specific
> > linker version (in this case, ld.lld 10.0.1).
> 
> Hi Nathan,
> This patch fails to apply for me via b4 on next-20201116 due to a
> conflict in arch/Kconfig:1028. Would you mind sending a rebased V2?

Hi Nick,

This series is intended to go into v5.10 so rebasing it against -next
defeats that; please test it against v5.10-rc4, where it still applies
cleanly. The conflicts will be handled by other entities (Stephen Rothwell
and Linus).

If you want to test it against -next, 'git am -3' will allow you to
easily handle the conflict.

Cheers,
Nathan
Michael Ellerman Nov. 17, 2020, 11:03 a.m. UTC | #3
Nathan Chancellor <natechancellor@gmail.com> writes:
> Currently, '--orphan-handling=warn' is spread out across four different
> architectures in their respective Makefiles, which makes it a little
> unruly to deal with in case it needs to be disabled for a specific
> linker version (in this case, ld.lld 10.0.1).
>
> To make it easier to control this, hoist this warning into Kconfig and
> the main Makefile so that disabling it is simpler, as the warning will
> only be enabled in a couple places (main Makefile and a couple of
> compressed boot folders that blow away LDFLAGS_vmlinx) and making it
> conditional is easier due to Kconfig syntax. One small additional
> benefit of this is saving a call to ld-option on incremental builds
> because we will have already evaluated it for CONFIG_LD_ORPHAN_WARN.
>
> To keep the list of supported architectures the same, introduce
> CONFIG_ARCH_WANT_LD_ORPHAN_WARN, which an architecture can select to
> gain this automatically after all of the sections are specified and size
> asserted. A special thanks to Kees Cook for the help text on this
> config.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1187
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> ---
>  Makefile                          | 6 ++++++
>  arch/Kconfig                      | 9 +++++++++
>  arch/arm/Kconfig                  | 1 +
>  arch/arm/Makefile                 | 4 ----
>  arch/arm/boot/compressed/Makefile | 4 +++-
>  arch/arm64/Kconfig                | 1 +
>  arch/arm64/Makefile               | 4 ----
>  arch/powerpc/Kconfig              | 1 +
>  arch/powerpc/Makefile             | 1 -

Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)


>  arch/x86/Kconfig                  | 1 +
>  arch/x86/Makefile                 | 3 ---
>  arch/x86/boot/compressed/Makefile | 4 +++-
>  init/Kconfig                      | 3 +++
>  13 files changed, 28 insertions(+), 14 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 008aba5f1a20..c443afd61886 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -984,6 +984,12 @@ ifeq ($(CONFIG_RELR),y)
>  LDFLAGS_vmlinux	+= --pack-dyn-relocs=relr
>  endif
>  
> +# We never want expected sections to be placed heuristically by the
> +# linker. All sections should be explicitly named in the linker script.
> +ifeq ($(CONFIG_LD_ORPHAN_WARN),y)
> +LDFLAGS_vmlinux += --orphan-handling=warn
> +endif

This is a nit, but you can use ifdef with bool CONFIG symbols in
Makefiles, which reads a bit nicer, eg:

ifdef CONFIG_LD_ORPHAN_WARN
LDFLAGS_vmlinux += --orphan-handling=warn
endif


cheers
Nathan Chancellor Nov. 17, 2020, 4:22 p.m. UTC | #4
On Tue, Nov 17, 2020 at 10:03:29PM +1100, Michael Ellerman wrote:
> Nathan Chancellor <natechancellor@gmail.com> writes:
> > Currently, '--orphan-handling=warn' is spread out across four different
> > architectures in their respective Makefiles, which makes it a little
> > unruly to deal with in case it needs to be disabled for a specific
> > linker version (in this case, ld.lld 10.0.1).
> >
> > To make it easier to control this, hoist this warning into Kconfig and
> > the main Makefile so that disabling it is simpler, as the warning will
> > only be enabled in a couple places (main Makefile and a couple of
> > compressed boot folders that blow away LDFLAGS_vmlinx) and making it
> > conditional is easier due to Kconfig syntax. One small additional
> > benefit of this is saving a call to ld-option on incremental builds
> > because we will have already evaluated it for CONFIG_LD_ORPHAN_WARN.
> >
> > To keep the list of supported architectures the same, introduce
> > CONFIG_ARCH_WANT_LD_ORPHAN_WARN, which an architecture can select to
> > gain this automatically after all of the sections are specified and size
> > asserted. A special thanks to Kees Cook for the help text on this
> > config.
> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1187
> > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> > ---
> >  Makefile                          | 6 ++++++
> >  arch/Kconfig                      | 9 +++++++++
> >  arch/arm/Kconfig                  | 1 +
> >  arch/arm/Makefile                 | 4 ----
> >  arch/arm/boot/compressed/Makefile | 4 +++-
> >  arch/arm64/Kconfig                | 1 +
> >  arch/arm64/Makefile               | 4 ----
> >  arch/powerpc/Kconfig              | 1 +
> >  arch/powerpc/Makefile             | 1 -
> 
> Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
> 
> 
> >  arch/x86/Kconfig                  | 1 +
> >  arch/x86/Makefile                 | 3 ---
> >  arch/x86/boot/compressed/Makefile | 4 +++-
> >  init/Kconfig                      | 3 +++
> >  13 files changed, 28 insertions(+), 14 deletions(-)
> >
> > diff --git a/Makefile b/Makefile
> > index 008aba5f1a20..c443afd61886 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -984,6 +984,12 @@ ifeq ($(CONFIG_RELR),y)
> >  LDFLAGS_vmlinux	+= --pack-dyn-relocs=relr
> >  endif
> >  
> > +# We never want expected sections to be placed heuristically by the
> > +# linker. All sections should be explicitly named in the linker script.
> > +ifeq ($(CONFIG_LD_ORPHAN_WARN),y)
> > +LDFLAGS_vmlinux += --orphan-handling=warn
> > +endif
> 
> This is a nit, but you can use ifdef with bool CONFIG symbols in
> Makefiles, which reads a bit nicer, eg:
> 
> ifdef CONFIG_LD_ORPHAN_WARN
> LDFLAGS_vmlinux += --orphan-handling=warn
> endif

That is indeed cleaner, I did not realize I could do that as long as the
config was a boolean. I will use that in v2, which I will send along
within the next few days to give Masahiro some time to comment.

Cheers,
Nathan
Nick Desaulniers Nov. 17, 2020, 7:26 p.m. UTC | #5
On Mon, Nov 16, 2020 at 5:54 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> On Mon, Nov 16, 2020 at 05:41:58PM -0800, Nick Desaulniers wrote:
> > On Fri, Nov 13, 2020 at 11:56 AM Nathan Chancellor
> > <natechancellor@gmail.com> wrote:
> > >
> > > Currently, '--orphan-handling=warn' is spread out across four different
> > > architectures in their respective Makefiles, which makes it a little
> > > unruly to deal with in case it needs to be disabled for a specific
> > > linker version (in this case, ld.lld 10.0.1).
> >
> > Hi Nathan,
> > This patch fails to apply for me via b4 on next-20201116 due to a
> > conflict in arch/Kconfig:1028. Would you mind sending a rebased V2?
>
> Hi Nick,
>
> This series is intended to go into v5.10 so rebasing it against -next
> defeats that; please test it against v5.10-rc4, where it still applies
> cleanly. The conflicts will be handled by other entities (Stephen Rothwell
> and Linus).

Got it.  Yeah, applies fine to v5.10-rc4.

Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>

Feel free to carry those with MPE's suggested change added.

>
> If you want to test it against -next, 'git am -3' will allow you to
> easily handle the conflict.
>
> Cheers,
> Nathan
Kees Cook Nov. 17, 2020, 9:52 p.m. UTC | #6
On Fri, Nov 13, 2020 at 12:55:52PM -0700, Nathan Chancellor wrote:
> Currently, '--orphan-handling=warn' is spread out across four different
> architectures in their respective Makefiles, which makes it a little
> unruly to deal with in case it needs to be disabled for a specific
> linker version (in this case, ld.lld 10.0.1).
> 
> To make it easier to control this, hoist this warning into Kconfig and
> the main Makefile so that disabling it is simpler, as the warning will
> only be enabled in a couple places (main Makefile and a couple of
> compressed boot folders that blow away LDFLAGS_vmlinx) and making it
> conditional is easier due to Kconfig syntax. One small additional
> benefit of this is saving a call to ld-option on incremental builds
> because we will have already evaluated it for CONFIG_LD_ORPHAN_WARN.
> 
> To keep the list of supported architectures the same, introduce
> CONFIG_ARCH_WANT_LD_ORPHAN_WARN, which an architecture can select to
> gain this automatically after all of the sections are specified and size
> asserted. A special thanks to Kees Cook for the help text on this
> config.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1187
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>

Looks good to me. With the other suggestions from the thread added,
please consider it:

Acked-by: Kees Cook <keescook@chromium.org>
diff mbox series

Patch

diff --git a/Makefile b/Makefile
index 008aba5f1a20..c443afd61886 100644
--- a/Makefile
+++ b/Makefile
@@ -984,6 +984,12 @@  ifeq ($(CONFIG_RELR),y)
 LDFLAGS_vmlinux	+= --pack-dyn-relocs=relr
 endif
 
+# We never want expected sections to be placed heuristically by the
+# linker. All sections should be explicitly named in the linker script.
+ifeq ($(CONFIG_LD_ORPHAN_WARN),y)
+LDFLAGS_vmlinux += --orphan-handling=warn
+endif
+
 # Align the bit size of userspace programs with the kernel
 KBUILD_USERCFLAGS  += $(filter -m32 -m64 --target=%, $(KBUILD_CFLAGS))
 KBUILD_USERLDFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CFLAGS))
diff --git a/arch/Kconfig b/arch/Kconfig
index 56b6ccc0e32d..ba4e966484ab 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1028,6 +1028,15 @@  config HAVE_STATIC_CALL_INLINE
 	bool
 	depends on HAVE_STATIC_CALL
 
+config ARCH_WANT_LD_ORPHAN_WARN
+	bool
+	help
+	  An arch should select this symbol once all linker sections are explicitly
+	  included, size-asserted, or discarded in the linker scripts. This is
+	  important because we never want expected sections to be placed heuristically
+	  by the linker, since the locations of such sections can change between linker
+	  versions.
+
 source "kernel/gcov/Kconfig"
 
 source "scripts/gcc-plugins/Kconfig"
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index fe2f17eb2b50..002e0cf025f5 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -35,6 +35,7 @@  config ARM
 	select ARCH_USE_CMPXCHG_LOCKREF
 	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU
 	select ARCH_WANT_IPC_PARSE_VERSION
+	select ARCH_WANT_LD_ORPHAN_WARN
 	select BINFMT_FLAT_ARGVP_ENVP_ON_STACK
 	select BUILDTIME_TABLE_SORT if MMU
 	select CLONE_BACKWARDS
diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index 4d76eab2b22d..e15f76ca2887 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -16,10 +16,6 @@  LDFLAGS_vmlinux	+= --be8
 KBUILD_LDFLAGS_MODULE	+= --be8
 endif
 
-# We never want expected sections to be placed heuristically by the
-# linker. All sections should be explicitly named in the linker script.
-LDFLAGS_vmlinux += $(call ld-option, --orphan-handling=warn)
-
 GZFLAGS		:=-9
 #KBUILD_CFLAGS	+=-pipe
 
diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
index 47f001ca5499..c6f9f3b61c5f 100644
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -129,7 +129,9 @@  LDFLAGS_vmlinux += --no-undefined
 # Delete all temporary local symbols
 LDFLAGS_vmlinux += -X
 # Report orphan sections
-LDFLAGS_vmlinux += $(call ld-option, --orphan-handling=warn)
+ifeq ($(CONFIG_LD_ORPHAN_WARN),y)
+LDFLAGS_vmlinux += --orphan-handling=warn
+endif
 # Next argument is a linker script
 LDFLAGS_vmlinux += -T
 
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 1515f6f153a0..a6b5b7ef40ae 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -81,6 +81,7 @@  config ARM64
 	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
 	select ARCH_WANT_FRAME_POINTERS
 	select ARCH_WANT_HUGE_PMD_SHARE if ARM64_4K_PAGES || (ARM64_16K_PAGES && !ARM64_VA_BITS_36)
+	select ARCH_WANT_LD_ORPHAN_WARN
 	select ARCH_HAS_UBSAN_SANITIZE_ALL
 	select ARM_AMBA
 	select ARM_ARCH_TIMER
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 5789c2d18d43..6a87d592bd00 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -28,10 +28,6 @@  LDFLAGS_vmlinux	+= --fix-cortex-a53-843419
   endif
 endif
 
-# We never want expected sections to be placed heuristically by the
-# linker. All sections should be explicitly named in the linker script.
-LDFLAGS_vmlinux += $(call ld-option, --orphan-handling=warn)
-
 ifeq ($(CONFIG_ARM64_USE_LSE_ATOMICS), y)
   ifneq ($(CONFIG_ARM64_LSE_ATOMICS), y)
 $(warning LSE atomics not supported by binutils)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index e9f13fe08492..5181872f9452 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -152,6 +152,7 @@  config PPC
 	select ARCH_USE_QUEUED_SPINLOCKS	if PPC_QUEUED_SPINLOCKS
 	select ARCH_WANT_IPC_PARSE_VERSION
 	select ARCH_WANT_IRQS_OFF_ACTIVATE_MM
+	select ARCH_WANT_LD_ORPHAN_WARN
 	select ARCH_WEAK_RELEASE_ACQUIRE
 	select BINFMT_ELF
 	select BUILDTIME_TABLE_SORT
diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index a4d56f0a41d9..d9eb0da845e1 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -123,7 +123,6 @@  endif
 LDFLAGS_vmlinux-y := -Bstatic
 LDFLAGS_vmlinux-$(CONFIG_RELOCATABLE) := -pie
 LDFLAGS_vmlinux	:= $(LDFLAGS_vmlinux-y)
-LDFLAGS_vmlinux += $(call ld-option,--orphan-handling=warn)
 
 ifdef CONFIG_PPC64
 ifeq ($(call cc-option-yn,-mcmodel=medium),y)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f6946b81f74a..fbf26e0f7a6a 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -100,6 +100,7 @@  config X86
 	select ARCH_WANT_DEFAULT_BPF_JIT	if X86_64
 	select ARCH_WANTS_DYNAMIC_TASK_STRUCT
 	select ARCH_WANT_HUGE_PMD_SHARE
+	select ARCH_WANT_LD_ORPHAN_WARN
 	select ARCH_WANTS_THP_SWAP		if X86_64
 	select BUILDTIME_TABLE_SORT
 	select CLKEVT_I8253
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 154259f18b8b..1bf21746f4ce 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -209,9 +209,6 @@  ifdef CONFIG_X86_64
 LDFLAGS_vmlinux += -z max-page-size=0x200000
 endif
 
-# We never want expected sections to be placed heuristically by the
-# linker. All sections should be explicitly named in the linker script.
-LDFLAGS_vmlinux += $(call ld-option, --orphan-handling=warn)
 
 archscripts: scripts_basic
 	$(Q)$(MAKE) $(build)=arch/x86/tools relocs
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index ee249088cbfe..fa1c9f83436c 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -61,7 +61,9 @@  KBUILD_LDFLAGS += $(call ld-option,--no-ld-generated-unwind-info)
 # Compressed kernel should be built as PIE since it may be loaded at any
 # address by the bootloader.
 LDFLAGS_vmlinux := -pie $(call ld-option, --no-dynamic-linker)
-LDFLAGS_vmlinux += $(call ld-option, --orphan-handling=warn)
+ifeq ($(CONFIG_LD_ORPHAN_WARN),y)
+LDFLAGS_vmlinux += --orphan-handling=warn
+endif
 LDFLAGS_vmlinux += -T
 
 hostprogs	:= mkpiggy
diff --git a/init/Kconfig b/init/Kconfig
index c9446911cf41..a270716562de 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1348,6 +1348,9 @@  config LD_DEAD_CODE_DATA_ELIMINATION
 	  present. This option is not well tested yet, so use at your
 	  own risk.
 
+config LD_ORPHAN_WARN
+	def_bool ARCH_WANT_LD_ORPHAN_WARN && $(ld-option,--orphan-handling=warn)
+
 config SYSCTL
 	bool