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

[Nathan Chancellor]

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 <natecha...@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(-)

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


base-commit: f8394f232b1eab649ce2df5c5f15b0e528c92091
--
2.29.2

[Nathan Chancellor]

ld.lld 10.0.1 spews a bunch of various warnings about .rela sections,
along with a few others. Newer versions of ld.lld do not have these
warnings. As a result, do not add '--orphan-handling=warn' to
LDFLAGS_vmlinux if ld.lld's version is not new enough.

Reported-by: Arvind Sankar <nive...@alum.mit.edu>
Reported-by: kernelci.org bot <b...@kernelci.org>
Reported-by: Mark Brown <bro...@kernel.org>
Link: https://github.com/ClangBuiltLinux/linux/issues/1187
Link: https://github.com/ClangBuiltLinux/linux/issues/1193

Signed-off-by: Nathan Chancellor <natecha...@gmail.com>
---

MAINTAINERS | 1 +
init/Kconfig | 6 +++++-
scripts/lld-version.sh | 20 ++++++++++++++++++++
3 files changed, 26 insertions(+), 1 deletion(-)
create mode 100755 scripts/lld-version.sh

diff --git a/MAINTAINERS b/MAINTAINERS
index 3da6d8c154e4..4b83d3591ec7 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4284,6 +4284,7 @@ B: https://github.com/ClangBuiltLinux/linux/issues
C: irc://chat.freenode.net/clangbuiltlinux
F: Documentation/kbuild/llvm.rst
F: scripts/clang-tools/
+F: scripts/lld-version.sh
K: \b(?i:clang|llvm)\b

CLEANCACHE API
diff --git a/init/Kconfig b/init/Kconfig
index a270716562de..40c9ca60ac1d 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -47,6 +47,10 @@ config CLANG_VERSION
int
default $(shell,$(srctree)/scripts/clang-version.sh $(CC))

+config LLD_VERSION
+ int
+ default $(shell,$(srctree)/scripts/lld-version.sh $(LD))
+
config CC_CAN_LINK
bool
default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m64-flag)) if 64BIT
@@ -1349,7 +1353,7 @@ config LD_DEAD_CODE_DATA_ELIMINATION
own risk.

config LD_ORPHAN_WARN
- def_bool ARCH_WANT_LD_ORPHAN_WARN && $(ld-option,--orphan-handling=warn)
+ def_bool ARCH_WANT_LD_ORPHAN_WARN && $(ld-option,--orphan-handling=warn) && (!LD_IS_LLD || LLD_VERSION >= 110000)

config SYSCTL
bool
diff --git a/scripts/lld-version.sh b/scripts/lld-version.sh
new file mode 100755
index 000000000000..cc779f412e39
--- /dev/null
+++ b/scripts/lld-version.sh
@@ -0,0 +1,20 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# ld.lld-version ld.lld-command
+#
+# Print the linker version of `ld.lld-command' in a 5 or 6-digit form
+# such as `100001' for ld.lld 10.0.1 etc.
+
+linker="$*"
+
+if ! ( $linker --version | grep -q LLD ); then
+ echo 0
+ exit 1
+fi
+
+VERSION=$($linker --version | cut -d ' ' -f 2)
+MAJOR=$(echo $VERSION | cut -d . -f 1)
+MINOR=$(echo $VERSION | cut -d . -f 2)
+PATCHLEVEL=$(echo $VERSION | cut -d . -f 3)
+printf "%d%02d%02d\\n" $MAJOR $MINOR $PATCHLEVEL
--
2.29.2

[Nick Desaulniers]

On Fri, Nov 13, 2020 at 11:56 AM Nathan Chancellor
<natecha...@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?
--
Thanks,
~Nick Desaulniers

[Nathan Chancellor]

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]

Acked-by: Michael Ellerman <m...@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]

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]

On Mon, Nov 16, 2020 at 5:54 PM Nathan Chancellor
<natecha...@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
> > <natecha...@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 <ndesau...@google.com>
Tested-by: Nick Desaulniers <ndesau...@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

--
Thanks,
~Nick Desaulniers

[Nick Desaulniers]

On Fri, Nov 13, 2020 at 11:56 AM Nathan Chancellor
<natecha...@gmail.com> wrote:
>

^ it looks like this format was copied from scripts/gcc-version, but
it's kind of curious/cryptic to me for a comment about usage. Is it
necessary? A comment in the form:

# Usage: ./scripts/lld-version.sh ld.lld

Would be clearer to me.

> +#
> +# Print the linker version of `ld.lld-command' in a 5 or 6-digit form
> +# such as `100001' for ld.lld 10.0.1 etc.
> +
> +linker="$*"
> +
> +if ! ( $linker --version | grep -q LLD ); then
> + echo 0
> + exit 1
> +fi
> +
> +VERSION=$($linker --version | cut -d ' ' -f 2)

This is going to invoke the linker potentially twice if it's LLD.
Would it be nicer to capture the output of `$linker --version`, check
which linker it is, then slice that up via `cut` to get the version?

This version is fine to me, but if you're going to send a v2, that
might be a nice slight cleanup. Otherwise,

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

(Please drop those tags if you modify this for v2 and I'll rereview/retest).

> +MAJOR=$(echo $VERSION | cut -d . -f 1)
> +MINOR=$(echo $VERSION | cut -d . -f 2)
> +PATCHLEVEL=$(echo $VERSION | cut -d . -f 3)
> +printf "%d%02d%02d\\n" $MAJOR $MINOR $PATCHLEVEL
> --
> 2.29.2
>

--
Thanks,
~Nick Desaulniers

[Kees Cook]

On Fri, Nov 13, 2020 at 12:55:53PM -0700, Nathan Chancellor wrote:
> config LD_ORPHAN_WARN
> - def_bool ARCH_WANT_LD_ORPHAN_WARN && $(ld-option,--orphan-handling=warn)
> + def_bool ARCH_WANT_LD_ORPHAN_WARN && $(ld-option,--orphan-handling=warn) && (!LD_IS_LLD || LLD_VERSION >= 110000)

Readability nit-pick... I prefer separate "depends" lines to make things
a little easier to parse, change, etc:

config LD_ORPHAN_WARN
def_bool y
depends on ARCH_WANT_LD_ORPHAN_WARN
depends on !LD_IS_LLD || LLD_VERSION >= 110000
depends on $(ld-option,--orphan-handling=warn)

Otherwise, yeah, looks good to me. With this and the other suggestions,
please consider it:

Reviewed-by: Kees Cook <kees...@chromium.org>

--
Kees Cook

[Kees Cook]

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 <natecha...@gmail.com>

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

Acked-by: Kees Cook <kees...@chromium.org>

--
Kees Cook

[Nathan Chancellor]

Below is the impending v2 if you wanted to give it an early test, I plan
to send it along formally Thursday morning with all of the addressed
feedback so far.

Cheers,
Nathan

======================================================================

From 1ef9b12daf2b19ed6687423483d5bb1f5cf82e13 Mon Sep 17 00:00:00 2001
From: Nathan Chancellor <natecha...@gmail.com>
Date: Tue, 17 Nov 2020 20:11:26 -0700
Subject: [PATCH] kbuild: Disable CONFIG_LD_ORPHAN_WARN for ld.lld 10.0.1

ld.lld 10.0.1 spews a bunch of various warnings about .rela sections,
along with a few others. Newer versions of ld.lld do not have these
warnings. As a result, do not add '--orphan-handling=warn' to
LDFLAGS_vmlinux if ld.lld's version is not new enough.

Link: https://github.com/ClangBuiltLinux/linux/issues/1187
Link: https://github.com/ClangBuiltLinux/linux/issues/1193
Reported-by: Arvind Sankar <nive...@alum.mit.edu>
Reported-by: kernelci.org bot <b...@kernelci.org>
Reported-by: Mark Brown <bro...@kernel.org>

Reviewed-by: Kees Cook <kees...@chromium.org>

Signed-off-by: Nathan Chancellor <natecha...@gmail.com>
---
MAINTAINERS | 1 +

init/Kconfig | 9 ++++++++-
scripts/lld-version.sh | 20 ++++++++++++++++++++
3 files changed, 29 insertions(+), 1 deletion(-)

create mode 100755 scripts/lld-version.sh

diff --git a/MAINTAINERS b/MAINTAINERS

index e451dcce054f..e6f74f130ae1 100644

--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4284,6 +4284,7 @@ B: https://github.com/ClangBuiltLinux/linux/issues
C: irc://chat.freenode.net/clangbuiltlinux
F: Documentation/kbuild/llvm.rst
F: scripts/clang-tools/
+F: scripts/lld-version.sh
K: \b(?i:clang|llvm)\b

CLEANCACHE API
diff --git a/init/Kconfig b/init/Kconfig

index a270716562de..b9037d6c5ab3 100644

--- a/init/Kconfig
+++ b/init/Kconfig
@@ -47,6 +47,10 @@ config CLANG_VERSION
int
default $(shell,$(srctree)/scripts/clang-version.sh $(CC))

+config LLD_VERSION
+ int
+ default $(shell,$(srctree)/scripts/lld-version.sh $(LD))
+
config CC_CAN_LINK
bool
default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m64-flag)) if 64BIT

@@ -1349,7 +1353,10 @@ config LD_DEAD_CODE_DATA_ELIMINATION

own risk.

config LD_ORPHAN_WARN
- def_bool ARCH_WANT_LD_ORPHAN_WARN && $(ld-option,--orphan-handling=warn)

+ def_bool y
+ depends on ARCH_WANT_LD_ORPHAN_WARN
+ depends on !LD_IS_LLD || LLD_VERSION >= 110000
+ depends on $(ld-option,--orphan-handling=warn)

config SYSCTL
bool
diff --git a/scripts/lld-version.sh b/scripts/lld-version.sh
new file mode 100755

index 000000000000..d70edb4d8a4f

--- /dev/null
+++ b/scripts/lld-version.sh
@@ -0,0 +1,20 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#

+# Usage: $ ./scripts/lld-version.sh ld.lld
+#
+# Print the linker version of `ld.lld' in a 5 or 6-digit form

+# such as `100001' for ld.lld 10.0.1 etc.
+

+linker_string="$($* --version)"
+
+if ! ( echo $linker_string | grep -q LLD ); then

+ echo 0
+ exit 1
+fi
+

+VERSION=$(echo $linker_string | cut -d ' ' -f 2)

[Nathan Chancellor]

Thank you, I have updated it locally for v2!

Cheers,
Nathan

[Nathan Chancellor]

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

Acked-by: Kees Cook <kees...@chromium.org>

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

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

Signed-off-by: Nathan Chancellor <natecha...@gmail.com>
---

v1 -> v2:

* Change

ifeq ($(CONFIG_LD_ORPHAN_WARN),y)

to

ifdef CONFIG_LD_ORPHAN_WARN

to improve readability (Michael Ellerman)

* Separate conditions for CONFIG_LD_ORPHAN warn to improve
readability (Kees Cook)

* Pick up tags from Kees, Michael, and Nick

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 | 5 +++++
13 files changed, 30 insertions(+), 14 deletions(-)

diff --git a/Makefile b/Makefile
index e2c3f65c4721..2c7116299f1f 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.

+ifdef CONFIG_LD_ORPHAN_WARN

index 47f001ca5499..e1567418a2b1 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)

+ifdef CONFIG_LD_ORPHAN_WARN

index ee249088cbfe..40b8fd375d52 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)

+ifdef CONFIG_LD_ORPHAN_WARN

+LDFLAGS_vmlinux += --orphan-handling=warn
+endif
LDFLAGS_vmlinux += -T

hostprogs := mkpiggy
diff --git a/init/Kconfig b/init/Kconfig

index c9446911cf41..92c58b45abb8 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1348,6 +1348,11 @@ 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 y
+ depends on ARCH_WANT_LD_ORPHAN_WARN

+ depends on $(ld-option,--orphan-handling=warn)
+
config SYSCTL
bool


base-commit: 09162bc32c880a791c6c0668ce0745cf7958f576
--
2.29.2

[Nathan Chancellor]

ld.lld 10.0.1 spews a bunch of various warnings about .rela sections,
along with a few others. Newer versions of ld.lld do not have these
warnings. As a result, do not add '--orphan-handling=warn' to
LDFLAGS_vmlinux if ld.lld's version is not new enough.

Link: https://github.com/ClangBuiltLinux/linux/issues/1187
Link: https://github.com/ClangBuiltLinux/linux/issues/1193
Reported-by: Arvind Sankar <nive...@alum.mit.edu>
Reported-by: kernelci.org bot <b...@kernelci.org>
Reported-by: Mark Brown <bro...@kernel.org>
Reviewed-by: Kees Cook <kees...@chromium.org>

Signed-off-by: Nathan Chancellor <natecha...@gmail.com>
---

v1 -> v2:

* Add condition as a depends on line (Kees Cook)

* Capture output of "$* --version" to avoid invoking linker twice (Nick
Desaulniers)

* Improve documentation of script in comments (Nick Desaulniers)

* Pick up review tag from Kees

MAINTAINERS | 1 +
init/Kconfig | 5 +++++

scripts/lld-version.sh | 20 ++++++++++++++++++++
3 files changed, 26 insertions(+)

create mode 100755 scripts/lld-version.sh

diff --git a/MAINTAINERS b/MAINTAINERS
index e451dcce054f..e6f74f130ae1 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4284,6 +4284,7 @@ B: https://github.com/ClangBuiltLinux/linux/issues
C: irc://chat.freenode.net/clangbuiltlinux
F: Documentation/kbuild/llvm.rst
F: scripts/clang-tools/
+F: scripts/lld-version.sh
K: \b(?i:clang|llvm)\b

CLEANCACHE API

diff --git a/init/Kconfig b/init/Kconfig
index 92c58b45abb8..b9037d6c5ab3 100644
--- a/init/Kconfig
+++ b/init/Kconfig

@@ -47,6 +47,10 @@ config CLANG_VERSION
int
default $(shell,$(srctree)/scripts/clang-version.sh $(CC))

+config LLD_VERSION
+ int
+ default $(shell,$(srctree)/scripts/lld-version.sh $(LD))
+
config CC_CAN_LINK
bool
default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m64-flag)) if 64BIT

@@ -1351,6 +1355,7 @@ config LD_DEAD_CODE_DATA_ELIMINATION
config LD_ORPHAN_WARN
def_bool y
depends on ARCH_WANT_LD_ORPHAN_WARN
+ depends on !LD_IS_LLD || LLD_VERSION >= 110000
depends on $(ld-option,--orphan-handling=warn)

config SYSCTL

[Nick Desaulniers]

On Thu, Nov 19, 2020 at 12:57 PM Nathan Chancellor
<natecha...@gmail.com> wrote:
>
> ld.lld 10.0.1 spews a bunch of various warnings about .rela sections,
> along with a few others. Newer versions of ld.lld do not have these
> warnings. As a result, do not add '--orphan-handling=warn' to
> LDFLAGS_vmlinux if ld.lld's version is not new enough.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1187
> Link: https://github.com/ClangBuiltLinux/linux/issues/1193
> Reported-by: Arvind Sankar <nive...@alum.mit.edu>
> Reported-by: kernelci.org bot <b...@kernelci.org>
> Reported-by: Mark Brown <bro...@kernel.org>
> Reviewed-by: Kees Cook <kees...@chromium.org>
> Signed-off-by: Nathan Chancellor <natecha...@gmail.com>

Thanks for the additions in v2.
Reviewed-by: Nick Desaulniers <ndesau...@google.com>

--
Thanks,
~Nick Desaulniers

[Kees Cook]

On Thu, Nov 19, 2020 at 01:46:56PM -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
> Acked-by: Kees Cook <kees...@chromium.org>
> Acked-by: Michael Ellerman <m...@ellerman.id.au> (powerpc)
> Reviewed-by: Nick Desaulniers <ndesau...@google.com>
> Tested-by: Nick Desaulniers <ndesau...@google.com>
> Signed-off-by: Nathan Chancellor <natecha...@gmail.com>

Masahiro, do you want to take these to get them to Linus for v5.10? I
can send them if you'd prefer.

-Kees

--
Kees Cook

[Kees Cook]

On Thu, Nov 19, 2020 at 01:13:27PM -0800, Nick Desaulniers wrote:
> On Thu, Nov 19, 2020 at 12:57 PM Nathan Chancellor
> <natecha...@gmail.com> wrote:
> >
> > ld.lld 10.0.1 spews a bunch of various warnings about .rela sections,
> > along with a few others. Newer versions of ld.lld do not have these
> > warnings. As a result, do not add '--orphan-handling=warn' to
> > LDFLAGS_vmlinux if ld.lld's version is not new enough.
> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1187
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1193
> > Reported-by: Arvind Sankar <nive...@alum.mit.edu>
> > Reported-by: kernelci.org bot <b...@kernelci.org>
> > Reported-by: Mark Brown <bro...@kernel.org>
> > Reviewed-by: Kees Cook <kees...@chromium.org>
> > Signed-off-by: Nathan Chancellor <natecha...@gmail.com>
>
> Thanks for the additions in v2.
> Reviewed-by: Nick Desaulniers <ndesau...@google.com>

I'm going to carry this for a few days in -next, and if no one screams,
ask Linus to pull it for v5.10-rc6.

Thanks!

--
Kees Cook

[Masahiro Yamada]

Sorry for the delay.

Applied to linux-kbuild.





> -Kees
>
> --
> Kees Cook
>
> --
> You received this message because you are subscribed to the Google Groups "Clang Built Linux" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-li...@googlegroups.com.
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--
Best Regards
Masahiro Yamada

[Masahiro Yamada]

Sorry for the delay.
Applied to linux-kbuild.

But, I already see this in linux-next.

Please let me know if I should drop it from my tree.

[Kees Cook]

Great, thanks!

> But, I already see this in linux-next.
> Please let me know if I should drop it from my tree.

My intention was to get this to Linus this week. Do you want to do that
yourself, or Ack the patches in my tree and I'll send it?

-Kees

--
Kees Cook

[Masahiro Yamada]

I will send a kbuild pull request myself this week.

[Kees Cook]

> I will send a kbuild pull request myself this week.

Okay, thanks! I've removed it from my -next tree now.

--
Kees Cook