[PATCH 5.10 0/4] Backport of e89c2e815e76 to linux-5.10.y

[PATCH 5.10 0/4] Backport of e89c2e815e76 to linux-5.10.y

[Nathan Chancellor]

Hi all,

This series is a backport of upstream commit e89c2e815e76 ("riscv:
Handle zicsr/zifencei issues between clang and binutils") to
linux-5.10.y, with the necessary machinery for CONFIG_AS_IS_GNU and
CONFIG_AS_VERSION, which that commit requires.

While the middle two patches are not strictly necessary, they are good
clean ups that ensure consistency with mainline. The first three changes
are already present in 5.15, so there is no risk of a regression moving
forward.

If there are any issues, please let me know.

NOTE: I am sending this series with 'b4 send', as that is what I am used
to at this point. Please accept my apologies if this causes any issues.

---
Masahiro Yamada (2):
      kbuild: check the minimum assembler version in Kconfig
      kbuild: check CONFIG_AS_IS_LLVM instead of LLVM_IAS

Nathan Chancellor (2):
      kbuild: Switch to 'f' variants of integrated assembler flag
      riscv: Handle zicsr/zifencei issues between clang and binutils

 Makefile                |  8 +++---
 arch/riscv/Kconfig      | 22 ++++++++++++++++
 arch/riscv/Makefile     | 12 +++++----
 init/Kconfig            | 12 +++++++++
 scripts/Kconfig.include |  6 +++++
 scripts/as-version.sh   | 69 +++++++++++++++++++++++++++++++++++++++++++++++++
 scripts/dummy-tools/gcc |  6 +++++
 7 files changed, 127 insertions(+), 8 deletions(-)
---
base-commit: ca9787bdecfa2174b0a169a54916e22b89b0ef5b
change-id: 20230328-riscv-zifencei-zicsr-5-10-65596f2cac9e

Best regards,
-- 
Nathan Chancellor <nathan@kernel.org>

[PATCH 5.10 1/4] kbuild: check the minimum assembler version in Kconfig

[Nathan Chancellor]

From: Masahiro Yamada <masahiroy@kernel.org>

commit ba64beb17493a4bfec563100c86a462a15926f24 upstream.

Documentation/process/changes.rst defines the minimum assembler version
(binutils version), but we have never checked it in the build time.

Kbuild never invokes 'as' directly because all assembly files in the
kernel tree are *.S, hence must be preprocessed. I do not expect
raw assembly source files (*.s) would be added to the kernel tree.

Therefore, we always use $(CC) as the assembler driver, and commit
aa824e0c962b ("kbuild: remove AS variable") removed 'AS'. However,
we are still interested in the version of the assembler acting behind.

As usual, the --version option prints the version string.

  $ as --version | head -n 1
  GNU assembler (GNU Binutils for Ubuntu) 2.35.1

But, we do not have $(AS). So, we can add the -Wa prefix so that
$(CC) passes --version down to the backing assembler.

  $ gcc -Wa,--version | head -n 1
  gcc: fatal error: no input files
  compilation terminated.

OK, we need to input something to satisfy gcc.

  $ gcc -Wa,--version -c -x assembler /dev/null -o /dev/null | head -n 1
  GNU assembler (GNU Binutils for Ubuntu) 2.35.1

The combination of Clang and GNU assembler works in the same way:

  $ clang -no-integrated-as -Wa,--version -c -x assembler /dev/null -o /dev/null | head -n 1
  GNU assembler (GNU Binutils for Ubuntu) 2.35.1

Clang with the integrated assembler fails like this:

  $ clang -integrated-as -Wa,--version -c -x assembler /dev/null -o /dev/null | head -n 1
  clang: error: unsupported argument '--version' to option 'Wa,'

For the last case, checking the error message is fragile. If the
proposal for -Wa,--version support [1] is accepted, this may not be
even an error in the future.

One easy way is to check if -integrated-as is present in the passed
arguments. We did not pass -integrated-as to CLANG_FLAGS before, but
we can make it explicit.

Nathan pointed out -integrated-as is the default for all of the
architectures/targets that the kernel cares about, but it goes
along with "explicit is better than implicit" policy. [2]

With all this in my mind, I implemented scripts/as-version.sh to
check the assembler version in Kconfig time.

  $ scripts/as-version.sh gcc
  GNU 23501
  $ scripts/as-version.sh clang -no-integrated-as
  GNU 23501
  $ scripts/as-version.sh clang -integrated-as
  LLVM 0

[1]: https://github.com/ClangBuiltLinux/linux/issues/1320
[2]: https://lore.kernel.org/linux-kbuild/20210307044253.v3h47ucq6ng25iay@archlinux-ax161/

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
[nathan: Backport to 5.10. Drop minimum version checking, as it is not
         required in 5.10]
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 Makefile                |  4 ++-
 init/Kconfig            | 12 +++++++++
 scripts/Kconfig.include |  6 +++++
 scripts/as-version.sh   | 69 +++++++++++++++++++++++++++++++++++++++++++++++++
 scripts/dummy-tools/gcc |  6 +++++
 5 files changed, 96 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 71caf5938361..44d9aff4f66a 100644
--- a/Makefile
+++ b/Makefile
@@ -580,7 +580,9 @@ endif
 ifneq ($(GCC_TOOLCHAIN),)
 CLANG_FLAGS	+= --gcc-toolchain=$(GCC_TOOLCHAIN)
 endif
-ifneq ($(LLVM_IAS),1)
+ifeq ($(LLVM_IAS),1)
+CLANG_FLAGS	+= -integrated-as
+else
 CLANG_FLAGS	+= -no-integrated-as
 endif
 CLANG_FLAGS	+= -Werror=unknown-warning-option
diff --git a/init/Kconfig b/init/Kconfig
index eba883d6d9ed..9807c66b24bb 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -47,6 +47,18 @@ config CLANG_VERSION
 	int
 	default $(shell,$(srctree)/scripts/clang-version.sh $(CC))
 
+config AS_IS_GNU
+	def_bool $(success,test "$(as-name)" = GNU)
+
+config AS_IS_LLVM
+	def_bool $(success,test "$(as-name)" = LLVM)
+
+config AS_VERSION
+	int
+	# Use clang version if this is the integrated assembler
+	default CLANG_VERSION if AS_IS_LLVM
+	default $(as-version)
+
 config LLD_VERSION
 	int
 	default $(shell,$(srctree)/scripts/lld-version.sh $(LD))
diff --git a/scripts/Kconfig.include b/scripts/Kconfig.include
index a5fe72c504ff..6d37cb780452 100644
--- a/scripts/Kconfig.include
+++ b/scripts/Kconfig.include
@@ -42,6 +42,12 @@ $(error-if,$(failure,command -v $(LD)),linker '$(LD)' not found)
 # Fail if the linker is gold as it's not capable of linking the kernel proper
 $(error-if,$(success, $(LD) -v | grep -q gold), gold linker '$(LD)' not supported)
 
+# Get the assembler name, version, and error out if it is not supported.
+as-info := $(shell,$(srctree)/scripts/as-version.sh $(CC) $(CLANG_FLAGS))
+$(error-if,$(success,test -z "$(as-info)"),Sorry$(comma) this assembler is not supported.)
+as-name := $(shell,set -- $(as-info) && echo $1)
+as-version := $(shell,set -- $(as-info) && echo $2)
+
 # machine bit flags
 #  $(m32-flag): -m32 if the compiler supports it, or an empty string otherwise.
 #  $(m64-flag): -m64 if the compiler supports it, or an empty string otherwise.
diff --git a/scripts/as-version.sh b/scripts/as-version.sh
new file mode 100755
index 000000000000..851dcb8a0e68
--- /dev/null
+++ b/scripts/as-version.sh
@@ -0,0 +1,69 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Print the assembler name and its version in a 5 or 6-digit form.
+# Also, perform the minimum version check.
+# (If it is the integrated assembler, return 0 as the version, and
+# skip the version check.)
+
+set -e
+
+# Convert the version string x.y.z to a canonical 5 or 6-digit form.
+get_canonical_version()
+{
+	IFS=.
+	set -- $1
+
+	# If the 2nd or 3rd field is missing, fill it with a zero.
+	#
+	# The 4th field, if present, is ignored.
+	# This occurs in development snapshots as in 2.35.1.20201116
+	echo $((10000 * $1 + 100 * ${2:-0} + ${3:-0}))
+}
+
+# Clang fails to handle -Wa,--version unless -no-integrated-as is given.
+# We check -(f)integrated-as, expecting it is explicitly passed in for the
+# integrated assembler case.
+check_integrated_as()
+{
+	while [ $# -gt 0 ]; do
+		if [ "$1" = -integrated-as -o "$1" = -fintegrated-as ]; then
+			# For the intergrated assembler, we do not check the
+			# version here. It is the same as the clang version, and
+			# it has been already checked by scripts/cc-version.sh.
+			echo LLVM 0
+			exit 0
+		fi
+		shift
+	done
+}
+
+check_integrated_as "$@"
+
+orig_args="$@"
+
+# Get the first line of the --version output.
+IFS='
+'
+set -- $(LC_ALL=C "$@" -Wa,--version -c -x assembler /dev/null -o /dev/null 2>/dev/null)
+
+# Split the line on spaces.
+IFS=' '
+set -- $1
+
+if [ "$1" = GNU -a "$2" = assembler ]; then
+	shift $(($# - 1))
+	version=$1
+	name=GNU
+else
+	echo "$orig_args: unknown assembler invoked" >&2
+	exit 1
+fi
+
+# Some distributions append a package release number, as in 2.34-4.fc32
+# Trim the hyphen and any characters that follow.
+version=${version%-*}
+
+cversion=$(get_canonical_version $version)
+
+echo $name $cversion
diff --git a/scripts/dummy-tools/gcc b/scripts/dummy-tools/gcc
index 346757a87dbc..485427f40dba 100755
--- a/scripts/dummy-tools/gcc
+++ b/scripts/dummy-tools/gcc
@@ -67,6 +67,12 @@ if arg_contain -E "$@"; then
 	fi
 fi
 
+# To set CONFIG_AS_IS_GNU
+if arg_contain -Wa,--version "$@"; then
+	echo "GNU assembler (scripts/dummy-tools) 2.50"
+	exit 0
+fi
+
 if arg_contain -S "$@"; then
 	# For scripts/gcc-x86-*-has-stack-protector.sh
 	if arg_contain -fstack-protector "$@"; then

-- 
2.40.0

[PATCH 5.10 2/4] kbuild: Switch to 'f' variants of integrated assembler flag

[Nathan Chancellor]

commit 2185a7e4b0ade86c2c57fc63d4a7535c40254bd0 upstream.

It has been brought up a few times in various code reviews that clang
3.5 introduced -f{,no-}integrated-as as the preferred way to enable and
disable the integrated assembler, mentioning that -{no-,}integrated-as
are now considered legacy flags.

Switch the kernel over to using those variants in case there is ever a
time where clang decides to remove the non-'f' variants of the flag.

Also, fix a typo in a comment ("intergrated" -> "integrated").

Link: https://releases.llvm.org/3.5.0/tools/clang/docs/ReleaseNotes.html#new-compiler-flags
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
[nathan: Backport to 5.10]
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 Makefile              | 4 ++--
 scripts/as-version.sh | 8 ++++----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/Makefile b/Makefile
index 44d9aff4f66a..1272e482abbe 100644
--- a/Makefile
+++ b/Makefile
@@ -581,9 +581,9 @@ ifneq ($(GCC_TOOLCHAIN),)
 CLANG_FLAGS	+= --gcc-toolchain=$(GCC_TOOLCHAIN)
 endif
 ifeq ($(LLVM_IAS),1)
-CLANG_FLAGS	+= -integrated-as
+CLANG_FLAGS	+= -fintegrated-as
 else
-CLANG_FLAGS	+= -no-integrated-as
+CLANG_FLAGS	+= -fno-integrated-as
 endif
 CLANG_FLAGS	+= -Werror=unknown-warning-option
 KBUILD_CFLAGS	+= $(CLANG_FLAGS)
diff --git a/scripts/as-version.sh b/scripts/as-version.sh
index 851dcb8a0e68..532270bd4b7e 100755
--- a/scripts/as-version.sh
+++ b/scripts/as-version.sh
@@ -21,14 +21,14 @@ get_canonical_version()
 	echo $((10000 * $1 + 100 * ${2:-0} + ${3:-0}))
 }
 
-# Clang fails to handle -Wa,--version unless -no-integrated-as is given.
-# We check -(f)integrated-as, expecting it is explicitly passed in for the
+# Clang fails to handle -Wa,--version unless -fno-integrated-as is given.
+# We check -fintegrated-as, expecting it is explicitly passed in for the
 # integrated assembler case.
 check_integrated_as()
 {
 	while [ $# -gt 0 ]; do
-		if [ "$1" = -integrated-as -o "$1" = -fintegrated-as ]; then
-			# For the intergrated assembler, we do not check the
+		if [ "$1" = -fintegrated-as ]; then
+			# For the integrated assembler, we do not check the
 			# version here. It is the same as the clang version, and
 			# it has been already checked by scripts/cc-version.sh.
 			echo LLVM 0

-- 
2.40.0

[PATCH 5.10 3/4] kbuild: check CONFIG_AS_IS_LLVM instead of LLVM_IAS

[Nathan Chancellor]

From: Masahiro Yamada <masahiroy@kernel.org>

commit 52cc02b910284d6bddba46cce402044ab775f314 upstream.

LLVM_IAS is the user interface to set the -(no-)integrated-as flag,
and it should be used only for that purpose.

LLVM_IAS is checked in some places to determine the assembler type,
but it is not precise.

For example,

 $ make CC=gcc LLVM_IAS=1

... will use the GNU assembler (i.e. binutils) since LLVM_IAS=1 is
effective only when $(CC) is clang.

Of course, 'CC=gcc LLVM_IAS=1' is an odd combination, but the build
system can be more robust against such insane input.

Commit ba64beb17493a ("kbuild: check the minimum assembler version in
Kconfig") introduced CONFIG_AS_IS_GNU/LLVM, which is more precise
because Kconfig checks the version string from the assembler in use.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
[nathan: Backport to 5.10]
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 Makefile            | 2 +-
 arch/riscv/Makefile | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 1272e482abbe..3dfacb6fa973 100644
--- a/Makefile
+++ b/Makefile
@@ -851,7 +851,7 @@ else
 DEBUG_CFLAGS	+= -g
 endif
 
-ifeq ($(LLVM_IAS),1)
+ifdef CONFIG_AS_IS_LLVM
 KBUILD_AFLAGS	+= -g
 else
 KBUILD_AFLAGS	+= -Wa,-gdwarf-2
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 9446282b52ba..14cdeaa2bb32 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -40,7 +40,7 @@ ifeq ($(CONFIG_LD_IS_LLD),y)
 ifeq ($(shell test $(CONFIG_LLD_VERSION) -lt 150000; echo $$?),0)
 	KBUILD_CFLAGS += -mno-relax
 	KBUILD_AFLAGS += -mno-relax
-ifneq ($(LLVM_IAS),1)
+ifndef CONFIG_AS_IS_LLVM
 	KBUILD_CFLAGS += -Wa,-mno-relax
 	KBUILD_AFLAGS += -Wa,-mno-relax
 endif

-- 
2.40.0

[PATCH 5.10 4/4] riscv: Handle zicsr/zifencei issues between clang and binutils

[Nathan Chancellor]

commit e89c2e815e76471cb507bd95728bf26da7976430 upstream.

There are two related issues that appear in certain combinations with
clang and GNU binutils.

The first occurs when a version of clang that supports zicsr or zifencei
via '-march=' [1] (i.e, >= 17.x) is used in combination with a version
of GNU binutils that do not recognize zicsr and zifencei in the
'-march=' value (i.e., < 2.36):

  riscv64-linux-gnu-ld: -march=rv64i2p0_m2p0_a2p0_c2p0_zicsr2p0_zifencei2p0: Invalid or unknown z ISA extension: 'zifencei'
  riscv64-linux-gnu-ld: failed to merge target specific data of file fs/efivarfs/file.o
  riscv64-linux-gnu-ld: -march=rv64i2p0_m2p0_a2p0_c2p0_zicsr2p0_zifencei2p0: Invalid or unknown z ISA extension: 'zifencei'
  riscv64-linux-gnu-ld: failed to merge target specific data of file fs/efivarfs/super.o

The second occurs when a version of clang that does not support zicsr or
zifencei via '-march=' (i.e., <= 16.x) is used in combination with a
version of GNU as that defaults to a newer ISA base spec, which requires
specifying zicsr and zifencei in the '-march=' value explicitly (i.e, >=
2.38):

  ../arch/riscv/kernel/kexec_relocate.S: Assembler messages:
  ../arch/riscv/kernel/kexec_relocate.S:147: Error: unrecognized opcode `fence.i', extension `zifencei' required
  clang-12: error: assembler command failed with exit code 1 (use -v to see invocation)

This is the same issue addressed by commit 6df2a016c0c8 ("riscv: fix
build with binutils 2.38") (see [2] for additional information) but
older versions of clang miss out on it because the cc-option check
fails:

  clang-12: error: invalid arch name 'rv64imac_zicsr_zifencei', unsupported standard user-level extension 'zicsr'
  clang-12: error: invalid arch name 'rv64imac_zicsr_zifencei', unsupported standard user-level extension 'zicsr'

To resolve the first issue, only attempt to add zicsr and zifencei to
the march string when using the GNU assembler 2.38 or newer, which is
when the default ISA spec was updated, requiring these extensions to be
specified explicitly. LLVM implements an older version of the base
specification for all currently released versions, so these instructions
are available as part of the 'i' extension. If LLVM's implementation is
updated in the future, a CONFIG_AS_IS_LLVM condition can be added to
CONFIG_TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI.

To resolve the second issue, use version 2.2 of the base ISA spec when
using an older version of clang that does not support zicsr or zifencei
via '-march=', as that is the spec version most compatible with the one
clang/LLVM implements and avoids the need to specify zicsr and zifencei
explicitly due to still being a part of 'i'.

[1]: https://github.com/llvm/llvm-project/commit/22e199e6afb1263c943c0c0d4498694e15bf8a16
[2]: https://lore.kernel.org/ZAxT7T9Xy1Fo3d5W@aurel32.net/

Cc: stable@vger.kernel.org
Link: https://github.com/ClangBuiltLinux/linux/issues/1808
Co-developed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230313-riscv-zicsr-zifencei-fiasco-v1-1-dd1b7840a551@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 arch/riscv/Kconfig  | 22 ++++++++++++++++++++++
 arch/riscv/Makefile | 10 ++++++----
 2 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 557c4a8c4087..c192bd7305dc 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -331,6 +331,28 @@ config RISCV_BASE_PMU
 
 endmenu
 
+config TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI
+	def_bool y
+	# https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=aed44286efa8ae8717a77d94b51ac3614e2ca6dc
+	depends on AS_IS_GNU && AS_VERSION >= 23800
+	help
+	  Newer binutils versions default to ISA spec version 20191213 which
+	  moves some instructions from the I extension to the Zicsr and Zifencei
+	  extensions.
+
+config TOOLCHAIN_NEEDS_OLD_ISA_SPEC
+	def_bool y
+	depends on TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI
+	# https://github.com/llvm/llvm-project/commit/22e199e6afb1263c943c0c0d4498694e15bf8a16
+	depends on CC_IS_CLANG && CLANG_VERSION < 170000
+	help
+	  Certain versions of clang do not support zicsr and zifencei via -march
+	  but newer versions of binutils require it for the reasons noted in the
+	  help text of CONFIG_TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI. This
+	  option causes an older ISA spec compatible with these older versions
+	  of clang to be passed to GAS, which has the same result as passing zicsr
+	  and zifencei to -march.
+
 config FPU
 	bool "FPU support"
 	default y
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 14cdeaa2bb32..daa679440000 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -53,10 +53,12 @@ riscv-march-$(CONFIG_ARCH_RV64I)	:= rv64ima
 riscv-march-$(CONFIG_FPU)		:= $(riscv-march-y)fd
 riscv-march-$(CONFIG_RISCV_ISA_C)	:= $(riscv-march-y)c
 
-# Newer binutils versions default to ISA spec version 20191213 which moves some
-# instructions from the I extension to the Zicsr and Zifencei extensions.
-toolchain-need-zicsr-zifencei := $(call cc-option-yn, -march=$(riscv-march-y)_zicsr_zifencei)
-riscv-march-$(toolchain-need-zicsr-zifencei) := $(riscv-march-y)_zicsr_zifencei
+ifdef CONFIG_TOOLCHAIN_NEEDS_OLD_ISA_SPEC
+KBUILD_CFLAGS += -Wa,-misa-spec=2.2
+KBUILD_AFLAGS += -Wa,-misa-spec=2.2
+else
+riscv-march-$(CONFIG_TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI) := $(riscv-march-y)_zicsr_zifencei
+endif
 
 KBUILD_CFLAGS += -march=$(subst fd,,$(riscv-march-y))
 KBUILD_AFLAGS += -march=$(riscv-march-y)

-- 
2.40.0

Re: [PATCH 5.10 0/4] Backport of e89c2e815e76 to linux-5.10.y

[Nathan Chancellor]

Gentle ping, did this get lost?

On Tue, Mar 28, 2023 at 05:08:28PM -0700, Nathan Chancellor wrote:
> Hi all,
> 
> This series is a backport of upstream commit e89c2e815e76 ("riscv:
> Handle zicsr/zifencei issues between clang and binutils") to
> linux-5.10.y, with the necessary machinery for CONFIG_AS_IS_GNU and
> CONFIG_AS_VERSION, which that commit requires.
> 
> While the middle two patches are not strictly necessary, they are good
> clean ups that ensure consistency with mainline. The first three changes
> are already present in 5.15, so there is no risk of a regression moving
> forward.
> 
> If there are any issues, please let me know.
> 
> NOTE: I am sending this series with 'b4 send', as that is what I am used
> to at this point. Please accept my apologies if this causes any issues.
> 
> ---
> Masahiro Yamada (2):
>       kbuild: check the minimum assembler version in Kconfig
>       kbuild: check CONFIG_AS_IS_LLVM instead of LLVM_IAS
> 
> Nathan Chancellor (2):
>       kbuild: Switch to 'f' variants of integrated assembler flag
>       riscv: Handle zicsr/zifencei issues between clang and binutils
> 
>  Makefile                |  8 +++---
>  arch/riscv/Kconfig      | 22 ++++++++++++++++
>  arch/riscv/Makefile     | 12 +++++----
>  init/Kconfig            | 12 +++++++++
>  scripts/Kconfig.include |  6 +++++
>  scripts/as-version.sh   | 69 +++++++++++++++++++++++++++++++++++++++++++++++++
>  scripts/dummy-tools/gcc |  6 +++++
>  7 files changed, 127 insertions(+), 8 deletions(-)
> ---
> base-commit: ca9787bdecfa2174b0a169a54916e22b89b0ef5b
> change-id: 20230328-riscv-zifencei-zicsr-5-10-65596f2cac9e
> 
> Best regards,
> -- 
> Nathan Chancellor <nathan@kernel.org>
> 
> 

Re: [PATCH 5.10 0/4] Backport of e89c2e815e76 to linux-5.10.y

[Greg KH]

On Tue, Apr 11, 2023 at 09:20:01AM -0700, Nathan Chancellor wrote:
> Gentle ping, did this get lost?

Nope, just burried under a raft of other proposed backports.  It's still
in my review queue, will get to it eventually...

thanks,

greg k-h

Re: [PATCH 5.10 0/4] Backport of e89c2e815e76 to linux-5.10.y

[Greg KH]

On Wed, Apr 12, 2023 at 08:17:06AM +0200, Greg KH wrote:
> On Tue, Apr 11, 2023 at 09:20:01AM -0700, Nathan Chancellor wrote:
> > Gentle ping, did this get lost?
> 
> Nope, just burried under a raft of other proposed backports.  It's still
> in my review queue, will get to it eventually...

All now queued up, sorry for the delay.

greg k-h

Patch "kbuild: check CONFIG_AS_IS_LLVM instead of LLVM_IAS" has been added to the 5.10-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    kbuild: check CONFIG_AS_IS_LLVM instead of LLVM_IAS

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kbuild-check-config_as_is_llvm-instead-of-llvm_ias.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From stable-owner@vger.kernel.org Wed Mar 29 02:08:43 2023
From: Nathan Chancellor <nathan@kernel.org>
Date: Tue, 28 Mar 2023 17:08:31 -0700
Subject: kbuild: check CONFIG_AS_IS_LLVM instead of LLVM_IAS
To: gregkh@linuxfoundation.org, sashal@kernel.org
Cc: conor@kernel.org, stable@vger.kernel.org, llvm@lists.linux.dev, Masahiro Yamada <masahiroy@kernel.org>, Nick Desaulniers <ndesaulniers@google.com>, Nathan Chancellor <nathan@kernel.org>
Message-ID: <20230328-riscv-zifencei-zicsr-5-10-v1-3-bccb3e16dc46@kernel.org>

From: Masahiro Yamada <masahiroy@kernel.org>

commit 52cc02b910284d6bddba46cce402044ab775f314 upstream.

LLVM_IAS is the user interface to set the -(no-)integrated-as flag,
and it should be used only for that purpose.

LLVM_IAS is checked in some places to determine the assembler type,
but it is not precise.

For example,

 $ make CC=gcc LLVM_IAS=1

... will use the GNU assembler (i.e. binutils) since LLVM_IAS=1 is
effective only when $(CC) is clang.

Of course, 'CC=gcc LLVM_IAS=1' is an odd combination, but the build
system can be more robust against such insane input.

Commit ba64beb17493a ("kbuild: check the minimum assembler version in
Kconfig") introduced CONFIG_AS_IS_GNU/LLVM, which is more precise
because Kconfig checks the version string from the assembler in use.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
[nathan: Backport to 5.10]
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 Makefile            |    2 +-
 arch/riscv/Makefile |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

--- a/Makefile
+++ b/Makefile
@@ -851,7 +851,7 @@ else
 DEBUG_CFLAGS	+= -g
 endif
 
-ifeq ($(LLVM_IAS),1)
+ifdef CONFIG_AS_IS_LLVM
 KBUILD_AFLAGS	+= -g
 else
 KBUILD_AFLAGS	+= -Wa,-gdwarf-2
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -40,7 +40,7 @@ ifeq ($(CONFIG_LD_IS_LLD),y)
 ifeq ($(shell test $(CONFIG_LLD_VERSION) -lt 150000; echo $$?),0)
 	KBUILD_CFLAGS += -mno-relax
 	KBUILD_AFLAGS += -mno-relax
-ifneq ($(LLVM_IAS),1)
+ifndef CONFIG_AS_IS_LLVM
 	KBUILD_CFLAGS += -Wa,-mno-relax
 	KBUILD_AFLAGS += -Wa,-mno-relax
 endif


Patches currently in stable-queue which might be from stable-owner@vger.kernel.org are

queue-5.10/kbuild-check-the-minimum-assembler-version-in-kconfig.patch
queue-5.10/cgroup-cpuset-make-cpuset_fork-handle-clone_into_cgroup-properly.patch
queue-5.10/kbuild-check-config_as_is_llvm-instead-of-llvm_ias.patch
queue-5.10/riscv-handle-zicsr-zifencei-issues-between-clang-and-binutils.patch
queue-5.10/kbuild-switch-to-f-variants-of-integrated-assembler-flag.patch
queue-5.10/cgroup-cpuset-add-cpuset_can_fork-and-cpuset_cancel_fork-methods.patch
queue-5.10/cgroup-cpuset-change-references-of-cpuset_mutex-to-cpuset_rwsem.patch
queue-5.10/cgroup-cpuset-skip-spread-flags-update-on-v2.patch

Patch "kbuild: check the minimum assembler version in Kconfig" has been added to the 5.10-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    kbuild: check the minimum assembler version in Kconfig

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kbuild-check-the-minimum-assembler-version-in-kconfig.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From stable-owner@vger.kernel.org Wed Mar 29 02:08:38 2023
From: Nathan Chancellor <nathan@kernel.org>
Date: Tue, 28 Mar 2023 17:08:29 -0700
Subject: kbuild: check the minimum assembler version in Kconfig
To: gregkh@linuxfoundation.org, sashal@kernel.org
Cc: conor@kernel.org, stable@vger.kernel.org, llvm@lists.linux.dev, Masahiro Yamada <masahiroy@kernel.org>, Nathan Chancellor <nathan@kernel.org>
Message-ID: <20230328-riscv-zifencei-zicsr-5-10-v1-1-bccb3e16dc46@kernel.org>

From: Masahiro Yamada <masahiroy@kernel.org>

commit ba64beb17493a4bfec563100c86a462a15926f24 upstream.

Documentation/process/changes.rst defines the minimum assembler version
(binutils version), but we have never checked it in the build time.

Kbuild never invokes 'as' directly because all assembly files in the
kernel tree are *.S, hence must be preprocessed. I do not expect
raw assembly source files (*.s) would be added to the kernel tree.

Therefore, we always use $(CC) as the assembler driver, and commit
aa824e0c962b ("kbuild: remove AS variable") removed 'AS'. However,
we are still interested in the version of the assembler acting behind.

As usual, the --version option prints the version string.

  $ as --version | head -n 1
  GNU assembler (GNU Binutils for Ubuntu) 2.35.1

But, we do not have $(AS). So, we can add the -Wa prefix so that
$(CC) passes --version down to the backing assembler.

  $ gcc -Wa,--version | head -n 1
  gcc: fatal error: no input files
  compilation terminated.

OK, we need to input something to satisfy gcc.

  $ gcc -Wa,--version -c -x assembler /dev/null -o /dev/null | head -n 1
  GNU assembler (GNU Binutils for Ubuntu) 2.35.1

The combination of Clang and GNU assembler works in the same way:

  $ clang -no-integrated-as -Wa,--version -c -x assembler /dev/null -o /dev/null | head -n 1
  GNU assembler (GNU Binutils for Ubuntu) 2.35.1

Clang with the integrated assembler fails like this:

  $ clang -integrated-as -Wa,--version -c -x assembler /dev/null -o /dev/null | head -n 1
  clang: error: unsupported argument '--version' to option 'Wa,'

For the last case, checking the error message is fragile. If the
proposal for -Wa,--version support [1] is accepted, this may not be
even an error in the future.

One easy way is to check if -integrated-as is present in the passed
arguments. We did not pass -integrated-as to CLANG_FLAGS before, but
we can make it explicit.

Nathan pointed out -integrated-as is the default for all of the
architectures/targets that the kernel cares about, but it goes
along with "explicit is better than implicit" policy. [2]

With all this in my mind, I implemented scripts/as-version.sh to
check the assembler version in Kconfig time.

  $ scripts/as-version.sh gcc
  GNU 23501
  $ scripts/as-version.sh clang -no-integrated-as
  GNU 23501
  $ scripts/as-version.sh clang -integrated-as
  LLVM 0

[1]: https://github.com/ClangBuiltLinux/linux/issues/1320
[2]: https://lore.kernel.org/linux-kbuild/20210307044253.v3h47ucq6ng25iay@archlinux-ax161/

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
[nathan: Backport to 5.10. Drop minimum version checking, as it is not
         required in 5.10]
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 Makefile                |    4 ++
 init/Kconfig            |   12 ++++++++
 scripts/Kconfig.include |    6 ++++
 scripts/as-version.sh   |   69 ++++++++++++++++++++++++++++++++++++++++++++++++
 scripts/dummy-tools/gcc |    6 ++++
 5 files changed, 96 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 71caf5938361..44d9aff4f66a 100644
--- a/Makefile
+++ b/Makefile
@@ -580,7 +580,9 @@ endif
 ifneq ($(GCC_TOOLCHAIN),)
 CLANG_FLAGS	+= --gcc-toolchain=$(GCC_TOOLCHAIN)
 endif
-ifneq ($(LLVM_IAS),1)
+ifeq ($(LLVM_IAS),1)
+CLANG_FLAGS	+= -integrated-as
+else
 CLANG_FLAGS	+= -no-integrated-as
 endif
 CLANG_FLAGS	+= -Werror=unknown-warning-option
diff --git a/init/Kconfig b/init/Kconfig
index eba883d6d9ed..9807c66b24bb 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -47,6 +47,18 @@ config CLANG_VERSION
 	int
 	default $(shell,$(srctree)/scripts/clang-version.sh $(CC))
 
+config AS_IS_GNU
+	def_bool $(success,test "$(as-name)" = GNU)
+
+config AS_IS_LLVM
+	def_bool $(success,test "$(as-name)" = LLVM)
+
+config AS_VERSION
+	int
+	# Use clang version if this is the integrated assembler
+	default CLANG_VERSION if AS_IS_LLVM
+	default $(as-version)
+
 config LLD_VERSION
 	int
 	default $(shell,$(srctree)/scripts/lld-version.sh $(LD))
diff --git a/scripts/Kconfig.include b/scripts/Kconfig.include
index a5fe72c504ff..6d37cb780452 100644
--- a/scripts/Kconfig.include
+++ b/scripts/Kconfig.include
@@ -42,6 +42,12 @@ $(error-if,$(failure,command -v $(LD)),linker '$(LD)' not found)
 # Fail if the linker is gold as it's not capable of linking the kernel proper
 $(error-if,$(success, $(LD) -v | grep -q gold), gold linker '$(LD)' not supported)
 
+# Get the assembler name, version, and error out if it is not supported.
+as-info := $(shell,$(srctree)/scripts/as-version.sh $(CC) $(CLANG_FLAGS))
+$(error-if,$(success,test -z "$(as-info)"),Sorry$(comma) this assembler is not supported.)
+as-name := $(shell,set -- $(as-info) && echo $1)
+as-version := $(shell,set -- $(as-info) && echo $2)
+
 # machine bit flags
 #  $(m32-flag): -m32 if the compiler supports it, or an empty string otherwise.
 #  $(m64-flag): -m64 if the compiler supports it, or an empty string otherwise.
diff --git a/scripts/as-version.sh b/scripts/as-version.sh
new file mode 100755
index 000000000000..851dcb8a0e68
--- /dev/null
+++ b/scripts/as-version.sh
@@ -0,0 +1,69 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Print the assembler name and its version in a 5 or 6-digit form.
+# Also, perform the minimum version check.
+# (If it is the integrated assembler, return 0 as the version, and
+# skip the version check.)
+
+set -e
+
+# Convert the version string x.y.z to a canonical 5 or 6-digit form.
+get_canonical_version()
+{
+	IFS=.
+	set -- $1
+
+	# If the 2nd or 3rd field is missing, fill it with a zero.
+	#
+	# The 4th field, if present, is ignored.
+	# This occurs in development snapshots as in 2.35.1.20201116
+	echo $((10000 * $1 + 100 * ${2:-0} + ${3:-0}))
+}
+
+# Clang fails to handle -Wa,--version unless -no-integrated-as is given.
+# We check -(f)integrated-as, expecting it is explicitly passed in for the
+# integrated assembler case.
+check_integrated_as()
+{
+	while [ $# -gt 0 ]; do
+		if [ "$1" = -integrated-as -o "$1" = -fintegrated-as ]; then
+			# For the intergrated assembler, we do not check the
+			# version here. It is the same as the clang version, and
+			# it has been already checked by scripts/cc-version.sh.
+			echo LLVM 0
+			exit 0
+		fi
+		shift
+	done
+}
+
+check_integrated_as "$@"
+
+orig_args="$@"
+
+# Get the first line of the --version output.
+IFS='
+'
+set -- $(LC_ALL=C "$@" -Wa,--version -c -x assembler /dev/null -o /dev/null 2>/dev/null)
+
+# Split the line on spaces.
+IFS=' '
+set -- $1
+
+if [ "$1" = GNU -a "$2" = assembler ]; then
+	shift $(($# - 1))
+	version=$1
+	name=GNU
+else
+	echo "$orig_args: unknown assembler invoked" >&2
+	exit 1
+fi
+
+# Some distributions append a package release number, as in 2.34-4.fc32
+# Trim the hyphen and any characters that follow.
+version=${version%-*}
+
+cversion=$(get_canonical_version $version)
+
+echo $name $cversion
diff --git a/scripts/dummy-tools/gcc b/scripts/dummy-tools/gcc
index 346757a87dbc..485427f40dba 100755
--- a/scripts/dummy-tools/gcc
+++ b/scripts/dummy-tools/gcc
@@ -67,6 +67,12 @@ if arg_contain -E "$@"; then
 	fi
 fi
 
+# To set CONFIG_AS_IS_GNU
+if arg_contain -Wa,--version "$@"; then
+	echo "GNU assembler (scripts/dummy-tools) 2.50"
+	exit 0
+fi
+
 if arg_contain -S "$@"; then
 	# For scripts/gcc-x86-*-has-stack-protector.sh
 	if arg_contain -fstack-protector "$@"; then

-- 
2.40.0



Patches currently in stable-queue which might be from stable-owner@vger.kernel.org are

queue-5.10/kbuild-check-the-minimum-assembler-version-in-kconfig.patch
queue-5.10/cgroup-cpuset-make-cpuset_fork-handle-clone_into_cgroup-properly.patch
queue-5.10/kbuild-check-config_as_is_llvm-instead-of-llvm_ias.patch
queue-5.10/riscv-handle-zicsr-zifencei-issues-between-clang-and-binutils.patch
queue-5.10/kbuild-switch-to-f-variants-of-integrated-assembler-flag.patch
queue-5.10/cgroup-cpuset-add-cpuset_can_fork-and-cpuset_cancel_fork-methods.patch
queue-5.10/cgroup-cpuset-change-references-of-cpuset_mutex-to-cpuset_rwsem.patch
queue-5.10/cgroup-cpuset-skip-spread-flags-update-on-v2.patch

Patch "kbuild: Switch to 'f' variants of integrated assembler flag" has been added to the 5.10-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    kbuild: Switch to 'f' variants of integrated assembler flag

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kbuild-switch-to-f-variants-of-integrated-assembler-flag.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From stable-owner@vger.kernel.org Wed Mar 29 02:08:38 2023
From: Nathan Chancellor <nathan@kernel.org>
Date: Tue, 28 Mar 2023 17:08:30 -0700
Subject: kbuild: Switch to 'f' variants of integrated assembler flag
To: gregkh@linuxfoundation.org, sashal@kernel.org
Cc: conor@kernel.org, stable@vger.kernel.org, llvm@lists.linux.dev, Nick Desaulniers <ndesaulniers@google.com>, Nathan Chancellor <nathan@kernel.org>, Masahiro Yamada <masahiroy@kernel.org>
Message-ID: <20230328-riscv-zifencei-zicsr-5-10-v1-2-bccb3e16dc46@kernel.org>

From: Nathan Chancellor <nathan@kernel.org>

commit 2185a7e4b0ade86c2c57fc63d4a7535c40254bd0 upstream.

It has been brought up a few times in various code reviews that clang
3.5 introduced -f{,no-}integrated-as as the preferred way to enable and
disable the integrated assembler, mentioning that -{no-,}integrated-as
are now considered legacy flags.

Switch the kernel over to using those variants in case there is ever a
time where clang decides to remove the non-'f' variants of the flag.

Also, fix a typo in a comment ("intergrated" -> "integrated").

Link: https://releases.llvm.org/3.5.0/tools/clang/docs/ReleaseNotes.html#new-compiler-flags
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
[nathan: Backport to 5.10]
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 Makefile              |    4 ++--
 scripts/as-version.sh |    8 ++++----
 2 files changed, 6 insertions(+), 6 deletions(-)

--- a/Makefile
+++ b/Makefile
@@ -581,9 +581,9 @@ ifneq ($(GCC_TOOLCHAIN),)
 CLANG_FLAGS	+= --gcc-toolchain=$(GCC_TOOLCHAIN)
 endif
 ifeq ($(LLVM_IAS),1)
-CLANG_FLAGS	+= -integrated-as
+CLANG_FLAGS	+= -fintegrated-as
 else
-CLANG_FLAGS	+= -no-integrated-as
+CLANG_FLAGS	+= -fno-integrated-as
 endif
 CLANG_FLAGS	+= -Werror=unknown-warning-option
 KBUILD_CFLAGS	+= $(CLANG_FLAGS)
--- a/scripts/as-version.sh
+++ b/scripts/as-version.sh
@@ -21,14 +21,14 @@ get_canonical_version()
 	echo $((10000 * $1 + 100 * ${2:-0} + ${3:-0}))
 }
 
-# Clang fails to handle -Wa,--version unless -no-integrated-as is given.
-# We check -(f)integrated-as, expecting it is explicitly passed in for the
+# Clang fails to handle -Wa,--version unless -fno-integrated-as is given.
+# We check -fintegrated-as, expecting it is explicitly passed in for the
 # integrated assembler case.
 check_integrated_as()
 {
 	while [ $# -gt 0 ]; do
-		if [ "$1" = -integrated-as -o "$1" = -fintegrated-as ]; then
-			# For the intergrated assembler, we do not check the
+		if [ "$1" = -fintegrated-as ]; then
+			# For the integrated assembler, we do not check the
 			# version here. It is the same as the clang version, and
 			# it has been already checked by scripts/cc-version.sh.
 			echo LLVM 0


Patches currently in stable-queue which might be from stable-owner@vger.kernel.org are

queue-5.10/kbuild-check-the-minimum-assembler-version-in-kconfig.patch
queue-5.10/cgroup-cpuset-make-cpuset_fork-handle-clone_into_cgroup-properly.patch
queue-5.10/kbuild-check-config_as_is_llvm-instead-of-llvm_ias.patch
queue-5.10/riscv-handle-zicsr-zifencei-issues-between-clang-and-binutils.patch
queue-5.10/kbuild-switch-to-f-variants-of-integrated-assembler-flag.patch
queue-5.10/cgroup-cpuset-add-cpuset_can_fork-and-cpuset_cancel_fork-methods.patch
queue-5.10/cgroup-cpuset-change-references-of-cpuset_mutex-to-cpuset_rwsem.patch
queue-5.10/cgroup-cpuset-skip-spread-flags-update-on-v2.patch

Patch "riscv: Handle zicsr/zifencei issues between clang and binutils" has been added to the 5.10-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    riscv: Handle zicsr/zifencei issues between clang and binutils

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     riscv-handle-zicsr-zifencei-issues-between-clang-and-binutils.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From stable-owner@vger.kernel.org Wed Mar 29 02:08:41 2023
From: Nathan Chancellor <nathan@kernel.org>
Date: Tue, 28 Mar 2023 17:08:32 -0700
Subject: riscv: Handle zicsr/zifencei issues between clang and binutils
To: gregkh@linuxfoundation.org, sashal@kernel.org
Cc: conor@kernel.org, stable@vger.kernel.org, llvm@lists.linux.dev, Conor Dooley <conor.dooley@microchip.com>, Nathan Chancellor <nathan@kernel.org>, Palmer Dabbelt <palmer@rivosinc.com>
Message-ID: <20230328-riscv-zifencei-zicsr-5-10-v1-4-bccb3e16dc46@kernel.org>

From: Nathan Chancellor <nathan@kernel.org>

commit e89c2e815e76471cb507bd95728bf26da7976430 upstream.

There are two related issues that appear in certain combinations with
clang and GNU binutils.

The first occurs when a version of clang that supports zicsr or zifencei
via '-march=' [1] (i.e, >= 17.x) is used in combination with a version
of GNU binutils that do not recognize zicsr and zifencei in the
'-march=' value (i.e., < 2.36):

  riscv64-linux-gnu-ld: -march=rv64i2p0_m2p0_a2p0_c2p0_zicsr2p0_zifencei2p0: Invalid or unknown z ISA extension: 'zifencei'
  riscv64-linux-gnu-ld: failed to merge target specific data of file fs/efivarfs/file.o
  riscv64-linux-gnu-ld: -march=rv64i2p0_m2p0_a2p0_c2p0_zicsr2p0_zifencei2p0: Invalid or unknown z ISA extension: 'zifencei'
  riscv64-linux-gnu-ld: failed to merge target specific data of file fs/efivarfs/super.o

The second occurs when a version of clang that does not support zicsr or
zifencei via '-march=' (i.e., <= 16.x) is used in combination with a
version of GNU as that defaults to a newer ISA base spec, which requires
specifying zicsr and zifencei in the '-march=' value explicitly (i.e, >=
2.38):

  ../arch/riscv/kernel/kexec_relocate.S: Assembler messages:
  ../arch/riscv/kernel/kexec_relocate.S:147: Error: unrecognized opcode `fence.i', extension `zifencei' required
  clang-12: error: assembler command failed with exit code 1 (use -v to see invocation)

This is the same issue addressed by commit 6df2a016c0c8 ("riscv: fix
build with binutils 2.38") (see [2] for additional information) but
older versions of clang miss out on it because the cc-option check
fails:

  clang-12: error: invalid arch name 'rv64imac_zicsr_zifencei', unsupported standard user-level extension 'zicsr'
  clang-12: error: invalid arch name 'rv64imac_zicsr_zifencei', unsupported standard user-level extension 'zicsr'

To resolve the first issue, only attempt to add zicsr and zifencei to
the march string when using the GNU assembler 2.38 or newer, which is
when the default ISA spec was updated, requiring these extensions to be
specified explicitly. LLVM implements an older version of the base
specification for all currently released versions, so these instructions
are available as part of the 'i' extension. If LLVM's implementation is
updated in the future, a CONFIG_AS_IS_LLVM condition can be added to
CONFIG_TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI.

To resolve the second issue, use version 2.2 of the base ISA spec when
using an older version of clang that does not support zicsr or zifencei
via '-march=', as that is the spec version most compatible with the one
clang/LLVM implements and avoids the need to specify zicsr and zifencei
explicitly due to still being a part of 'i'.

[1]: https://github.com/llvm/llvm-project/commit/22e199e6afb1263c943c0c0d4498694e15bf8a16
[2]: https://lore.kernel.org/ZAxT7T9Xy1Fo3d5W@aurel32.net/

Cc: stable@vger.kernel.org
Link: https://github.com/ClangBuiltLinux/linux/issues/1808
Co-developed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230313-riscv-zicsr-zifencei-fiasco-v1-1-dd1b7840a551@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/riscv/Kconfig  |   22 ++++++++++++++++++++++
 arch/riscv/Makefile |   10 ++++++----
 2 files changed, 28 insertions(+), 4 deletions(-)

--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -331,6 +331,28 @@ config RISCV_BASE_PMU
 
 endmenu
 
+config TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI
+	def_bool y
+	# https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=aed44286efa8ae8717a77d94b51ac3614e2ca6dc
+	depends on AS_IS_GNU && AS_VERSION >= 23800
+	help
+	  Newer binutils versions default to ISA spec version 20191213 which
+	  moves some instructions from the I extension to the Zicsr and Zifencei
+	  extensions.
+
+config TOOLCHAIN_NEEDS_OLD_ISA_SPEC
+	def_bool y
+	depends on TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI
+	# https://github.com/llvm/llvm-project/commit/22e199e6afb1263c943c0c0d4498694e15bf8a16
+	depends on CC_IS_CLANG && CLANG_VERSION < 170000
+	help
+	  Certain versions of clang do not support zicsr and zifencei via -march
+	  but newer versions of binutils require it for the reasons noted in the
+	  help text of CONFIG_TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI. This
+	  option causes an older ISA spec compatible with these older versions
+	  of clang to be passed to GAS, which has the same result as passing zicsr
+	  and zifencei to -march.
+
 config FPU
 	bool "FPU support"
 	default y
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -53,10 +53,12 @@ riscv-march-$(CONFIG_ARCH_RV64I)	:= rv64
 riscv-march-$(CONFIG_FPU)		:= $(riscv-march-y)fd
 riscv-march-$(CONFIG_RISCV_ISA_C)	:= $(riscv-march-y)c
 
-# Newer binutils versions default to ISA spec version 20191213 which moves some
-# instructions from the I extension to the Zicsr and Zifencei extensions.
-toolchain-need-zicsr-zifencei := $(call cc-option-yn, -march=$(riscv-march-y)_zicsr_zifencei)
-riscv-march-$(toolchain-need-zicsr-zifencei) := $(riscv-march-y)_zicsr_zifencei
+ifdef CONFIG_TOOLCHAIN_NEEDS_OLD_ISA_SPEC
+KBUILD_CFLAGS += -Wa,-misa-spec=2.2
+KBUILD_AFLAGS += -Wa,-misa-spec=2.2
+else
+riscv-march-$(CONFIG_TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI) := $(riscv-march-y)_zicsr_zifencei
+endif
 
 KBUILD_CFLAGS += -march=$(subst fd,,$(riscv-march-y))
 KBUILD_AFLAGS += -march=$(riscv-march-y)


Patches currently in stable-queue which might be from stable-owner@vger.kernel.org are

queue-5.10/kbuild-check-the-minimum-assembler-version-in-kconfig.patch
queue-5.10/cgroup-cpuset-make-cpuset_fork-handle-clone_into_cgroup-properly.patch
queue-5.10/kbuild-check-config_as_is_llvm-instead-of-llvm_ias.patch
queue-5.10/riscv-handle-zicsr-zifencei-issues-between-clang-and-binutils.patch
queue-5.10/kbuild-switch-to-f-variants-of-integrated-assembler-flag.patch
queue-5.10/cgroup-cpuset-add-cpuset_can_fork-and-cpuset_cancel_fork-methods.patch
queue-5.10/cgroup-cpuset-change-references-of-cpuset_mutex-to-cpuset_rwsem.patch
queue-5.10/cgroup-cpuset-skip-spread-flags-update-on-v2.patch

Re: [PATCH 5.10 0/4] Backport of e89c2e815e76 to linux-5.10.y

[Nathan Chancellor]

On Tue, Apr 18, 2023 at 11:46:56AM +0200, Greg KH wrote:
> On Wed, Apr 12, 2023 at 08:17:06AM +0200, Greg KH wrote:
> > On Tue, Apr 11, 2023 at 09:20:01AM -0700, Nathan Chancellor wrote:
> > > Gentle ping, did this get lost?
> > 
> > Nope, just burried under a raft of other proposed backports.  It's still
> > in my review queue, will get to it eventually...
> 
> All now queued up, sorry for the delay.

Thanks a lot, I will take later over never :)

Cheers
Nathan