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@archlin...

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

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