[PATCH 3/4] kbuild: check the minimum assembler version in Kconfig

[Masahiro Yamada <masahiroy@kernel.org>]

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 sitting 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,'

With all this in my mind, I implemented scripts/as-version.sh.

  $ 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

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

 arch/Kconfig            |  3 +-
 init/Kconfig            | 12 +++++++
 scripts/Kconfig.include |  6 ++++
 scripts/as-version.sh   | 77 +++++++++++++++++++++++++++++++++++++++++
 4 files changed, 96 insertions(+), 2 deletions(-)
 create mode 100755 scripts/as-version.sh

diff --git a/arch/Kconfig b/arch/Kconfig
index 2af10ebe5ed0..d7214f4ae1f7 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -631,8 +631,7 @@ config ARCH_SUPPORTS_LTO_CLANG_THIN
 config HAS_LTO_CLANG
 	def_bool y
 	# Clang >= 11: https://github.com/ClangBuiltLinux/linux/issues/510
-	depends on CC_IS_CLANG && CLANG_VERSION >= 110000 && LD_IS_LLD
-	depends on $(success,test $(LLVM_IAS) -eq 1)
+	depends on CC_IS_CLANG && CLANG_VERSION >= 110000 && LD_IS_LLD && AS_IS_LLVM
 	depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm)
 	depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
 	depends on ARCH_SUPPORTS_LTO_CLANG
diff --git a/init/Kconfig b/init/Kconfig
index 22946fe5ded9..f76e5a44e4fe 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -41,6 +41,18 @@ config CLANG_VERSION
 	default $(cc-version) if CC_IS_CLANG
 	default 0
 
+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
+	# If it is integrated assembler, the version is the same as Clang's one.
+	default CLANG_VERSION if AS_IS_LLVM
+	default $(as-version)
+
 config LD_IS_BFD
 	def_bool $(success,test "$(ld-name)" = BFD)
 
diff --git a/scripts/Kconfig.include b/scripts/Kconfig.include
index 58fdb5308725..0496efd6e117 100644
--- a/scripts/Kconfig.include
+++ b/scripts/Kconfig.include
@@ -45,6 +45,12 @@ $(error-if,$(success,test -z "$(cc-info)"),Sorry$(comma) this compiler is not su
 cc-name := $(shell,set -- $(cc-info) && echo $1)
 cc-version := $(shell,set -- $(cc-info) && echo $2)
 
+# 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)
+
 # Get the linker name, version, and error out if it is not supported.
 ld-info := $(shell,$(srctree)/scripts/ld-version.sh $(LD))
 $(error-if,$(success,test -z "$(ld-info)"),Sorry$(comma) this linker is not supported.)
diff --git a/scripts/as-version.sh b/scripts/as-version.sh
new file mode 100755
index 000000000000..205d8b9fc4d4
--- /dev/null
+++ b/scripts/as-version.sh
@@ -0,0 +1,77 @@
+#!/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
+# the version check is skipped.)
+
+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} + ${3:-0}))
+}
+
+orig_args="$@"
+
+# Get the first line of the --version output.
+IFS='
+'
+# Add 2>&1 to check both stdout and stderr.
+# If the backing assembler is binutils, we get the version string in stdout.
+# If it is clang's integrated assembler, we get the following error in stderr:
+#   clang: error: unsupported argument '--version' to option 'Wa,'
+# To avoid the error message affected by locale, set LC_MESSAGES=C just in case.
+set -- $(LC_MESSAGES=C "$@" -Wno-unused-command-line-argument -Wa,--version -c -x assembler /dev/null -o /dev/null 2>&1)
+line="$1"
+
+if [ "$line" = "clang: error: unsupported argument '--version' to option 'Wa,'" ]; 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
+
+# Split the line on spaces.
+IFS=' '
+set -- $line
+
+tool_version=$(dirname $0)/tool-version.sh
+
+if [ "$1" = GNU -a "$2" = assembler ]; then
+	shift $(($# - 1))
+	version=$1
+	min_version=$($tool_version binutils)
+	name=GNU
+else
+	echo "$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 $version)
+min_cversion=$(get_canonical_version $min_version)
+
+if [ "$cversion" -lt "$min_cversion" ]; then
+	echo >&2 "***"
+	echo >&2 "*** Assembler is too old."
+	echo >&2 "***   Your $name assembler version:    $version"
+	echo >&2 "***   Minimum $name assembler version: $min_version"
+	echo >&2 "***"
+	exit 1
+fi
+
+echo $name $cversion
-- 
2.27.0