kbuild: check the minimum compiler version in Kconfig

Paul Gortmaker reported a regression in the GCC version check. [1]
If you use GCC 4.8, the build breaks before showing the error message
"error Sorry, your version of GCC is too old - please use 4.9 or newer."

I do not want to apply his fix-up since it implies we would not be able
to remove any cc-option test. Anyway, I admit checking the GCC version
in <linux/compiler-gcc.h> is too late.

Almost at the same time, Linus also suggested to move the compiler
version error to Kconfig time. [2]

I unified the two similar scripts, gcc-version.sh and clang-version.sh
into cc-version.sh. The old scripts invoked the compiler multiple times
(3 times for gcc-version.sh, 4 times for clang-version.sh). I refactored
the code so the new one invokes the compiler just once, and also tried
my best to use shell-builtin commands where possible.

The new script runs faster.

  $ time ./scripts/clang-version.sh clang
  120000

  real    0m0.029s
  user    0m0.012s
  sys     0m0.021s

  $ time ./scripts/cc-version.sh clang
  Clang 120000

  real    0m0.009s
  user    0m0.006s
  sys     0m0.004s

cc-version.sh also shows an error message if the compiler is too old:

  $ make defconfig CC=clang-9
  *** Default configuration is based on 'x86_64_defconfig'
  ***
  *** Compiler is too old.
  ***   Your Clang version:    9.0.1
  ***   Minimum Clang version: 10.0.1
  ***
  scripts/Kconfig.include:46: Sorry, this compiler is not supported.
  make[1]: *** [scripts/kconfig/Makefile:81: defconfig] Error 1
  make: *** [Makefile:602: defconfig] Error 2

The new script takes care of ICC because we have <linux/compiler-intel.h>
although I am not sure if building the kernel with ICC is well-supported.

[1]: https://lore.kernel.org/r/[email protected]
[2]: https://lore.kernel.org/r/CAHk-=wh-+TMHPTFo1qs-MYyK7tZh-OQovA=pP3=e06aCVp6_kA@mail.gmail.com

Fixes: 87de84c ("kbuild: remove cc-option test of -Werror=date-time")
Reported-by: Paul Gortmaker <[email protected]>
Suggested-by: Linus Torvalds <[email protected]>
Reviewed-by: Nick Desaulniers <[email protected]>
Tested-by: Nick Desaulniers <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
Tested-by: Nathan Chancellor <[email protected]>
Reviewed-by: Miguel Ojeda <[email protected]>
Tested-by: Miguel Ojeda <[email protected]>
Tested-by: Sedat Dilek <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>

MAINTAINERS

@@ -4314,7 +4314,6 @@ C:	irc://chat.freenode.net/clangbuiltlinux
 F:	Documentation/kbuild/llvm.rst
 F:	include/linux/compiler-clang.h
 F:	scripts/clang-tools/
-F:	scripts/clang-version.sh
 F:	scripts/lld-version.sh
 K:	\b(?i:clang|llvm)\b
 

include/linux/compiler-clang.h

@@ -3,16 +3,6 @@
 #error "Please don't include <linux/compiler-clang.h> directly, include <linux/compiler.h> instead."
 #endif
 
-#define CLANG_VERSION (__clang_major__ * 10000	\
-		     + __clang_minor__ * 100	\
-		     + __clang_patchlevel__)
-
-#if CLANG_VERSION < 100001
-#ifndef __BPF_TRACING__
-# error Sorry, your version of Clang is too old - please use 10.0.1 or newer.
-#endif
-#endif
-
 /* Compiler specific definitions for Clang compiler */
 
 /* same as gcc, this was present in clang-2.6 so we can assume it works

include/linux/compiler-gcc.h

@@ -10,17 +10,6 @@
 		     + __GNUC_MINOR__ * 100	\
 		     + __GNUC_PATCHLEVEL__)
 
-/* https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 */
-#if GCC_VERSION < 40900
-# error Sorry, your version of GCC is too old - please use 4.9 or newer.
-#elif defined(CONFIG_ARM64) && GCC_VERSION < 50100
-/*
- * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63293
- * https://lore.kernel.org/r/[email protected]
- */
-# error Sorry, your version of GCC is too old - please use 5.1 or newer.
-#endif
-
 /*
  * This macro obfuscates arithmetic on a variable address so that gcc
  * shouldn't recognize the original var, and make assumptions about it.

init/Kconfig

@@ -26,26 +26,27 @@ config CC_VERSION_TEXT
 	    and then every file will be rebuilt.
 
 config CC_IS_GCC
-	def_bool $(success,echo "$(CC_VERSION_TEXT)" | grep -q gcc)
+	def_bool $(success,test "$(cc-name)" = GCC)
 
 config GCC_VERSION
 	int
-	default $(shell,$(srctree)/scripts/gcc-version.sh $(CC)) if CC_IS_GCC
+	default $(cc-version) if CC_IS_GCC
 	default 0
 
 config LD_VERSION
 	int
 	default $(shell,$(LD) --version | $(srctree)/scripts/ld-version.sh)
 
 config CC_IS_CLANG
-	def_bool $(success,echo "$(CC_VERSION_TEXT)" | grep -q clang)
+	def_bool $(success,test "$(cc-name)" = Clang)
 
 config LD_IS_LLD
 	def_bool $(success,$(LD) -v | head -n 1 | grep -q LLD)
 
 config CLANG_VERSION
 	int
-	default $(shell,$(srctree)/scripts/clang-version.sh $(CC))
+	default $(cc-version) if CC_IS_CLANG
+	default 0
 
 config LLD_VERSION
 	int

scripts/Kconfig.include

@@ -39,6 +39,12 @@ as-instr = $(success,printf "%b\n" "$(1)" | $(CC) $(CLANG_FLAGS) -c -x assembler
 $(error-if,$(failure,command -v $(CC)),compiler '$(CC)' not found)
 $(error-if,$(failure,command -v $(LD)),linker '$(LD)' not found)
 
+# Get the compiler name, version, and error out if it is not supported.
+cc-info := $(shell,$(srctree)/scripts/cc-version.sh $(CC))
+$(error-if,$(success,test -z "$(cc-info)"),Sorry$(comma) this compiler is not supported.)
+cc-name := $(shell,set -- $(cc-info) && echo $1)
+cc-version := $(shell,set -- $(cc-info) && echo $2)
+
 # 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)
 

scripts/cc-version.sh

@@ -0,0 +1,82 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# Print the compiler name and its version in a 5 or 6-digit form.
+# Also, perform the minimum version check.
+
+set -e
+
+# When you raise the minimum compiler version, please update
+# Documentation/process/changes.rst as well.
+gcc_min_version=4.9.0
+clang_min_version=10.0.1
+icc_min_version=16.0.3 # temporary
+
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63293
+# https://lore.kernel.org/r/[email protected]
+if [ "$SRCARCH" = arm64 ]; then
+	gcc_min_version=5.1.0
+fi
+
+# Print the compiler name and some version components.
+get_compiler_info()
+{
+	cat <<- EOF | "$@" -E -P -x c - 2>/dev/null
+	#if defined(__clang__)
+	Clang	__clang_major__  __clang_minor__  __clang_patchlevel__
+	#elif defined(__INTEL_COMPILER)
+	ICC	__INTEL_COMPILER  __INTEL_COMPILER_UPDATE
+	#elif defined(__GNUC__)
+	GCC	__GNUC__  __GNUC_MINOR__  __GNUC_PATCHLEVEL__
+	#else
+	unknown
+	#endif
+	EOF
+}
+
+# Convert the version string x.y.z to a canonical 5 or 6-digit form.
+get_canonical_version()
+{
+	IFS=.
+	set -- $1
+	echo $((10000 * $1 + 100 * $2 + $3))
+}
+
+# $@ instead of $1 because multiple words might be given, e.g. CC="ccache gcc".
+orig_args="$@"
+set -- $(get_compiler_info "$@")
+
+name=$1
+
+case "$name" in
+GCC)
+	version=$2.$3.$4
+	min_version=$gcc_min_version
+	;;
+Clang)
+	version=$2.$3.$4
+	min_version=$clang_min_version
+	;;
+ICC)
+	version=$(($2 / 100)).$(($2 % 100)).$3
+	min_version=$icc_min_version
+	;;
+*)
+	echo "$orig_args: unknown compiler" >&2
+	exit 1
+	;;
+esac
+
+cversion=$(get_canonical_version $version)
+min_cversion=$(get_canonical_version $min_version)
+
+if [ "$cversion" -lt "$min_cversion" ]; then
+	echo >&2 "***"
+	echo >&2 "*** Compiler is too old."
+	echo >&2 "***   Your $name version:    $version"
+	echo >&2 "***   Minimum $name version: $min_version"
+	echo >&2 "***"
+	exit 1
+fi
+
+echo $name $cversion