Date:   Thu, 14 Jan 2021 10:07:10 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Will Deacon <will@...nel.org>,
        clang-built-linux@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] kbuild: check the minimum compiler version in Kconfig

On Thu, Jan 14, 2021 at 01:24:19PM +0900, Masahiro Yamada wrote:
> 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 similar two scripts, gcc-version.sh and clang-version.sh
> into the new 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
> 
> The cc-version.sh also shows the error if the compiler is 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 unsupported.
>   make[1]: *** [scripts/kconfig/Makefile:81: defconfig] Error 1
>   make: *** [Makefile:602: defconfig] Error 2
> 
> I removed the clang version check from <linux/compiler-clang.h>
> 
> For now, I did not touch <linux/compiler-gcc.h> in order to avoid
> merge conflict with [3], which has been queued up in the arm64 tree.
> We will be able to clean it up later.
> 
> I put the stub for ICC because I see <linux/compiler-intel.h> although
> I am not sure if building the kernel with ICC is well-supported.
> 
> [1] https://lkml.org/lkml/2021/1/10/250
> [2] https://lkml.org/lkml/2021/1/12/1708
> [3] https://lkml.org/lkml/2021/1/12/1533

I would recommend the lore version of these links:

[1]: https://lore.kernel.org/r/20210110190807.134996-1-paul.gortmaker@windriver.com
[2]: https://lore.kernel.org/r/CAHk-=wh-+TMHPTFo1qs-MYyK7tZh-OQovA=pP3=e06aCVp6_kA@mail.gmail.com
[3]: https://lore.kernel.org/r/20210112224832.10980-1-will@kernel.org

> Fixes: 87de84c9140e ("kbuild: remove cc-option test of -Werror=date-time")
> Reported-by: Paul Gortmaker <paul.gortmaker@...driver.com>
> Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

I like this a lot, I think that erroring as early as possible when
something is misconfigured is a good user experience.

Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
Tested-by: Nathan Chancellor <natechancellor@...il.com>

> ---
> 
> Changes in v2:
>   - fix the function name
> 
>  include/linux/compiler-clang.h | 10 -----
>  init/Kconfig                   |  9 +++--
>  scripts/Kconfig.include        |  6 +++
>  scripts/cc-version.sh          | 69 ++++++++++++++++++++++++++++++++++
>  scripts/clang-version.sh       | 19 ----------
>  scripts/gcc-version.sh         | 20 ----------
>  6 files changed, 80 insertions(+), 53 deletions(-)
>  create mode 100755 scripts/cc-version.sh
>  delete mode 100755 scripts/clang-version.sh
>  delete mode 100755 scripts/gcc-version.sh
> 
> diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
> index 98cff1b4b088..04c0a5a717f7 100644
> --- a/include/linux/compiler-clang.h
> +++ 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
> diff --git a/init/Kconfig b/init/Kconfig
> index b77c60f8b963..01108dd1318b 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -26,11 +26,11 @@ 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
> @@ -38,14 +38,15 @@ config LD_VERSION
>  	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
> diff --git a/scripts/Kconfig.include b/scripts/Kconfig.include
> index a5fe72c504ff..cdc8726d2904 100644
> --- a/scripts/Kconfig.include
> +++ b/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 unsupported.
> +cc-info := $(shell,scripts/cc-version.sh $(CC))
> +$(error-if,$(success,test -z "$(cc-info)"),Sorry$(comma) this compiler is unsupported.)
> +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)
>  
> diff --git a/scripts/cc-version.sh b/scripts/cc-version.sh
> new file mode 100755
> index 000000000000..9c17c1de401c
> --- /dev/null
> +++ b/scripts/cc-version.sh
> @@ -0,0 +1,69 @@
> +#!/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 compiler version, please update
> +# Documentation/process/changes.rst as well.
> +gcc_min_version=4.9.0
> +clang_min_version=10.0.1
> +
> +# print the compiler name, major version, minor version, patchlevel version
> +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)
> +	/* How to get the version of intel compiler? */
> +	ICC	0		0		0
> +	#elif defined(__GNUC__)
> +	GCC	__GNUC__	__GNUC_MINOR__	__GNUC_PATCHLEVEL__
> +	#else
> +	unsupported	0		0		0
> +	#endif
> +	EOF
> +}
> +
> +# convert the version to a canonical 5 or 6-digit form for numerical comparison
> +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
> +version=$2.$3.$4
> +
> +case "$name" in
> +GCC) min_version=$gcc_min_version;;
> +Clang) min_version=$clang_min_version;;
> +ICC) ;; # ICC min version undefined?
> +*) echo "$orig_args: unknown compiler" >&2; exit 1;;
> +esac
> +
> +cversion=$(get_canonical_version $version)
> +
> +if [ -n "$min_version" ]; then
> +
> +	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
> +fi
> +
> +echo $name $cversion
> diff --git a/scripts/clang-version.sh b/scripts/clang-version.sh
> deleted file mode 100755
> index 6fabf0695761..000000000000
> --- a/scripts/clang-version.sh
> +++ /dev/null
> @@ -1,19 +0,0 @@
> -#!/bin/sh
> -# SPDX-License-Identifier: GPL-2.0
> -#
> -# clang-version clang-command
> -#
> -# Print the compiler version of `clang-command' in a 5 or 6-digit form
> -# such as `50001' for clang-5.0.1 etc.
> -
> -compiler="$*"
> -
> -if ! ( $compiler --version | grep -q clang) ; then
> -	echo 0
> -	exit 1
> -fi
> -
> -MAJOR=$(echo __clang_major__ | $compiler -E -x c - | tail -n 1)
> -MINOR=$(echo __clang_minor__ | $compiler -E -x c - | tail -n 1)
> -PATCHLEVEL=$(echo __clang_patchlevel__ | $compiler -E -x c - | tail -n 1)
> -printf "%d%02d%02d\\n" $MAJOR $MINOR $PATCHLEVEL
> diff --git a/scripts/gcc-version.sh b/scripts/gcc-version.sh
> deleted file mode 100755
> index ae353432539b..000000000000
> --- a/scripts/gcc-version.sh
> +++ /dev/null
> @@ -1,20 +0,0 @@
> -#!/bin/sh
> -# SPDX-License-Identifier: GPL-2.0
> -#
> -# gcc-version gcc-command
> -#
> -# Print the gcc version of `gcc-command' in a 5 or 6-digit form
> -# such as `29503' for gcc-2.95.3, `30301' for gcc-3.3.1, etc.
> -
> -compiler="$*"
> -
> -if [ ${#compiler} -eq 0 ]; then
> -	echo "Error: No compiler specified." >&2
> -	printf "Usage:\n\t$0 <gcc-command>\n" >&2
> -	exit 1
> -fi
> -
> -MAJOR=$(echo __GNUC__ | $compiler -E -x c - | tail -n 1)
> -MINOR=$(echo __GNUC_MINOR__ | $compiler -E -x c - | tail -n 1)
> -PATCHLEVEL=$(echo __GNUC_PATCHLEVEL__ | $compiler -E -x c - | tail -n 1)
> -printf "%d%02d%02d\\n" $MAJOR $MINOR $PATCHLEVEL
> -- 
> 2.27.0
> 

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