kbuild: add dummy toolchains to enable all cc-option etc. in Kconfig

Staring v4.18, Kconfig evaluates compiler capabilities, and hides CONFIG
options your compiler does not support. This works well if you configure
and build the kernel on the same host machine.

It is inconvenient if you prepare the .config that is carried to a
different build environment (typically this happens when you package
the kernel for distros) because using a different compiler potentially
produces different CONFIG options than the real build environment.
So, you probably want to make as many options visible as possible.
In other words, you need to create a super-set of CONFIG options that
cover any build environment. If some of the CONFIG options turned out
to be unsupported on the build machine, they are automatically disabled
by the nature of Kconfig.

However, it is not feasible to get a full-featured compiler for every
arch.

This issue was discussed here:

https://lkml.org/lkml/2019/12/9/620

Other than distros, savedefconfig is also a problem. Some arch sub-systems
periodically resync defconfig files. If you use a less-capable compiler
for savedefconfig, options that do not meet 'depends on $(cc-option,...)'
will be forcibly disabled. So, 'make defconfig && make savedefconfig'
may silently change the behavior.

This commit adds a set of dummy toolchains that pretend to support any
feature.

Most of compiler features are tested by cc-option, which simply checks
the exit code of $(CC). The dummy tools are shell scripts that always
exit with 0. So, $(cc-option, ...) is evaluated as 'y'.

There are more complicated checks such as:

scripts/gcc-x86_{32,64}-has-stack-protector.sh
scripts/gcc-plugin.sh
scripts/tools-support-relr.sh

scripts/dummy-tools/gcc passes all checks.

From the top directory of the source tree, you can do:

$ make CROSS_COMPILE=scripts/dummy-tools/ oldconfig

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Philipp Rudo <prudo@linux.ibm.com>
Tested-by: Jeremy Cline <jcline@redhat.com>

Masahiro Yamada 6 years ago 76426e23 7273ad2b

+121

2 changed files

expand all

scripts

dummy-tools

gcc

+91

scripts/dummy-tools/gcc

··· 1 + #!/bin/sh 2 + # SPDX-License-Identifier: GPL-2.0-only 3 + # 4 + # Staring v4.18, Kconfig evaluates compiler capabilities, and hides CONFIG 5 + # options your compiler does not support. This works well if you configure and 6 + # build the kernel on the same host machine. 7 + # 8 + # It is inconvenient if you prepare the .config that is carried to a different 9 + # build environment (typically this happens when you package the kernel for 10 + # distros) because using a different compiler potentially produces different 11 + # CONFIG options than the real build environment. So, you probably want to make 12 + # as many options visible as possible. In other words, you need to create a 13 + # super-set of CONFIG options that cover any build environment. If some of the 14 + # CONFIG options turned out to be unsupported on the build machine, they are 15 + # automatically disabled by the nature of Kconfig. 16 + # 17 + # However, it is not feasible to get a full-featured compiler for every arch. 18 + # Hence these dummy toolchains to make all compiler tests pass. 19 + # 20 + # Usage: 21 + # 22 + # From the top directory of the source tree, run 23 + # 24 + # $ make CROSS_COMPILE=scripts/dummy-tools/ oldconfig 25 + # 26 + # Most of compiler features are tested by cc-option, which simply checks the 27 + # exit code of $(CC). This script does nothing and just exits with 0 in most 28 + # cases. So, $(cc-option, ...) is evaluated as 'y'. 29 + # 30 + # This scripts caters to more checks; handle --version and pre-process __GNUC__ 31 + # etc. to pretend to be GCC, and also do right things to satisfy some scripts. 32 + 33 + # Check if the first parameter appears in the rest. Succeeds if found. 34 + # This helper is useful if a particular option was passed to this script. 35 + # Typically used like this: 36 + # arg_contain <word-you-are-searching-for> "$@" 37 + arg_contain () 38 + { 39 + search="$1" 40 + shift 41 + 42 + while [ $# -gt 0 ] 43 + do 44 + if [ "$search" = "$1" ]; then 45 + return 0 46 + fi 47 + shift 48 + done 49 + 50 + return 1 51 + } 52 + 53 + # To set CONFIG_CC_IS_GCC=y 54 + if arg_contain --version "$@"; then 55 + echo "gcc (scripts/dummy-tools/gcc)" 56 + exit 0 57 + fi 58 + 59 + if arg_contain -E "$@"; then 60 + # For scripts/gcc-version.sh; This emulates GCC 20.0.0 61 + if arg_contain - "$@"; then 62 + sed 's/^__GNUC__$/20/; s/^__GNUC_MINOR__$/0/; s/^__GNUC_PATCHLEVEL__$/0/' 63 + exit 0 64 + else 65 + echo "no input files" >&2 66 + exit 1 67 + fi 68 + fi 69 + 70 + if arg_contain -S "$@"; then 71 + # For scripts/gcc-x86-*-has-stack-protector.sh 72 + if arg_contain -fstack-protector "$@"; then 73 + echo "%gs" 74 + exit 0 75 + fi 76 + fi 77 + 78 + # For scripts/gcc-plugin.sh 79 + if arg_contain -print-file-name=plugin "$@"; then 80 + plugin_dir=$(mktemp -d) 81 + 82 + sed -n 's/.*#include "$.*$"/\1/p' $(dirname $0)/../gcc-plugins/gcc-common.h | 83 + while read header 84 + do 85 + mkdir -p $plugin_dir/include/$(dirname $header) 86 + touch $plugin_dir/include/$header 87 + done 88 + 89 + echo $plugin_dir 90 + exit 0 91 + fi

+30

scripts/dummy-tools/ld

··· 1 + #!/bin/sh 2 + # SPDX-License-Identifier: GPL-2.0-only 3 + 4 + # Dummy script that always succeeds. 5 + 6 + # Check if the first parameter appears in the rest. Succeeds if found. 7 + # This helper is useful if a particular option was passed to this script. 8 + # Typically used like this: 9 + # arg_contain <word-you-are-searching-for> "$@" 10 + arg_contain () 11 + { 12 + search="$1" 13 + shift 14 + 15 + while [ $# -gt 0 ] 16 + do 17 + if [ "$search" = "$1" ]; then 18 + return 0 19 + fi 20 + shift 21 + done 22 + 23 + return 1 24 + } 25 + 26 + if arg_contain --version "$@" || arg_contain -v "$@"; then 27 + progname=$(basename $0) 28 + echo "GNU $progname (scripts/dummy-tools/$progname) 2.50" 29 + exit 0 30 + fi

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