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gcc-plugins: simplify GCC plugin-dev capability test

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Linus pointed out a third of the time in the Kconfig parse stage comes
from the single invocation of cc1plus in scripts/gcc-plugin.sh [1],
and directly testing plugin-version.h for existence cuts down the
overhead a lot. [2]

This commit takes one step further to kill the build test entirely.

The small piece of code was probably intended to test the C++ designated
initializer, which was not supported until C++20.

In fact, with -pedantic option given, both GCC and Clang emit a warning.

$ echo 'class test { public: int test; } test = { .test = 1 };' | g++ -x c++ -pedantic - -fsyntax-only
<stdin>:1:43: warning: C++ designated initializers only available with '-std=c++2a' or '-std=gnu++2a' [-Wpedantic]
$ echo 'class test { public: int test; } test = { .test = 1 };' | clang++ -x c++ -pedantic - -fsyntax-only
<stdin>:1:43: warning: designated initializers are a C++20 extension [-Wc++20-designator]
class test { public: int test; } test = { .test = 1 };
                                          ^
1 warning generated.

Otherwise, modern C++ compilers should be able to build the code, and
hopefully skipping this test should not make any practical problem.

Checking the existence of plugin-version.h is still needed to ensure
the plugin-dev package is installed. The test code is now small enough
to be embedded in scripts/gcc-plugins/Kconfig.

[1] https://lore.kernel.org/lkml/CAHk-=wjU4DCuwQ4pXshRbwDCUQB31ScaeuDo1tjoZ0_PjhLHzQ@mail.gmail.com/
[2] https://lore.kernel.org/lkml/CAHk-=whK0aQxs6Q5ijJmYF1n2ch8cVFSUzU5yUM_HOjig=+vnw@mail.gmail.com/

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20201203125700.161354-1-masahiroy@kernel.org
This commit is contained in:
Masahiro Yamada 2020-12-03 21:57:00 +09:00 committed by Kees Cook
parent af2d22254e
commit 1e860048c5
2 changed files with 1 additions and 20 deletions
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19
scripts/gcc-plugin.sh
View File

@ -1,19 +0,0 @@
#!/bin/sh
# SPDX-License-Identifier: GPL-2.0
set -e
srctree=$(dirname "$0")
gccplugins_dir=$($* -print-file-name=plugin)
# we need a c++ compiler that supports the designated initializer GNU extension
$HOSTCC -c -x c++ -std=gnu++98 - -fsyntax-only -I $srctree/gcc-plugins -I $gccplugins_dir/include 2>/dev/null <<EOF
#include "gcc-common.h"
class test {
public:
int test;
} test = {
.test = 1
};
EOF

2
scripts/gcc-plugins/Kconfig
View File

@ -9,7 +9,7 @@ menuconfig GCC_PLUGINS
bool "GCC plugins"
depends on HAVE_GCC_PLUGINS
depends on CC_IS_GCC
depends on $(success,$(srctree)/scripts/gcc-plugin.sh $(CC))
depends on $(success,test -e $(shell,$(CC) -print-file-name=plugin)/include/plugin-version.h)
default y
help
GCC plugins are loadable modules that provide extra features to the