linux-hardening - [PATCH AUTOSEL 6.1 30/49] gcc-plugins: drop -std=gnu++11 to fix GCC 13 build

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Date:   Sun, 26 Feb 2023 09:46:30 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Sam James <sam@...too.org>, Kees Cook <keescook@...omium.org>,
        Sasha Levin <sashal@...nel.org>,
        linux-hardening@...r.kernel.org
Subject: [PATCH AUTOSEL 6.1 30/49] gcc-plugins: drop -std=gnu++11 to fix GCC 13 build

From: Sam James <sam@...too.org>

[ Upstream commit 5a6b64adc18d9adfb497a529ff004d59b6df151f ]

The latest GCC 13 snapshot (13.0.1 20230129) gives the following:
```
cc1: error: cannot load plugin ./scripts/gcc-plugins/randomize_layout_plugin.so
 :./scripts/gcc-plugins/randomize_layout_plugin.so: undefined symbol: tree_code_type
```

This ends up being because of https://gcc.gnu.org/git/gitweb.cgi?p=gcc.git;h=b0241ce6e37031
upstream in GCC which changes the visibility of some types used by the kernel's
plugin infrastructure like tree_code_type.

After discussion with the GCC folks, we found that the kernel needs to be building
plugins with the same flags used to build GCC - and GCC defaults to gnu++17
right now. The minimum GCC version needed to build the kernel is GCC 5.1
and GCC 5.1 already defaults to gnu++14 anyway, so just drop the flag, as
all GCCs that could be used to build GCC already default to an acceptable
version which was >= the version we forced via flags until now.

Bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108634
Signed-off-by: Sam James <sam@...too.org>
Signed-off-by: Kees Cook <keescook@...omium.org>
Link: https://lore.kernel.org/r/20230201230009.2252783-1-sam@gentoo.org
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 scripts/gcc-plugins/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/gcc-plugins/Makefile b/scripts/gcc-plugins/Makefile
index b34d11e226366..320afd3cf8e82 100644
--- a/scripts/gcc-plugins/Makefile
+++ b/scripts/gcc-plugins/Makefile
@@ -29,7 +29,7 @@ GCC_PLUGINS_DIR = $(shell $(CC) -print-file-name=plugin)
 plugin_cxxflags	= -Wp,-MMD,$(depfile) $(KBUILD_HOSTCXXFLAGS) -fPIC \
 		  -include $(srctree)/include/linux/compiler-version.h \
 		  -DPLUGIN_VERSION=$(call stringify,$(KERNELVERSION)) \
-		  -I $(GCC_PLUGINS_DIR)/include -I $(obj) -std=gnu++11 \
+		  -I $(GCC_PLUGINS_DIR)/include -I $(obj) \
 		  -fno-rtti -fno-exceptions -fasynchronous-unwind-tables \
 		  -ggdb -Wno-narrowing -Wno-unused-variable \
 		  -Wno-format-diag
-- 
2.39.0