2023-02-01 23:00:27

by Sam James

Subject: [PATCH] gcc-plugins: drop -std=gnu++11 to fix GCC 13 build

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 <[email protected]>
---
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 b34d11e22636..320afd3cf8e8 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
--
2.39.1

2023-02-02 18:50:13

by Kees Cook

Subject: Re: [PATCH] gcc-plugins: drop -std=gnu++11 to fix GCC 13 build

On Wed, 1 Feb 2023 23:00:09 +0000, Sam James wrote:
> 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.
>
> [...]

Applied to for-next/hardening, thanks!

[1/1] gcc-plugins: drop -std=gnu++11 to fix GCC 13 build
https://git.kernel.org/kees/c/5a6b64adc18d

--
Kees Cook