linux-hardening - Re: [PATCH v2] gcc-plugins: fix gcc 11 indigestion with plugins...

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Date:   Wed, 13 Jan 2021 11:08:36 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Valdis Klētnieks <valdis.kletnieks@...edu>
Cc:     Kees Cook <keescook@...omium.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-hardening@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] gcc-plugins: fix gcc 11 indigestion with plugins...

On Tue, Jan 12, 2021 at 08:19:16PM -0500, Valdis Klētnieks wrote:
> Fedora Rawhide has started including gcc 11,and the g++ compiler
> throws a wobbly when it hits scripts/gcc-plugins:
> 
>   HOSTCXX scripts/gcc-plugins/latent_entropy_plugin.so
> In file included from /usr/include/c++/11/type_traits:35,
>                  from /usr/lib/gcc/x86_64-redhat-linux/11/plugin/include/system.h:244,
>                  from /usr/lib/gcc/x86_64-redhat-linux/11/plugin/include/gcc-plugin.h:28,
>                  from scripts/gcc-plugins/gcc-common.h:7,
>                  from scripts/gcc-plugins/latent_entropy_plugin.c:78:
> /usr/include/c++/11/bits/c++0x_warning.h:32:2: error: #error This file requires compiler and library support for the ISO
>  C++ 2011 standard. This support must be enabled with the -std=c++11 or -std=gnu++11 compiler options.
>    32 | #error This file requires compiler and library support \
> 
> Patch is more complicated than would otherwise be needed, because
> older gcc (4.9, 5.4) have gnu++11 but throw an error due to a gcc bug
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69959
> 
> Signed-off-by: Valdis Kletnieks <valdis.kletnieks@...edu>
> ---
> diff --git a/scripts/gcc-plugins/Makefile b/scripts/gcc-plugins/Makefile
> index d66949bfeba4..cc779973724a 100644
> --- a/scripts/gcc-plugins/Makefile
> +++ b/scripts/gcc-plugins/Makefile
> @@ -21,10 +21,13 @@ always-y += $(GCC_PLUGIN)
>  
>  GCC_PLUGINS_DIR = $(shell $(CC) -print-file-name=plugin)
>  
> +# need gnu++11 for gcc 11, but 4.9 and 5.4 need gnu++98
> +GCC_FLAVOR = $(call cc-ifversion, -ge, 1100, 11, 98)
> +
>  plugin_cxxflags	= -Wp,-MMD,$(depfile) $(KBUILD_HOSTCXXFLAGS) -fPIC \
> -		   -I $(GCC_PLUGINS_DIR)/include -I $(obj) -std=gnu++98 \
> +		   -I $(GCC_PLUGINS_DIR)/include -I $(obj) -std=gnu++$(GCC_FLAVOR) \
>  		   -fno-rtti -fno-exceptions -fasynchronous-unwind-tables \
> -		   -ggdb -Wno-narrowing -Wno-unused-variable -Wno-c++11-compat \
> +		   -ggdb -Wno-narrowing -Wno-unused-variable \
>  		   -Wno-format-diag
>  
>  plugin_ldflags	= -shared

The first patch has already been merged into Linus' tree, so this
probably should be an incremental fix on top, with a Fixes: tag.

-- 
Josh