linux-kernel - Re: [PATCH 2/2] kbuild: add -Wall to KBUILD

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Message-ID: <202003251906.973AD868@keescook>
Date:   Wed, 25 Mar 2020 19:06:30 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, kernel-hardening@...ts.openwall.com,
        Emese Revfy <re.emese@...il.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] kbuild: add -Wall to KBUILD_HOSTCXXFLAGS

On Wed, Mar 25, 2020 at 12:14:32PM +0900, Masahiro Yamada wrote:
> Add -Wall to catch more warnings for C++ host programs.
> 
> When I submitted the previous version, the 0-day bot reported
> -Wc++11-compat warnings for old GCC:
> 
>   HOSTCXX -fPIC scripts/gcc-plugins/latent_entropy_plugin.o
> In file included from /usr/lib/gcc/x86_64-linux-gnu/4.8/plugin/include/tm.h:28:0,
>                  from scripts/gcc-plugins/gcc-common.h:15,
>                  from scripts/gcc-plugins/latent_entropy_plugin.c:78:
> /usr/lib/gcc/x86_64-linux-gnu/4.8/plugin/include/config/elfos.h:102:21: warning: C++11 requires a space between string literal and macro [-Wc++11-compat]
>     fprintf ((FILE), "%s"HOST_WIDE_INT_PRINT_UNSIGNED"\n",\
>                      ^
> /usr/lib/gcc/x86_64-linux-gnu/4.8/plugin/include/config/elfos.h:170:24: warning: C++11 requires a space between string literal and macro [-Wc++11-compat]
>        fprintf ((FILE), ","HOST_WIDE_INT_PRINT_UNSIGNED",%u\n",  \
>                         ^
> In file included from /usr/lib/gcc/x86_64-linux-gnu/4.8/plugin/include/tm.h:42:0,
>                  from scripts/gcc-plugins/gcc-common.h:15,
>                  from scripts/gcc-plugins/latent_entropy_plugin.c:78:
> /usr/lib/gcc/x86_64-linux-gnu/4.8/plugin/include/defaults.h:126:24: warning: C++11 requires a space between string literal and macro [-Wc++11-compat]
>        fprintf ((FILE), ","HOST_WIDE_INT_PRINT_UNSIGNED",%u\n",  \
>                         ^
> 
> The source of the warnings is in the plugin headers, so we have no
> control of it. I just suppressed them by adding -Wno-c++11-compat to
> scripts/gcc-plugins/Makefile.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

Acked-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
> 
>  Makefile                     | 2 +-
>  scripts/gcc-plugins/Makefile | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index 3b57ccab367b..593d8f1bbe90 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -400,7 +400,7 @@ HOSTCXX      = g++
>  KBUILD_HOSTCFLAGS   := -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 \
>  		-fomit-frame-pointer -std=gnu89 $(HOST_LFS_CFLAGS) \
>  		$(HOSTCFLAGS)
> -KBUILD_HOSTCXXFLAGS := -O2 $(HOST_LFS_CFLAGS) $(HOSTCXXFLAGS)
> +KBUILD_HOSTCXXFLAGS := -Wall -O2 $(HOST_LFS_CFLAGS) $(HOSTCXXFLAGS)
>  KBUILD_HOSTLDFLAGS  := $(HOST_LFS_LDFLAGS) $(HOSTLDFLAGS)
>  KBUILD_HOSTLDLIBS   := $(HOST_LFS_LIBS) $(HOSTLDLIBS)
>  
> diff --git a/scripts/gcc-plugins/Makefile b/scripts/gcc-plugins/Makefile
> index f2ee8bd7abc6..efff00959a9c 100644
> --- a/scripts/gcc-plugins/Makefile
> +++ b/scripts/gcc-plugins/Makefile
> @@ -10,7 +10,7 @@ else
>    HOSTLIBS := hostcxxlibs
>    HOST_EXTRACXXFLAGS += -I$(GCC_PLUGINS_DIR)/include -I$(src) -std=gnu++98 -fno-rtti
>    HOST_EXTRACXXFLAGS += -fno-exceptions -fasynchronous-unwind-tables -ggdb
> -  HOST_EXTRACXXFLAGS += -Wno-narrowing -Wno-unused-variable
> +  HOST_EXTRACXXFLAGS += -Wno-narrowing -Wno-unused-variable -Wno-c++11-compat
>    export HOST_EXTRACXXFLAGS
>  endif
>  
> -- 
> 2.17.1
> 

-- 
Kees Cook