linux-kernel - [PATCH 2/3] x86/build: Use cc-option-no-kbuild for boot code compiler options

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Message-Id: <20170613005531.77656-3-mka@chromium.org>
Date:   Mon, 12 Jun 2017 17:55:30 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        "H . J . Lu" <hjl.tools@...il.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <mmarek@...e.com>
Cc:     x86@...nel.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, Michael Davidson <md@...gle.com>,
        Greg Hackmann <ghackmann@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Stephen Hines <srhines@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Arnd Bergmann <arnd@...db.de>,
        Bernhard.Rosenkranzer@...aro.org,
        Peter Foley <pefoley2@...oley.com>,
        Behan Webster <behanw@...verseincode.com>,
        Douglas Anderson <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: [PATCH 2/3] x86/build: Use cc-option-no-kbuild for boot code compiler options

cc-option uses KBUILD_CFLAGS and KBUILD_CPPFLAGS when checking if a
compiler option is available. These flags aren't used to build the boot
code, in consequence cc-option can yield wrong results. For example
-mpreferred-stack-boundary=2 is never set with a 64 bit compiler,
since the setting is only valid for 16 and 32 bit binaries. This
is also the case for 32 bit kernel builds, because the option -m32 is
added to KBUILD_CFLAGS after the assignment of REALMODE_CFLAGS.

Use cc-option-no-kbuild instead of cc-option for the boot mode options.
The macro receives the compiler options as parameter instead of using
KBUILD_C*FLAGS. For the boot code we pass REALMODE_CFLAGS.

Also use separate statements for the cc-option-no-kbuild checks instead
of performing them in the initial assignment of REALMODE_CFLAGS since
the variable is an input of the macro.

Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
---
 arch/x86/Makefile | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index bf240b920473..86b725d69423 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -24,10 +24,11 @@ REALMODE_CFLAGS	:= $(M16_CFLAGS) -g -Os -D__KERNEL__ \
 		   -DDISABLE_BRANCH_PROFILING \
 		   -Wall -Wstrict-prototypes -march=i386 -mregparm=3 \
 		   -fno-strict-aliasing -fomit-frame-pointer -fno-pic \
-		   -mno-mmx -mno-sse \
-		   $(call cc-option, -ffreestanding) \
-		   $(call cc-option, -fno-stack-protector) \
-		   $(call cc-option, -mpreferred-stack-boundary=2)
+		   -mno-mmx -mno-sse
+
+REALMODE_CFLAGS += $(call cc-option-no-kbuild, $(REALMODE_CFLAGS), -ffreestanding)
+REALMODE_CFLAGS += $(call cc-option-no-kbuild, $(REALMODE_CFLAGS), -fno-stack-protector)
+REALMODE_CFLAGS += $(call cc-option-no-kbuild, $(REALMODE_CFLAGS), -mpreferred-stack-boundary=2)
 export REALMODE_CFLAGS
 
 # BITS is used as extension for files which are available in a 32 bit
-- 
2.13.1.508.gb3defc5cc-goog