linux-kernel - [PATCH] kbuild: disable Android-specific compiler features

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Date:	Fri, 5 Feb 2016 16:44:38 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Michal Marek <mmarek@...e.com>
Cc:	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org
Subject: [PATCH] kbuild: disable Android-specific compiler features

The Android compilers enable some non-standard features by default. While
most Android build systems inject the needed "-mno-android" option via
KCFLAGS, it happens too late (at least on x86_64), since KBUILD_CFLAGS
gains KCFLAGS after running (and failing) many cc-option tests. (For
example, the stack-protector tests happen after arch-specific
KBUILD_CFLAGS are added but before the external KCFLAGS are added.) As
such, we should notice this option and immediately turn it on as the
first cc-option test we run.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 Makefile | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Makefile b/Makefile
index 6c1a3c247988..126c98b582bb 100644
--- a/Makefile
+++ b/Makefile
@@ -393,6 +393,10 @@ KBUILD_CFLAGS   := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
 		   -Wno-format-security \
 		   -std=gnu89

+# We must turn off the Android-specific compiler options as early as possible
+# otherwise cc-option calls below may erroneously fail.
+KBUILD_CFLAGS	+= $(call cc-option,-mno-android,)
+
 KBUILD_AFLAGS_KERNEL :=
 KBUILD_CFLAGS_KERNEL :=
 KBUILD_AFLAGS   := -D__ASSEMBLY__
-- 
2.6.3

-- 
Kees Cook
Chrome OS & Brillo Security