[PATCH v2 2/2] kernel.h: Disable -Wreturn-stack-address for _THIS_IP_

From: Nick Desaulniers <ndesaulniers@google.com>
To: akpm@linux-foundation.org, natechancellor@gmail.com
Cc: arnd@arndb.de, paul.burton@mips.com, christophe.leroy@c-s.fr,
	shorne@gmail.com, yamada.masahiro@socionext.com,
	keescook@chromium.org, mingo@kernel.org,
	gregkh@linuxfoundation.org, tglx@linutronix.de,
	rdunlap@infradead.org, bp@suse.de, neilb@suse.com,
	linux-kernel@vger.kernel.org, aryabinin@virtuozzo.com,
	dwmw@amazon.co.uk, sandipan@linux.vnet.ibm.com,
	linux@rasmusvillemoes.dk, paullawrence@google.com,
	andreyknvl@google.com, will.deacon@arm.com,
	ghackmann@android.com, stable@vger.kernel.org,
	ghackmann@google.com, mka@chromium.org, jpoimboe@redhat.com,
	wvw@google.com, avagin@openvz.org,
	Nick Desaulniers <ndesaulniers@google.com>
Subject: [PATCH v2 2/2] kernel.h: Disable -Wreturn-stack-address for _THIS_IP_
Date: Mon, 30 Jul 2018 14:34:12 -0700	[thread overview]
Message-ID: <20180730213412.242849-3-ndesaulniers@google.com> (raw)
In-Reply-To: <20180730213412.242849-1-ndesaulniers@google.com>

Starting with Clang-7.0, _THIS_IP_ generates -Wreturn-stack-address
warnings for almost every translation unit. In general, I'd prefer to
leave this on (returning the address of a stack allocated variable is in
general a bad idea) and disable it only at whitelisted call sites.

We can't do something like:
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wreturn-stack-address"
 <code>
 #pragma clang diagnostic pop

in a GNU Statement Expression or macro, hence we use _Pragma, which is
its raison d'être: https://gcc.gnu.org/onlinedocs/cpp/Pragmas.html

We also can't use compiler specific pragma's without triggering
-Werror=unknown-pragmas in other compilers, so use __diag.

Cc: stable@vger.kernel.org # 4.17, 4.14, 4.9, 4.4
Suggested-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 include/linux/kernel.h | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 941dc0a5a877..909bb771c0ca 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -168,7 +168,15 @@
 
 
 #define _RET_IP_		(unsigned long)__builtin_return_address(0)
-#define _THIS_IP_  ({ __label__ __here; __here: (unsigned long)&&__here; })
+#define _THIS_IP_  (							\
+{									\
+	__label__ __here;						\
+	__diag_push()							\
+	__diag_ignore(CLANG, 7, "-Wreturn-stack-address", "")		\
+__here: (unsigned long)&&__here;					\
+	__diag_pop()							\
+}									\
+)
 
 #ifdef CONFIG_LBDAF
 # include <asm/div64.h>
-- 
2.18.0.345.g5c9ce644c3-goog

