linux-kernel - [PATCH] kernel.h: Disable -Wreturn-stack-address for _THIS_IP

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Date:   Mon, 30 Jul 2018 10:06:20 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     akpm@...ux-foundation.org
Cc:     mka@...omium.org, ghackmann@...roid.com, ghackmann@...gle.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        stable@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Ingo Molnar <mingo@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Wei Wang <wvw@...gle.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        NeilBrown <neilb@...e.com>, linux-kernel@...r.kernel.org
Subject: [PATCH] kernel.h: Disable -Wreturn-stack-address for _THIS_IP_

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

Cc: stable@...r.kernel.org # 4.17, 4.14, 4.9, 4.4
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.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..5906f5727f90 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_  (							\
+{									\
+	_Pragma("clang diagnostic push")				\
+	_Pragma("clang diagnostic ignored \"-Wreturn-stack-address\"")	\
+	__label__ __here;						\
+__here: (unsigned long)&&__here;					\
+	_Pragma("clang diagnostic pop")					\
+}									\
+)
 
 #ifdef CONFIG_LBDAF
 # include <asm/div64.h>
-- 
2.18.0.233.g985f88cf7e-goog