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

[Nick Desaulniers]

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'Ãtre: 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@xxxxxxxxxxxxxxx # 4.17, 4.14, 4.9, 4.4
Suggested-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
---
 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