Patch "Makefile: Mute warning for __builtin_return_address(>0) for tracing only" has been added to the 4.7-stable tree

This is a note to let you know that I've just added the patch titled

Makefile: Mute warning for __builtin_return_address(>0) for tracing only

to the 4.7-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
makefile-mute-warning-for-__builtin_return_address-0-for-tracing-only.patch
and it can be found in the queue-4.7 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Steven Rostedt <[email protected]>
Date: Thu, 28 Jul 2016 22:30:43 -0400
Subject: Makefile: Mute warning for __builtin_return_address(>0) for tracing only

From: Steven Rostedt <[email protected]>

commit 377ccbb483738f84400ddf5840c7dd8825716985 upstream.

With the latest gcc compilers, they give a warning if __builtin_return_address() parameter is greater than 0. That is because if it is used by a function called by a top level function (or in the case of the kernel, by assembly), it can try to access stack frames outside the stack and crash the system.

The tracing system uses __builtin_return_address() of up to 2! But it is well aware of the dangers that it may have, and has even added precautions to protect against it (see the thunk code in arch/x86/entry/thunk*.S)

Linus originally added KBUILD_CFLAGS that would suppress the warning for the entire kernel, as simply adding KBUILD_CFLAGS to the tracing directory wouldn't work. The tracing directory plays a bit with the CFLAGS and requires a little more logic.

This adds that special logic to only suppress the warning for the tracing directory. If it is used anywhere else outside of tracing, the warning will still be triggered.

---
 Makefile              |    1 -
 kernel/trace/Makefile |    4 ++++
 2 files changed, 4 insertions(+), 1 deletion(-)

@@ -620,7 +620,6 @@ include arch/$(SRCARCH)/Makefile
 
 KBUILD_CFLAGS	+= $(call cc-option,-fno-delete-null-pointer-checks,)
 KBUILD_CFLAGS	+= $(call cc-disable-warning,maybe-uninitialized,)
-KBUILD_CFLAGS	+= $(call cc-disable-warning,frame-address,)
 
 ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
 KBUILD_CFLAGS	+= -Os

@@ -1,4 +1,8 @@
 
+# We are fully aware of the dangers of __builtin_return_address()
+FRAME_CFLAGS := $(call cc-disable-warning,frame-address)
+KBUILD_CFLAGS += $(FRAME_CFLAGS)
+
 # Do not instrument the tracer itself:
 
 ifdef CONFIG_FUNCTION_TRACER

Patches currently in stable-queue which might be from [email protected] are

queue-4.7/makefile-mute-warning-for-__builtin_return_address-0-for-tracing-only.patch queue-4.7/disable-frame-address-warning.patch