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

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

[gregkh]

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 <stable@vger.kernel.org> know about it.


>From 377ccbb483738f84400ddf5840c7dd8825716985 Mon Sep 17 00:00:00 2001
From: Steven Rostedt <rostedt@goodmis.org>
Date: Thu, 28 Jul 2016 22:30:43 -0400
Subject: Makefile: Mute warning for __builtin_return_address(>0) for tracing only

From: Steven Rostedt <rostedt@goodmis.org>

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.

Link: http://lkml.kernel.org/r/20160728223043.51996267@grimm.local.home

Tested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/Makefile
+++ b/Makefile
@@ -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
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -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 rostedt@goodmis.org are

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