linux-kernel - [PATCH 4.8 21/67] Disable the __builtin_return

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Date:   Thu, 24 Nov 2016 16:27:15 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>, Peter Anvin <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.8 21/67] Disable the __builtin_return_address() warning globally after all

4.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Linus Torvalds <torvalds@...ux-foundation.org>

commit ef6000b4c6706cbb1787836442b5a74542b1809f upstream.

This affectively reverts commit 377ccbb48373 ("Makefile: Mute warning
for __builtin_return_address(>0) for tracing only") because it turns out
that it really isn't tracing only - it's all over the tree.

We already also had the warning disabled separately for mm/usercopy.c
(which this commit also removes), and it turns out that we will also
want to disable it for get_lock_parent_ip(), that is used for at least
TRACE_IRQFLAGS.  Which (when enabled) ends up being all over the tree.

Steven Rostedt had a patch that tried to limit it to just the config
options that actually triggered this, but quite frankly, the extra
complexity and abstraction just isn't worth it.  We have never actually
had a case where the warning is actually useful, so let's just disable
it globally and not worry about it.

Acked-by: Steven Rostedt <rostedt@...dmis.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Anvin <hpa@...or.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 Makefile              |    1 +
 kernel/trace/Makefile |    4 ----
 mm/Makefile           |    3 ---
 3 files changed, 1 insertion(+), 7 deletions(-)

--- a/Makefile
+++ b/Makefile
@@ -621,6 +621,7 @@ 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
@@ -1,8 +1,4 @@
 
-# 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
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -21,9 +21,6 @@ KCOV_INSTRUMENT_memcontrol.o := n
 KCOV_INSTRUMENT_mmzone.o := n
 KCOV_INSTRUMENT_vmstat.o := n
 
-# Since __builtin_frame_address does work as used, disable the warning.
-CFLAGS_usercopy.o += $(call cc-disable-warning, frame-address)
-
 mmu-y			:= nommu.o
 mmu-$(CONFIG_MMU)	:= gup.o highmem.o memory.o mincore.o \
 			   mlock.o mmap.o mprotect.o mremap.o msync.o rmap.o \