Patch "Disable "frame-address" warning" has been added to the 4.4-stable tree

Patch "Disable "frame-address" warning" has been added to the 4.4-stable tree

[gregkh]

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

    Disable "frame-address" warning

to the 4.4-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:
     disable-frame-address-warning.patch
and it can be found in the queue-4.4 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 124a3d88fa20e1869fc229d7d8c740cc81944264 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Wed, 27 Jul 2016 19:03:04 -0700
Subject: Disable "frame-address" warning
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

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

commit 124a3d88fa20e1869fc229d7d8c740cc81944264 upstream.

Newer versions of gcc warn about the use of __builtin_return_address()
with a non-zero argument when "-Wall" is specified:

  kernel/trace/trace_irqsoff.c: In function ‘stop_critical_timings’:
  kernel/trace/trace_irqsoff.c:433:86: warning: calling ‘__builtin_return_address’ with a nonzero argument is unsafe [-Wframe-address]
     stop_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
  [ .. repeats a few times for other similar cases .. ]

It is true that a non-zero argument is somewhat dangerous, and we do not
actually have very many uses of that in the kernel - but the ftrace code
does use it, and as Stephen Rostedt says:

 "We are well aware of the danger of using __builtin_return_address() of
  > 0.  In fact that's part of the reason for having the "thunk" code in
  x86 (See arch/x86/entry/thunk_{64,32}.S).  [..] it adds extra frames
  when tracking irqs off sections, to prevent __builtin_return_address()
  from accessing bad areas.  In fact the thunk_32.S states: 'Trampoline to
  trace irqs off.  (otherwise CALLER_ADDR1 might crash)'."

For now, __builtin_return_address() with a non-zero argument is the best
we can do, and the warning is not helpful and can end up making people
miss other warnings for real problems.

So disable the frame-address warning on compilers that need it.

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

---
 Makefile |    1 +
 1 file changed, 1 insertion(+)

--- a/Makefile
+++ b/Makefile
@@ -617,6 +617,7 @@ 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


Patches currently in stable-queue which might be from torvalds@linux-foundation.org are

queue-4.4/disable-maybe-uninitialized-warning-globally.patch
queue-4.4/include-linux-kernel.h-change-abs-macro-so-it-uses-consistent-return-type.patch
queue-4.4/makefile-mute-warning-for-__builtin_return_address-0-for-tracing-only.patch
queue-4.4/add-braces-to-avoid-ambiguous-else-compiler-warnings.patch
queue-4.4/ocfs2-fix-start-offset-to-ocfs2_zero_range_for_truncate.patch
queue-4.4/tools-support-relative-directory-path-for-o.patch
queue-4.4/disable-frame-address-warning.patch
queue-4.4/ocfs2-dlm-fix-race-between-convert-and-migration.patch
queue-4.4/reiserfs-fix-new_insert_key-may-be-used-uninitialized.patch

Patch "Disable "frame-address" warning" has been added to the 4.4-stable tree

[gregkh]

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

    Disable "frame-address" warning

to the 4.4-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:
     disable-frame-address-warning.patch
and it can be found in the queue-4.4 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 124a3d88fa20e1869fc229d7d8c740cc81944264 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Wed, 27 Jul 2016 19:03:04 -0700
Subject: Disable "frame-address" warning
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

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

commit 124a3d88fa20e1869fc229d7d8c740cc81944264 upstream.

Newer versions of gcc warn about the use of __builtin_return_address()
with a non-zero argument when "-Wall" is specified:

  kernel/trace/trace_irqsoff.c: In function ‘stop_critical_timings’:
  kernel/trace/trace_irqsoff.c:433:86: warning: calling ‘__builtin_return_address’ with a nonzero argument is unsafe [-Wframe-address]
     stop_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
  [ .. repeats a few times for other similar cases .. ]

It is true that a non-zero argument is somewhat dangerous, and we do not
actually have very many uses of that in the kernel - but the ftrace code
does use it, and as Stephen Rostedt says:

 "We are well aware of the danger of using __builtin_return_address() of
  > 0.  In fact that's part of the reason for having the "thunk" code in
  x86 (See arch/x86/entry/thunk_{64,32}.S).  [..] it adds extra frames
  when tracking irqs off sections, to prevent __builtin_return_address()
  from accessing bad areas.  In fact the thunk_32.S states: 'Trampoline to
  trace irqs off.  (otherwise CALLER_ADDR1 might crash)'."

For now, __builtin_return_address() with a non-zero argument is the best
we can do, and the warning is not helpful and can end up making people
miss other warnings for real problems.

So disable the frame-address warning on compilers that need it.

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

---
 Makefile |    1 +
 1 file changed, 1 insertion(+)

--- a/Makefile
+++ b/Makefile
@@ -617,6 +617,7 @@ 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


Patches currently in stable-queue which might be from torvalds@linux-foundation.org are

queue-4.4/mm-list_lru.c-avoid-error-path-null-pointer-deref.patch
queue-4.4/mm-memcontrol-do-not-recurse-in-direct-reclaim.patch
queue-4.4/disable-frame-address-warning.patch
queue-4.4/x86-xen-fix-upper-bound-of-pmd-loop-in-xen_cleanhighmap.patch
queue-4.4/mm-cma-silence-warnings-due-to-max-usage.patch
queue-4.4/h8300-fix-syscall-restarting.patch
queue-4.4/fix-potential-infoleak-in-older-kernels.patch