Patch "ACPI: Fix incompatibility with mcount-based function graph tracing" has been added to the 4.4-stable tree

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

ACPI: Fix incompatibility with mcount-based function graph tracing

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:
acpi-fix-incompatibility-with-mcount-based-function-graph-tracing.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 <[email protected]> know about it.

From: Josh Poimboeuf <[email protected]>
Date: Thu, 16 Mar 2017 08:56:28 -0500
Subject: ACPI: Fix incompatibility with mcount-based function graph tracing

From: Josh Poimboeuf <[email protected]>

commit 61b79e16c68d703dde58c25d3935d67210b7d71b upstream.

Paul Menzel reported a warning:

  WARNING: CPU: 0 PID: 774 at /build/linux-ROBWaj/linux-4.9.13/kernel/trace/trace_functions_graph.c:233 ftrace_return_to_handler+0x1aa/0x1e0
  Bad frame pointer: expected f6919d98, received f6919db0
    from func acpi_pm_device_sleep_wake return to c43b6f9d

The warning means that function graph tracing is broken for the acpi_pm_device_sleep_wake() function. That's because the ACPI Makefile unconditionally sets the '-Os' gcc flag to optimize for size. That's an issue because mcount-based function graph tracing is incompatible with '-Os' on x86, thanks to the following gcc bug:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42109

I have another patch pending which will ensure that mcount-based function graph tracing is never used with CONFIG_CC_OPTIMIZE_FOR_SIZE on x86.

But this patch is needed in addition to that one because the ACPI Makefile overrides that config option for no apparent reason. It has had this flag since the beginning of git history, and there's no related comment, so I don't know why it's there. As far as I can tell, there's no reason for it to be there. The appropriate behavior is for it to honor CONFIG_CC_OPTIMIZE_FOR_{SIZE,PERFORMANCE} like the rest of the kernel.

---
 drivers/acpi/Makefile |    1 -
 1 file changed, 1 deletion(-)

@@ -2,7 +2,6 @@
 # Makefile for the Linux ACPI interpreter
 #
 
-ccflags-y			:= -Os
 ccflags-$(CONFIG_ACPI_DEBUG)	+= -DACPI_DEBUG_OUTPUT
 
 #

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

queue-4.4/acpi-fix-incompatibility-with-mcount-based-function-graph-tracing.patch