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    Subject[PATCH 3.12 114/142] ACPI: Fix incompatibility with mcount-based function graph tracing
    Date
    From: Josh Poimboeuf <jpoimboe@redhat.com>

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

    ===============

    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.

    Reported-by: Paul Menzel <pmenzel@molgen.mpg.de>
    Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
    Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    Signed-off-by: Jiri Slaby <jslaby@suse.cz>
    ---
    drivers/acpi/Makefile | 1 -
    1 file changed, 1 deletion(-)

    diff --git a/drivers/acpi/Makefile b/drivers/acpi/Makefile
    index cdaf68b58b00..447ba3cd3f8c 100644
    --- a/drivers/acpi/Makefile
    +++ b/drivers/acpi/Makefile
    @@ -2,7 +2,6 @@
    # Makefile for the Linux ACPI interpreter
    #

    -ccflags-y := -Os
    ccflags-$(CONFIG_ACPI_DEBUG) += -DACPI_DEBUG_OUTPUT

    #
    --
    2.12.2
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