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    SubjectRe: [PATCH 2.6.21] m32r: Fix switch_to macro to push/pop frame pointer if needed
    From: Andrew Morton <akpm@linux-foundation.org>
    > On Thu, 10 May 2007 13:58:36 +0900 Hirokazu Takata <takata.hirokazu@renesas.com> wrote:
    >
    > > +#if defined(CONFIG_FRAME_POINTER)
    > > + || !defined(CONFIG_SCHED_NO_NO_OMIT_FRAME_POINTER)
    >
    > hm, I didn't know that the preprocessor permitted that.
    >
    > I'll stick a \ in there to be safe.
    >

    Oops! It was my mistake.
    Here is a revised patch, please replace the previous one.

    Thanks,

    -- Takata

    This patch fixes a rarely-happened but severe scheduling problem of
    the recent m32r kernel of 2.6.17-rc3 or later.

    In the following previous m32r patch, the switch_to macro was
    modified not to do unnecessary push/pop operations for tuning.
    > [PATCH] m32r: update switch_to macro for tuning
    > 4127272c38619c56f0c1aa01d01c7bd757db70a1

    In this modification, only 'lr' and 'sp' registers are push/pop'ed,
    assuming that the m32r kernel is always compiled with
    -fomit-frame-pointer option.

    However, in 2.6 kernel, kernel/sched.c is irregularly compiled
    with -fno-omit-frame-pointer if CONFIG_SCHED_NO_NO_OMIT_FRAME_POINTER
    is not defined.

    -- kernel/Makefile --
    :
    ifneq ($(CONFIG_SCHED_NO_NO_OMIT_FRAME_POINTER),y)
    # According to Alan Modra <alan@linuxcare.com.au>, the -fno-omit-frame-pointer is
    # needed for x86 only. Why this used to be enabled for all architectures is beyond
    # me. I suspect most platforms don't need this, but until we know that for sure
    # I turn this off for IA-64 only. Andreas Schwab says it's also needed on m68k
    # to get a correct value for the wait-channel (WCHAN in ps). --davidm
    CFLAGS_sched.o := $(PROFILING) -fno-omit-frame-pointer
    endif
    :
    ---

    Therefore, for the recent m32r kernel, we have to push/pop 'fp'
    (frame pointer) if CONFIG_FRAME_POINTER is defined or
    CONFIG_SCHED_NO_NO_OMIT_FRAME_POINTER is not defined.

    Signed-off-by: Hitoshi Yamamoto <hitoshiy@linux-m32r.org>
    Signed-off-by: Hirokazu Takata <takata@linux-m32r.org>
    ---
    arch/m32r/Kconfig | 4 ++++
    include/asm-m32r/system.h | 11 +++++++++++
    2 files changed, 15 insertions(+), 0 deletions(-)

    diff --git a/arch/m32r/Kconfig b/arch/m32r/Kconfig
    index 9740d6b..c3bb8a7 100644
    --- a/arch/m32r/Kconfig
    +++ b/arch/m32r/Kconfig
    @@ -241,6 +241,10 @@ config GENERIC_CALIBRATE_DELAY
    bool
    default y

    +config SCHED_NO_NO_OMIT_FRAME_POINTER
    + bool
    + default y
    +
    config PREEMPT
    bool "Preemptible Kernel"
    help
    diff --git a/include/asm-m32r/system.h b/include/asm-m32r/system.h
    index 99ee098..76a6255 100644
    --- a/include/asm-m32r/system.h
    +++ b/include/asm-m32r/system.h
    @@ -21,12 +21,22 @@
    * `next' and `prev' should be struct task_struct, but it isn't always defined
    */

    +#if defined(CONFIG_FRAME_POINTER) \
    + || !defined(CONFIG_SCHED_NO_NO_OMIT_FRAME_POINTER)
    +#define M32R_PUSH_FP " push fp\n"
    +#define M32R_POP_FP " pop fp\n"
    +#else
    +#define M32R_PUSH_FP ""
    +#define M32R_POP_FP ""
    +#endif
    +
    #define switch_to(prev, next, last) do { \
    __asm__ __volatile__ ( \
    " seth lr, #high(1f) \n" \
    " or3 lr, lr, #low(1f) \n" \
    " st lr, @%4 ; store old LR \n" \
    " ld lr, @%5 ; load new LR \n" \
    + M32R_PUSH_FP \
    " st sp, @%2 ; store old SP \n" \
    " ld sp, @%3 ; load new SP \n" \
    " push %1 ; store `prev' on new stack \n" \
    @@ -34,6 +44,7 @@
    " .fillinsn \n" \
    "1: \n" \
    " pop %0 ; restore `__last' from new stack \n" \
    + M32R_POP_FP \
    : "=r" (last) \
    : "0" (prev), \
    "r" (&(prev->thread.sp)), "r" (&(next->thread.sp)), \
    --
    1.5.1
    -
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