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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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