According to this discussion:
http://lkml.org/lkml/2008/7/25/338
http://lkml.org/lkml/2008/7/26/72
Frame pointers do nothing useful on PowerPC, so lib/Kconfig.debug
makes CONFIG_FRAME_POINTER unselectable on PPC targets. But ftrace.h
requires CONFIG_FRAME_POINTER for CALLER_ADDR macros. Therefore
tracing is completely useless on PowerPC:
[...]
<idle>-0 0X.h3 2us+: 0:140:R + [000] 1733:120:S mvtsd
<idle>-0 0X.h3 9us+: 0 (0)
<idle>-0 0X..3 72us : 0 (0)
<idle>-0 0X..3 73us : 0:140:R ==> [000] 1733:120:R mvtsd
This patch introduces a ARCH_HAS_NORMAL_FRAME_POINTERS Kconfig symbol,
when selected the CALLER_ADDR macros are available without the
FRAME_POINTER Kconfig symbol.
With this patch the trace output turns into:
[...]
<idle>-0 0X.h3 2us+: 0:140:R + [000] 1740:120:S mvtsd
<idle>-0 0X.h3 9us+: hrtimer_wakeup (__run_hrtimer)
<idle>-0 0X..3 87us : cpu_idle (__got2_end)
<idle>-0 0X..3 89us : 0:140:R ==> [000] 1740:120:R mvtsd
Signed-off-by: Anton Vorontsov <avoront...@ru.mvista.com>
---
On Mon, Feb 02, 2009 at 09:04:15AM -0500, Steven Rostedt wrote:
[...]
> > > -#ifdef CONFIG_FRAME_POINTER
> > > +#if defined(CONFIG_FRAME_POINTER) || defined(CONFIG_PPC)
>
> Perhaps we should add a HAVE_NORMAL_FRAME_POINTERS in
> arch/powerpc/Kconfig under PPC and then we can change the above line to:
>
> #if defined(CONFIG_FRAME_POINTERS) || \
> defined(CONFIG_HAVE_NORMAL_FRAME_POINTERS)
>
> This way when another arch wants to belong to this, we do not need to
> have a list of archs here.
Would it be better if we introduce ARCH_HAS_NORMAL_FRAME_POINTERS
in lib/Kconfig.debug, along with ARCH_WANT_FRAME_POINTERS?
Note that we can't use ARCH_WANT_FRAME_POINTERS for our needs since
that symbol is used for other (mostly cosmetic) purposes: whether we
we want CONFIG_FRAME_POINTER depend on CONFIG_DEBUG_KERNEL, and
whether frame pointers should be default =y (see commit
da4276b8299a6544dc41ac2485d3ffca5811b3fb).
arch/powerpc/Kconfig | 1 +
include/linux/ftrace.h | 3 ++-
lib/Kconfig.debug | 6 ++++++
3 files changed, 9 insertions(+), 1 deletions(-)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 74cc312..d1c67bd 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -111,6 +111,7 @@ config PPC
select HAVE_FTRACE_MCOUNT_RECORD
select HAVE_DYNAMIC_FTRACE
select HAVE_FUNCTION_TRACER
+ select ARCH_HAS_NORMAL_FRAME_POINTERS
select ARCH_WANT_OPTIONAL_GPIOLIB
select HAVE_IDE
select HAVE_IOREMAP_PROT
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 7840e71..ede3fe2 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -237,7 +237,8 @@ static inline void __ftrace_enabled_restore(int enabled)
#endif
}
-#ifdef CONFIG_FRAME_POINTER
+#if defined(CONFIG_FRAME_POINTER) || \
+ defined(CONFIG_ARCH_HAS_NORMAL_FRAME_POINTERS)
/* TODO: need to fix this for ARM */
# define CALLER_ADDR0 ((unsigned long)__builtin_return_address(0))
# define CALLER_ADDR1 ((unsigned long)__builtin_return_address(1))
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 29044f5..808f4e2 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -579,6 +579,12 @@ config ARCH_WANT_FRAME_POINTERS
bool
help
+config ARCH_HAS_NORMAL_FRAME_POINTERS
+ bool
+ help
+ Architectures should select this symbol if their ABI implies
+ having a frame pointer.
+
config FRAME_POINTER
bool "Compile the kernel with frame pointers"
depends on DEBUG_KERNEL && \
--
1.5.6.5
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