[PATCH v5 0/3] Tracers vs. CALLER_ADDR on PowerPC

[PATCH v5 0/3] Tracers vs. CALLER_ADDR on PowerPC

[Anton Vorontsov]

Hi all,

In v5 there are few fixes suggested by Sam Ravnborg:

- Use 8 spaces for indentation in Makefile;
- Rename ARCH_HAS_NORMAL_FRAME_POINTERS to HAVE_NORMAL_FRAME_POINTER;

Thanks,

--- 

Preface for those who don't know or forgot what the problem is:

Gcc frame pointers do nothing useful on PowerPC (they're harmful,
actually), and thus lib/Kconfig.debug makes CONFIG_FRAME_POINTER
unselectable on PPC targets, but CALLER_ADDR macros are available
only with CONFIG_FRAME_POINTER, 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

While it should look like this:

[...]
  <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

I've tried to fix the issue via expanding the #ifdef in the ftrace.h:
http://lkml.org/lkml/2009/1/31/141

Then Steven Rostedt suggested to implement something more generic,
i.e. HAVE_NORMAL_FRAME_POINTERS Kconfig symbol.

I found a way to solve the problem w/o additional symbols, but
with some Makefile magic (http://lkml.org/lkml/2009/2/4/273).
But because of top-level Makefile issues on other arches
(http://lkml.org/lkml/2009/2/14/89) I had to abandon the approach.

So, this patch set combines Steven Rostedt's idea and a small
Makefile change, so that now only top-level Makefile has to know
about the new symbol, and the rest of the kernel can stay with
using CONFIG_FRAME_POINTER.

I'm aware of

  commit c79a61f55773d2519fd0525bf58385f7d20752d3
  Author: Uwe Kleine-Koenig <u.kleine-koenig@pengutronix.de>
  Date:   Fri Feb 27 21:30:03 2009 +0100

      tracing: make CALLER_ADDRx overwriteable

But I think the patch set is still applicable, considering that
it removes gcc bug workaround in a nice way, and makes
CONFIG_FRAME_POINTER available on PowerPC, thus other code
can rely on that.

If not, I can just fill-in the asm/ftrace.h for PowerPC.

-- 
Anton Vorontsov
email: cbouatmailru@gmail.com
irc://irc.freenode.net/bd2

[PATCH v5 0/3] Tracers vs. CALLER_ADDR on PowerPC

[Anton Vorontsov]

Hi all,

In v5 there are few fixes suggested by Sam Ravnborg:

- Use 8 spaces for indentation in Makefile;
- Rename ARCH_HAS_NORMAL_FRAME_POINTERS to HAVE_NORMAL_FRAME_POINTER;

Thanks,

--- 

Preface for those who don't know or forgot what the problem is:

Gcc frame pointers do nothing useful on PowerPC (they're harmful,
actually), and thus lib/Kconfig.debug makes CONFIG_FRAME_POINTER
unselectable on PPC targets, but CALLER_ADDR macros are available
only with CONFIG_FRAME_POINTER, 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

While it should look like this:

[...]
  <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

I've tried to fix the issue via expanding the #ifdef in the ftrace.h:
http://lkml.org/lkml/2009/1/31/141

Then Steven Rostedt suggested to implement something more generic,
i.e. HAVE_NORMAL_FRAME_POINTERS Kconfig symbol.

I found a way to solve the problem w/o additional symbols, but
with some Makefile magic (http://lkml.org/lkml/2009/2/4/273).
But because of top-level Makefile issues on other arches
(http://lkml.org/lkml/2009/2/14/89) I had to abandon the approach.

So, this patch set combines Steven Rostedt's idea and a small
Makefile change, so that now only top-level Makefile has to know
about the new symbol, and the rest of the kernel can stay with
using CONFIG_FRAME_POINTER.

I'm aware of

  commit c79a61f55773d2519fd0525bf58385f7d20752d3
  Author: Uwe Kleine-Koenig <u.kleine-koenig@pengutronix.de>
  Date:   Fri Feb 27 21:30:03 2009 +0100

      tracing: make CALLER_ADDRx overwriteable

But I think the patch set is still applicable, considering that
it removes gcc bug workaround in a nice way, and makes
CONFIG_FRAME_POINTER available on PowerPC, thus other code
can rely on that.

If not, I can just fill-in the asm/ftrace.h for PowerPC.

-- 
Anton Vorontsov
email: cbouatmailru@gmail.com
irc://irc.freenode.net/bd2

[PATCH 1/3] powerpc, Makefile: Make it possible to safely select CONFIG_FRAME_POINTER

[Anton Vorontsov]

This patch introduces HAVE_NORMAL_FRAME_POINTER Kconfig symbol. When
defined, the top level Makefile won't add -fno-omit-frame-pointer
cflag (the flag is useless for PowerPC kernels, and also makes gcc
generate wrong code).

Also move ARCH_WANT_FRAME_POINTERS's help text.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
---
 Makefile             |    7 +++++--
 arch/powerpc/Kconfig |    1 +
 lib/Kconfig.debug    |   16 ++++++++++------
 3 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/Makefile b/Makefile
index b18afad..bfa58ea 100644
--- a/Makefile
+++ b/Makefile
@@ -543,9 +543,12 @@ KBUILD_CFLAGS += $(call cc-option, -fno-stack-protector)
 endif
 
 ifdef CONFIG_FRAME_POINTER
-KBUILD_CFLAGS	+= -fno-omit-frame-pointer -fno-optimize-sibling-calls
+        KBUILD_CFLAGS += -fno-optimize-sibling-calls
+        ifndef CONFIG_HAVE_NORMAL_FRAME_POINTER
+                KBUILD_CFLAGS += -fno-omit-frame-pointer
+        endif
 else
-KBUILD_CFLAGS	+= -fomit-frame-pointer
+        KBUILD_CFLAGS += -fomit-frame-pointer
 endif
 
 ifdef CONFIG_DEBUG_INFO
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 4c78045..b29a6c3 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -119,6 +119,7 @@ config PPC
 	select HAVE_KPROBES
 	select HAVE_ARCH_KGDB
 	select HAVE_KRETPROBES
+	select HAVE_NORMAL_FRAME_POINTER
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_LMB
 	select HAVE_DMA_ATTRS if PPC64
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 444002b..1f1633b 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -660,20 +660,24 @@ config DEBUG_NOTIFIERS
 	  This is a relatively cheap check but if you care about maximum
 	  performance, say N.
 
-#
-# Select this config option from the architecture Kconfig, if it
-# it is preferred to always offer frame pointers as a config
-# option on the architecture (regardless of KERNEL_DEBUG):
-#
 config ARCH_WANT_FRAME_POINTERS
 	bool
 	help
+	  Select this config option from the architecture Kconfig, if it
+	  it is preferred to always offer frame pointers as a config
+	  option on the architecture (regardless of KERNEL_DEBUG).
+
+config HAVE_NORMAL_FRAME_POINTER
+	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 && \
 		(CRIS || M68K || M68KNOMMU || FRV || UML || \
-		 AVR32 || SUPERH || BLACKFIN || MN10300) || \
+		 AVR32 || SUPERH || BLACKFIN || MN10300 || PPC) || \
 		ARCH_WANT_FRAME_POINTERS
 	default y if (DEBUG_INFO && UML) || ARCH_WANT_FRAME_POINTERS
 	help
-- 
1.6.2.2

[PATCH 1/3] powerpc, Makefile: Make it possible to safely select CONFIG_FRAME_POINTER

[Anton Vorontsov]

This patch introduces HAVE_NORMAL_FRAME_POINTER Kconfig symbol. When
defined, the top level Makefile won't add -fno-omit-frame-pointer
cflag (the flag is useless for PowerPC kernels, and also makes gcc
generate wrong code).

Also move ARCH_WANT_FRAME_POINTERS's help text.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
---
 Makefile             |    7 +++++--
 arch/powerpc/Kconfig |    1 +
 lib/Kconfig.debug    |   16 ++++++++++------
 3 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/Makefile b/Makefile
index b18afad..bfa58ea 100644
--- a/Makefile
+++ b/Makefile
@@ -543,9 +543,12 @@ KBUILD_CFLAGS += $(call cc-option, -fno-stack-protector)
 endif
 
 ifdef CONFIG_FRAME_POINTER
-KBUILD_CFLAGS	+= -fno-omit-frame-pointer -fno-optimize-sibling-calls
+        KBUILD_CFLAGS += -fno-optimize-sibling-calls
+        ifndef CONFIG_HAVE_NORMAL_FRAME_POINTER
+                KBUILD_CFLAGS += -fno-omit-frame-pointer
+        endif
 else
-KBUILD_CFLAGS	+= -fomit-frame-pointer
+        KBUILD_CFLAGS += -fomit-frame-pointer
 endif
 
 ifdef CONFIG_DEBUG_INFO
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 4c78045..b29a6c3 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -119,6 +119,7 @@ config PPC
 	select HAVE_KPROBES
 	select HAVE_ARCH_KGDB
 	select HAVE_KRETPROBES
+	select HAVE_NORMAL_FRAME_POINTER
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_LMB
 	select HAVE_DMA_ATTRS if PPC64
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 444002b..1f1633b 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -660,20 +660,24 @@ config DEBUG_NOTIFIERS
 	  This is a relatively cheap check but if you care about maximum
 	  performance, say N.
 
-#
-# Select this config option from the architecture Kconfig, if it
-# it is preferred to always offer frame pointers as a config
-# option on the architecture (regardless of KERNEL_DEBUG):
-#
 config ARCH_WANT_FRAME_POINTERS
 	bool
 	help
+	  Select this config option from the architecture Kconfig, if it
+	  it is preferred to always offer frame pointers as a config
+	  option on the architecture (regardless of KERNEL_DEBUG).
+
+config HAVE_NORMAL_FRAME_POINTER
+	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 && \
 		(CRIS || M68K || M68KNOMMU || FRV || UML || \
-		 AVR32 || SUPERH || BLACKFIN || MN10300) || \
+		 AVR32 || SUPERH || BLACKFIN || MN10300 || PPC) || \
 		ARCH_WANT_FRAME_POINTERS
 	default y if (DEBUG_INFO && UML) || ARCH_WANT_FRAME_POINTERS
 	help
-- 
1.6.2.2

Re: [PATCH 1/3] powerpc, Makefile: Make it possible to safely select CONFIG_FRAME_POINTER

[Segher Boessenkool]

> This patch introduces HAVE_NORMAL_FRAME_POINTER Kconfig symbol. When
> defined, the top level Makefile won't add -fno-omit-frame-pointer
> cflag (the flag is useless for PowerPC kernels, and also makes gcc
> generate wrong code).

> +++ b/arch/powerpc/Kconfig

> +	select HAVE_NORMAL_FRAME_POINTER

> +config HAVE_NORMAL_FRAME_POINTER
> +	bool
> +	help
> +	  Architectures should select this symbol if their ABI implies
> +	  having a frame pointer.

I am totally confused what you call a frame pointer here.
None of the relevant PowerPC ABIs have a frame pointer
separate from the stack pointer; the compiler can create
one, of course.  A better config symbol name and help text
would help understand this patch :-)


Segher

Re: [PATCH 1/3] powerpc, Makefile: Make it possible to safely select CONFIG_FRAME_POINTER

[Segher Boessenkool]

> This patch introduces HAVE_NORMAL_FRAME_POINTER Kconfig symbol. When
> defined, the top level Makefile won't add -fno-omit-frame-pointer
> cflag (the flag is useless for PowerPC kernels, and also makes gcc
> generate wrong code).

> +++ b/arch/powerpc/Kconfig

> +	select HAVE_NORMAL_FRAME_POINTER

> +config HAVE_NORMAL_FRAME_POINTER
> +	bool
> +	help
> +	  Architectures should select this symbol if their ABI implies
> +	  having a frame pointer.

I am totally confused what you call a frame pointer here.
None of the relevant PowerPC ABIs have a frame pointer
separate from the stack pointer; the compiler can create
one, of course.  A better config symbol name and help text
would help understand this patch :-)


Segher

Re: [PATCH 1/3] powerpc, Makefile: Make it possible to safely select CONFIG_FRAME_POINTER

[Steven Rostedt]

On Sat, 2009-05-02 at 21:48 +0200, Segher Boessenkool wrote:
> > This patch introduces HAVE_NORMAL_FRAME_POINTER Kconfig symbol. When
> > defined, the top level Makefile won't add -fno-omit-frame-pointer
> > cflag (the flag is useless for PowerPC kernels, and also makes gcc
> > generate wrong code).
> 
> > +++ b/arch/powerpc/Kconfig
> 
> > +	select HAVE_NORMAL_FRAME_POINTER
> 
> > +config HAVE_NORMAL_FRAME_POINTER
> > +	bool
> > +	help
> > +	  Architectures should select this symbol if their ABI implies
> > +	  having a frame pointer.
> 
> I am totally confused what you call a frame pointer here.
> None of the relevant PowerPC ABIs have a frame pointer
> separate from the stack pointer; the compiler can create
> one, of course.  A better config symbol name and help text
> would help understand this patch :-)

Yeah, I agree. This needs a better description. I only know what's going
on because I was there for the start of the discussion.

But just to be sure, this is what I think is happening.

When we add "-pg" to gcc, it automatically causes frame pointers to be
used.

But with PPC, it always has frame pointers and there's no problem.

But with Linux, when you add CONFIG_FRAME_POINTER, it automatically
adds:  -fno-omit-frame-pointer. Thus the config will add
"-fomit-frame-pointer" when CONFIG_FRAME_POINTER is not set, or it will
add "-fno-omit-frame-pointer" when it is set.

The problem with PPC is that "-fno-omit-frame-pointer" is buggy and
causes gcc to produce bad code.

Perhaps a better name would be:

HAVE_FRAME_POINTER_AS_DEFAULT

??

Or am I totally wrong in my analysis?

-- Steve

Re: [PATCH 1/3] powerpc, Makefile: Make it possible to safely select CONFIG_FRAME_POINTER

[Steven Rostedt]

On Sat, 2009-05-02 at 21:48 +0200, Segher Boessenkool wrote:
> > This patch introduces HAVE_NORMAL_FRAME_POINTER Kconfig symbol. When
> > defined, the top level Makefile won't add -fno-omit-frame-pointer
> > cflag (the flag is useless for PowerPC kernels, and also makes gcc
> > generate wrong code).
> 
> > +++ b/arch/powerpc/Kconfig
> 
> > +	select HAVE_NORMAL_FRAME_POINTER
> 
> > +config HAVE_NORMAL_FRAME_POINTER
> > +	bool
> > +	help
> > +	  Architectures should select this symbol if their ABI implies
> > +	  having a frame pointer.
> 
> I am totally confused what you call a frame pointer here.
> None of the relevant PowerPC ABIs have a frame pointer
> separate from the stack pointer; the compiler can create
> one, of course.  A better config symbol name and help text
> would help understand this patch :-)

Yeah, I agree. This needs a better description. I only know what's going
on because I was there for the start of the discussion.

But just to be sure, this is what I think is happening.

When we add "-pg" to gcc, it automatically causes frame pointers to be
used.

But with PPC, it always has frame pointers and there's no problem.

But with Linux, when you add CONFIG_FRAME_POINTER, it automatically
adds:  -fno-omit-frame-pointer. Thus the config will add
"-fomit-frame-pointer" when CONFIG_FRAME_POINTER is not set, or it will
add "-fno-omit-frame-pointer" when it is set.

The problem with PPC is that "-fno-omit-frame-pointer" is buggy and
causes gcc to produce bad code.

Perhaps a better name would be:

HAVE_FRAME_POINTER_AS_DEFAULT

??

Or am I totally wrong in my analysis?

-- Steve

Re: [PATCH 1/3] powerpc, Makefile: Make it possible to safely select CONFIG_FRAME_POINTER

[Segher Boessenkool]

> Yeah, I agree. This needs a better description. I only know what's  
> going
> on because I was there for the start of the discussion.
>
> But just to be sure, this is what I think is happening.
>
> When we add "-pg" to gcc, it automatically causes frame pointers to be
> used.

Nope, it does no such thing.

> But with PPC, it always has frame pointers and there's no problem.

Well, what do you call a "frame pointer"?  In the general meaning
of "some register that points to the incoming function arguments
and the function local variables", PowerPC can _usually_ use GPR1,
the stack pointer (and indeed it is called "stack frame pointer"
in the ABI).  In the more narrow meaning of "what GCC calls the
frame pointer", "the thing that -fomit-frame-pointer optimises
away" -- on PowerPC (and many other targets), -fomit-frame-pointer
is the *default* when optimisation is enabled!

There is a GCC bug here though: it won't allow both -pg and
-fomit-frame-pointer be set at the command line at the same time,
even on targets where that is not problematic.

> But with Linux, when you add CONFIG_FRAME_POINTER, it automatically
> adds:  -fno-omit-frame-pointer. Thus the config will add
> "-fomit-frame-pointer" when CONFIG_FRAME_POINTER is not set, or it  
> will
> add "-fno-omit-frame-pointer" when it is set.
>
> The problem with PPC is that "-fno-omit-frame-pointer" is buggy and
> causes gcc to produce bad code.

It's a deeper problem that is only _exposed_ by -fno-o-f-p (and can be
hidden by -mno-sched-epilog in the one spot where it hit us).

> Perhaps a better name would be:
>
> HAVE_FRAME_POINTER_AS_DEFAULT

NO_NO_OMIT_FRAME_POINTER ?  Or better, just never use -fno-o-f-p,
I don't see why you would ever need it.


Segher

Re: [PATCH 1/3] powerpc, Makefile: Make it possible to safely select CONFIG_FRAME_POINTER

[Segher Boessenkool]

> Yeah, I agree. This needs a better description. I only know what's  
> going
> on because I was there for the start of the discussion.
>
> But just to be sure, this is what I think is happening.
>
> When we add "-pg" to gcc, it automatically causes frame pointers to be
> used.

Nope, it does no such thing.

> But with PPC, it always has frame pointers and there's no problem.

Well, what do you call a "frame pointer"?  In the general meaning
of "some register that points to the incoming function arguments
and the function local variables", PowerPC can _usually_ use GPR1,
the stack pointer (and indeed it is called "stack frame pointer"
in the ABI).  In the more narrow meaning of "what GCC calls the
frame pointer", "the thing that -fomit-frame-pointer optimises
away" -- on PowerPC (and many other targets), -fomit-frame-pointer
is the *default* when optimisation is enabled!

There is a GCC bug here though: it won't allow both -pg and
-fomit-frame-pointer be set at the command line at the same time,
even on targets where that is not problematic.

> But with Linux, when you add CONFIG_FRAME_POINTER, it automatically
> adds:  -fno-omit-frame-pointer. Thus the config will add
> "-fomit-frame-pointer" when CONFIG_FRAME_POINTER is not set, or it  
> will
> add "-fno-omit-frame-pointer" when it is set.
>
> The problem with PPC is that "-fno-omit-frame-pointer" is buggy and
> causes gcc to produce bad code.

It's a deeper problem that is only _exposed_ by -fno-o-f-p (and can be
hidden by -mno-sched-epilog in the one spot where it hit us).

> Perhaps a better name would be:
>
> HAVE_FRAME_POINTER_AS_DEFAULT

NO_NO_OMIT_FRAME_POINTER ?  Or better, just never use -fno-o-f-p,
I don't see why you would ever need it.


Segher

Re: [PATCH 1/3] powerpc, Makefile: Make it possible to safely select CONFIG_FRAME_POINTER

[Steven Rostedt]

On Tue, 2009-05-05 at 09:56 +0200, Segher Boessenkool wrote:
> > Yeah, I agree. This needs a better description. I only know what's  
> > going
> > on because I was there for the start of the discussion.
> >
> > But just to be sure, this is what I think is happening.
> >
> > When we add "-pg" to gcc, it automatically causes frame pointers to be
> > used.
> 
> Nope, it does no such thing.

Well, mcount is expected to be able to get to not just who called
mcount, but also the parent of that function. The way mcount is
implemented does not let you do that. If mcount was the first thing to
be called in a function, then it would have been perfect. We could get
to the caller, its parent, and even the parameters. But unfortunately,
mcount is called after the stack is set up. Thus, without frame pointers
(the way to find a previous frame) there's no way (on some archs) to
find the parent. Nor can we figure out the parameters, which really
sucks.


> 
> > But with PPC, it always has frame pointers and there's no problem.
> 
> Well, what do you call a "frame pointer"?  In the general meaning
> of "some register that points to the incoming function arguments
> and the function local variables", PowerPC can _usually_ use GPR1,
> the stack pointer (and indeed it is called "stack frame pointer"
> in the ABI).  In the more narrow meaning of "what GCC calls the
> frame pointer", "the thing that -fomit-frame-pointer optimises
> away" -- on PowerPC (and many other targets), -fomit-frame-pointer
> is the *default* when optimisation is enabled!
> 
> There is a GCC bug here though: it won't allow both -pg and
> -fomit-frame-pointer be set at the command line at the same time,
> even on targets where that is not problematic.
> 
> > But with Linux, when you add CONFIG_FRAME_POINTER, it automatically
> > adds:  -fno-omit-frame-pointer. Thus the config will add
> > "-fomit-frame-pointer" when CONFIG_FRAME_POINTER is not set, or it  
> > will
> > add "-fno-omit-frame-pointer" when it is set.
> >
> > The problem with PPC is that "-fno-omit-frame-pointer" is buggy and
> > causes gcc to produce bad code.
> 
> It's a deeper problem that is only _exposed_ by -fno-o-f-p (and can be
> hidden by -mno-sched-epilog in the one spot where it hit us).
> 
> > Perhaps a better name would be:
> >
> > HAVE_FRAME_POINTER_AS_DEFAULT
> 
> NO_NO_OMIT_FRAME_POINTER ?  Or better, just never use -fno-o-f-p,
> I don't see why you would ever need it.

Because on x86_64 it gives better back traces. x86_64 has no way to get
to the previous frames without it. There's code to use other debug
metadata to get back tracing, but for uses of things like the stack
tracer, we need to be able to use the actual stack frames.

As you said above, -fomit-frame-pointer is default when we optimize, and
that is how the kernel is built. If we optimize on x86_64 and do not use
-fno-omit-frame-pointer, the stack tracer is useless.

-- Steve

Re: [PATCH 1/3] powerpc, Makefile: Make it possible to safely select CONFIG_FRAME_POINTER

[Steven Rostedt]

On Tue, 2009-05-05 at 09:56 +0200, Segher Boessenkool wrote:
> > Yeah, I agree. This needs a better description. I only know what's  
> > going
> > on because I was there for the start of the discussion.
> >
> > But just to be sure, this is what I think is happening.
> >
> > When we add "-pg" to gcc, it automatically causes frame pointers to be
> > used.
> 
> Nope, it does no such thing.

Well, mcount is expected to be able to get to not just who called
mcount, but also the parent of that function. The way mcount is
implemented does not let you do that. If mcount was the first thing to
be called in a function, then it would have been perfect. We could get
to the caller, its parent, and even the parameters. But unfortunately,
mcount is called after the stack is set up. Thus, without frame pointers
(the way to find a previous frame) there's no way (on some archs) to
find the parent. Nor can we figure out the parameters, which really
sucks.


> 
> > But with PPC, it always has frame pointers and there's no problem.
> 
> Well, what do you call a "frame pointer"?  In the general meaning
> of "some register that points to the incoming function arguments
> and the function local variables", PowerPC can _usually_ use GPR1,
> the stack pointer (and indeed it is called "stack frame pointer"
> in the ABI).  In the more narrow meaning of "what GCC calls the
> frame pointer", "the thing that -fomit-frame-pointer optimises
> away" -- on PowerPC (and many other targets), -fomit-frame-pointer
> is the *default* when optimisation is enabled!
> 
> There is a GCC bug here though: it won't allow both -pg and
> -fomit-frame-pointer be set at the command line at the same time,
> even on targets where that is not problematic.
> 
> > But with Linux, when you add CONFIG_FRAME_POINTER, it automatically
> > adds:  -fno-omit-frame-pointer. Thus the config will add
> > "-fomit-frame-pointer" when CONFIG_FRAME_POINTER is not set, or it  
> > will
> > add "-fno-omit-frame-pointer" when it is set.
> >
> > The problem with PPC is that "-fno-omit-frame-pointer" is buggy and
> > causes gcc to produce bad code.
> 
> It's a deeper problem that is only _exposed_ by -fno-o-f-p (and can be
> hidden by -mno-sched-epilog in the one spot where it hit us).
> 
> > Perhaps a better name would be:
> >
> > HAVE_FRAME_POINTER_AS_DEFAULT
> 
> NO_NO_OMIT_FRAME_POINTER ?  Or better, just never use -fno-o-f-p,
> I don't see why you would ever need it.

Because on x86_64 it gives better back traces. x86_64 has no way to get
to the previous frames without it. There's code to use other debug
metadata to get back tracing, but for uses of things like the stack
tracer, we need to be able to use the actual stack frames.

As you said above, -fomit-frame-pointer is default when we optimize, and
that is how the kernel is built. If we optimize on x86_64 and do not use
-fno-omit-frame-pointer, the stack tracer is useless.

-- Steve

Re: [PATCH 1/3] powerpc, Makefile: Make it possible to safely select CONFIG_FRAME_POINTER

[Segher Boessenkool]

>>> When we add "-pg" to gcc, it automatically causes frame pointers  
>>> to be
>>> used.
>>
>> Nope, it does no such thing.
>
> Well, mcount is expected to be able to get to not just who called
> mcount, but also the parent of that function. The way mcount is
> implemented does not let you do that. If mcount was the first thing to
> be called in a function, then it would have been perfect. We could get
> to the caller, its parent, and even the parameters. But unfortunately,
> mcount is called after the stack is set up. Thus, without frame  
> pointers
> (the way to find a previous frame) there's no way (on some archs) to
> find the parent. Nor can we figure out the parameters, which really
> sucks.

Yes, and this is (supposedly) why GCC does not like seeing -pg and
-fomit-frame-pointer at the same time -- because that cannot work
*on some architectures*.  These are the same architectures that
do not enable -fomit-frame-pointer automatically at -O.

>> NO_NO_OMIT_FRAME_POINTER ?  Or better, just never use -fno-o-f-p,
>> I don't see why you would ever need it.
>
> Because on x86_64 it gives better back traces. x86_64 has no way to  
> get
> to the previous frames without it. There's code to use other debug
> metadata to get back tracing, but for uses of things like the stack
> tracer, we need to be able to use the actual stack frames.
>
> As you said above, -fomit-frame-pointer is default when we  
> optimize, and
> that is how the kernel is built. If we optimize on x86_64 and do  
> not use
> -fno-omit-frame-pointer, the stack tracer is useless.

No.  -fomit-frame-pointer is only the default when optimising on
archs/ABIs where it doesn't hinder debugging and -pg and all that
goodness; specifically, you do not get it by default on x86, not
at any optimisation level.


Segher

Re: [PATCH 1/3] powerpc, Makefile: Make it possible to safely select CONFIG_FRAME_POINTER

[Segher Boessenkool]

>>> When we add "-pg" to gcc, it automatically causes frame pointers  
>>> to be
>>> used.
>>
>> Nope, it does no such thing.
>
> Well, mcount is expected to be able to get to not just who called
> mcount, but also the parent of that function. The way mcount is
> implemented does not let you do that. If mcount was the first thing to
> be called in a function, then it would have been perfect. We could get
> to the caller, its parent, and even the parameters. But unfortunately,
> mcount is called after the stack is set up. Thus, without frame  
> pointers
> (the way to find a previous frame) there's no way (on some archs) to
> find the parent. Nor can we figure out the parameters, which really
> sucks.

Yes, and this is (supposedly) why GCC does not like seeing -pg and
-fomit-frame-pointer at the same time -- because that cannot work
*on some architectures*.  These are the same architectures that
do not enable -fomit-frame-pointer automatically at -O.

>> NO_NO_OMIT_FRAME_POINTER ?  Or better, just never use -fno-o-f-p,
>> I don't see why you would ever need it.
>
> Because on x86_64 it gives better back traces. x86_64 has no way to  
> get
> to the previous frames without it. There's code to use other debug
> metadata to get back tracing, but for uses of things like the stack
> tracer, we need to be able to use the actual stack frames.
>
> As you said above, -fomit-frame-pointer is default when we  
> optimize, and
> that is how the kernel is built. If we optimize on x86_64 and do  
> not use
> -fno-omit-frame-pointer, the stack tracer is useless.

No.  -fomit-frame-pointer is only the default when optimising on
archs/ABIs where it doesn't hinder debugging and -pg and all that
goodness; specifically, you do not get it by default on x86, not
at any optimisation level.


Segher

Re: [PATCH 1/3] powerpc, Makefile: Make it possible to safely select CONFIG_FRAME_POINTER

[Steven Rostedt]

On Tue, 2009-05-05 at 15:51 +0200, Segher Boessenkool wrote:
> >>> When we add "-pg" to gcc, it automatically causes frame pointers  
> >>> to be
> >>> used.
> >>
> >> Nope, it does no such thing.
> >
> > Well, mcount is expected to be able to get to not just who called
> > mcount, but also the parent of that function. The way mcount is
> > implemented does not let you do that. If mcount was the first thing to
> > be called in a function, then it would have been perfect. We could get
> > to the caller, its parent, and even the parameters. But unfortunately,
> > mcount is called after the stack is set up. Thus, without frame  
> > pointers
> > (the way to find a previous frame) there's no way (on some archs) to
> > find the parent. Nor can we figure out the parameters, which really
> > sucks.
> 
> Yes, and this is (supposedly) why GCC does not like seeing -pg and
> -fomit-frame-pointer at the same time -- because that cannot work
> *on some architectures*.  These are the same architectures that
> do not enable -fomit-frame-pointer automatically at -O.
> 
> >> NO_NO_OMIT_FRAME_POINTER ?  Or better, just never use -fno-o-f-p,
> >> I don't see why you would ever need it.
> >
> > Because on x86_64 it gives better back traces. x86_64 has no way to  
> > get
> > to the previous frames without it. There's code to use other debug
> > metadata to get back tracing, but for uses of things like the stack
> > tracer, we need to be able to use the actual stack frames.
> >
> > As you said above, -fomit-frame-pointer is default when we  
> > optimize, and
> > that is how the kernel is built. If we optimize on x86_64 and do  
> > not use
> > -fno-omit-frame-pointer, the stack tracer is useless.
> 
> No.  -fomit-frame-pointer is only the default when optimising on
> archs/ABIs where it doesn't hinder debugging and -pg and all that
> goodness; specifically, you do not get it by default on x86, not
> at any optimisation level.


OK, so what's the status with this patch series?

I don't want to pull it in unless I have an ack from Sam, and now
there's issues with having -fno-omit-frame-pointer. Should we add a
patch instead that simply removes that?

If we eliminate the -fno-omit-frame-pointer, would that solve the PPC
problem? And would it cause any other issues with other archs?

-- Steve

Re: [PATCH 1/3] powerpc, Makefile: Make it possible to safely select CONFIG_FRAME_POINTER

[Steven Rostedt]

On Tue, 2009-05-05 at 15:51 +0200, Segher Boessenkool wrote:
> >>> When we add "-pg" to gcc, it automatically causes frame pointers  
> >>> to be
> >>> used.
> >>
> >> Nope, it does no such thing.
> >
> > Well, mcount is expected to be able to get to not just who called
> > mcount, but also the parent of that function. The way mcount is
> > implemented does not let you do that. If mcount was the first thing to
> > be called in a function, then it would have been perfect. We could get
> > to the caller, its parent, and even the parameters. But unfortunately,
> > mcount is called after the stack is set up. Thus, without frame  
> > pointers
> > (the way to find a previous frame) there's no way (on some archs) to
> > find the parent. Nor can we figure out the parameters, which really
> > sucks.
> 
> Yes, and this is (supposedly) why GCC does not like seeing -pg and
> -fomit-frame-pointer at the same time -- because that cannot work
> *on some architectures*.  These are the same architectures that
> do not enable -fomit-frame-pointer automatically at -O.
> 
> >> NO_NO_OMIT_FRAME_POINTER ?  Or better, just never use -fno-o-f-p,
> >> I don't see why you would ever need it.
> >
> > Because on x86_64 it gives better back traces. x86_64 has no way to  
> > get
> > to the previous frames without it. There's code to use other debug
> > metadata to get back tracing, but for uses of things like the stack
> > tracer, we need to be able to use the actual stack frames.
> >
> > As you said above, -fomit-frame-pointer is default when we  
> > optimize, and
> > that is how the kernel is built. If we optimize on x86_64 and do  
> > not use
> > -fno-omit-frame-pointer, the stack tracer is useless.
> 
> No.  -fomit-frame-pointer is only the default when optimising on
> archs/ABIs where it doesn't hinder debugging and -pg and all that
> goodness; specifically, you do not get it by default on x86, not
> at any optimisation level.


OK, so what's the status with this patch series?

I don't want to pull it in unless I have an ack from Sam, and now
there's issues with having -fno-omit-frame-pointer. Should we add a
patch instead that simply removes that?

If we eliminate the -fno-omit-frame-pointer, would that solve the PPC
problem? And would it cause any other issues with other archs?

-- Steve

Re: [PATCH 1/3] powerpc, Makefile: Make it possible to safely select CONFIG_FRAME_POINTER

[Benjamin Herrenschmidt]

On Tue, 2009-05-05 at 19:11 -0400, Steven Rostedt wrote:

> OK, so what's the status with this patch series?
> 
> I don't want to pull it in unless I have an ack from Sam, and now
> there's issues with having -fno-omit-frame-pointer. Should we add a
> patch instead that simply removes that?
> 
> If we eliminate the -fno-omit-frame-pointer, would that solve the PPC
> problem? And would it cause any other issues with other archs?

Well, the patch looks fine to me to be honest I'm not sure what the
complaint is above... 

IE. On arch that define the new HAVE_NORMAL_FRAME_POINTER (let's just
call it HAVE_IMPLIED_FRAME_POINTER then :-)  we just don't do
-fno-omit-frame-pointer and avoid triggering the bug...

Segher, what are we missing here ?

Ben.

Re: [PATCH 1/3] powerpc, Makefile: Make it possible to safely select CONFIG_FRAME_POINTER

[Benjamin Herrenschmidt]

On Tue, 2009-05-05 at 19:11 -0400, Steven Rostedt wrote:

> OK, so what's the status with this patch series?
> 
> I don't want to pull it in unless I have an ack from Sam, and now
> there's issues with having -fno-omit-frame-pointer. Should we add a
> patch instead that simply removes that?
> 
> If we eliminate the -fno-omit-frame-pointer, would that solve the PPC
> problem? And would it cause any other issues with other archs?

Well, the patch looks fine to me to be honest I'm not sure what the
complaint is above... 

IE. On arch that define the new HAVE_NORMAL_FRAME_POINTER (let's just
call it HAVE_IMPLIED_FRAME_POINTER then :-)  we just don't do
-fno-omit-frame-pointer and avoid triggering the bug...

Segher, what are we missing here ?

Ben.

Re: [PATCH 1/3] powerpc, Makefile: Make it possible to safely select CONFIG_FRAME_POINTER

[Segher Boessenkool]

> Segher, what are we missing here ?

The symbol name is misleading, and the help text is incorrect.

With those things fixed, I won't oppose the patch; it would
be nice if the logic here was cleaned up to avoid all the
double negations, but I'm not going to do it, so I won't ask
others to either.


Segher

Re: [PATCH 1/3] powerpc, Makefile: Make it possible to safely select CONFIG_FRAME_POINTER

[Segher Boessenkool]

> Segher, what are we missing here ?

The symbol name is misleading, and the help text is incorrect.

With those things fixed, I won't oppose the patch; it would
be nice if the logic here was cleaned up to avoid all the
double negations, but I'm not going to do it, so I won't ask
others to either.


Segher

[PATCH 2/3] powerpc: Remove -fno-omit-frame-pointer workarounds

[Anton Vorontsov]

The workarounds aren't needed any longer since the top level Makefile
doesn't pass -fno-omit-frame-pointer cflag for PowerPC builds.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
---
 arch/powerpc/Makefile                    |    5 -----
 arch/powerpc/kernel/Makefile             |   12 ++++++------
 arch/powerpc/platforms/powermac/Makefile |    2 +-
 lib/Kconfig.debug                        |    6 +++---
 4 files changed, 10 insertions(+), 15 deletions(-)

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 551fc58..1dd7748 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -120,11 +120,6 @@ ifeq ($(CONFIG_6xx),y)
 KBUILD_CFLAGS		+= -mcpu=powerpc
 endif
 
-# Work around a gcc code-gen bug with -fno-omit-frame-pointer.
-ifeq ($(CONFIG_FUNCTION_TRACER),y)
-KBUILD_CFLAGS		+= -mno-sched-epilog
-endif
-
 cpu-as-$(CONFIG_4xx)		+= -Wa,-m405
 cpu-as-$(CONFIG_6xx)		+= -Wa,-maltivec
 cpu-as-$(CONFIG_POWER4)		+= -Wa,-maltivec
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 71901fb..fdbca81 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -14,14 +14,14 @@ endif
 
 ifdef CONFIG_FUNCTION_TRACER
 # Do not trace early boot code
-CFLAGS_REMOVE_cputable.o = -pg -mno-sched-epilog
-CFLAGS_REMOVE_prom_init.o = -pg -mno-sched-epilog
-CFLAGS_REMOVE_btext.o = -pg -mno-sched-epilog
-CFLAGS_REMOVE_prom.o = -pg -mno-sched-epilog
+CFLAGS_REMOVE_cputable.o = -pg
+CFLAGS_REMOVE_prom_init.o = -pg
+CFLAGS_REMOVE_btext.o = -pg
+CFLAGS_REMOVE_prom.o = -pg
 # do not trace tracer code
-CFLAGS_REMOVE_ftrace.o = -pg -mno-sched-epilog
+CFLAGS_REMOVE_ftrace.o = -pg
 # timers used by tracing
-CFLAGS_REMOVE_time.o = -pg -mno-sched-epilog
+CFLAGS_REMOVE_time.o = -pg
 endif
 
 obj-y				:= cputable.o ptrace.o syscalls.o \
diff --git a/arch/powerpc/platforms/powermac/Makefile b/arch/powerpc/platforms/powermac/Makefile
index 50f1693..0eb8781 100644
--- a/arch/powerpc/platforms/powermac/Makefile
+++ b/arch/powerpc/platforms/powermac/Makefile
@@ -2,7 +2,7 @@ CFLAGS_bootx_init.o  		+= -fPIC
 
 ifdef CONFIG_FUNCTION_TRACER
 # Do not trace early boot code
-CFLAGS_REMOVE_bootx_init.o = -pg -mno-sched-epilog
+CFLAGS_REMOVE_bootx_init.o = -pg
 endif
 
 obj-y				+= pic.o setup.o time.o feature.o pci.o \
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 1f1633b..cffbfc4 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -492,7 +492,7 @@ config LOCKDEP
 	bool
 	depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
 	select STACKTRACE
-	select FRAME_POINTER if !X86 && !MIPS && !PPC && !ARM_UNWIND && !S390
+	select FRAME_POINTER if !X86 && !MIPS && !ARM_UNWIND && !S390
 	select KALLSYMS
 	select KALLSYMS_ALL
 
@@ -865,13 +865,13 @@ config FAULT_INJECTION_STACKTRACE_FILTER
 	depends on FAULT_INJECTION_DEBUG_FS && STACKTRACE_SUPPORT
 	depends on !X86_64
 	select STACKTRACE
-	select FRAME_POINTER if !PPC && !S390
+	select FRAME_POINTER if !S390
 	help
 	  Provide stacktrace filter for fault-injection capabilities
 
 config LATENCYTOP
 	bool "Latency measuring infrastructure"
-	select FRAME_POINTER if !MIPS && !PPC && !S390
+	select FRAME_POINTER if !MIPS && !S390
 	select KALLSYMS
 	select KALLSYMS_ALL
 	select STACKTRACE
-- 
1.6.2.2

[PATCH 2/3] powerpc: Remove -fno-omit-frame-pointer workarounds

[Anton Vorontsov]

The workarounds aren't needed any longer since the top level Makefile
doesn't pass -fno-omit-frame-pointer cflag for PowerPC builds.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
---
 arch/powerpc/Makefile                    |    5 -----
 arch/powerpc/kernel/Makefile             |   12 ++++++------
 arch/powerpc/platforms/powermac/Makefile |    2 +-
 lib/Kconfig.debug                        |    6 +++---
 4 files changed, 10 insertions(+), 15 deletions(-)

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 551fc58..1dd7748 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -120,11 +120,6 @@ ifeq ($(CONFIG_6xx),y)
 KBUILD_CFLAGS		+= -mcpu=powerpc
 endif
 
-# Work around a gcc code-gen bug with -fno-omit-frame-pointer.
-ifeq ($(CONFIG_FUNCTION_TRACER),y)
-KBUILD_CFLAGS		+= -mno-sched-epilog
-endif
-
 cpu-as-$(CONFIG_4xx)		+= -Wa,-m405
 cpu-as-$(CONFIG_6xx)		+= -Wa,-maltivec
 cpu-as-$(CONFIG_POWER4)		+= -Wa,-maltivec
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 71901fb..fdbca81 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -14,14 +14,14 @@ endif
 
 ifdef CONFIG_FUNCTION_TRACER
 # Do not trace early boot code
-CFLAGS_REMOVE_cputable.o = -pg -mno-sched-epilog
-CFLAGS_REMOVE_prom_init.o = -pg -mno-sched-epilog
-CFLAGS_REMOVE_btext.o = -pg -mno-sched-epilog
-CFLAGS_REMOVE_prom.o = -pg -mno-sched-epilog
+CFLAGS_REMOVE_cputable.o = -pg
+CFLAGS_REMOVE_prom_init.o = -pg
+CFLAGS_REMOVE_btext.o = -pg
+CFLAGS_REMOVE_prom.o = -pg
 # do not trace tracer code
-CFLAGS_REMOVE_ftrace.o = -pg -mno-sched-epilog
+CFLAGS_REMOVE_ftrace.o = -pg
 # timers used by tracing
-CFLAGS_REMOVE_time.o = -pg -mno-sched-epilog
+CFLAGS_REMOVE_time.o = -pg
 endif
 
 obj-y				:= cputable.o ptrace.o syscalls.o \
diff --git a/arch/powerpc/platforms/powermac/Makefile b/arch/powerpc/platforms/powermac/Makefile
index 50f1693..0eb8781 100644
--- a/arch/powerpc/platforms/powermac/Makefile
+++ b/arch/powerpc/platforms/powermac/Makefile
@@ -2,7 +2,7 @@ CFLAGS_bootx_init.o  		+= -fPIC
 
 ifdef CONFIG_FUNCTION_TRACER
 # Do not trace early boot code
-CFLAGS_REMOVE_bootx_init.o = -pg -mno-sched-epilog
+CFLAGS_REMOVE_bootx_init.o = -pg
 endif
 
 obj-y				+= pic.o setup.o time.o feature.o pci.o \
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 1f1633b..cffbfc4 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -492,7 +492,7 @@ config LOCKDEP
 	bool
 	depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
 	select STACKTRACE
-	select FRAME_POINTER if !X86 && !MIPS && !PPC && !ARM_UNWIND && !S390
+	select FRAME_POINTER if !X86 && !MIPS && !ARM_UNWIND && !S390
 	select KALLSYMS
 	select KALLSYMS_ALL
 
@@ -865,13 +865,13 @@ config FAULT_INJECTION_STACKTRACE_FILTER
 	depends on FAULT_INJECTION_DEBUG_FS && STACKTRACE_SUPPORT
 	depends on !X86_64
 	select STACKTRACE
-	select FRAME_POINTER if !PPC && !S390
+	select FRAME_POINTER if !S390
 	help
 	  Provide stacktrace filter for fault-injection capabilities
 
 config LATENCYTOP
 	bool "Latency measuring infrastructure"
-	select FRAME_POINTER if !MIPS && !PPC && !S390
+	select FRAME_POINTER if !MIPS && !S390
 	select KALLSYMS
 	select KALLSYMS_ALL
 	select STACKTRACE
-- 
1.6.2.2

[PATCH 3/3] tracing: Tracers that use CALLER_ADDR macros should select FRAME_POINTER

[Anton Vorontsov]

Irqsoff, switch and preempt tracers use CALLER_ADDR macros, so they
should select FRAME_POINTER. Otherwise traces are meaningless.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
---
 kernel/trace/Kconfig |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 450d3c2..ad44791 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -122,6 +122,7 @@ config IRQSOFF_TRACER
 	select TRACE_IRQFLAGS
 	select TRACING
 	select TRACER_MAX_TRACE
+	select FRAME_POINTER
 	help
 	  This option measures the time spent in irqs-off critical
 	  sections, with microsecond accuracy.
@@ -143,6 +144,7 @@ config PREEMPT_TRACER
 	depends on PREEMPT
 	select TRACING
 	select TRACER_MAX_TRACE
+	select FRAME_POINTER
 	help
 	  This option measures the time spent in preemption off critical
 	  sections, with microsecond accuracy.
@@ -171,6 +173,7 @@ config SCHED_TRACER
 	select TRACING
 	select CONTEXT_SWITCH_TRACER
 	select TRACER_MAX_TRACE
+	select FRAME_POINTER
 	help
 	  This tracer tracks the latency of the highest priority task
 	  to be scheduled in, starting from the point it has woken up.
-- 
1.6.2.2

[PATCH 3/3] tracing: Tracers that use CALLER_ADDR macros should select FRAME_POINTER

[Anton Vorontsov]

Irqsoff, switch and preempt tracers use CALLER_ADDR macros, so they
should select FRAME_POINTER. Otherwise traces are meaningless.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
---
 kernel/trace/Kconfig |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 450d3c2..ad44791 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -122,6 +122,7 @@ config IRQSOFF_TRACER
 	select TRACE_IRQFLAGS
 	select TRACING
 	select TRACER_MAX_TRACE
+	select FRAME_POINTER
 	help
 	  This option measures the time spent in irqs-off critical
 	  sections, with microsecond accuracy.
@@ -143,6 +144,7 @@ config PREEMPT_TRACER
 	depends on PREEMPT
 	select TRACING
 	select TRACER_MAX_TRACE
+	select FRAME_POINTER
 	help
 	  This option measures the time spent in preemption off critical
 	  sections, with microsecond accuracy.
@@ -171,6 +173,7 @@ config SCHED_TRACER
 	select TRACING
 	select CONTEXT_SWITCH_TRACER
 	select TRACER_MAX_TRACE
+	select FRAME_POINTER
 	help
 	  This tracer tracks the latency of the highest priority task
 	  to be scheduled in, starting from the point it has woken up.
-- 
1.6.2.2

[PATCH v4 0/3] Tracers vs. CALLER_ADDR on PowerPC

[Anton Vorontsov]

Hi all,

Here is another approach to fixing tracers vs. CALLER_ADDR problem
on PowerPC.

Preface for those who don't know or forgot what the problem is:

Gcc frame pointers do nothing useful on PowerPC (they're harmful,
actually), and thus lib/Kconfig.debug makes CONFIG_FRAME_POINTER
unselectable on PPC targets, but CALLER_ADDR macros are available
only with CONFIG_FRAME_POINTER, 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

While it should look like this:

[...]
  <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

I've tried to fix the issue via expanding the #ifdef in the ftrace.h:
http://lkml.org/lkml/2009/1/31/141

Then Steven Rostedt suggested to implement something more generic,
i.e. HAVE_NORMAL_FRAME_POINTERS Kconfig symbol.

I found a way to solve the problem w/o additional symbols, but
with some Makefile magic (http://lkml.org/lkml/2009/2/4/273).
But because of top-level Makefile issues on other arches
(http://lkml.org/lkml/2009/2/14/89) I had to abandon the approach.


So, this patch set combines Steven Rostedt's idea and a small
Makefile change, so that now only top-level Makefile has to know
about the new symbol, and the rest of the kernel can stay with
using CONFIG_FRAME_POINTER.

-- 
Anton Vorontsov
email: cbouatmailru@gmail.com
irc://irc.freenode.net/bd2

[PATCH 2/3] powerpc: Remove -fno-omit-frame-pointer workarounds

[Anton Vorontsov]

The workarounds aren't needed any longer since the top level Makefile
doesn't pass -fno-omit-frame-pointer cflag for PowerPC.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
---
 arch/powerpc/Makefile                    |    5 -----
 arch/powerpc/kernel/Makefile             |   12 ++++++------
 arch/powerpc/platforms/powermac/Makefile |    2 +-
 lib/Kconfig.debug                        |    6 +++---
 4 files changed, 10 insertions(+), 15 deletions(-)

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 551fc58..1dd7748 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -120,11 +120,6 @@ ifeq ($(CONFIG_6xx),y)
 KBUILD_CFLAGS		+= -mcpu=powerpc
 endif
 
-# Work around a gcc code-gen bug with -fno-omit-frame-pointer.
-ifeq ($(CONFIG_FUNCTION_TRACER),y)
-KBUILD_CFLAGS		+= -mno-sched-epilog
-endif
-
 cpu-as-$(CONFIG_4xx)		+= -Wa,-m405
 cpu-as-$(CONFIG_6xx)		+= -Wa,-maltivec
 cpu-as-$(CONFIG_POWER4)		+= -Wa,-maltivec
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index dfec3d2..f86caeb 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -14,14 +14,14 @@ endif
 
 ifdef CONFIG_FUNCTION_TRACER
 # Do not trace early boot code
-CFLAGS_REMOVE_cputable.o = -pg -mno-sched-epilog
-CFLAGS_REMOVE_prom_init.o = -pg -mno-sched-epilog
-CFLAGS_REMOVE_btext.o = -pg -mno-sched-epilog
-CFLAGS_REMOVE_prom.o = -pg -mno-sched-epilog
+CFLAGS_REMOVE_cputable.o = -pg
+CFLAGS_REMOVE_prom_init.o = -pg
+CFLAGS_REMOVE_btext.o = -pg
+CFLAGS_REMOVE_prom.o = -pg
 # do not trace tracer code
-CFLAGS_REMOVE_ftrace.o = -pg -mno-sched-epilog
+CFLAGS_REMOVE_ftrace.o = -pg
 # timers used by tracing
-CFLAGS_REMOVE_time.o = -pg -mno-sched-epilog
+CFLAGS_REMOVE_time.o = -pg
 endif
 
 obj-y				:= cputable.o ptrace.o syscalls.o \
diff --git a/arch/powerpc/platforms/powermac/Makefile b/arch/powerpc/platforms/powermac/Makefile
index 50f1693..0eb8781 100644
--- a/arch/powerpc/platforms/powermac/Makefile
+++ b/arch/powerpc/platforms/powermac/Makefile
@@ -2,7 +2,7 @@ CFLAGS_bootx_init.o  		+= -fPIC
 
 ifdef CONFIG_FUNCTION_TRACER
 # Do not trace early boot code
-CFLAGS_REMOVE_bootx_init.o = -pg -mno-sched-epilog
+CFLAGS_REMOVE_bootx_init.o = -pg
 endif
 
 obj-y				+= pic.o setup.o time.o feature.o pci.o \
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index fc8cd1f..713620d 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -493,7 +493,7 @@ config LOCKDEP
 	bool
 	depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
 	select STACKTRACE
-	select FRAME_POINTER if !MIPS && !PPC && !ARM_UNWIND
+	select FRAME_POINTER if !MIPS && !ARM_UNWIND
 	select KALLSYMS
 	select KALLSYMS_ALL
 
@@ -866,13 +866,13 @@ config FAULT_INJECTION_STACKTRACE_FILTER
 	depends on FAULT_INJECTION_DEBUG_FS && STACKTRACE_SUPPORT
 	depends on !X86_64
 	select STACKTRACE
-	select FRAME_POINTER if !PPC
+	select FRAME_POINTER
 	help
 	  Provide stacktrace filter for fault-injection capabilities
 
 config LATENCYTOP
 	bool "Latency measuring infrastructure"
-	select FRAME_POINTER if !MIPS && !PPC
+	select FRAME_POINTER if !MIPS
 	select KALLSYMS
 	select KALLSYMS_ALL
 	select STACKTRACE
-- 
1.5.6.5

[PATCH 2/3] powerpc: Remove -fno-omit-frame-pointer workarounds

[Anton Vorontsov]

The workarounds aren't needed any longer since the top level Makefile
doesn't pass -fno-omit-frame-pointer cflag for PowerPC.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
---
 arch/powerpc/Makefile                    |    5 -----
 arch/powerpc/kernel/Makefile             |   12 ++++++------
 arch/powerpc/platforms/powermac/Makefile |    2 +-
 lib/Kconfig.debug                        |    6 +++---
 4 files changed, 10 insertions(+), 15 deletions(-)

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 551fc58..1dd7748 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -120,11 +120,6 @@ ifeq ($(CONFIG_6xx),y)
 KBUILD_CFLAGS		+= -mcpu=powerpc
 endif
 
-# Work around a gcc code-gen bug with -fno-omit-frame-pointer.
-ifeq ($(CONFIG_FUNCTION_TRACER),y)
-KBUILD_CFLAGS		+= -mno-sched-epilog
-endif
-
 cpu-as-$(CONFIG_4xx)		+= -Wa,-m405
 cpu-as-$(CONFIG_6xx)		+= -Wa,-maltivec
 cpu-as-$(CONFIG_POWER4)		+= -Wa,-maltivec
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index dfec3d2..f86caeb 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -14,14 +14,14 @@ endif
 
 ifdef CONFIG_FUNCTION_TRACER
 # Do not trace early boot code
-CFLAGS_REMOVE_cputable.o = -pg -mno-sched-epilog
-CFLAGS_REMOVE_prom_init.o = -pg -mno-sched-epilog
-CFLAGS_REMOVE_btext.o = -pg -mno-sched-epilog
-CFLAGS_REMOVE_prom.o = -pg -mno-sched-epilog
+CFLAGS_REMOVE_cputable.o = -pg
+CFLAGS_REMOVE_prom_init.o = -pg
+CFLAGS_REMOVE_btext.o = -pg
+CFLAGS_REMOVE_prom.o = -pg
 # do not trace tracer code
-CFLAGS_REMOVE_ftrace.o = -pg -mno-sched-epilog
+CFLAGS_REMOVE_ftrace.o = -pg
 # timers used by tracing
-CFLAGS_REMOVE_time.o = -pg -mno-sched-epilog
+CFLAGS_REMOVE_time.o = -pg
 endif
 
 obj-y				:= cputable.o ptrace.o syscalls.o \
diff --git a/arch/powerpc/platforms/powermac/Makefile b/arch/powerpc/platforms/powermac/Makefile
index 50f1693..0eb8781 100644
--- a/arch/powerpc/platforms/powermac/Makefile
+++ b/arch/powerpc/platforms/powermac/Makefile
@@ -2,7 +2,7 @@ CFLAGS_bootx_init.o  		+= -fPIC
 
 ifdef CONFIG_FUNCTION_TRACER
 # Do not trace early boot code
-CFLAGS_REMOVE_bootx_init.o = -pg -mno-sched-epilog
+CFLAGS_REMOVE_bootx_init.o = -pg
 endif
 
 obj-y				+= pic.o setup.o time.o feature.o pci.o \
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index fc8cd1f..713620d 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -493,7 +493,7 @@ config LOCKDEP
 	bool
 	depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
 	select STACKTRACE
-	select FRAME_POINTER if !MIPS && !PPC && !ARM_UNWIND
+	select FRAME_POINTER if !MIPS && !ARM_UNWIND
 	select KALLSYMS
 	select KALLSYMS_ALL
 
@@ -866,13 +866,13 @@ config FAULT_INJECTION_STACKTRACE_FILTER
 	depends on FAULT_INJECTION_DEBUG_FS && STACKTRACE_SUPPORT
 	depends on !X86_64
 	select STACKTRACE
-	select FRAME_POINTER if !PPC
+	select FRAME_POINTER
 	help
 	  Provide stacktrace filter for fault-injection capabilities
 
 config LATENCYTOP
 	bool "Latency measuring infrastructure"
-	select FRAME_POINTER if !MIPS && !PPC
+	select FRAME_POINTER if !MIPS
 	select KALLSYMS
 	select KALLSYMS_ALL
 	select STACKTRACE
-- 
1.5.6.5

Re: [PATCH 2/3] powerpc: Remove -fno-omit-frame-pointer workarounds

[Steven Rostedt]

Ben,

Can you ACK or take this patch too.

Thanks,

-- Steve


On Fri, 2009-03-20 at 19:44 +0300, Anton Vorontsov wrote:
> The workarounds aren't needed any longer since the top level Makefile
> doesn't pass -fno-omit-frame-pointer cflag for PowerPC.
> 
> Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
> ---
>  arch/powerpc/Makefile                    |    5 -----
>  arch/powerpc/kernel/Makefile             |   12 ++++++------
>  arch/powerpc/platforms/powermac/Makefile |    2 +-
>  lib/Kconfig.debug                        |    6 +++---
>  4 files changed, 10 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> index 551fc58..1dd7748 100644
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -120,11 +120,6 @@ ifeq ($(CONFIG_6xx),y)
>  KBUILD_CFLAGS		+= -mcpu=powerpc
>  endif
>  
> -# Work around a gcc code-gen bug with -fno-omit-frame-pointer.
> -ifeq ($(CONFIG_FUNCTION_TRACER),y)
> -KBUILD_CFLAGS		+= -mno-sched-epilog
> -endif
> -
>  cpu-as-$(CONFIG_4xx)		+= -Wa,-m405
>  cpu-as-$(CONFIG_6xx)		+= -Wa,-maltivec
>  cpu-as-$(CONFIG_POWER4)		+= -Wa,-maltivec
> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> index dfec3d2..f86caeb 100644
> --- a/arch/powerpc/kernel/Makefile
> +++ b/arch/powerpc/kernel/Makefile
> @@ -14,14 +14,14 @@ endif
>  
>  ifdef CONFIG_FUNCTION_TRACER
>  # Do not trace early boot code
> -CFLAGS_REMOVE_cputable.o = -pg -mno-sched-epilog
> -CFLAGS_REMOVE_prom_init.o = -pg -mno-sched-epilog
> -CFLAGS_REMOVE_btext.o = -pg -mno-sched-epilog
> -CFLAGS_REMOVE_prom.o = -pg -mno-sched-epilog
> +CFLAGS_REMOVE_cputable.o = -pg
> +CFLAGS_REMOVE_prom_init.o = -pg
> +CFLAGS_REMOVE_btext.o = -pg
> +CFLAGS_REMOVE_prom.o = -pg
>  # do not trace tracer code
> -CFLAGS_REMOVE_ftrace.o = -pg -mno-sched-epilog
> +CFLAGS_REMOVE_ftrace.o = -pg
>  # timers used by tracing
> -CFLAGS_REMOVE_time.o = -pg -mno-sched-epilog
> +CFLAGS_REMOVE_time.o = -pg
>  endif
>  
>  obj-y				:= cputable.o ptrace.o syscalls.o \
> diff --git a/arch/powerpc/platforms/powermac/Makefile b/arch/powerpc/platforms/powermac/Makefile
> index 50f1693..0eb8781 100644
> --- a/arch/powerpc/platforms/powermac/Makefile
> +++ b/arch/powerpc/platforms/powermac/Makefile
> @@ -2,7 +2,7 @@ CFLAGS_bootx_init.o  		+= -fPIC
>  
>  ifdef CONFIG_FUNCTION_TRACER
>  # Do not trace early boot code
> -CFLAGS_REMOVE_bootx_init.o = -pg -mno-sched-epilog
> +CFLAGS_REMOVE_bootx_init.o = -pg
>  endif
>  
>  obj-y				+= pic.o setup.o time.o feature.o pci.o \
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index fc8cd1f..713620d 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -493,7 +493,7 @@ config LOCKDEP
>  	bool
>  	depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
>  	select STACKTRACE
> -	select FRAME_POINTER if !MIPS && !PPC && !ARM_UNWIND
> +	select FRAME_POINTER if !MIPS && !ARM_UNWIND
>  	select KALLSYMS
>  	select KALLSYMS_ALL
>  
> @@ -866,13 +866,13 @@ config FAULT_INJECTION_STACKTRACE_FILTER
>  	depends on FAULT_INJECTION_DEBUG_FS && STACKTRACE_SUPPORT
>  	depends on !X86_64
>  	select STACKTRACE
> -	select FRAME_POINTER if !PPC
> +	select FRAME_POINTER
>  	help
>  	  Provide stacktrace filter for fault-injection capabilities
>  
>  config LATENCYTOP
>  	bool "Latency measuring infrastructure"
> -	select FRAME_POINTER if !MIPS && !PPC
> +	select FRAME_POINTER if !MIPS
>  	select KALLSYMS
>  	select KALLSYMS_ALL
>  	select STACKTRACE

Re: [PATCH 2/3] powerpc: Remove -fno-omit-frame-pointer workarounds

[Steven Rostedt]

Ben,

Can you ACK or take this patch too.

Thanks,

-- Steve


On Fri, 2009-03-20 at 19:44 +0300, Anton Vorontsov wrote:
> The workarounds aren't needed any longer since the top level Makefile
> doesn't pass -fno-omit-frame-pointer cflag for PowerPC.
> 
> Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
> ---
>  arch/powerpc/Makefile                    |    5 -----
>  arch/powerpc/kernel/Makefile             |   12 ++++++------
>  arch/powerpc/platforms/powermac/Makefile |    2 +-
>  lib/Kconfig.debug                        |    6 +++---
>  4 files changed, 10 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> index 551fc58..1dd7748 100644
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -120,11 +120,6 @@ ifeq ($(CONFIG_6xx),y)
>  KBUILD_CFLAGS		+= -mcpu=powerpc
>  endif
>  
> -# Work around a gcc code-gen bug with -fno-omit-frame-pointer.
> -ifeq ($(CONFIG_FUNCTION_TRACER),y)
> -KBUILD_CFLAGS		+= -mno-sched-epilog
> -endif
> -
>  cpu-as-$(CONFIG_4xx)		+= -Wa,-m405
>  cpu-as-$(CONFIG_6xx)		+= -Wa,-maltivec
>  cpu-as-$(CONFIG_POWER4)		+= -Wa,-maltivec
> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> index dfec3d2..f86caeb 100644
> --- a/arch/powerpc/kernel/Makefile
> +++ b/arch/powerpc/kernel/Makefile
> @@ -14,14 +14,14 @@ endif
>  
>  ifdef CONFIG_FUNCTION_TRACER
>  # Do not trace early boot code
> -CFLAGS_REMOVE_cputable.o = -pg -mno-sched-epilog
> -CFLAGS_REMOVE_prom_init.o = -pg -mno-sched-epilog
> -CFLAGS_REMOVE_btext.o = -pg -mno-sched-epilog
> -CFLAGS_REMOVE_prom.o = -pg -mno-sched-epilog
> +CFLAGS_REMOVE_cputable.o = -pg
> +CFLAGS_REMOVE_prom_init.o = -pg
> +CFLAGS_REMOVE_btext.o = -pg
> +CFLAGS_REMOVE_prom.o = -pg
>  # do not trace tracer code
> -CFLAGS_REMOVE_ftrace.o = -pg -mno-sched-epilog
> +CFLAGS_REMOVE_ftrace.o = -pg
>  # timers used by tracing
> -CFLAGS_REMOVE_time.o = -pg -mno-sched-epilog
> +CFLAGS_REMOVE_time.o = -pg
>  endif
>  
>  obj-y				:= cputable.o ptrace.o syscalls.o \
> diff --git a/arch/powerpc/platforms/powermac/Makefile b/arch/powerpc/platforms/powermac/Makefile
> index 50f1693..0eb8781 100644
> --- a/arch/powerpc/platforms/powermac/Makefile
> +++ b/arch/powerpc/platforms/powermac/Makefile
> @@ -2,7 +2,7 @@ CFLAGS_bootx_init.o  		+= -fPIC
>  
>  ifdef CONFIG_FUNCTION_TRACER
>  # Do not trace early boot code
> -CFLAGS_REMOVE_bootx_init.o = -pg -mno-sched-epilog
> +CFLAGS_REMOVE_bootx_init.o = -pg
>  endif
>  
>  obj-y				+= pic.o setup.o time.o feature.o pci.o \
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index fc8cd1f..713620d 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -493,7 +493,7 @@ config LOCKDEP
>  	bool
>  	depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
>  	select STACKTRACE
> -	select FRAME_POINTER if !MIPS && !PPC && !ARM_UNWIND
> +	select FRAME_POINTER if !MIPS && !ARM_UNWIND
>  	select KALLSYMS
>  	select KALLSYMS_ALL
>  
> @@ -866,13 +866,13 @@ config FAULT_INJECTION_STACKTRACE_FILTER
>  	depends on FAULT_INJECTION_DEBUG_FS && STACKTRACE_SUPPORT
>  	depends on !X86_64
>  	select STACKTRACE
> -	select FRAME_POINTER if !PPC
> +	select FRAME_POINTER
>  	help
>  	  Provide stacktrace filter for fault-injection capabilities
>  
>  config LATENCYTOP
>  	bool "Latency measuring infrastructure"
> -	select FRAME_POINTER if !MIPS && !PPC
> +	select FRAME_POINTER if !MIPS
>  	select KALLSYMS
>  	select KALLSYMS_ALL
>  	select STACKTRACE