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

From: Anton Vorontsov <[email-masked]>
Date: Sat, 2 May 2009 04:13:29 +0400

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 <[email-masked]>
  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: [email-masked]
irc://irc.freenode.net/bd2