On Fri, Mar 20, 2009 at 07:44:04PM +0300, Anton Vorontsov wrote:
> 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.
Oh, and btw, I'm aware of
commit c79a61f55773d2519fd0525bf58385f7d20752d3
Author: Uwe Kleine-Koenig <u.kleine-koe...@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.
Thanks,
--
Anton Vorontsov
email: cbouatmai...@gmail.com
irc://irc.freenode.net/bd2
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