Messages in this thread | | | Date | Sat, 2 May 2009 04:13:29 +0400 | From | Anton Vorontsov <> | Subject | [PATCH v5 0/3] Tracers vs. CALLER_ADDR on PowerPC |
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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,
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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
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