Re: Ftrace for Microblaze - notrace

From: Michal Simek
Date: Tue Nov 03 2009 - 11:46:53 EST

Steven Rostedt wrote:
On Tue, 2009-11-03 at 14:32 +0100, Michal Simek wrote:
Hi Thomas, Ingo, Steven and others

I am working on ftrace support for Microblaze. I have done basic ftrace
support - initcall, kmemtrace and other.
Currently I am working on function trace support. I did asm code as is
written in Documentation/trace/ftrace-design.txt.

I have two poins/questions.

I desided to use HAVE_FUNCTION_TRACE_MCOUNT_TEST - just test function_trace_stop in asm code - that shouldn't be a problem.

Yeah, and if you don't have that, it is taken care of in the generic
code too.

jj, I know - asm checking is just two instruction - that's why I use it.

I disable -pg in main Makefile because not work for me (more info below) and I enable it just for two file in arch/microblaze (irq.c and intc.c) - recompile kernel and test. Log is below and you can see that I am able to see output for function. That's why I think that my mcount function should be correct. Am I right?

uclinux login: root
# cd ; mkdir /debug; mount -t debugfs none /debug; cat /debug/tracing/available_
tracers; echo function > /debug/tracing/current_tracer;echo 1 > /debug/tracing/t
racing_enabled;cat /debug/tracing/trace | head -n 10
wakeup_rt wakeup function sched_switch nop
# tracer: function
# | | | | |
sh-52 [000] 184.940000: irq_call <-do_IRQ
sh-52 [000] 184.940000: do_IRQ <-get_irq
sh-52 [000] 184.940000: handle_level_irq <-intc_mask_ack
sh-52 [000] 184.950000: handle_level_irq <-intc_enable_or_unmask
sh-52 [000] 184.950000: do_IRQ <-get_irq
sh-52 [000] 184.950000: handle_level_irq <-intc_mask_ack

When is used -pg flag kernel stops when I enable function tracer.
Interesting is that freeze than I setup function tracing (echo function > .../current/tracer). Is it correct behavior? I think that trace should start after (echo 1> .../tracing_enabled).

No, tracing_enabled is default on and should not be used (may go away).
Tracing starts as soon as you echo function into current_tracer.


The next thing is about annotation notrace. I look at all arch. Is there any algorithm which function should use it? I think that this could be a reason why I my kernel freeze when enable function tracer.

I tested to add -pg flag for process.c file and after it kernel freeze too. Is it mean that problem could be there?


Is there any manual or instruction which functions are dangerous and especially why?

Any other suggestion?

Just remember that -pg is very intrusive. I don't know your arch, nor
have I seen the code you did to update it. You can disable the -pg from
process.c by adding in the Makefile:

CFLAGS_REMOVE_process.o = -pg

jj, I know how to do it.

And that will keep the process.c from being compiled with it. There may
be other files in the arch that should not have it. There's several in
x86 and in PowerPC.

Do you know why they exclude it?

Can I use any special debug features? I mean I look at kernel.h and there are some trace_printk function - but they don't work for me. Is it possible to use them or not?


-- Steve

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at