linux-kernel - Re: [PATCH] tracing/markers: make markers select tracepoints

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Date:	Fri, 20 Feb 2009 18:22:41 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Randy Dunlap <randy.dunlap@...cle.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org, zippel@...ux-m68k.org,
	linux-kbuild@...r.kernel.org
Subject: Re: [PATCH] tracing/markers: make markers select tracepoints


* Randy Dunlap <randy.dunlap@...cle.com> wrote:

> > This is what happens on the following build error:
> > 
> > kernel/built-in.o: In function `marker_update_probe_range':
> > (.text+0x52f64): undefined reference to `tracepoint_probe_register_noupdate'
> > kernel/built-in.o: In function `marker_update_probe_range':
> > (.text+0x52f74): undefined reference to `tracepoint_probe_unregister_noupdate'
> > kernel/built-in.o: In function `marker_update_probe_range':
> > (.text+0x52fb9): undefined reference to `tracepoint_probe_unregister_noupdate'
> > kernel/built-in.o: In function `marker_update_probes':
> > marker.c:(.text+0x530ba): undefined reference to `tracepoint_probe_update_all'
> > 
> > CONFIG_KVM_TRACE will select CONFIG_MARKER, but the latter 
> > depends on CONFIG_TRACEPOINTS which will not be selected.
> > 
> > A temporary fix is to make CONFIG_MARKER select 
> > CONFIG_TRACEPOINTS, though it doesn't fix the source KConfig 
> > dependency handling problem.
> > 
> > Reported-by: Ingo Molnar <mingo@...e.hu>
> > Cc: Roman Zippel <zippel@...ux-m68k.org>
> > Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> > ---
> >  init/Kconfig |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/init/Kconfig b/init/Kconfig
> > index b6400a5..a93f957 100644
> > --- a/init/Kconfig
> > +++ b/init/Kconfig
> > @@ -975,7 +975,7 @@ config TRACEPOINTS
> >  
> >  config MARKERS
> >  	bool "Activate markers"
> > -	depends on TRACEPOINTS
> > +	select TRACEPOINTS
> >  	help
> >  	  Place an empty function call at each marker site. Can be
> >  	  dynamically changed for a probe function.
> 
> but using "select" instead of "depends on" just causes the 
> kind of problem that you described, whereas using "depends on" 
> does follow dependency chains.

Well, as long as the secondary selects are 'expanded' along the 
line of dependencies, it should still be fine. With an 
increasing number of dependencies it quickly becomes ugly 
though. This might be one of the cases where it works.

Eventually we should eliminate markers, their uses can either be 
converted to new-style tracepoints, or to ftrace_printk().

	Ingo
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