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

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Date:	Fri, 20 Feb 2009 09:29:09 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Ingo Molnar <mingo@...e.hu>
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

Ingo Molnar wrote:
> * 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 

Agreed.

> increasing number of dependencies it quickly becomes ugly 
> though. This might be one of the cases where it works.

Agreed.

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


Thanks,
-- 
~Randy
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