Date: Tue, 24 Nov 2015 16:24:50 +0900
From: Namhyung Kim <namhyung@kernel.org>
To: Arnaldo Carvalho de Melo <acme@kernel.org>
CC: =?utf-8?B?5bmz5p2+6ZuF5bezIC8gSElSQU1BVFXvvIxNQVNBTUk=?= 
	<masami.hiramatsu.pt@hitachi.com>,
        Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>, Jiri Olsa <jolsa@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>, David Ahern <dsahern@gmail.com>,
        Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: [RFC/PATCH] perf tools: Introduce perf_thread for backtrace
Message-ID: <20151124072450.GC2636@sejong>
References: <1447999383-15456-1-git-send-email-namhyung@kernel.org>
 <50399556C9727B4D88A595C8584AAB375262792C@GSjpTKYDCembx32.service.hitachi.net>
 <20151120121044.GJ29361@kernel.org>
MIME-Version: 1.0
In-Reply-To: <20151120121044.GJ29361@kernel.org>
User-Agent: Mutt/1.5.24 (2015-08-30)
Content-Type: text/plain; charset="utf-8"
Content-Disposition: inline
Content-Transfer-Encoding: 8BIT
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1992
Lines: 47

Hi Arnaldo and Masami,

On Fri, Nov 20, 2015 at 09:10:44AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Fri, Nov 20, 2015 at 09:05:23AM +0000, 平松雅巳 / HIRAMATU，MASAMI escreveu:
> > >From: Namhyung Kim [mailto:namhyung@kernel.org]
> > >
> > >Backtrace is a crucial info for debugging.  And upcoming refcnt
> > >tracking facility also wants to use it.
> > >
> > >So instead of relying on glibc's backtrace_symbols[_fd] which misses
> > >some (static) functions , use our own symbol searching mechanism.  To
> > >do that, add perf_thread global variable to keep its maps and symbols.
> > 
> > Hmm, I doubt that this can work for debugging situation, because
> > sometimes backtrace facilities has to debug itself by itself.
> 
> That is a valid point, possibly we can have both and when we think that
> the code we rely on for resolving symbols has issues, activate the
> other, more expensive, binutils/elfutils spawned command line utilities
> to do compare the results?

Yeah, that's a possible solution.  We can start by using our own, and
if there's a certain amount of failure in symbol resolving, then
fallback to glibc's backtrace_symbols + addr2line.


>  
> > For the some (static) functions, I'd rather like to use glibc's 
> > backtrace_symbols and addr2line or even with raw address for
> > reliability...

I also printed the raw addresses in case of doubts, so you could
verify its correctness. :)  And IMHO, if something is severely broken,
we might not rely on glibc too.

Having said that, I agree with your concern and it needs the fallback
method for possible malfunction.  But I guess it'd work quite well for
most cases so it's worth trying to convert using it.  I'll work on the
fallback method then..

Thanks,
Namhyung
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/