linux-kernel - Re: [PATCH 1/3] tools lib traceevent: Add -O2 option to traceevent

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Message-ID: <20161019152156.4149ca74@gandalf.local.home>
Date:   Wed, 19 Oct 2016 15:21:56 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Namhyung Kim <namhyung@...nel.org>,
        Honggyu Kim <hong.gyu.kim@....com>,
        linux-kernel@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH 1/3] tools lib traceevent: Add -O2 option to traceevent

On Wed, 19 Oct 2016 15:05:48 -0300
Arnaldo Carvalho de Melo <acme@...nel.org> wrote:

 
> Some are the compiler not grokking logic where the compiler gets
> confused with logic that tests one variable to use another and thinks it
> is using garbage (uninitialized stuff), I tried to follow the logic and
> I think it got slightly more confused than me, as I _think_ its not a
> problem, but the one on the case entry for
> 
>   OLD_RINGBUF_TYPE_TIME_EXTEND
> 
> in old_update_pointers() looks like a bug, unless some macro magic is
> taking place that updates that 'lenght' variable.
> 
> Rostedt, that -O2 unleashed some warnings, please check, I'll defer
> applying those patches till it doesn't show these warnings, i.e. till
> other patches fixing these issues or simply silencing the compiler with
> a harmless init gets submitted,
> 
> Thanks,

Note, that code is for the first version of the ftrace ring buffer that
got changed around 2.6.32 I believe. And since trace-cmd was the only
tool that directly looked at the code, I was able to "break" abi and
update trace-cmd to have a new version. So that code isn't even used
anywhere on newer kernels.

That said, could you add in the case statement for
OLD_RINGBUF_TYPE_TIME_EXTEND:

	length = 0;

I think that should be fine.

-- Steve