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

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Date:   Wed, 19 Oct 2016 15:06:34 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.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

Em Wed, Oct 19, 2016 at 03:05:48PM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Wed, Oct 19, 2016 at 02:48:45PM -0300, Arnaldo Carvalho de Melo escreveu:
> > Em Tue, Oct 18, 2016 at 11:29:53AM -0400, Steven Rostedt escreveu:
> > > On Tue, 18 Oct 2016 11:01:09 +0900
> > > Namhyung Kim <namhyung@...nel.org> wrote:
> > > 
> > > > Hi Honggyu,
> > > > 
> > > > You need to CC relevant maintainers when you send patches to LKML.
> > > > For the libtraceevent, they are Arnaldo and Steven.  You can use
> > > > scripts/get_maintainer.pl for this job later.  In addition running
> > > > scripts/checkpatch.pl before sending patches is a good habit.
> > > > 
> > > > Arnaldo and Steve,
> > > > 
> > > > This is from uftrace building libtraceevent with the optimization flag
> > > > and we want to fix the upstream as well.
> > > > 
> > > 
> > > Acked-by: Steven Rostedt <rostedt@...dmis.org>
> > 
> > So right after applying this patch I get these new warnings, investigating...
> 
> 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,

Ah, the patch I had so far shutting off most of this is:


diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
index 664c90c8e22b..449056e96fe6 100644
--- a/tools/lib/traceevent/event-parse.c
+++ b/tools/lib/traceevent/event-parse.c
@@ -3490,7 +3490,7 @@ struct event_format *
 pevent_find_event_by_name(struct pevent *pevent,
 			  const char *sys, const char *name)
 {
-	struct event_format *event;
+	struct event_format *event = NULL;
 	int i;
 
 	if (pevent->last_event &&
@@ -4843,7 +4843,7 @@ static void pretty_print(struct trace_seq *s, void *data, int size, struct event
 	char format[32];
 	int show_func;
 	int len_as_arg;
-	int len_arg;
+	int len_arg = 0;
 	int len;
 	int ls;
 
@@ -5102,8 +5102,8 @@ void pevent_data_lat_fmt(struct pevent *pevent,
 	static int migrate_disable_exists;
 	unsigned int lat_flags;
 	unsigned int pc;
-	int lock_depth;
-	int migrate_disable;
+	int lock_depth = 0;
+	int migrate_disable = 0;
 	int hardirq;
 	int softirq;
 	void *data = record->data;