linux-kernel - Re: [PATCH] building libtraceevent with clang

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Date:   Mon, 13 Feb 2017 12:14:18 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Namhyung Kim <namhyung@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] building libtraceevent with clang

On Mon, 13 Feb 2017 13:26:22 -0300
Arnaldo Carvalho de Melo <acme@...nel.org> wrote:


> > diff --git a/tools/lib/traceevent/kbuffer-parse.c b/tools/lib/traceevent/kbuffer-parse.c
> > index 65984f1c2974..2009cb7d9675 100644
> > --- a/tools/lib/traceevent/kbuffer-parse.c
> > +++ b/tools/lib/traceevent/kbuffer-parse.c
> > @@ -315,6 +315,7 @@ static unsigned int old_update_pointers(struct kbuffer *kbuf)
> >  		extend += delta;
> >  		delta = extend;
> >  		ptr += 4;
> > +		lenght = 0;  
> 
> ouch, 'length' :-)
> 
> clang provides a really nice error message:
> 
> kbuffer-parse.c:318:3: error: use of undeclared identifier 'lenght'; did you mean 'length'?
>                 lenght = 0;
>                 ^~~~~~
>                 length
> kbuffer-parse.c:297:15: note: 'length' declared here
>         unsigned int length;
>                      ^
> 1 error generated.
> 
> I only had to test compile it :-)
> 
> >  		break;
> >  
> >  	case OLD_RINGBUF_TYPE_TIME_STAMP:
> >   

OK, I pulled the patch into git, and made it official ;-)
I also fixed the "lenght" in the change log too.

Could you use this instead.

-- Steve


>From 4f060a0577156acfdc0524a634f4afcc1657c929 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
Date: Mon, 13 Feb 2017 12:11:44 -0500
Subject: [PATCH] tools lib traceevent: Initialize lenght on
 OLD_RING_BUFFER_TYPE_TIME_STAMP

A undefined value was being used for the OLD_RING_BUFFER_TYPE_TIME_STAMP
case entry, as the 'length' variable was not being initialized, fix it.

Caught by the reporter when building tools/perf/ using clang, which emmitted
this warning:

  kbuffer-parse.c:312:7: warning: variable 'length' is used uninitialized whenever switch case is taken [-Wsometimes-uninitialized]
          case OLD_RINGBUF_TYPE_TIME_EXTEND:
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
  kbuffer-parse.c:339:29: note: uninitialized use occurs here
          kbuf->next = kbuf->index + length;
                                   ^~~~~~
  kbuffer-parse.c:297:21: note: initialize the variable 'length' to silence this warning
          unsigned int length;
                             ^
                              = 0

Reported-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Adrian Hunter <adrian.hunter@...el.com>
Cc: David Ahern <dsahern@...il.com>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Wang Nan <wangnan0@...wei.com>
Link: http://lkml.kernel.org/r/20170210141408.5eeb6e91@gandalf.local.home
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 tools/lib/traceevent/kbuffer-parse.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/lib/traceevent/kbuffer-parse.c b/tools/lib/traceevent/kbuffer-parse.c
index 65984f1..c94e364 100644
--- a/tools/lib/traceevent/kbuffer-parse.c
+++ b/tools/lib/traceevent/kbuffer-parse.c
@@ -315,6 +315,7 @@ static unsigned int old_update_pointers(struct kbuffer *kbuf)
 		extend += delta;
 		delta = extend;
 		ptr += 4;
+		length = 0;
 		break;
 
 	case OLD_RINGBUF_TYPE_TIME_STAMP:
-- 
2.9.3