Re: [PATCH] building libtraceevent with clang

[Arnaldo Carvalho de Melo]

Em Mon, Feb 13, 2017 at 12:14:18PM -0500, Steven Rostedt escreveu:
> On Mon, 13 Feb 2017 13:26:22 -0300
> Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> 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.

Sure, now take a look at this another one:

commit 6401e4361df183bd9953dce56f7c51d8ef28b11e
Author: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Date:   Mon Feb 13 13:33:57 2017 -0300

    tools lib traceevent plugin function: Initialize 'index' variable
    
    Detected with clang:
    
        CC       /tmp/build/perf/plugin_function.o
      plugin_function.c:145:6: warning: variable 'index' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
              if (parent && ftrace_indent->set)
                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
      plugin_function.c:148:29: note: uninitialized use occurs here
              trace_seq_printf(s, "%*s", index*3, "");
                                         ^~~~~
      plugin_function.c:145:2: note: remove the 'if' if its condition is always true
              if (parent && ftrace_indent->set)
              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      plugin_function.c:145:6: warning: variable 'index' is used uninitialized whenever '&&' condition is false [-Wsometimes-uninitialized]
              if (parent && ftrace_indent->set)
                  ^~~~~~
      plugin_function.c:148:29: note: uninitialized use occurs here
              trace_seq_printf(s, "%*s", index*3, "");
                                         ^~~~~
      plugin_function.c:145:6: note: remove the '&&' if its condition is always true
              if (parent && ftrace_indent->set)
                  ^~~~~~~~~
      plugin_function.c:133:11: note: initialize the variable 'index' to silence this warning
              int index;
                       ^
                        = 0
      2 warnings generated.
    
    Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
    Cc: David Ahern <dsahern@xxxxxxxxx>
    Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
    Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
    Cc: Wang Nan <wangnan0@xxxxxxxxxx>
    Link: http://lkml.kernel.org/n/tip-b5wyjocel55gorl2jq2cbxrr@xxxxxxxxxxxxxx
    Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

diff --git a/tools/lib/traceevent/plugin_function.c b/tools/lib/traceevent/plugin_function.c
index a00ec190821a..42dbf73758f3 100644
--- a/tools/lib/traceevent/plugin_function.c
+++ b/tools/lib/traceevent/plugin_function.c
@@ -130,7 +130,7 @@ static int function_handler(struct trace_seq *s, struct pevent_record *record,
 	unsigned long long pfunction;
 	const char *func;
 	const char *parent;
-	int index;
+	int index = 0;
 
 	if (pevent_get_field_val(s, event, "ip", record, &function, 1))
 		return trace_seq_putc(s, '!');
 
> -- Steve
> 
> 
> From 4f060a0577156acfdc0524a634f4afcc1657c929 Mon Sep 17 00:00:00 2001
> From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
> 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@xxxxxxxxxx>
> Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> Cc: David Ahern <dsahern@xxxxxxxxx>
> Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> Cc: Wang Nan <wangnan0@xxxxxxxxxx>
> Link: http://lkml.kernel.org/r/20170210141408.5eeb6e91@xxxxxxxxxxxxxxxxxx
> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
> ---
>  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