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

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Date:   Mon, 13 Feb 2017 12:46:53 -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 14:20:20 -0300
Arnaldo Carvalho de Melo <acme@...nel.org> wrote:


> Sure, now take a look at this another one:
> 
> commit 6401e4361df183bd9953dce56f7c51d8ef28b11e
> Author: Arnaldo Carvalho de Melo <acme@...hat.com>
> 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.

I wonder why gcc isn't catching these. These look pretty obvious to me.

>     
>     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/n/tip-b5wyjocel55gorl2jq2cbxrr@git.kernel.org
>     Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> 
> 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, '!');
>  

Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve