linux-kernel - Re: [PATCH 1/9] perf/jit: improve error messages from JVMTI

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Date:   Fri, 14 Oct 2016 08:13:59 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Nilay Vaish <nilayvaish@...il.com>
Cc:     Stephane Eranian <eranian@...gle.com>,
        Linux Kernel list <linux-kernel@...r.kernel.org>,
        jolsa@...hat.com, peterz@...radead.org, mingo@...e.hu,
        anton@...abs.org, namhyung@...nel.org
Subject: Re: [PATCH 1/9] perf/jit: improve error messages from JVMTI

Em Thu, Oct 13, 2016 at 03:05:40PM -0500, Nilay Vaish escreveu:
> On 13 October 2016 at 05:59, Stephane Eranian <eranian@...gle.com> wrote:
> > +++ b/tools/perf/jvmti/libjvmti.c
> > @@ -12,6 +12,17 @@
> > +static void print_error(jvmtiEnv *jvmti, const char *msg, jvmtiError ret)
> > +{
> > +       char *err_msg = NULL;
> > +       jvmtiError err;
> > +       err = (*jvmti)->GetErrorName(jvmti, ret, &err_msg);
> > +       if (err == JVMTI_ERROR_NONE) {
> > +               warnx("%s failed with %s", msg, err_msg);
> > +               (*jvmti)->Deallocate(jvmti, (unsigned char *)err_msg);
> > +       }
> > +}
> 
> Do we not need to release the memory for err_msg if the condition for
> the 'if' statement evaluates to false?  Is it that we are going to
> kill the process, so no need to release the memory?

I guess that print_error() is called only when an error was returned
somewhere, that ret parameter, then if there was no error
(JVMTI_ERROR_NONE) in translating that numeric code to an string,
err_msg, it can then be used with warnx() (the main purpose of
print_error()) and then deallocated.

For err != JVMTI_ERROR_NONE it silently goes back to the caller that
expected it to print something.

I.e. probably it should have an else clause, something like:

	if (err == JVMTI_ERROR_NONE) {
		warnx("%s failed with %s", msg, err_msg);
		(*jvmti)->Deallocate(jvmti, (unsigned char *)err_msg);
	} else {
		warnx("%s failed with an unknown error %d", msg, (int)ret);
	}

Stephane?

- Arnaldo