linux-kernel - Re: [PATCH v1 4/5] perf mem: Support record for hybrid platform

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Message-ID: <YK40uLOZC+4qGMl3@krava>
Date:   Wed, 26 May 2021 13:44:56 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     "Jin, Yao" <yao.jin@...ux.intel.com>
Cc:     acme@...nel.org, jolsa@...nel.org, peterz@...radead.org,
        mingo@...hat.com, alexander.shishkin@...ux.intel.com,
        Linux-kernel@...r.kernel.org, ak@...ux.intel.com,
        kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH v1 4/5] perf mem: Support record for hybrid platform

On Wed, May 26, 2021 at 09:51:34AM +0800, Jin, Yao wrote:
> Hi Jiri,
> 
> On 5/25/2021 3:39 PM, Jin, Yao wrote:
> > Hi Jiri,
> > 
> > > > >       rec_argv = calloc(rec_argc + 1, sizeof(char *));
> > > > >       if (!rec_argv)
> > > > >           return -1;
> > > > > +    /*
> > > > > +     * Save the allocated event name strings.
> > > > > +     */
> > > > > +    rec_tmp = calloc(rec_argc + 1, sizeof(char *));
> > > > > +    if (!rec_tmp) {
> > > > > +        free(rec_argv);
> > > > > +        return -1;
> > > > > +    }
> > > > 
> > > > why not do strdup on all of them and always call free instead?
> > > > that would get rid of the rec_tmp and tmp_nr
> > > > 
> > > 
> > > That is also one method. Let me try it.
> > > 
> > 
> > If we do strdup on all of them, such as,
> > 
> >      if (e->record)
> >          rec_argv[i++] = strdup("-W");
> > 
> >      rec_argv[i++] = strdup("-d");
> > 
> >      if (mem->phys_addr)
> >          rec_argv[i++] = strdup("--phys-data");
> >      ....
> > 
> > That looks too much strdup used here. So I choose to use a rec_tmp[] to
> > record the allocated string and free them before exit the function.
> > 
> > Or we record the start index and end index in rec_argv[] for the
> > allocated event string, use strdup on them and call free before exit the
> > function.
> > 
> 
> This method looks also not OK.
> 
> The rec_argv[] is changed in cmd_record() for some complex command lines.
> 
> For example,
> 
> ./perf mem record -- ./memtest -R0d -b2000 -d64 -n100
> 
> Before cmd_record(), rec_argv[3] = "-e".
> After cmd_record(), rec_argv[3] = "-d64"
> 
> Even we do strdup on all of rec_argv[], but the entries are probably changed
> in cmd_record(), so we can't free the entries at the end of __cmd_record().
> 
> Maybe we have to use the original way which just records the allocated event
> string to a temporary array and free the whole array at the end of
> __cmd_record().
> 
> What do you think?

ok, it was worth to try ;-)

thanks,
jirka