linux-kernel - Re: [PATCH v4 15/16] perf tools: add feature header record to pipe-mode

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Message-ID: <20170712073802.GA28985@krava>
Date:   Wed, 12 Jul 2017 09:38:02 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     David Carrillo-Cisneros <davidcc@...gle.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>, Simon Que <sque@...omium.org>,
        Wang Nan <wangnan0@...wei.com>, Jiri Olsa <jolsa@...nel.org>,
        He Kuang <hekuang@...wei.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Paul Turner <pjt@...gle.com>
Subject: Re: [PATCH v4 15/16] perf tools: add feature header record to
 pipe-mode

On Tue, Jul 11, 2017 at 05:32:40PM -0700, David Carrillo-Cisneros wrote:
> On Tue, Jun 13, 2017 at 11:54 AM, Jiri Olsa <jolsa@...hat.com> wrote:
> > On Mon, Jun 12, 2017 at 09:29:31PM -0700, David Carrillo-Cisneros wrote:
> >
> > SNIP
> >
> >>
> >>  void perf_event__print_totals(void);
> >> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> >> index ddfaf157913d..6f6a54c15cb0 100644
> >> --- a/tools/perf/util/header.c
> >> +++ b/tools/perf/util/header.c
> >> @@ -34,6 +34,7 @@
> >>  #include "data.h"
> >>  #include <api/fs/fs.h>
> >>  #include "asm/bug.h"
> >> +#include "tool.h"
> >>
> >>  #include "sane_ctype.h"
> >>
> >> @@ -97,11 +98,14 @@ static int __do_write_buf(struct feat_fd *ff,  const void *buf, size_t size)
> >>
> >>  retry:
> >>       if (size > (ff->size - ff->offset)) {
> >> -             addr = realloc(ff->buf, ff->size << 1);
> >> +             size = ff->size << 1;
> >> +             if (size > page_size)
> >
> > event size could be 0xffff - sizeof(struct perf_event_header)
> > also the initial size is most likely > page_size anyway
> >
> > please put this into the patch that introduced __do_write_buf
> >
> 
> Thank you for reviewing this. I just realized that I sent v5 without
> properly addressing this issue. In v4 I tried to add a quick check
> without properly understanding the issue. Why is 0xffff the maximum
> size for an event? where is this constraint coming from?

the struct perf_event_header::size is u16

jirka