linux-kernel - Re: [PATCH V3 04/25] perf tools: Add AUX area tracing index

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Message-ID: <5540CA74.9030508@intel.com>
Date:	Wed, 29 Apr 2015 15:11:32 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Jiri Olsa <jolsa@...hat.com>
CC:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Namhyung Kim <namhyung@...il.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH V3 04/25] perf tools: Add AUX area tracing index

On 28/04/15 15:32, Jiri Olsa wrote:
> On Fri, Apr 24, 2015 at 10:29:46PM +0300, Adrian Hunter wrote:
> 
> SNIP
> 
>> --- a/tools/perf/util/auxtrace.c
>> +++ b/tools/perf/util/auxtrace.c
>> @@ -344,6 +344,33 @@ out_err:
>>  	return err;
>>  }
>>  
>> +static int auxtrace_queues__add_indexed_event(struct auxtrace_queues *queues,
>> +					      struct perf_session *session,
>> +					      off_t file_offset, size_t sz)
>> +{
>> +	union perf_event *event;
>> +	int err;
>> +	char buf[PERF_SAMPLE_MAX_SIZE];
>> +
>> +	err = perf_session__peek_event(session, file_offset, buf,
>> +				       PERF_SAMPLE_MAX_SIZE, &event, NULL);
>> +	if (err)
>> +		return err;
>> +
>> +	if (event->header.type == PERF_RECORD_AUXTRACE) {
>> +		if (event->header.size != sizeof(struct auxtrace_event) ||
>> +		    event->header.size != sz) {
>> +			err = -EINVAL;
> 
> getting lost in here
> 
> as per auxtrace_mmap__read it looks like we store PERF_RECORD_AUXTRACE event with:
> 	ev.auxtrace.header.size = sizeof(ev.auxtrace);
> 
> and it's followed with more data with size:
> 	ev.auxtrace.size = size + padding;
> 
> so why the check for 'event->header.size != sz' ?

It checks the consistency of the file structure.

But it seems to me that the previous check could be:

	event->header.size < sizeof(struct auxtrace_event)

which would allow for the event being made bigger in a backward compatible way.

> 
> jirka
> 
>> +			goto out;
>> +		}
>> +		file_offset += event->header.size;
>> +		err = auxtrace_queues__add_event(queues, session, event,
>> +						 file_offset, NULL);
>> +	}
>> +out:
>> +	return err;
>> +}
> 
> SNIP
> 
> 

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