linux-kernel - Re: [PATCH V6 05/25] perf record: Add basic AUX area tracing support

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Date:	Tue, 24 Mar 2015 12:07:19 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	linux-kernel@...r.kernel.org, David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH V6 05/25] perf record: Add basic AUX area tracing support

On Mon, Mar 16, 2015 at 02:41:27PM +0200, Adrian Hunter wrote:
> Amend the perf record tool to read the
> AUX area tracing mmap and synthesize
> AUX area tracing events.
> 
> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> ---
>  tools/perf/builtin-record.c | 80 ++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 76 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 5a2ff51..8b3a50e 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -27,6 +27,7 @@
>  #include "util/cpumap.h"
>  #include "util/thread_map.h"
>  #include "util/data.h"
> +#include "util/auxtrace.h"
>  
>  #include <unistd.h>
>  #include <sched.h>
> @@ -38,6 +39,7 @@ struct record {
>  	struct record_opts	opts;
>  	u64			bytes_written;
>  	struct perf_data_file	file;
> +	struct auxtrace_record	*itr;
>  	struct perf_evlist	*evlist;
>  	struct perf_session	*session;
>  	const char		*progname;
> @@ -110,6 +112,43 @@ out:
>  	return rc;
>  }
>  
> +static int record__process_auxtrace(struct perf_tool *tool,
> +				    union perf_event *event, void *data1,
> +				    size_t len1, void *data2, size_t len2)
> +{
> +	struct record *rec = container_of(tool, struct record, tool);
> +	size_t padding;
> +	u8 pad[8] = {0};
> +
> +	/* event.auxtrace.size includes padding, see __auxtrace_mmap__read() */
> +	padding = (len1 + len2) & 7;
> +	if (padding)
> +		padding = 8 - padding;
> +
> +	record__write(rec, event, event->header.size);
> +	record__write(rec, data1, len1);
> +	record__write(rec, data2, len2);

record__write goes quite deep down the stack before it realizes
there's nothing to write (len2 == 0) which I'm guessing is the
likely case for data2/len2 (buffer wrap around) ?

maybe you want to check on that before calling that

jirka
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