[PATCH v2] perf tool: fix endianness handling of u32 data in samples

[PATCH v2] perf tool: fix endianness handling of u32 data in samples

[David Ahern]

Currently, analyzing PPC data files on x86 the cpu field is always 0 and
the tid and pid are backwards. For example, analyzing a PPC file on PPC
the pid/tid fields show:
        rsyslogd  1210/1212

and analyzing the same PPC file using an x86 perf binary shows:
        rsyslogd  1212/1210

The problem is that the swap_op method for samples is
perf_event__all64_swap which assumes all elements in the sample_data
struct are u64s. cpu, tid and pid are u32s and need to be handled
individually. Given that the swap is done before the sample is parsed,
the simplest solution is to undo the 64-bit swap of those elements when
the sample is parsed and do the proper swap.

The RAW data field is generic and perf cannot have programmatic knowledge
of how to treat that data. Instead a warning is given to the user.

Thanks to Anton Blanchard for providing a data file for a mult-CPU
PPC system so I could verify the fix for the CPU fields.

v1 -> v2:
- added a union for undoing the byte-swap on u64 and redoing swap on
  u32's to address compiler errors (see git commit 65014ab3)

Signed-off-by: David Ahern <dsahern@gmail.com>
---
 tools/perf/builtin-test.c |    2 +-
 tools/perf/util/event.h   |    2 +-
 tools/perf/util/evsel.c   |   61 ++++++++++++++++++++++++++++++++++++--------
 tools/perf/util/session.h |    3 +-
 4 files changed, 54 insertions(+), 14 deletions(-)

diff --git a/tools/perf/builtin-test.c b/tools/perf/builtin-test.c
index 55f4c76..efe696f 100644
--- a/tools/perf/builtin-test.c
+++ b/tools/perf/builtin-test.c
@@ -561,7 +561,7 @@ static int test__basic_mmap(void)
 		}
 
 		err = perf_event__parse_sample(event, attr.sample_type, sample_size,
-					       false, &sample);
+					       false, &sample, false);
 		if (err) {
 			pr_err("Can't parse sample, err = %d\n", err);
 			goto out_munmap;
diff --git a/tools/perf/util/event.h b/tools/perf/util/event.h
index 1d7f664..357a85b 100644
--- a/tools/perf/util/event.h
+++ b/tools/perf/util/event.h
@@ -186,6 +186,6 @@ const char *perf_event__name(unsigned int id);
 
 int perf_event__parse_sample(const union perf_event *event, u64 type,
 			     int sample_size, bool sample_id_all,
-			     struct perf_sample *sample);
+			     struct perf_sample *sample, bool swapped);
 
 #endif /* __PERF_RECORD_H */
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index a03a36b..c368c8a 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -7,6 +7,7 @@
  * Released under the GPL v2. (and only v2, not any later version)
  */
 
+#include <byteswap.h>
 #include "evsel.h"
 #include "evlist.h"
 #include "util.h"
@@ -342,9 +343,21 @@ static bool sample_overlap(const union perf_event *event,
 
 int perf_event__parse_sample(const union perf_event *event, u64 type,
 			     int sample_size, bool sample_id_all,
-			     struct perf_sample *data)
+			     struct perf_sample *data, bool swapped)
 {
 	const u64 *array;
+	
+	/* 
+	 * used for cross-endian analysis. See git commit 65014ab3
+	 * for why this goofiness is needed.
+	 */
+	struct {
+		union {
+			u64 val64;
+			u32 val32[2];
+		};
+	} u;
+
 
 	data->cpu = data->pid = data->tid = -1;
 	data->stream_id = data->id = data->time = -1ULL;
@@ -366,9 +379,16 @@ int perf_event__parse_sample(const union perf_event *event, u64 type,
 	}
 
 	if (type & PERF_SAMPLE_TID) {
-		u32 *p = (u32 *)array;
-		data->pid = p[0];
-		data->tid = p[1];
+		u.val64 = *array;
+		if (swapped) {
+			/* undo swap of u64, then swap on individual u32s */
+			u.val64 = bswap_64(u.val64);
+			u.val32[0] = bswap_32(u.val32[0]);
+			u.val32[1] = bswap_32(u.val32[1]);
+		}
+
+		data->pid = u.val32[0];
+		data->tid = u.val32[1];
 		array++;
 	}
 
@@ -395,8 +415,15 @@ int perf_event__parse_sample(const union perf_event *event, u64 type,
 	}
 
 	if (type & PERF_SAMPLE_CPU) {
-		u32 *p = (u32 *)array;
-		data->cpu = *p;
+
+		u.val64 = *array;
+		if (swapped) {
+			/* undo swap of u64, then swap on individual u32s */
+			u.val64 = bswap_64(u.val64);
+			u.val32[0] = bswap_32(u.val32[0]);
+		}
+
+		data->cpu = u.val32[0];
 		array++;
 	}
 
@@ -423,18 +450,30 @@ int perf_event__parse_sample(const union perf_event *event, u64 type,
 	}
 
 	if (type & PERF_SAMPLE_RAW) {
-		u32 *p = (u32 *)array;
+		u.val64 = *array;
+		if (swapped) {
+			static bool show_warn = true;
+
+			/* undo swap of u64, then swap on individual u32s */
+			u.val64 = bswap_64(u.val64);
+			u.val32[0] = bswap_32(u.val32[0]);
+			u.val32[1] = bswap_32(u.val32[1]);
+
+			if (show_warn) {
+				pr_warning("Endianness of raw data not corrected!\n");
+				show_warn = false;
+			}
+		}
 
 		if (sample_overlap(event, array, sizeof(u32)))
 			return -EFAULT;
 
-		data->raw_size = *p;
-		p++;
+		data->raw_size = u.val32[0];
 
-		if (sample_overlap(event, p, data->raw_size))
+		if (sample_overlap(event, &u.val32[1], data->raw_size))
 			return -EFAULT;
 
-		data->raw_data = p;
+		data->raw_data = &u.val32[1];
 	}
 
 	return 0;
diff --git a/tools/perf/util/session.h b/tools/perf/util/session.h
index 170601e..974d0cb 100644
--- a/tools/perf/util/session.h
+++ b/tools/perf/util/session.h
@@ -162,7 +162,8 @@ static inline int perf_session__parse_sample(struct perf_session *session,
 {
 	return perf_event__parse_sample(event, session->sample_type,
 					session->sample_size,
-					session->sample_id_all, sample);
+					session->sample_id_all, sample,
+					session->header.needs_swap);
 }
 
 struct perf_evsel *perf_session__find_first_evtype(struct perf_session *session,
-- 
1.7.6

Re: [PATCH v2] perf tool: fix endianness handling of u32 data in samples

[Arnaldo Carvalho de Melo]

Em Fri, Sep 02, 2011 at 10:03:46AM -0600, David Ahern escreveu:
>  	if (type & PERF_SAMPLE_RAW) {
> -		u32 *p = (u32 *)array;
> +		u.val64 = *array;
> +		if (swapped) {
> +			static bool show_warn = true;
> +
> +			/* undo swap of u64, then swap on individual u32s */
> +			u.val64 = bswap_64(u.val64);
> +			u.val32[0] = bswap_32(u.val32[0]);
> +			u.val32[1] = bswap_32(u.val32[1]);
> +
> +			if (show_warn) {
> +				pr_warning("Endianness of raw data not corrected!\n");
> +				show_warn = false;
> +			}
> +		}

Can you use WARN_ONCE? Would become:
	
		if (WARN_ONCE(swapped, "Endianness of raw data not corrected!\n")) {
			/* undo swap of u64, then swap on individual u32s */
			u.val64 = bswap_64(u.val64);
			u.val32[0] = bswap_32(u.val32[0]);
			u.val32[1] = bswap_32(u.val32[1]);
		}

We have that and its the usual idiom in the kernel proper :-)

See tools/perf/util/include/asm/bug.h and net/can/af_can.c can_rcv for
an example.

Thanks,

- Arnaldo

Re: [PATCH v2] perf tool: fix endianness handling of u32 data in samples

[David Ahern]

On 09/02/2011 12:18 PM, Arnaldo Carvalho de Melo wrote:
> Em Fri, Sep 02, 2011 at 10:03:46AM -0600, David Ahern escreveu:
>>  	if (type & PERF_SAMPLE_RAW) {
>> -		u32 *p = (u32 *)array;
>> +		u.val64 = *array;
>> +		if (swapped) {
>> +			static bool show_warn = true;
>> +
>> +			/* undo swap of u64, then swap on individual u32s */
>> +			u.val64 = bswap_64(u.val64);
>> +			u.val32[0] = bswap_32(u.val32[0]);
>> +			u.val32[1] = bswap_32(u.val32[1]);
>> +
>> +			if (show_warn) {
>> +				pr_warning("Endianness of raw data not corrected!\n");
>> +				show_warn = false;
>> +			}
>> +		}
> 
> Can you use WARN_ONCE? Would become:
> 	
> 		if (WARN_ONCE(swapped, "Endianness of raw data not corrected!\n")) {
> 			/* undo swap of u64, then swap on individual u32s */
> 			u.val64 = bswap_64(u.val64);
> 			u.val32[0] = bswap_32(u.val32[0]);
> 			u.val32[1] = bswap_32(u.val32[1]);
> 		}

That's not quite what we need. The bswap's happen all the time; the warn
once is to tell the user one time that samples in the file contain raw
data and those cannot be programmatically adjusted for endianness.

ie., more like:
    WARN_ONCE(swapped, "Endianness of raw data not corrected!\n");
and no action taken (the 'if (WARN_ONCE())'part).

David


> 
> We have that and its the usual idiom in the kernel proper :-)
> 
> See tools/perf/util/include/asm/bug.h and net/can/af_can.c can_rcv for
> an example.
> 
> Thanks,
> 
> - Arnaldo

Re: [PATCH v2] perf tool: fix endianness handling of u32 data in samples

[Arnaldo Carvalho de Melo]

Em Fri, Sep 02, 2011 at 01:12:30PM -0600, David Ahern escreveu:
> On 09/02/2011 12:18 PM, Arnaldo Carvalho de Melo wrote:
> > Em Fri, Sep 02, 2011 at 10:03:46AM -0600, David Ahern escreveu:
> >>  	if (type & PERF_SAMPLE_RAW) {
> >> -		u32 *p = (u32 *)array;
> >> +		u.val64 = *array;
> >> +		if (swapped) {
> >> +			static bool show_warn = true;
> >> +
> >> +			/* undo swap of u64, then swap on individual u32s */
> >> +			u.val64 = bswap_64(u.val64);
> >> +			u.val32[0] = bswap_32(u.val32[0]);
> >> +			u.val32[1] = bswap_32(u.val32[1]);
> >> +
> >> +			if (show_warn) {
> >> +				pr_warning("Endianness of raw data not corrected!\n");
> >> +				show_warn = false;
> >> +			}
> >> +		}
> > 
> > Can you use WARN_ONCE? Would become:
> > 	
> > 		if (WARN_ONCE(swapped, "Endianness of raw data not corrected!\n")) {
> > 			/* undo swap of u64, then swap on individual u32s */
> > 			u.val64 = bswap_64(u.val64);
> > 			u.val32[0] = bswap_32(u.val32[0]);
> > 			u.val32[1] = bswap_32(u.val32[1]);
> > 		}
> 
> That's not quite what we need. The bswap's happen all the time; the warn
> once is to tell the user one time that samples in the file contain raw
> data and those cannot be programmatically adjusted for endianness.
> 
> ie., more like:
>     WARN_ONCE(swapped, "Endianness of raw data not corrected!\n");
> and no action taken (the 'if (WARN_ONCE())'part).

Look again:

#define WARN_ONCE(condition, format...) ({                      \
        static bool __warned;                                   \
        int __ret_warn_once = !!(condition);                    \
                                                                \
        if (unlikely(__ret_warn_once))                          \
                if (WARN(!__warned, format))                    \
                        __warned = true;                        \
        unlikely(__ret_warn_once);                              \
}) 


See that ({ }) construct? It evaluates to what is in its last statement,
which is...

	unlikely(__ret_warn_once);

Forget about the unlikely, __ret_warn_once is:

	!!condition

I.e. it always evaluates to what is passed as condition, so in fact it
could be seen as:

             if (swapped) {
                     /* undo swap of u64, then swap on individual
                     u32s */
                     u.val64 = bswap_64(u.val64);
                     u.val32[0] = bswap_32(u.val32[0]);
                     u.val32[1] = bswap_32(u.val32[1]);
             }

The rest is the boilerplate needed to warn the user the first time
condition is true.

- Arnaldo

Re: [PATCH v2] perf tool: fix endianness handling of u32 data in samples

[David Ahern]

On 09/02/2011 02:01 PM, Arnaldo Carvalho de Melo wrote:
> Look again:
> 
> #define WARN_ONCE(condition, format...) ({                      \
>         static bool __warned;                                   \
>         int __ret_warn_once = !!(condition);                    \
>                                                                 \
>         if (unlikely(__ret_warn_once))                          \
>                 if (WARN(!__warned, format))                    \
>                         __warned = true;                        \
>         unlikely(__ret_warn_once);                              \
> }) 
> 
> 
> See that ({ }) construct? It evaluates to what is in its last statement,
> which is...
> 
> 	unlikely(__ret_warn_once);
> 
> Forget about the unlikely, __ret_warn_once is:
> 
> 	!!condition
> 
> I.e. it always evaluates to what is passed as condition, so in fact it
> could be seen as:
> 
>              if (swapped) {
>                      /* undo swap of u64, then swap on individual
>                      u32s */
>                      u.val64 = bswap_64(u.val64);
>                      u.val32[0] = bswap_32(u.val32[0]);
>                      u.val32[1] = bswap_32(u.val32[1]);
>              }
> 
> The rest is the boilerplate needed to warn the user the first time
> condition is true.
> 
> - Arnaldo

Ok, I get it now.

David