[PATCH v3 1/2] tools/perf: Add bitfield_swap to handle branch_stack endian issue

[PATCH v3 1/2] tools/perf: Add bitfield_swap to handle branch_stack endian issue

[Madhavan Srinivasan]

branch_stack struct has bit field definition which
produces different bit ordering for big/little endian.
Because of this, when branch_stack sample is collected
in a BE system and viewed/reported in a LE system, bit
fields of the branch stack are not presented properly.
To address this issue, a evsel__bitfield_swap_branch_stack()
is defined and introduced in evsel__parse_sample.

Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
---
Changelog v2:
- used tep_is_bigendian() instead bigendian()
  to avoid perf test python fail.
 
Changelog v1:
- Renamed function and macro
- Added comments in code

 tools/perf/util/evsel.c | 77 +++++++++++++++++++++++++++++++++++++++--
 tools/perf/util/evsel.h | 13 +++++++
 2 files changed, 88 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index dbfeceb2546c..4e929b9d9718 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -2221,6 +2221,54 @@ void __weak arch_perf_parse_sample_weight(struct perf_sample *data,
 	data->weight = *array;
 }
 
+u64 evsel__bitfield_swap_branch_flags(u64 value)
+{
+	u64 new_val = 0;
+
+	/*
+	 * branch_flags
+	 * union {
+	 * 	u64 values;
+	 * 	struct {
+	 * 		mispred:1	//target mispredicted
+	 * 		predicted:1	//target predicted
+	 * 		in_tx:1		//in transaction
+	 * 		abort:1		//transaction abort
+	 * 		cycles:16	//cycle count to last branch
+	 * 		type:4		//branch type
+	 * 		reserved:40
+	 * 	}
+	 * }
+	 *
+	 * Avoid bswap64() the entire branch_flag.value,
+	 * as it has variable bit-field sizes. Instead the
+	 * macro takes the bit-field position/size,
+	 * swaps it based on the host endianness.
+	 *
+	 * tep_is_bigendian() is used here instead of
+	 * bigendian() to avoid python test fails.
+	 */
+	if (tep_is_bigendian()) {
+		new_val = bitfield_swap(value, 0, 1);
+		new_val |= bitfield_swap(value, 1, 1);
+		new_val |= bitfield_swap(value, 2, 1);
+		new_val |= bitfield_swap(value, 3, 1);
+		new_val |= bitfield_swap(value, 4, 16);
+		new_val |= bitfield_swap(value, 20, 4);
+		new_val |= bitfield_swap(value, 24, 40);
+	} else {
+		new_val = bitfield_swap(value, 63, 1);
+		new_val |= bitfield_swap(value, 62, 1);
+		new_val |= bitfield_swap(value, 61, 1);
+		new_val |= bitfield_swap(value, 60, 1);
+		new_val |= bitfield_swap(value, 44, 16);
+		new_val |= bitfield_swap(value, 40, 4);
+		new_val |= bitfield_swap(value, 0, 40);
+	}
+
+	return new_val;
+}
+
 int evsel__parse_sample(struct evsel *evsel, union perf_event *event,
 			struct perf_sample *data)
 {
@@ -2408,6 +2456,8 @@ int evsel__parse_sample(struct evsel *evsel, union perf_event *event,
 	if (type & PERF_SAMPLE_BRANCH_STACK) {
 		const u64 max_branch_nr = UINT64_MAX /
 					  sizeof(struct branch_entry);
+		struct branch_entry *e;
+		unsigned int i;
 
 		OVERFLOW_CHECK_u64(array);
 		data->branch_stack = (struct branch_stack *)array++;
@@ -2416,10 +2466,33 @@ int evsel__parse_sample(struct evsel *evsel, union perf_event *event,
 			return -EFAULT;
 
 		sz = data->branch_stack->nr * sizeof(struct branch_entry);
-		if (evsel__has_branch_hw_idx(evsel))
+		if (evsel__has_branch_hw_idx(evsel)) {
 			sz += sizeof(u64);
-		else
+			e = &data->branch_stack->entries[0];
+		} else {
 			data->no_hw_idx = true;
+			/*
+			 * if the PERF_SAMPLE_BRANCH_HW_INDEX is not applied,
+			 * only nr and entries[] will be output by kernel.
+			 */
+			e = (struct branch_entry *)&data->branch_stack->hw_idx;
+		}
+
+		if (swapped) {
+			/*
+			 * struct branch_flag does not have endian
+			 * specific bit field definition. And bswap
+			 * will not resolve the issue, since these
+			 * are bit fields.
+			 *
+			 * evsel__bitfield_swap_branch_flags() uses a
+			 * bitfield_swap macro to swap the bit position
+			 * based on the host endians.
+			 */
+			for (i = 0; i < data->branch_stack->nr; i++, e++)
+				e->flags.value = evsel__bitfield_swap_branch_flags(e->flags.value);
+		}
+
 		OVERFLOW_CHECK(array, sz, max_size);
 		array = (void *)array + sz;
 	}
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index 1f7edfa8568a..2e82cdbe2c08 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -482,4 +482,17 @@ struct evsel *evsel__leader(struct evsel *evsel);
 bool evsel__has_leader(struct evsel *evsel, struct evsel *leader);
 bool evsel__is_leader(struct evsel *evsel);
 void evsel__set_leader(struct evsel *evsel, struct evsel *leader);
+
+/*
+ * Macro to swap the bit-field postition and size.
+ * Used when,
+ * - dont need to swap the entire u64 &&
+ * - when u64 has variable bit-field sizes &&
+ * - when presented in a host endian which is different
+ *   than the source endian of the perf.data file
+ */
+#define bitfield_swap(src, pos, size)	\
+	((((src) >> (pos)) & ((1ull << (size)) - 1)) << (63 - ((pos) + (size) - 1)))
+
+u64 evsel__bitfield_swap_branch_flags(u64 value);
 #endif /* __PERF_EVSEL_H */
-- 
2.31.1

[PATCH v3 2/2] tools/perf/test: Add endian test for struct branch_flags

[Madhavan Srinivasan]

Extend sample-parsing test to include branch_flag
bitfield-endian swap test. Patch include "util/trace-event.h"
to sample-parsing for importing tep_is_bigendian() and
extends samples_same() to include "needs_swap" to
detect/enable check for bitfield-endian swap.

Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
---
Changelog v2:
- used tep_is_bigendian() instead bigendian()
  to avoid perf test python fail.
- Updated commit message

Changelog v1:
- Updated commit message

 tools/perf/tests/sample-parsing.c | 43 +++++++++++++++++++++++++++----
 1 file changed, 38 insertions(+), 5 deletions(-)

diff --git a/tools/perf/tests/sample-parsing.c b/tools/perf/tests/sample-parsing.c
index 8fd8a4ef97da..c83a11514129 100644
--- a/tools/perf/tests/sample-parsing.c
+++ b/tools/perf/tests/sample-parsing.c
@@ -13,6 +13,7 @@
 #include "evsel.h"
 #include "debug.h"
 #include "util/synthetic-events.h"
+#include "util/trace-event.h"
 
 #include "tests.h"
 
@@ -30,9 +31,18 @@
 	}						\
 } while (0)
 
+/*
+ * Hardcode the expected values for branch_entry flags.
+ * These are based on the input value (213) specified
+ * in branch_stack variable.
+ */
+#define BS_EXPECTED_BE	0xa00d000000000000
+#define BS_EXPECTED_LE	0xd5000000
+#define FLAG(s)	s->branch_stack->entries[i].flags
+
 static bool samples_same(const struct perf_sample *s1,
 			 const struct perf_sample *s2,
-			 u64 type, u64 read_format)
+			 u64 type, u64 read_format, bool needs_swap)
 {
 	size_t i;
 
@@ -100,8 +110,14 @@ static bool samples_same(const struct perf_sample *s1,
 	if (type & PERF_SAMPLE_BRANCH_STACK) {
 		COMP(branch_stack->nr);
 		COMP(branch_stack->hw_idx);
-		for (i = 0; i < s1->branch_stack->nr; i++)
-			MCOMP(branch_stack->entries[i]);
+		for (i = 0; i < s1->branch_stack->nr; i++) {
+			if (needs_swap)
+				return ((tep_is_bigendian()) ?
+					(FLAG(s2).value == BS_EXPECTED_BE) :
+					(FLAG(s2).value == BS_EXPECTED_LE));
+			else
+				MCOMP(branch_stack->entries[i]);
+		}
 	}
 
 	if (type & PERF_SAMPLE_REGS_USER) {
@@ -248,7 +264,7 @@ static int do_test(u64 sample_type, u64 sample_regs, u64 read_format)
 		},
 	};
 	struct sample_read_value values[] = {{1, 5}, {9, 3}, {2, 7}, {6, 4},};
-	struct perf_sample sample_out;
+	struct perf_sample sample_out, sample_out_endian;
 	size_t i, sz, bufsz;
 	int err, ret = -1;
 
@@ -313,12 +329,29 @@ static int do_test(u64 sample_type, u64 sample_regs, u64 read_format)
 		goto out_free;
 	}
 
-	if (!samples_same(&sample, &sample_out, sample_type, read_format)) {
+	if (!samples_same(&sample, &sample_out, sample_type, read_format, evsel.needs_swap)) {
 		pr_debug("parsing failed for sample_type %#"PRIx64"\n",
 			 sample_type);
 		goto out_free;
 	}
 
+	if (sample_type == PERF_SAMPLE_BRANCH_STACK) {
+		evsel.needs_swap = true;
+		evsel.sample_size = __evsel__sample_size(sample_type);
+		err = evsel__parse_sample(&evsel, event, &sample_out_endian);
+		if (err) {
+			pr_debug("%s failed for sample_type %#"PRIx64", error %d\n",
+				 "evsel__parse_sample", sample_type, err);
+			goto out_free;
+		}
+
+		if (!samples_same(&sample, &sample_out_endian, sample_type, read_format, evsel.needs_swap)) {
+			pr_debug("parsing failed for sample_type %#"PRIx64"\n",
+				 sample_type);
+			goto out_free;
+		}
+	}
+
 	ret = 0;
 out_free:
 	free(event);
-- 
2.31.1

Re: [PATCH v3 1/2] tools/perf: Add bitfield_swap to handle branch_stack endian issue

[Arnaldo Carvalho de Melo]

Em Thu, Oct 28, 2021 at 05:07:13PM +0530, Madhavan Srinivasan escreveu:
> branch_stack struct has bit field definition which
> produces different bit ordering for big/little endian.
> Because of this, when branch_stack sample is collected
> in a BE system and viewed/reported in a LE system, bit
> fields of the branch stack are not presented properly.
> To address this issue, a evsel__bitfield_swap_branch_stack()
> is defined and introduced in evsel__parse_sample.

Jiri,

	This is a minor change, he just switched to an inline equivalent
(the code is slightly different, but should be ok), can I apply yout
v2 Acked-by tags?

- Arnaldo
 
> Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
> ---
> Changelog v2:
> - used tep_is_bigendian() instead bigendian()
>   to avoid perf test python fail.
>  
> Changelog v1:
> - Renamed function and macro
> - Added comments in code
> 
>  tools/perf/util/evsel.c | 77 +++++++++++++++++++++++++++++++++++++++--
>  tools/perf/util/evsel.h | 13 +++++++
>  2 files changed, 88 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index dbfeceb2546c..4e929b9d9718 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -2221,6 +2221,54 @@ void __weak arch_perf_parse_sample_weight(struct perf_sample *data,
>  	data->weight = *array;
>  }
>  
> +u64 evsel__bitfield_swap_branch_flags(u64 value)
> +{
> +	u64 new_val = 0;
> +
> +	/*
> +	 * branch_flags
> +	 * union {
> +	 * 	u64 values;
> +	 * 	struct {
> +	 * 		mispred:1	//target mispredicted
> +	 * 		predicted:1	//target predicted
> +	 * 		in_tx:1		//in transaction
> +	 * 		abort:1		//transaction abort
> +	 * 		cycles:16	//cycle count to last branch
> +	 * 		type:4		//branch type
> +	 * 		reserved:40
> +	 * 	}
> +	 * }
> +	 *
> +	 * Avoid bswap64() the entire branch_flag.value,
> +	 * as it has variable bit-field sizes. Instead the
> +	 * macro takes the bit-field position/size,
> +	 * swaps it based on the host endianness.
> +	 *
> +	 * tep_is_bigendian() is used here instead of
> +	 * bigendian() to avoid python test fails.
> +	 */
> +	if (tep_is_bigendian()) {
> +		new_val = bitfield_swap(value, 0, 1);
> +		new_val |= bitfield_swap(value, 1, 1);
> +		new_val |= bitfield_swap(value, 2, 1);
> +		new_val |= bitfield_swap(value, 3, 1);
> +		new_val |= bitfield_swap(value, 4, 16);
> +		new_val |= bitfield_swap(value, 20, 4);
> +		new_val |= bitfield_swap(value, 24, 40);
> +	} else {
> +		new_val = bitfield_swap(value, 63, 1);
> +		new_val |= bitfield_swap(value, 62, 1);
> +		new_val |= bitfield_swap(value, 61, 1);
> +		new_val |= bitfield_swap(value, 60, 1);
> +		new_val |= bitfield_swap(value, 44, 16);
> +		new_val |= bitfield_swap(value, 40, 4);
> +		new_val |= bitfield_swap(value, 0, 40);
> +	}
> +
> +	return new_val;
> +}
> +
>  int evsel__parse_sample(struct evsel *evsel, union perf_event *event,
>  			struct perf_sample *data)
>  {
> @@ -2408,6 +2456,8 @@ int evsel__parse_sample(struct evsel *evsel, union perf_event *event,
>  	if (type & PERF_SAMPLE_BRANCH_STACK) {
>  		const u64 max_branch_nr = UINT64_MAX /
>  					  sizeof(struct branch_entry);
> +		struct branch_entry *e;
> +		unsigned int i;
>  
>  		OVERFLOW_CHECK_u64(array);
>  		data->branch_stack = (struct branch_stack *)array++;
> @@ -2416,10 +2466,33 @@ int evsel__parse_sample(struct evsel *evsel, union perf_event *event,
>  			return -EFAULT;
>  
>  		sz = data->branch_stack->nr * sizeof(struct branch_entry);
> -		if (evsel__has_branch_hw_idx(evsel))
> +		if (evsel__has_branch_hw_idx(evsel)) {
>  			sz += sizeof(u64);
> -		else
> +			e = &data->branch_stack->entries[0];
> +		} else {
>  			data->no_hw_idx = true;
> +			/*
> +			 * if the PERF_SAMPLE_BRANCH_HW_INDEX is not applied,
> +			 * only nr and entries[] will be output by kernel.
> +			 */
> +			e = (struct branch_entry *)&data->branch_stack->hw_idx;
> +		}
> +
> +		if (swapped) {
> +			/*
> +			 * struct branch_flag does not have endian
> +			 * specific bit field definition. And bswap
> +			 * will not resolve the issue, since these
> +			 * are bit fields.
> +			 *
> +			 * evsel__bitfield_swap_branch_flags() uses a
> +			 * bitfield_swap macro to swap the bit position
> +			 * based on the host endians.
> +			 */
> +			for (i = 0; i < data->branch_stack->nr; i++, e++)
> +				e->flags.value = evsel__bitfield_swap_branch_flags(e->flags.value);
> +		}
> +
>  		OVERFLOW_CHECK(array, sz, max_size);
>  		array = (void *)array + sz;
>  	}
> diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
> index 1f7edfa8568a..2e82cdbe2c08 100644
> --- a/tools/perf/util/evsel.h
> +++ b/tools/perf/util/evsel.h
> @@ -482,4 +482,17 @@ struct evsel *evsel__leader(struct evsel *evsel);
>  bool evsel__has_leader(struct evsel *evsel, struct evsel *leader);
>  bool evsel__is_leader(struct evsel *evsel);
>  void evsel__set_leader(struct evsel *evsel, struct evsel *leader);
> +
> +/*
> + * Macro to swap the bit-field postition and size.
> + * Used when,
> + * - dont need to swap the entire u64 &&
> + * - when u64 has variable bit-field sizes &&
> + * - when presented in a host endian which is different
> + *   than the source endian of the perf.data file
> + */
> +#define bitfield_swap(src, pos, size)	\
> +	((((src) >> (pos)) & ((1ull << (size)) - 1)) << (63 - ((pos) + (size) - 1)))
> +
> +u64 evsel__bitfield_swap_branch_flags(u64 value);
>  #endif /* __PERF_EVSEL_H */
> -- 
> 2.31.1

-- 

- Arnaldo