Commit 63c12ae2 authored by Madhavan Srinivasan's avatar Madhavan Srinivasan Committed by Arnaldo Carvalho de Melo
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perf evsel: Add bitfield_swap() to handle branch_stack endian issue 



The 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: default avatarMadhavan Srinivasan <maddy@linux.ibm.com>
Acked-by: default avatarJiri Olsa <jolsa@redhat.com>
Cc: Athira Jajeev <atrajeev@linux.vnet.ibm.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Ellerman <michael@ellerman.id.au>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20211028113714.600549-1-maddy@linux.ibm.com


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 6ea5d1a3

tools/perf/util/evsel.c

+75 −2
Original line number Diff line number Diff line
@@ -2238,6 +2238,54 @@ 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)

{
@@ -2425,6 +2473,8 @@ 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++;
@@ -2433,10 +2483,33 @@ 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;

	}

tools/perf/util/evsel.h

+13 −0
Original line number Diff line number Diff line
@@ -484,4 +484,17 @@ 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 */