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perf evsel: Add bitfield_swap() to handle branch_stack endian issue

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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: Madhavan Srinivasan <maddy@linux.ibm.com>
Acked-by: Jiri 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: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Madhavan Srinivasan 2021-10-28 17:07:13 +05:30 committed by Arnaldo Carvalho de Melo
parent 6ea5d1a3e3
commit 63c12ae2f2
2 changed files with 88 additions and 2 deletions
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77
tools/perf/util/evsel.c
View File

@ -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;
}

13
tools/perf/util/evsel.h
View File

@ -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 */