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__reverse64_branch_stack_flags()
is defined and introduced in evsel__parse_sample.
Signed-off-by: Madhavan Srinivasan <[email protected]>
---
tools/perf/util/evsel.c | 64 +++++++++++++++++++++++++++++++++++++++--
tools/perf/util/evsel.h | 5 ++++
2 files changed, 67 insertions(+), 2 deletions(-)
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index dbfeceb2546c..007be66b69a2 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -2221,6 +2221,46 @@ void __weak arch_perf_parse_sample_weight(struct perf_sample *data,
data->weight = *array;
}
+u64 evsel__reverse64_branch_stack_flags(u64 value)
+{
+ u64 new_val = 0;
+
+ /*
+ * branch_stack flag (u64)
+ * 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
+ * }
+ * }
+ */
+ if (bigendian()) {
+ new_val = reverse_64(value, 0, 1);
+ new_val |= reverse_64(value, 1, 1);
+ new_val |= reverse_64(value, 2, 1);
+ new_val |= reverse_64(value, 3, 1);
+ new_val |= reverse_64(value, 4, 16);
+ new_val |= reverse_64(value, 20, 4);
+ new_val |= reverse_64(value, 24, 40);
+ } else {
+ new_val = reverse_64(value, 63, 1);
+ new_val |= reverse_64(value, 62, 1);
+ new_val |= reverse_64(value, 61, 1);
+ new_val |= reverse_64(value, 60, 1);
+ new_val |= reverse_64(value, 44, 16);
+ new_val |= reverse_64(value, 40, 4);
+ new_val |= reverse_64(value, 0, 40);
+ }
+
+ return new_val;
+}
+
int evsel__parse_sample(struct evsel *evsel, union perf_event *event,
struct perf_sample *data)
{
@@ -2408,6 +2448,8 @@ 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 +2458,28 @@ 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;
+ 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__reverse64_branch_stack_flags() uses a reverse64
+ * macro to reverse the bit position based on the host
+ * endians.
+ */
+ for (i = 0; i < data->branch_stack->nr; i++, e++)
+ e->flags.value = evsel__reverse64_branch_stack_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..1127c23710cf 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -482,4 +482,9 @@ 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);
+
+#define reverse_64(src, pos, size) \
+ ((((src) >> (pos)) & ((1ull << (size)) - 1)) << (63 - ((pos) + (size) - 1)))
+
+u64 evsel__reverse64_branch_stack_flags(u64 value);
#endif /* __PERF_EVSEL_H */
--
2.31.1
On Thu, Sep 30, 2021 at 12:34:09PM +0530, Madhavan Srinivasan wrote:
> 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__reverse64_branch_stack_flags()
> is defined and introduced in evsel__parse_sample.
>
> Signed-off-by: Madhavan Srinivasan <[email protected]>
> ---
> tools/perf/util/evsel.c | 64 +++++++++++++++++++++++++++++++++++++++--
> tools/perf/util/evsel.h | 5 ++++
> 2 files changed, 67 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index dbfeceb2546c..007be66b69a2 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -2221,6 +2221,46 @@ void __weak arch_perf_parse_sample_weight(struct perf_sample *data,
> data->weight = *array;
> }
>
> +u64 evsel__reverse64_branch_stack_flags(u64 value)
> +{
> + u64 new_val = 0;
> +
> + /*
> + * branch_stack flag (u64)
> + * 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
> + * }
> + * }
> + */
please describe in comment how the bitfield is swapped
> + if (bigendian()) {
> + new_val = reverse_64(value, 0, 1);
> + new_val |= reverse_64(value, 1, 1);
> + new_val |= reverse_64(value, 2, 1);
> + new_val |= reverse_64(value, 3, 1);
> + new_val |= reverse_64(value, 4, 16);
> + new_val |= reverse_64(value, 20, 4);
> + new_val |= reverse_64(value, 24, 40);
> + } else {
> + new_val = reverse_64(value, 63, 1);
> + new_val |= reverse_64(value, 62, 1);
> + new_val |= reverse_64(value, 61, 1);
> + new_val |= reverse_64(value, 60, 1);
> + new_val |= reverse_64(value, 44, 16);
> + new_val |= reverse_64(value, 40, 4);
> + new_val |= reverse_64(value, 0, 40);
> + }
> +
> + return new_val;
> +}
> +
> int evsel__parse_sample(struct evsel *evsel, union perf_event *event,
> struct perf_sample *data)
> {
> @@ -2408,6 +2448,8 @@ 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 +2458,28 @@ 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;
> + e = (struct branch_entry *)&data->branch_stack->hw_idx;
hum, why do we convert hw_idx? it's the same struct as entries?
please explain this in comment as well
> + }
> +
> + 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__reverse64_branch_stack_flags() uses a reverse64
> + * macro to reverse the bit position based on the host
> + * endians.
> + */
> + for (i = 0; i < data->branch_stack->nr; i++, e++)
> + e->flags.value = evsel__reverse64_branch_stack_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..1127c23710cf 100644
> --- a/tools/perf/util/evsel.h
> +++ b/tools/perf/util/evsel.h
> @@ -482,4 +482,9 @@ 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);
> +
> +#define reverse_64(src, pos, size) \
> + ((((src) >> (pos)) & ((1ull << (size)) - 1)) << (63 - ((pos) + (size) - 1)))
hum, is this reversing anything?
could you please add comment describing what this is doing?
thanks,
jirka
> +
> +u64 evsel__reverse64_branch_stack_flags(u64 value);
> #endif /* __PERF_EVSEL_H */
> --
> 2.31.1
>
On 10/7/21 11:12 PM, Jiri Olsa wrote:
> On Thu, Sep 30, 2021 at 12:34:09PM +0530, Madhavan Srinivasan wrote:
>> 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__reverse64_branch_stack_flags()
>> is defined and introduced in evsel__parse_sample.
>>
>> Signed-off-by: Madhavan Srinivasan <[email protected]>
>> ---
>> tools/perf/util/evsel.c | 64 +++++++++++++++++++++++++++++++++++++++--
>> tools/perf/util/evsel.h | 5 ++++
>> 2 files changed, 67 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
>> index dbfeceb2546c..007be66b69a2 100644
>> --- a/tools/perf/util/evsel.c
>> +++ b/tools/perf/util/evsel.c
>> @@ -2221,6 +2221,46 @@ void __weak arch_perf_parse_sample_weight(struct perf_sample *data,
>> data->weight = *array;
>> }
>>
>> +u64 evsel__reverse64_branch_stack_flags(u64 value)
>> +{
>> + u64 new_val = 0;
>> +
>> + /*
>> + * branch_stack flag (u64)
>> + * 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
>> + * }
>> + * }
>> + */
> please describe in comment how the bitfield is swapped
Sure will do.
>> + if (bigendian()) {
>> + new_val = reverse_64(value, 0, 1);
>> + new_val |= reverse_64(value, 1, 1);
>> + new_val |= reverse_64(value, 2, 1);
>> + new_val |= reverse_64(value, 3, 1);
>> + new_val |= reverse_64(value, 4, 16);
>> + new_val |= reverse_64(value, 20, 4);
>> + new_val |= reverse_64(value, 24, 40);
>> + } else {
>> + new_val = reverse_64(value, 63, 1);
>> + new_val |= reverse_64(value, 62, 1);
>> + new_val |= reverse_64(value, 61, 1);
>> + new_val |= reverse_64(value, 60, 1);
>> + new_val |= reverse_64(value, 44, 16);
>> + new_val |= reverse_64(value, 40, 4);
>> + new_val |= reverse_64(value, 0, 40);
>> + }
>> +
>> + return new_val;
>> +}
>> +
>> int evsel__parse_sample(struct evsel *evsel, union perf_event *event,
>> struct perf_sample *data)
>> {
>> @@ -2408,6 +2448,8 @@ 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 +2458,28 @@ 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;
>> + e = (struct branch_entry *)&data->branch_stack->hw_idx;
> hum, why do we convert hw_idx? it's the same struct as entries?
> please explain this in comment as well
No. IIUC, hw_idx is valid only if PERF_SAMPLE_BRANCH_HW_INDEX is applied.
If not, then only nr and entries[] will be output-ed by kernel
42bbabed09ce ('perf tools: Add hw_idx in struct branch_stack')
>
>> + }
>> +
>> + 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__reverse64_branch_stack_flags() uses a reverse64
>> + * macro to reverse the bit position based on the host
>> + * endians.
>> + */
>> + for (i = 0; i < data->branch_stack->nr; i++, e++)
>> + e->flags.value = evsel__reverse64_branch_stack_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..1127c23710cf 100644
>> --- a/tools/perf/util/evsel.h
>> +++ b/tools/perf/util/evsel.h
>> @@ -482,4 +482,9 @@ 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);
>> +
>> +#define reverse_64(src, pos, size) \
>> + ((((src) >> (pos)) & ((1ull << (size)) - 1)) << (63 - ((pos) + (size) - 1)))
> hum, is this reversing anything?
> could you please add comment describing what this is doing?
Sure will do.
Thanks for review
Maddy
> thanks, jirka
>> +
>> +u64 evsel__reverse64_branch_stack_flags(u64 value);
>> #endif /* __PERF_EVSEL_H */
>> --
>> 2.31.1
>>