[PATCH 4/7] perf cs-etm: Don't use hard coded config bits when setting up ETMCR

James Clark
2025-12-01T16:41:58Z

Perf only looks at attr.config when determining what was programmed into
ETMCR. These bits could theoretically be in any of the config fields.
Add a generic helper to find the value of any named format field in any
config field and then use it to get the attributes relevant to ETMCR.

The kernel will also stop publishing the ETMCR register bits in a header
[1] so preempt that by defining them here.

[1]: https://lore.kernel.org/linux-arm-kernel/20251128-james-cs-syncfreq-v8-10-4d319764cc58@linaro.org/
Signed-off-by: James Clark <james.clark@linaro.org>
---
tools/perf/arch/arm/util/cs-etm.c | 35 ++++++++++++++++++++++++++++++++++-
tools/perf/util/evsel.h | 2 ++
tools/perf/util/pmu.c | 33 +++++++++++++++++++++++++++++++++
3 files changed, 69 insertions(+), 1 deletion(-)

diff --git a/tools/perf/arch/arm/util/cs-etm.c b/tools/perf/arch/arm/util/cs-etm.c
index 22c6272e8c36..414cafb21c98 100644
--- a/tools/perf/arch/arm/util/cs-etm.c
+++ b/tools/perf/arch/arm/util/cs-etm.c
@@ -68,6 +68,12 @@ static const char * const metadata_ete_ro[] = {

enum cs_etm_version { CS_NOT_PRESENT, CS_ETMV3, CS_ETMV4, CS_ETE };

+
+/* ETMv3 ETMCR register bits */
+#define ETMCR_CYC_ACC BIT(12)
+#define ETMCR_TIMESTAMP_EN BIT(28)
+#define ETMCR_RETURN_STACK BIT(29)
+
static bool cs_etm_is_ete(struct perf_pmu *cs_etm_pmu, struct perf_cpu cpu);
static int cs_etm_get_ro(struct perf_pmu *pmu, struct perf_cpu cpu, const char *path, __u64 *val);
static bool cs_etm_pmu_path_exists(struct perf_pmu *pmu, struct perf_cpu cpu, const char *path);
@@ -487,6 +493,33 @@ static int cs_etm_recording_options(struct auxtrace_record *itr,
return err;
}

+static u64 cs_etm_guess_etmcr(struct auxtrace_record *itr)
+{
+ struct cs_etm_recording *ptr =
+ container_of(itr, struct cs_etm_recording, itr);
+ struct perf_pmu *cs_etm_pmu = ptr->cs_etm_pmu;
+ struct evsel *evsel = cs_etm_get_evsel(ptr->evlist, cs_etm_pmu);
+ u64 etmcr = 0;
+ u64 val;
+
+ if (!evsel)
+ return 0;
+
+ /*
+ * Roughly guess what the kernel programmed into ETMCR based on
+ * what options the event was opened with. This doesn't have to be
+ * complete or 100% accurate, not all bits used by OpenCSD anyway.
+ */
+ if (!evsel__get_config_val(cs_etm_pmu, evsel, "cycacc", &val) && val)
+ etmcr |= ETMCR_CYC_ACC;
+ if (!evsel__get_config_val(cs_etm_pmu, evsel, "timestamp", &val) && val)
+ etmcr |= ETMCR_TIMESTAMP_EN;
+ if (!evsel__get_config_val(cs_etm_pmu, evsel, "retstack", &val) && val)
+ etmcr |= ETMCR_RETURN_STACK;
+
+ return etmcr;
+}
+
static u64 cs_etm_get_config(struct auxtrace_record *itr)
{
struct cs_etm_recording *ptr =
@@ -746,7 +779,7 @@ static void cs_etm_get_metadata(struct perf_cpu cpu, u32 *offset,
case CS_ETMV3:
magic = __perf_cs_etmv3_magic;
/* Get configuration register */
- info->priv[*offset + CS_ETM_ETMCR] = cs_etm_get_config(itr);
+ info->priv[*offset + CS_ETM_ETMCR] = cs_etm_guess_etmcr(itr);
/* traceID set to legacy value in case new perf running on old system */
info->priv[*offset + CS_ETM_ETMTRACEIDR] = cs_etm_get_legacy_trace_id(cpu);
/* Get read-only information from sysFS */
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index 3ae4ac8f9a37..1c567cc70a82 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -574,6 +574,8 @@ void evsel__uniquify_counter(struct evsel *counter);
((((src) >> (pos)) & ((1ull << (size)) - 1)) << (63 - ((pos) + (size) - 1)))

u64 evsel__bitfield_swap_branch_flags(u64 value);
+int evsel__get_config_val(struct perf_pmu *pmu, struct evsel *evsel,
+ const char *config_name, u64 *val);
void evsel__set_config_if_unset(struct perf_pmu *pmu, struct evsel *evsel,
const char *config_name, u64 val);

diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
index c8968cddc0a9..5501b0230097 100644
--- a/tools/perf/util/pmu.c
+++ b/tools/perf/util/pmu.c
@@ -1384,6 +1384,39 @@ pmu_find_format(const struct list_head *formats, const char *name)
return NULL;
}

+int evsel__get_config_val(struct perf_pmu *pmu, struct evsel *evsel,
+ const char *config_name, u64 *val)
+{
+ struct perf_pmu_format *format = pmu_find_format(&pmu->format, config_name);
+ u64 bits = perf_pmu__format_bits(pmu, config_name);
+
+ if (!format || !bits) {
+ pr_err("Unknown/empty format name: %s\n", config_name);
+ return -EINVAL;
+ }
+
+ switch (format->value) {
+ case PERF_PMU_FORMAT_VALUE_CONFIG:
+ *val = FIELD_GET(bits, evsel->core.attr.config);
+ return 0;
+ case PERF_PMU_FORMAT_VALUE_CONFIG1:
+ *val = FIELD_GET(bits, evsel->core.attr.config1);
+ return 0;
+ case PERF_PMU_FORMAT_VALUE_CONFIG2:
+ *val = FIELD_GET(bits, evsel->core.attr.config2);
+ return 0;
+ case PERF_PMU_FORMAT_VALUE_CONFIG3:
+ *val = FIELD_GET(bits, evsel->core.attr.config3);
+ return 0;
+ case PERF_PMU_FORMAT_VALUE_CONFIG4:
+ *val = FIELD_GET(bits, evsel->core.attr.config4);
+ return 0;
+ default:
+ pr_err("Unknown format value: %d\n", format->value);
+ return -EINVAL;
+ }
+}
+
/*
* Set @config_name to @val as long as the user hasn't already set or cleared it
* by passing a config term on the command line.

--
2.34.1