On Thu, Apr 27, 2023 at 04:52:06PM +0100, James Clark wrote:
[...]
-static int cs_etm_set_context_id(struct auxtrace_record *itr,
struct evsel *evsel, int cpu)+static int cs_etm_validate_context_id(struct auxtrace_record *itr,
struct evsel *evsel, int cpu){
- struct cs_etm_recording *ptr;
- struct perf_pmu *cs_etm_pmu;
- struct cs_etm_recording *ptr =
container_of(itr, struct cs_etm_recording, itr);- struct perf_pmu *cs_etm_pmu = ptr->cs_etm_pmu; char path[PATH_MAX];
- int err = -EINVAL;
- int err; u32 val;
- u64 contextid;
- u64 contextid =
evsel->core.attr.config &(perf_pmu__format_bits(&cs_etm_pmu->format, "contextid1") |perf_pmu__format_bits(&cs_etm_pmu->format, "contextid2"));Seems to me, this would break backward compability.
The old kernel (before 5.11) doesn't provide 'contextid1' and 'contextid2', so we always check the entry 'contextid' rather than 'contextid1' and 'contextid2'.
With this change, if a kernel doesn't contain 'contextid1' and 'contextid2' formats, will perf tool never trace for contexid?
No because I changed to to be purely validation, so the format flags would still be applied. But yes I think you are right there is a small issue.
Now validation of 'contextid' isn't done on pre 5.11 kernels. But that only checks for ETMv3 anyway.
IIUC, 'contextid' is not only used for ETMv3. Just quotes the comments from drivers/hwtracing/coresight/coresight-etm-perf.c:
73 /* 74 * contextid always traces the "PID". The PID is in CONTEXTIDR_EL1 75 * when the kernel is running at EL1; when the kernel is at EL2, 76 * the PID is in CONTEXTIDR_EL2. 77 */
ETMv4 uses 'contextid' as well, since the user space needs to know which exception level's PID should be traced, e.g. when CPU runs in EL2 'contextid' is set as ETM_OPT_CTXTID2, the perf tool will set 'contextid2' to tell driver to trace CONTEXTIDR_EL2.
We can only verify 'contextid', and set 'contextid1' or 'contextid2' based on CPU running exception level, finally driver knows how to trace PID.
Thanks, Leo
Validation of 'contextid1' and 'contextid2' isn't a problem, because if the kernel doesn't support them they can't be applied on the command line anyway.
I can fix it by checking for 'contextid' and ETMv3 first and then doing 'contextid1' and 'contextid2' after.