feat: Publish OTel process context

[ivoanjo]

Description

This PR adds support for publishing the OpenTelemetry Process Context (aka OTEP 4719 -- https://github.com/open-telemetry/opentelemetry-specification/blob/main/oteps/profiles/4719-process-ctx.md).

This mechanism is very similar to Datadog's existing "process discovery"/"tracer-info" mechanism, so the actual change in trace.cpp is very minimal (this is by design :p ).

This data will be read by OTel-compliant tools, of which the eBPF Profiler (which Datadog will also support as part of our Continuous Profiler product) is the first one.

Motivation

We're adding support for OTEP 4719 to all Datadog SDKs, so dd-trace-cpp is actually one of the last ones to adopt this.

See https://docs.google.com/document/d/1IwjjVJzEChcFPcnVV2N5Kkjg-4_Q4v4Q3ojpxntbdvY/edit?pli=1&tab=t.s7dfru3a9hnl (Datadog-only link) for an up-to-date list of all SDKs.

Additional Notes

Jira ticket: PROF-14789

The otel_process_ctx.cpp and otel_process_ctx.h come from the reference implementation we're maintaining upstream with OTel in https://github.com/open-telemetry/sig-profiling/tree/main/process-context/c-and-cpp.

They are already in use in dd-trace-java as well.

Review-wise, my suggestion for those would be to focus on correctness -- ideally we want to be able to quickly update to the latest version when needed, which is made easier if we have a minimal delta on upstream.

(I'm the one maintaining this upstream so I can propagate fixes/changes as well so we don't have to diverge).

How to test the change?

This change includes test coverage. Also, I've tested this in practice using the otel_process_ctx_dump.sh script from the https://github.com/open-telemetry/sig-profiling/ repo.

Here's how that looks:

$ sudo ./otel_process_ctx_dump.sh 2394947
Found OTEL context for PID 2394947
Start address: 7c072aace000
00000000  4f 54 45 4c 5f 43 54 58  02 00 00 00 c3 01 00 00  |OTEL_CTX........|
00000010  68 5b 15 20 9a 25 21 00  60 f0 6e 16 c5 5b 00 00  |h[. .%!.`.n..[..|
00000020
Parsed struct:
  otel_process_ctx_signature             : "OTEL_CTX"
  otel_process_ctx_version               : 2
  otel_process_payload_size              : 451
  otel_process_monotonic_published_at_ns : 9330018124913512
  otel_process_payload                   : 0x00005bc5166ef060
Payload dump (451 bytes):
00000000  0a af 02 0a 21 0a 1b 64  65 70 6c 6f 79 6d 65 6e  |....!..deploymen|
00000010  74 2e 65 6e 76 69 72 6f  6e 6d 65 6e 74 2e 6e 61  |t.environment.na|
00000020  6d 65 12 02 0a 00 0a 3d  0a 13 73 65 72 76 69 63  |me.....=..servic|
00000030  65 2e 69 6e 73 74 61 6e  63 65 2e 69 64 12 26 0a  |e.instance.id.&.|
00000040  24 38 32 65 39 38 38 38  64 2d 33 36 65 62 2d 34  |$82e9888d-36eb-4|
00000050  39 63 66 2d 61 63 63 38  2d 36 38 32 39 34 39 63  |9cf-acc8-682949c|
00000060  34 39 32 37 33 0a 20 0a  0c 73 65 72 76 69 63 65  |49273. ..service|
00000070  2e 6e 61 6d 65 12 10 0a  0e 63 70 70 2d 65 78 70  |.name....cpp-exp|
00000080  65 72 69 6d 65 6e 74 0a  15 0a 0f 73 65 72 76 69  |eriment....servi|
00000090  63 65 2e 76 65 72 73 69  6f 6e 12 02 0a 00 0a 1f  |ce.version......|
000000a0  0a 16 74 65 6c 65 6d 65  74 72 79 2e 73 64 6b 2e  |..telemetry.sdk.|
000000b0  6c 61 6e 67 75 61 67 65  12 05 0a 03 63 70 70 0a  |language....cpp.|
000000c0  21 0a 15 74 65 6c 65 6d  65 74 72 79 2e 73 64 6b  |!..telemetry.sdk|
000000d0  2e 76 65 72 73 69 6f 6e  12 08 0a 06 76 32 2e 31  |.version....v2.1|
000000e0  2e 31 0a 24 0a 12 74 65  6c 65 6d 65 74 72 79 2e  |.1.$..telemetry.|
000000f0  73 64 6b 2e 6e 61 6d 65  12 0e 0a 0c 64 64 2d 74  |sdk.name....dd-t|
00000100  72 61 63 65 2d 63 70 70  0a 0f 0a 09 68 6f 73 74  |race-cpp....host|
00000110  2e 6e 61 6d 65 12 02 0a  00 0a 17 0a 0c 63 6f 6e  |.name........con|
00000120  74 61 69 6e 65 72 2e 69  64 12 07 0a 05 31 32 39  |tainer.id....129|
00000130  37 30 12 8e 01 0a 14 64  61 74 61 64 6f 67 2e 70  |70.....datadog.p|
00000140  72 6f 63 65 73 73 5f 74  61 67 73 12 76 0a 74 65  |rocess_tags.v.te|
00000150  6e 74 72 79 70 6f 69 6e  74 2e 62 61 73 65 64 69  |ntrypoint.basedi|
00000160  72 3a 62 75 69 6c 64 2c  65 6e 74 72 79 70 6f 69  |r:build,entrypoi|
00000170  6e 74 2e 77 6f 72 6b 64  69 72 3a 63 70 70 2d 65  |nt.workdir:cpp-e|
00000180  78 70 65 72 69 6d 65 6e  74 2c 65 6e 74 72 79 70  |xperiment,entryp|
00000190  6f 69 6e 74 2e 74 79 70  65 3a 65 78 65 63 75 74  |oint.type:execut|
000001a0  61 62 6c 65 2c 65 6e 74  72 79 70 6f 69 6e 74 2e  |able,entrypoint.|
000001b0  6e 61 6d 65 3a 63 70 70  2d 65 78 70 65 72 69 6d  |name:cpp-experim|
000001c0  65 6e 74                                          |ent|
000001c3
Protobuf decode:
resource {
  attributes {
    key: "deployment.environment.name"
    value {
      string_value: ""
    }
  }
  attributes {
    key: "service.instance.id"
    value {
      string_value: "82e9888d-36eb-49cf-acc8-682949c49273"
    }
  }
  attributes {
    key: "service.name"
    value {
      string_value: "cpp-experiment"
    }
  }
  attributes {
    key: "service.version"
    value {
      string_value: ""
    }
  }
  attributes {
    key: "telemetry.sdk.language"
    value {
      string_value: "cpp"
    }
  }
  attributes {
    key: "telemetry.sdk.version"
    value {
      string_value: "v2.1.1"
    }
  }
  attributes {
    key: "telemetry.sdk.name"
    value {
      string_value: "dd-trace-cpp"
    }
  }
  attributes {
    key: "host.name"
    value {
      string_value: ""
    }
  }
  attributes {
    key: "container.id"
    value {
      string_value: "12970"
    }
  }
}
extra_attributes {
  key: "datadog.process_tags"
  value {
    string_value: "entrypoint.basedir:build,entrypoint.workdir:cpp-experiment,entrypoint.type:executable,entrypoint.name:cpp-experiment"
  }
}

[datadog-official]

🎯 Code Coverage (details)
• Patch Coverage: 75.14%
• Overall Coverage: 84.45% (-7.30%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: fe98617 | Docs | Datadog PR Page | Give us feedback!}

[chatgpt-codex-connector]

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[pr-commenter]

Benchmarks

Benchmark execution time: 2026-08-10 06:57:44

Comparing candidate commit fe98617 in PR branch ivoanjo/prof-14789-otel-process-ctx with baseline commit eb64048 in branch main.

Found 4 performance improvements and 1 performance regressions! Performance is the same for 2 metrics, 1 unstable metrics.

Explanation

This is an A/B test comparing a candidate commit's performance against that of a baseline commit. Performance changes are noted in the tables below as:

• 🟩 = significantly better candidate vs. baseline
• 🟥 = significantly worse candidate vs. baseline

We compute a confidence interval (CI) over the relative difference of means between metrics from the candidate and baseline commits, considering the baseline as the reference.

If the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD), the change is considered significant.

Feel free to reach out to #apm-benchmarking-platform on Slack if you have any questions.

More details about the CI and significant changes

You can imagine this CI as a range of values that is likely to contain the true difference of means between the candidate and baseline commits.

CIs of the difference of means are often centered around 0%, because often changes are not that big:

---------------------------------(------|---^--------)-------------------------------->
                              -0.6%    0%  0.3%     +1.2%
                                 |          |        |
         lower bound of the CI --'          |        |
sample mean (center of the CI) -------------'        |
         upper bound of the CI ----------------------'

As described above, a change is considered significant if the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD).

For instance, for an execution time metric, this confidence interval indicates a significantly worse performance:

----------------------------------------|---------|---(---------^---------)---------->
                                       0%        1%  1.3%      2.2%      3.1%
                                                  |   |         |         |
       significant impact threshold --------------'   |         |         |
                      lower bound of CI --------------'         |         |
       sample mean (center of the CI) --------------------------'         |
                      upper bound of CI ----------------------------------'

scenario:BM_HexPadded_uint64/NoPadding

• 🟩 execution_time [-1.391ns; -1.300ns] or [-2.587%; -2.418%]

scenario:BM_Hex_uint64

• 🟩 execution_time [-0.736ns; -0.714ns] or [-3.102%; -3.011%]

scenario:BM_TraceID_ParseHex/128bit

• 🟩 execution_time [-12.829ns; -12.783ns] or [-9.417%; -9.383%]

scenario:BM_TraceID_ParseHex/64bit

• 🟩 execution_time [-4.924ns; -4.892ns] or [-6.639%; -6.596%]

scenario:BM_TraceTinyCCSource

• 🟥 execution_time [+1.854ms; +1.997ms] or [+2.490%; +2.683%]

[ivoanjo]

I had to push force to fix the missing commit signatures. Going to fix that merge conflict next...