[PROF-12372] (Draft) Hack for experimental support for publishing process context for fullhost profiler

[ivoanjo]

What does this PR do?

This PR imports the experimental code from
https://github.com/DataDog/fullhost-code-hotspots-wip/pull/2 (Datadog-internal repo for now!) into Ruby so we can test out the code on Ruby apps easily. See that original PR for more details on what that is and how it works.

I don't expect this PR to ever be merged, it's only for easier testing.

Motivation:

I'm opening this draft PR so I can add this to test apps in our reliability environment a bit more easily.

Change log entry

None. This is not expected to be merged.

Additional Notes:

Since this is a quick hack, I piggy-backed on the existing process discovery support, rather than separating it out too much.

How to test the change?

The PR linked above has a script that can be used to read the data.

Here's how it looks for me:

$ sudo otel_process_ctx_dump.sh 205306
Found OTEL context for PID 205306
Start address: 7f0f25efd000
00000000  4f 54 45 4c 5f 43 54 58  01 00 00 00 93 00 00 00  |OTEL_CTX........|
00000010  60 8a 1c 91 9c 5c 00 00                           |`....\..|
00000018
Parsed struct:
  otel_process_ctx_signature : "OTEL_CTX"
  otel_process_ctx_version   : 1
  otel_process_payload_size  : 147
  otel_process_payload       : 0x00005c9c911c8a60

Payload dump (147 bytes):
00000000  de 00 03 da 00 0c 73 65  72 76 69 63 65 2e 6e 61  |......service.na|
00000010  6d 65 da 00 11 74 65 73  74 2d 73 65 72 76 69 63  |me...test-servic|
00000020  65 2d 6e 61 6d 65 da 00  13 73 65 72 76 69 63 65  |e-name...service|
00000030  2e 69 6e 73 74 61 6e 63  65 2e 69 64 da 00 24 64  |.instance.id..$d|
00000040  35 30 63 33 33 63 30 2d  31 37 39 33 2d 34 37 63  |50c33c0-1793-47c|
00000050  30 2d 61 38 63 62 2d 65  38 36 62 38 62 36 61 35  |0-a8cb-e86b8b6a5|
00000060  38 62 36 da 00 1b 64 65  70 6c 6f 79 6d 65 6e 74  |8b6...deployment|
00000070  2e 65 6e 76 69 72 6f 6e  6d 65 6e 74 2e 6e 61 6d  |.environment.nam|
00000080  65 da 00 0f 74 68 69 73  2d 69 73 2d 74 68 65 2d  |e...this-is-the-|
00000090  65 6e 76                                          |env|
00000093

[datadog-official]

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[pr-commenter]

Benchmarks

Benchmark execution time: 2025-09-04 12:54:43

Comparing candidate commit db57078 in PR branch ivoanjo/experimental-process-ctx with baseline commit 299da4e in branch master.

Found 0 performance improvements and 2 performance regressions! Performance is the same for 42 metrics, 2 unstable metrics.

scenario:profiling - stack collector (varying depth)

• 🟥 throughput [-63.902op/s; -63.157op/s] or [-6.243%; -6.171%]

scenario:tracing - Propagation - Trace Context

• 🟥 throughput [-2969.131op/s; -2851.759op/s] or [-8.029%; -7.712%]