[PROF-12743] Runtime stack collection callback registration #4984

gyuheon0h · 2025-10-16T09:34:25Z

What does this PR do?
We want to collect runtime frames for the crashtracker. This approach follows how we access the call stack for profiling.

CI fails currently because we are not on libdatadog v24 yet. Once this PR is merged and this PR is rebased, we should be green

Motivation:

Change log entry

Additional Notes:

How to test the change?

"Ruby and C method runtime stack capture" RSpec test

Run a ruby program with the crashtracker initialized. Runtime stacks should be visible in the experimental section of the crash report. Stacktrace emitted from an example script I wrote to test

{
  "format": "Datadog Runtime Callback 1.0",
  "frames": [
    {
      "file": "<Fiddle (C extension)>",
      "function": "free"
    },
    {
      "file": "debug_runtime_callback.rb",
      "function": "final_crash_point",
      "line": 244
    },
    {
      "file": "<Integer (C extension)>",
      "function": "times"
    },
    {
      "file": "debug_runtime_callback.rb",
      "function": "final_crash_point",
      "line": 243
    },
   .....
    {
      "file": "debug_runtime_callback.rb",
      "function": "main_crash_test",
      "line": 251
    },
    {
      "file": "debug_runtime_callback.rb",
      "function": "<main>",
      "line": 276
    },
    {
      "file": "<Kernel (C extension)>",
      "function": "fork"
    }
  ]
}

github-actions · 2025-10-16T09:34:37Z

👋 Hey @DataDog/ruby-guild, please fill "Change log entry" section in the pull request description.

If changes need to be present in CHANGELOG.md you can state it this way

**Change log entry**

Yes. A brief summary to be placed into the CHANGELOG.md

(possible answers Yes/Yep/Yeah)

Or you can opt out like that

**Change log entry**

None.

(possible answers No/Nope/None)

^{Visited at: 2025-11-17 03:53:49 UTC}

github-actions · 2025-10-16T09:34:46Z

Typing analysis

This PR does not change typing compared to the base branch.

gyuheon0h · 2025-10-24T15:37:59Z

[PROF-12743] Runtime stack collection callback registration #4984 👈 (View in Graphite)
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gyuheon0h · 2025-11-08T07:46:02Z

Paper trail

[ ] Checking unreasonable string sizes
[ ] Checking that string pointers point to valid strings
[ ] Checking that control frames are valid
[ ] Checking that iseq is valid, and the instruction size is not unreasonable
[ ] Validating that pointers are readable using mincore
[ ] Checking for recursive frames
[ ] Strings can have different representations, take that into account
[ ] Ruby apps commonly have very deep stacks. We default in the profiler to collecting 400 and we've seen GitHub go close to 600, handle this
[ ] Pay attention to structure keeping the bytecode-to-line mapping

gyuheon0h · 2025-11-17T03:05:15Z

ext/libdatadog_api/extconf.rb

 # * by msgpack, another datadog gem dependency
 #   (https://github.com/msgpack/msgpack-ruby/blob/18ce08f6d612fe973843c366ac9a0b74c4e50599/ext/msgpack/extconf.rb#L8)
 append_cflags '-std=gnu99'



Taken from ext/datadog_profiling_native_extension/extconf.rb, so that we can access private Ruby headers

gyuheon0h · 2025-11-17T03:41:59Z

.gitignore


 # Benchmark result files
 /benchmarks/*.json
+


Will be removed when this repo is updated to use libdatadog v24; just for lower friction when local dev rn

gyuheon0h · 2025-11-17T03:42:52Z

ext/libdatadog_api/crashtracker.c

@@ -1,7 +1,49 @@
-#include <ruby.h>
-#include <datadog/crashtracker.h>
+#include "extconf.h"


Taken from ext/datadog_profiling_native_extension/private_vm_api_access.c so that we can access internal Ruby structures

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lib/datadog/core/crashtracking/component.rb

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ext/libdatadog_api/datadog_runtime_stack.c

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ext/libdatadog_api/datadog_runtime_stack.c

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chatgpt-codex-connector · 2025-11-17T04:39:02Z

lib/datadog/core/crashtracking/component.rb

          Utils::AtForkMonkeyPatch.apply!

          start_or_update_on_fork(action: :start, tags: tags)
+          register_runtime_stack_callback


Guard runtime callback registration on repeated starts

The new start path always invokes register_runtime_stack_callback, and register_runtime_stack_callback raises whenever the native call returns false (e.g. callback already registered). Because the crash tracker component is process‑wide and Datadog.configure can instantiate and start a new component multiple times, the second start now raises Failed to register runtime stack callback and prevents reconfiguration or restarts from succeeding. Consider checking _native_is_runtime_callback_registered or otherwise making the registration idempotent so that later start calls do not blow up.

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Not true, if a callback is already registered, it should replace it

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ext/libdatadog_api/datadog_runtime_stack.c

gyuheon0h requested review from a team as code owners October 16, 2025 09:34

gyuheon0h marked this pull request as draft October 16, 2025 09:34

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gyuheon0h force-pushed the gyuheon0h/prof-12743-runtime-stack-callback branch from e628919 to 564c828 Compare October 24, 2025 15:37

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github-actions bot added the profiling Involves Datadog profiling label Nov 17, 2025

gyuheon0h marked this pull request as ready for review November 17, 2025 03:52

gyuheon0h changed the title ~~[WIP][crashtracking] Runtime stack collection callback registration~~ [crashtracking] Runtime stack collection callback registration Nov 17, 2025

gyuheon0h changed the title ~~[crashtracking] Runtime stack collection callback registration~~ [PROF-12743] Runtime stack collection callback registration Nov 17, 2025

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gyuheon0h added 9 commits November 17, 2025 13:12

First commit; declare libdatadog ext api

4fb84de

Dummy frame emitted

bc46b26

Include internal structures (at least try to))

604d91b

Can walk the stack, but no func names yet

e97441f

Add safety checks when walking stack

b912f78

Get C frames, and also add some AI generated sanity check tests

3bb2234

Clean up tests

622bb37

Use all safety checks

47c757d

Category specific runtime callback

929cde0

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gyuheon0h requested a review from ivoanjo November 17, 2025 13:17

Move runtime stuff to own file

50da69c

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gyuheon0h marked this pull request as draft November 17, 2025 15:17

gyuheon0h force-pushed the gyuheon0h/prof-12743-runtime-stack-callback branch from 3ff1774 to af340dd Compare November 17, 2025 16:15

Try to fix issues across diff ruby versions

bc7eb46

gyuheon0h force-pushed the gyuheon0h/prof-12743-runtime-stack-callback branch from af340dd to bc7eb46 Compare November 17, 2025 16:24

[PROF-12743] Runtime stack collection callback registration #4984

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