WIP: use a trampoline for FLF functions to intercept timings

[bwoebi]

They don't check EG(vm_interrupt) by design, so we manually handle this.

[datadog-datadog-prod-us1]

⚠️ Tests

✨ Fix all issues with Cursor

⚠️ Warnings

🧪 1024 Tests failed

    testSearchPhpBinaries from integration.DDTrace\Tests\Integration\PHPInstallerTest (Fix with Cursor)

    testSimplePushAndProcess from laravel-58-test.DDTrace\Tests\Integrations\Laravel\V5_8\QueueTest (Fix with Cursor)

testSimplePushAndProcess from laravel-8x-test.DDTrace\Tests\Integrations\Laravel\V8_x\QueueTest (Datadog) (Fix with Cursor)

DDTrace\Tests\Integrations\Laravel\V8_x\QueueTest::testSimplePushAndProcess
Test code or tested code printed unexpected output: spanLinksTraceId: 697a1bac00000000f3eadda2c887b2cb
tid: 697a1bac00000000
hexProcessTraceId: f3eadda2c887b2cb
hexProcessSpanId: 9e2fa866b114acc9
processTraceId: 17576104186985558731
processSpanId: 11398514340909067465

View all

ℹ️ Info

❄️ No new flaky tests detected

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: e11b3fc | Docs | Datadog PR Page | Was this helpful? Give us feedback!}

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.91%. Comparing base (5456721) to head (e11b3fc).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3595      +/-   ##
==========================================
- Coverage   61.92%   61.91%   -0.02%     
==========================================
  Files         140      140              
  Lines       13312    13312              
  Branches     1762     1762              
==========================================
- Hits         8244     8242       -2     
- Misses       4277     4280       +3     
+ Partials      791      790       -1     

see 1 file with indirect coverage changes

---

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[morrisonlevi]

I assume this can run afoul of permissions somehow, since we're making executable code at runtime? I'm not well versed here, and yes, if the JIT is enabled you'd have to have that capability anyway, but I'm trying to understand implications of this WIP.

[pr-commenter]

Benchmarks [ profiler ]

Benchmark execution time: 2026-01-28 14:25:44

Comparing candidate commit e11b3fc in PR branch bob/prof-flf-test with baseline commit 5456721 in branch master.

Found 1 performance improvements and 0 performance regressions! Performance is the same for 28 metrics, 7 unstable metrics.

scenario:walk_stack/99

• 🟩 wall_time [-332.149ns; -328.592ns] or [-2.136%; -2.113%]

[bwoebi]

@morrisonlevi dynasmrt takes care of setting RX permissions after compiling the code. As long as you're not running this under a hardened runtime (like app store apps or android (?)), there's no fundamental problem. Also I currently call assembler.finalize().unwrap() (which takes care of settign RX) - proper usage should just handle the potential error here and abort.

[cataphract]

I assume original is not returning anything, because you're writing over RAX.

[bwoebi]

Correct

[cataphract]

this overwrites x30/lr, aren't you gonna lose the original return location of the handler? so when br x16 returns, it goes back to calling interrupt_addr

[bwoebi]

Ah, right. call on x86_64 pushes %eip to the stack, but blr doesn't.

[bwoebi]

Fixed up, is it correct now?