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

❄️ 1 New flaky test detected

ext/gd/tests/bug77272.phpt (Bug #77272 (imagescale() may return image resource on failure)) from php.ext.gd.tests (Datadog) (Fix with Cursor)

002-  in %s on line %d
003- bool(false)
001+ Killed
002+ 
003+ Termsig=9

🧪 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: 6973525c000000004d5565ab599608c4
tid: 6973525c00000000
hexProcessTraceId: 4d5565ab599608c4
hexProcessSpanId: ead63bed90829e17
processTraceId: 5572471900557674692
processSpanId: 16921778541408984599

View all

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 2f81b3a | 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 62.00%. Comparing base (4df27be) to head (2f81b3a).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3595      +/-   ##
==========================================
- Coverage   62.01%   62.00%   -0.02%     
==========================================
  Files         140      140              
  Lines       13312    13312              
  Branches     1762     1762              
==========================================
- Hits         8256     8254       -2     
- Misses       4267     4270       +3     
+ Partials      789      788       -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: 2026-01-23 10:57:23

Comparing candidate commit 2f81b3a in PR branch bob/prof-flf-test with baseline commit 4df27be in branch master.

Found 0 performance improvements and 2 performance regressions! Performance is the same for 27 metrics, 7 unstable metrics.

scenario:php-profiler-timeline-memory-control

• 🟥 cpu_user_time [+27.300ms; +40.564ms] or [+4.460%; +6.627%]
• 🟥 execution_time [+33.796ms; +38.388ms] or [+5.296%; +6.016%]

[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?

[cataphract]

I think you also need a sub rsp, 8 to align the stack to 16 bytes and satisfy the abi requirements

[bwoebi]

Right, compilers often handle that by just pushing rbp anyway. Will do.

[bwoebi]

I need to actually push and pop to restore rsp too, for the final jump.