1716712 - Use C++ to JIT entry registers on Mac&Linux/x64 to resume frame stack walking when lost

Status: RESOLVED FIXED

(Core :: Gecko Profiler, enhancement, P2)

Description

[Gerald Squelart (he/him) (not at Mozilla since 2022-09-15)]

Similar to https://phabricator.services.mozilla.com/D116379 , it is possible to restart the frame stack walker (used on Mac Nightly, and on Linux but only for backtraces) using x86-64 JIT information.

Quick test on Mac: Before, after
It's not as dramatic as on Windows, but still good: The "Web Content" main thread for Reddit went from 17% of "bad" stacks down to 3.6%.

Comment 1

[Gerald Squelart (he/him) (not at Mozilla since 2022-09-15)]

Attachment: Bug 1716712 - Use JIT information in DoFramePointerBacktrace on x64 - r?canaltinova

This is similar to what DoMozStackWalkBacktrace does, by looking where the stack walker stopped, and if it can be restarted at a calling C++-to-JIT entry frame.

Note: The code is pretty much a modified copy, but factoring out the common parts would be difficult because of the specific local variables, the different stack-walking functions, and the different register storages.

Also, instead of mentioning the OS (was only Windows), the choice of platform support is now based on the actual Profiler stack walkers that are used.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/f12d9f8337b0
Use JIT information in DoFramePointerBacktrace on x64 - r=canaltinova

Comment 3

[Marian-Vasile Laza]

https://hg.mozilla.org/mozilla-central/rev/f12d9f8337b0