[bug] Possible for frame entry in stack table to be null

[dalehamel]

A production app generated profiles which failed to load in any version of firefox-profiler we tried. One of our devs filed this issue upstream firefox-devtools/profiler#5074, but I believe the true issue is that the output from vernier is not a valid gecko profile.

The profile does not load in https://vernier.prof either. Here is the profile.

Looking closely at the error, I was able to determine that a thread has an invalid stack table:

    {
      "name": "(2051520)",
      "isMainThread": false,
      "processStartupTime": 995739.389136,
      "registerTime": 995739.389136,
      "pausedRanges": [],
      "pid": 123,
      "tid": 0,
      "frameTable": {
        "address": [],
        "inlineDepth": [],
        "category": [],
        "subcategory": null,
        "func": [],
        "nativeSymbol": [],
        "innerWindowID": [],
        "implementation": [],
        "line": [],
        "column": [],
        "length": 0
      },
      "funcTable": {
        "name": [],
        "isJS": [],
        "relevantForJS": [],
        "resource": [],
        "fileName": [],
        "lineNumber": [],
        "columnNumber": [],
        "length": 0
      },
      "nativeSymbols": {},
      "samples": {
        "stack": [
          0,
          1
        ],
        "weight": [
          1,
          1032
        ],
        "weightType": "samples",
        "length": 2
      },
      "stackTable": {
        "frame": [
          null,
          null
        ],
        "category": [
          2,
          1
        ],
        "subcategory": [
          0,
          0
        ],
        "prefix": [
          null,
          null
        ],
        "length": 2
      },

The root cause seems to be that the "frame" entry itself is somehow "null". This gets input as a numeric index, and ends up exploding in the UI.

If I delete the invalid thread, the profile can now be displayed.

This seems like a legitimate bug in vernier, as we're somehow getting invalid output where the top stack frame references a null value, which is an invalid index into the frame table. The frametable is also empty, as the example shows.

[dalehamel]

Note that the profile was generated from the latest released version of vernier, 1.1.1

[Earlopain]

I'm encountering the same thing. I'm profiling something with bundler/inline and I believe the issue has something to do with me specifying git dependencies:

# frozen_string_literal: true

require "bundler/inline"

gemfile do
  source "https://rubygems.org"
  gem "rails", github: "rails/rails"
end

This consistently produces a profile I'm unable to load for what I assume are the same reasons as OP. trace.json

I run vernier like so: vernier run --output trace.json -- ruby test.rb. Ruby is 3.3.4

[Earlopain]

Reduced it a bit further and it seems to boil down to this:

# frozen_string_literal: true

pid = Process.spawn("sleep", "1")
wait_thr = Process.detach(pid)
wait_thr.join

The issue seems to be with Process.detach. I also have this other case which doesn't terminate when running with vernier (though perhaps a different issue altogether, #82 maybe?):

# frozen_string_literal: true

pid = Process.fork do
  sleep 1
end
wait_thr = Process.detach(pid)
wait_thr.join

[jhawthorn]

Thank you both! I just merged #89 which should fix this and released that as 1.1.2

[Earlopain]

This works nicely, thanks!

[dalehamel]

@jhawthorn thank you! We'll try it out and report back if it is not resolved.