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101 lines
3.4 KiB
ReStructuredText
101 lines
3.4 KiB
ReStructuredText
Debugging Firefox with Pernosco
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===============================
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This page is intended to help Firefox/Gecko developers get started using `Pernosco <https://pernos.co/>`_
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to debug Firefox.
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Mozilla employees have a paid subscription to Pernosco, and are encouraged to use it.
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Contributors can use Pernosco as well. `A free account <https://pernos.co/pricing/>`_
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comes with 5 uploads to see if it is suitable for your workflow.
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Prerequisites
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-------------
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- You need the ability to produce an :code:`rr` trace. See :doc:`debugging_firefox_with_rr`
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- Employees, you can also generate traces for Pernosco for some CI job failures via
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Treeherder.
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Workflow
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--------
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At a high level, working with Pernosco consists of recording a trace then uploading
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the trace for processing.
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Install your Pernosco configuration
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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If you are using your own Pernoso account, follow the instructions
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`here <https://pernos.co/account>`_ to install your credentials.
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Mozilla employees, see the `Pernosco install and configuration doc
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<https://docs.google.com/document/d/1cb-mkNyJYMudpS0a-R6zxy0kOMIRUSKrxxL-E9zFGKE/edit>`_
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for credentials.
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In general, you will want:
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* Your email in :code:`~/.config/pernosco/user`
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* Your group in :code:`~/.config/pernosco/group`
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* Your key in :code:`~/.config/pernosco/user_secret_key`
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Gather a Local Trace
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~~~~~~~~~~~~~~~~~~~~
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In general, to gather a trace follow the instruction for recording :code:`rr` traces
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in :doc:`debugging_firefox_with_rr`. However, to gather a local rr trace that’s
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compatible with Pernosco you need to disable some incompatible CPU features (currently
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only AVX-512)
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On an Intel machine, you can disable this at the command line. To simplify things a
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shell script :code:`pernosco-record` can be created like so,
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.. code:: bash
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#!/bin/bash
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rr record --disable-avx-512 "$@"
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replacing plain :code:`rr` in command lines (:code:`mach --debugger pernosco-record`)
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On AMD Zen Machines, you can disable AVX-512 and 5 level page tables at boot.
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On a Debian derived distro this involves editing :code:`/etc/default/grub` and
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adding :code:`clearcpuid=304,no5lvl` to :code:`GRUB_CMDLINE_LINUX_DEFAULT`, then
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running :code:`sudo update-grub` after.
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Upload the trace
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~~~~~~~~~~~~~~~~
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Find the trace you’re interested in :code:`~/.local/share/rr/<trace>`, and call :code:`pernosco-submit`
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.. code:: bash
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pernosco-submit upload ~/.local/share/rr/<trace> PATH_TO_CENTRAL --title "Name Of Trace"
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where :code:`PATH TO CENTRAL` is the path to the source of your build, checked out
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to the revision matching the build.
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The last trace recorded is always symlinked, so you can use :code:`~/.local/share/rr/latest-trace` too.
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Wait for email
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~~~~~~~~~~~~~~
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After the trace is processed, you'll get an email with a link to your trace. Good
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hunting!
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Treeherder Workflow
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-------------------
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You can also try to get traces generated via the Treeherder interface. On a failing
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test that is eligible, in "Artifacts and Debugging Tools", you'll see a link to
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.. image:: ../img/record-this-failure.png
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:width: 35 %
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This link brings you to the self-service reproducer:
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.. image:: ../img/self-service.png
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:width: 60 %
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Select a test and a count, and whether or not chaos-mode should be used, then click
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reproduce. At this point there is a **long** wait; the page will notify you when
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reproduction has started with an :code:`alert` dialog.
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