[vm] Fix handling of WeakSerializationReferences in v8 profile.

Instead of trying to lazily create artificial nodes when needed for
WeakSerializationReference (WSR) targets in all cases, create them
eagerly for targets in reachable WSRs, since those are guaranteed
to be needed.

Those for unreachable WSRs are still lazily created as needed, since the
WSR won't even be accessed by the clustered snapshot writer unless the
unreachable WSR is part of another unreachable object that has an
artificial node created.

This rework avoids some issues seen on upcoming CLs where the artificial
nodes for WSR targets weren't getting correctly generated.

-----

Also extend the v8 snapshot profile writer tests to check the sizes of
the text and data sections in ELF snapshots. That means the v8 snapshot
profile writer tests check up to three different measures, from most
precise to least precise, depending on the output mode:

* If writing an ELF snapshot directly: the sum of the sizes attributed
  to the text and data section symbols are checked to be exactly the
  same as the sum of the sizes of the objects in the profile.

* If writing an ELF snapshot either directly or via assembly: the sum
  of the sizes of the text and data sections are checked to be the same
  as the sum of the sizes of the objects in the profile. If using an
  assembler that merges text and data sections, then account for the
  padding between the sections using an approximate check.

* For all: Check that the size of the snapshot as a whole is
  approximately equal to the sum of the sizes of the objects in the
  profile, accounting both for possible padding and for the global
  header information and non-data/non-text sections like the dynamic
  symbol section.

TEST=vm/data{,_2}/v8_snapshot_profile_writer_test

Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-linux-debug-x64-try,vm-kernel-precomp-linux-debug-x64c-try,vm-kernel-precomp-nnbd-linux-debug-x64-try,vm-kernel-precomp-mac-release-simarm64-try
Change-Id: I66e0e7fdb5bb98045621bf516f150a4723e08147
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/198942
Commit-Queue: Tess Strickland <sstrickl@google.com>
Reviewed-by: Clement Skau <cskau@google.com>
Reviewed-by: Daco Harkes <dacoharkes@google.com>
6 files changed
tree: a83a974243b98ae49fbc716c786948e32551983d
  1. .dart_tool/
  2. .github/
  3. benchmarks/
  4. build/
  5. client/
  6. docs/
  7. pkg/
  8. runtime/
  9. samples/
  10. samples-dev/
  11. samples_2/
  12. sdk/
  13. tests/
  14. third_party/
  15. tools/
  16. utils/
  17. .clang-format
  18. .gitattributes
  19. .gitconfig
  20. .gitignore
  21. .gn
  22. .mailmap
  23. .packages
  24. .style.yapf
  25. .vpython
  26. AUTHORS
  27. BUILD.gn
  28. CHANGELOG.md
  29. codereview.settings
  30. CONTRIBUTING.md
  31. DEPS
  32. LICENSE
  33. PATENT_GRANT
  34. PRESUBMIT.py
  35. README.dart-sdk
  36. README.md
  37. sdk_args.gni
  38. WATCHLISTS
README.md

Dart

A client-optimized language for fast apps on any platform

Dart is:

  • Optimized for UI: Develop with a programming language specialized around the needs of user interface creation.

  • Productive: Make changes iteratively: use hot reload to see the result instantly in your running app.

  • Fast on all platforms: Compile to ARM & x64 machine code for mobile, desktop, and backend. Or compile to JavaScript for the web.

Dart's flexible compiler technology lets you run Dart code in different ways, depending on your target platform and goals:

  • Dart Native: For programs targeting devices (mobile, desktop, server, and more), Dart Native includes both a Dart VM with JIT (just-in-time) compilation and an AOT (ahead-of-time) compiler for producing machine code.

  • Dart Web: For programs targeting the web, Dart Web includes both a development time compiler (dartdevc) and a production time compiler (dart2js).

Dart platforms illustration

License & patents

Dart is free and open source.

See LICENSE and PATENT_GRANT.

Using Dart

Visit dart.dev to learn more about the language, tools, and to find codelabs.

Browse pub.dev for more packages and libraries contributed by the community and the Dart team.

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Building Dart

If you want to build Dart yourself, here is a guide to getting the source, preparing your machine to build the SDK, and building.

There are more documents on our wiki.

Contributing to Dart

The easiest way to contribute to Dart is to file issues.

You can also contribute patches, as described in Contributing.