The current hacked together location API we added to drgn works extremely
poorly with modern C++ compilers. It largely works with the clang-12 compiler
on CircleCI, but works very poorly with clang 15/16/17/18 in Nix or when
updating the CircleCI compiler to clang-15.
This change adds a backup mechanism for locating arguments when drgn has
failed. The mechanism is extremely naive and makes several assumptions which
are often not correct. Currently, however, it drastically reduces the number of
tests that must be skipped in the Nix CI.
Test plan:
- CI
Add LLVM-16 to the Nix builds and CI matrix. Also add the option to explicitly
select an LLVM version so the CircleCI build can still work as before.
We should support at least LLVM-17 currently, but there appears to be a
significant performance regression in compiling the generated code for large
variants that I'm going to debug separately. The long term goal is to support
and test all versions 15 and up.
Test plan:
- CI
OI's build is challenging and has often been a problem for the Open Source
community. It requires an extremely specific set of dependencies that are very
hard to achieve on most systems. There are frequent breakages, like when
updating to CentOS Stream 9, or when trying to update the CI's clang from
clang-12 to clang-15 - OI requires the clang libraries to be version 15 but
can't be compiled with it on the CI!
This changes provides a mostly working build environment with `nix`. This
environment is pinned to a specific nixpkgs revision using `flake.lock`, and
only updates when we explicitly tell it to.
Summary of changes:
- Update CMakeLists.txt required version to 3.24. This allows specifying
`FIND_PACKAGE_ARGS` in `FetchContent`, meaning we can use system packages.
This is available on most up to date distros (3.30.2 is current).
- Extends `flake.nix` to be able to build OI. Adds instructions for building
and developing OI using `nix`.
- Partially runs the tests in GitHub Actions. A huge amount must be excluded
because of incompatibilites between the clangStdenv compiler and drgn. We
have similar, though fewer, issues when building with the clang-12/libstdcxx
mix on the Ubuntu 22.04 CircleCI, though this is at least reproducible.
- Updates CircleCI to build CMake from source as we don't have a newer image
available. Also add some newly found dependencies (not sure how it was
working without them before).
Test plan:
This change requires less testing than previous build related changes because
it deprecates most of the build types.
- The internal BUCK build is unaffected. No special testing.
- The semi-internal CMake build is gone. Use Nix.
- The Nix build for clang-15 and some tests are continuously tested in GitHub
actions.
- Tested the set of Nix commands in the README. All work except the one that
points to GitHub as this must be merged first.
- The existing CircleCI runs on Ubuntu 20.04 are maintained.
- Unable to test the new `test-report.yml` as it must be merged due to the
permissions it needs. Will follow up with testing after this is merged. See:
https://github.com/dorny/test-reporter?tab=readme-ov-file#recommended-setup-for-public-repositories
The list of exclusions for GitHub Actions/nix testing is currently very long, I
think 29% of the tests. This should be stable and reproducible though, and
likely needs deep changes to OI to fix. That's why fixes are excluded from this
PR. It's all to do with the forked drgn not being able to parse clang's newer
DWARF output, and can't be fixed by rolling back as we required a relatively
new libcxx.
