CPython Pixi packages

This directory contains definitions for Pixi packages which can be built from the CPython source code.

Downstream developers can make use of these packages by adding them as Git dependencies in a Pixi workspace, like:

[dependencies]
python.git = "https://github.com/python/cpython"
python.subdirectory = "Tools/pixi-packages/asan"

This is particularly useful when developers need to build CPython from source (for example, for an ASan or TSan-instrumented build), as it does not require any manual clone or build steps. Instead, Pixi will automatically handle both the build and installation of the package.

Each package definition is contained in a subdirectory, but they share the build script build.sh in this directory. Currently defined package variants:

default
freethreading
asan: ASan-instrumented build
tsan-freethreading: TSan-instrumented free-threading build

Maintenance

Keep the abi_tag and version fields in each variants.yaml up to date with the Python version
Update build.sh for any breaking changes in the configure and make workflow

Opportunities for future improvement

More package variants (such as UBSan)
Support for Windows
Using a single pixi.toml and recipe.yaml for all package variants is blocked on pixi-build-backends#532 and pixi#5248

Troubleshooting

TSan builds may crash on Linux with

FATAL: ThreadSanitizer: unexpected memory mapping 0x7977bd072000-0x7977bd500000

To fix it, try reducing mmap_rnd_bits:

$ sudo sysctl vm.mmap_rnd_bits
vm.mmap_rnd_bits = 32  # too high for TSan
$ sudo sysctl vm.mmap_rnd_bits=28  # reduce it
vm.mmap_rnd_bits = 28