Project:LLVM/LLVM slotting

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Starting with 4.0.0, the LLVM packages are once more slotted. This means it is now possible to have multiple versions of LLVM/clang installed simultaneously.

Why slot?

Slotting serves three goals:

  1. Making it possible to upgrade split clang package without intermediate breakage. In particular, when upgrading from clang-X to clang-Y, the package manager must not uninstall llvm-X before clang-Y is installed.
  2. Making it possible to use multiple versions of clang simultaneously, e.g. to test your programs against multiple versions of the compiler.
  3. Making it possible to at least partially upgrade to a newer version of LLVM before all software supports it. Previously, a single package not supporting a newer LLVM version prevented the system from upgrading to a newer one.

Which packages are slotted?

There are degrees of slotting applied to various LLVM packages:

  • packages that are not slotted -- only one version can be installed,
  • packages that are slotted by major version -- one release of every major version can be installed (i.e. LLVM x),
  • packages that are slotted by full version -- one revision of every full version can be installed (i.e. LLVM x.y.z).

The use of slotting is summarized in the table following.

Package Slotting Dep type Required LLVM version Notes
Toolchain packages
sys-devel/llvm by major - -
sys-devel/clang by major revdep of LLVM exact match
dev-util/lldb no revdep of LLVM+clang exact match
sys-devel/lld no revdep of LLVM exact match
Auxiliary packages
dev-ml/llvm-ocaml no revdep of LLVM exact match
dev-python/clang-python no revdep of clang any? dlopen()s clang libraries without SONAME, probably dangerous
dev-python/lit no dep of most pkgs exact match required for tests only, can cause conflict when trying to install multiple LLVM versions simultaneously
sys-devel/clang-common no dep of clang any
sys-devel/llvm-common no dep of LLVM any
sys-devel/llvmgold no circ pdep of LLVM any just a symlink to the newest version for binutils' ar & nm
Runtime packages
sys-devel/clang-runtime by fullver pdep of LLVM exact match
sys-libs/compiler-rt by fullver dep of clang-runtime exact match strictly speaking, does not require exact match to clang version but needs to be installed in path containing fullver
sys-libs/libcxx no dep of clang-runtime any
sys-libs/libcxxabi no dep of clang-runtime any
sys-libs/libomp no dep of clang-runtime any
sys-libs/llvm-libunwind no dep of clang-runtime any