[libc-commits] [libc] [libc] Add baremetal minor archive support. (PR #203015)

[Simi Pallipurath via libc-commits]

simpal01 wrote:

> Can you elaborate a bit more on the use case for this feature (an example would be helpful)?

This is part of optimising multilibs  , a layered library variant selection.  

Current multilib layout work well when a compiler flag affects broad portions of the runtime or standard libraries. However, they are less effective for handling minor variants, where only a small subset of objects within a library is impacted, and the majority of the library remains unaffected.

Representative cases are -fno-exceptions and -munaligned-access—only impact a specific subset of libraries:

1. --munaligned-access only benefits low-level C string functions (e.g., memcpy, memcmp) and has no bearing on headers or the C++ standard library (libc++).
2. -fno-exceptions influences only C++ libraries.

As a result, building and duplicating the entire standard library set for each flag combination—when only a portion is affected—can lead to significant redundancy.  So ATFE would like to introduce a layered multilib structure that enables selective specialisation of affected routines, while reusing common libraries across multiple variants to reduce duplication and simplify maintenance.

https://github.com/llvm/llvm-project/pull/203015