Layering Over Another libc

When meaningful and practically possible on a platform, llvm-libc will be developed in a fashion that it will be possible to layer it over the system libc. This does not mean that one can mix llvm-libc with the system-libc. Also, it does not mean that layering is the only way to use llvm-libc. What it means is that, llvm-libc can optionally be packaged in a way that it can delegate parts of the functionality to the system-libc. The delegation happens internal to llvm-libc and is invisible to the users. From the user’s point of view, they only call into llvm-libc.

There are a few problems one needs to be mindful of when implementing such a delegation scheme in llvm-libc. Examples of such problems are:

1. One cannot mix data structures from llvm-libc with those from the system-libc. A translation from one set of data structures to the other should happen internal to llvm-libc. 2. The delegation mechanism has to be implemented over a related set of functions. For example, one cannot delegate just the fopen function to the system-libc. One will have to delegate all FILE related functions to the system-libc.