Ixemul signal implementation is fairly complete. It's not fully POSIX though as real-time signals are missing.
As a side note: Older ixemul was stuck on some partial implementation of early 1990s POSIX. Many functions were outright missing. I've spent considerable effort to modernize ixemul, bringing it in sync with latest POSIX versions in many regards. The work isn't completed though, and there are some gaps still I'd like to bridge.
However, we won't be implementing exec on top of ixemul. If we would need to do something like that, we'd just add the necessary things in the core components as required rather than mess about with ixemul.
Ixemul has a clear function: To provide easy way to port GNU and OSS tooling. This way we can for example enable easy porting of modern components for the SDK (including git, perl, python etc). Ixemul of course doesn't not prevent porting the components to libnix as well, and in fact many components live as both ixemul and libnix ports. However, keeping clear separation between ixemul and libnix has proven a wise decision as this allows us to update SDK even though some update would cause complications on the libnix side. Trying to port every OSS component to libnix would be an insane task, and we very much prefer focus on other, more important tasks.
