> One advice I'd give you is to _really_ take care regarding SysV/ELF ABI conventions, there's tons of undocumented stuff in there and it's really easy to mess something up or cause a security defect (see AT_SECURE)

Yes, it's not trivial, but I hope that over time everything will settle down.

> if I understood your implementation correctly you're hooking this into an already running musl which could cause backwards compatibility issues if musl changes under you

No, I hook this to musl, which is statically linked into my binary, and I have complete control over it.