1. The hc files are generated by nhc98comp? I will still need to modify nhc98comp to always produce the unsigned char*?
Yes, and yes. The latter will be easy - it should be a single line change in src/compiler98/EmitState.hs
2. I am also bypassing nhc98 script during the prelude build. I am created a separate script to compile prelude under plan9. The script just loads the hc files into the C compiler.
Might be reasonable. The main reason for using the nhc98 script is just to ensure that the right header files etc are visible.
3. I am still guessing here, but If item 2 is an ok approach is it possible to simply compile src/runtime/Runtime.a and use the .o files from a unix build?
Yes, that might well work, if the .o files are ABI-compatible across unix and plan9. Regards, Malcolm