C code calling into the rts, eg to initialise it, uses header files like HsFFI.h or RtsAPI.h. However these header files that describe the public API of the rts are installed in $libdir/ghc-x.y/include where as the standard location for public header files should be $prefix/include/ghc-x.y.

The private header files that are only used by .hc files when compiling -fvia-C should remain where they are. So this would involve identifying which headers are public and which are private.

Once we have a set of public header files it might be nice to provide a pkg-config .pc file to make it easy for C programs to locate the header files and libraries. Eg it should be possible to compile and link a C program that uses the RTS public API with just:

gcc -o main main.c `pkg-config --cflags --libs ghc-rts-6.12.1`

and this would supply the flags like

-I/usr/include/ghc-6.12.1 -lHSrts -L/usr/lib/ghc-6.12.1

Note that pkg-config supports both shared and static libs (ie allows specifying the extra private deps of a static lib, eg -lm -ldl etc).