I think I'll just rewrite the signal related stuff in rts-rt0.c, implement some BSD/SYSV independant routines that ONLY mask signals that are actually present on the target system.

I don't have handson experience with signals, but it seems to me that POSIX already did this. I suggest using signals according to the POSIX standard. And every unix box should come with some decent posix library these days. Groetjes, Berend.