Bernd wrote: > We also had a self-written batch debugger, which relied completely on > S0C1 and SPIE to do its instrumentation and implement the breakpoints; > at least in the first version.
Reminds me of a debugger I used with Orvyl/370 in S/370 days. I believe it used SVC 255 for breakpoints, which was fine. The when you continue from the breakpoint, it has to somehow execute the instruction at the breakpoint before continuing. I had put a breakpoint on a BR 0 instruction, which was common in the object code from PL/I (F). The debugger branched to the address in register 0. Fortunately, I knew who to contact to fix the bug. No-one had ever tried that before.
