I wonder if setjmp/longjmp can be implemented in hardware, i.e. introduce an instruction set that points, save and switch the current registers called register window that can be switched by saving a pointer.
This way both setjmp and longjmp are basically few cycles and exception handling would be hella fast.
The DEC VAX-11 instruction set had SVPCTX and LDPCTX for the kernel which made context switch simple. But they were reserved instructions; so they couldn't be used for setjmp() and longjmp(). VAX-11 also had queue instructions which made rescheduling simple. This was basically:
This way both setjmp and longjmp are basically few cycles and exception handling would be hella fast.