OpenEuphoria

Original date:2022-02-26 23:17:15 Edited by: ghaberek Subject: Re: BREAKing into Euphoria

So much for that, I already figured it out. Turns out it was pretty easy, but I'm still not sure how safe this is. The SIGINT (Ctrl+C) signal interrupt handler is configured in InitExecute(). The first step was to borrow some code from trace_command() and plop that into INT_Handler().

// be_rterror.c:1668 
void INT_Handler(int sig_no) 
/* control-c, control-break */ 
{ 
	UNUSED(sig_no); 
	if (trace_enabled) { 
		/* start tracing */ 
		signal(SIGINT, INT_Handler); 
		TraceOn = TRUE; 
		color_trace = TRUE; 
#ifdef _WIN32 
		show_console(); 
#endif 
		return; 
	} 
	... 

This worked great... when with trace was enabled. Turns out trace_enabled is always set to TRUE and the backend relies on the frontend to emit the necessary tracing ops. So my trick would act like allow_break(FALSE) without trace enabled. My solution was to grab trace_enabled from the parser section for with/without trace and pass that through to the backend.

-- global.e:617 
export integer trace_enabled = FALSE 

-- parser.e:4529 
... 
elsif equal(option, "trace") then 
	if not BIND then 
		OpTrace = on_off 
		trace_enabled = on_off 
	end if 
... 

-- backend.e:285 
machine_proc(65, { 
	... 
	trace_lines, 
	trace_enabled, 
	$ 
}) 

// be_machine.c:2842 
object start_backend(object x) 
/* called by Euphoria-written front-end to run the back-end 
 * 
 * x is {symtab, topcode, subcode, names, line_table, miscellaneous } 
 */ 
{ 
	... 
	trace_lines = get_pos_int(w, *(x_ptr->base+16)); 
	trace_enabled = get_pos_int(w, *(x_ptr->base+17)); 
	... 

That seems to do the trick. I made a simple little program that goes into a loop for 60 seconds and when I press Ctrl+C it jumps into the trace screen. Pressing q resumes execution until I press Ctrl+C again to jump back to trace, and pressing Q resumes execution and disables trace. Pressing Ctrl+C again from there stops the program normally.

include std/os.e 
 
with trace 
 
atom t0 = 0 
atom t1 = time() 
atom t2 = t1 + 60 
 
while t1 < t2 do 
 
    if t1 > t0 then 
        t0 = t1 
        ? t0 
    end if 
 
    sleep(rand(10)/100) 
    t1 = time() 
 
end while 

This is a pretty neat feature to have, but I'll say it again loudly: I don't know enough about the interpreter yet to say how safe this is. Your app might crash. Weird things might happen.

-Greg