Simon Marlow wrote:
On 19/08/2009 10:18, Peter Hercek wrote:
Why is stg_nofoceIO_info added as last argument to IO actions in unregistered mode? Do I still need to pass it in even when (I think) my IO action does not need it? E.g. is it required for every IO action by some stack walking code or something?
The comment in Interpreter.c says
// Note [unreg]: in unregisterised mode, the return // convention for IO is different. The // stg_noForceIO_info stack frame is necessary to // account for this difference.
However, the return convention for IO is now the same under both registerised and unregisterised builds (I made the change becuase of the proliferation of obscure conditional RTS code like the above), so I'm guessing the stg_noforceIO_info hack, and the above comment, are now redundant. It needs testing though.
Just for your information. I was curious and tried to remove the additional stg_noforceIO_info argument. Breakpoints stopped to be called but otherwise ghci seemed to work fine. It was surprising. It looked like the call to rts_breakpoint_io_action was somehow optimized away but I would not expect any optimizations at this level. Maybe I did not do it correctly. The patch I used is at the end of this email. Thanks, Peter. hunk ./rts/Interpreter.c 879 // in a reasonable state for the GC and so that // execution of this BCO can continue when we resume ioAction = (StgClosure *) deRefStablePtr (rts_breakpoint_io_action); - Sp -= 9; - Sp[8] = (W_)obj; $ - Sp[7] = (W_)&stg_apply_interp_info; - Sp[6] = (W_)&stg_noforceIO_info; // see [unreg] below + Sp -= 8; + Sp[7] = (W_)obj; $ + Sp[6] = (W_)&stg_apply_interp_info; Sp[5] = (W_)new_aps; // the AP_STACK Sp[4] = (W_)BCO_PTR(arg3_freeVars); // the info about local vars of the breakpoint Sp[3] = (W_)False_closure; // True <=> a breakpoint hunk ./rts/Interpreter.c 885 - Sp[2] = (W_)&stg_ap_pppv_info; + Sp[2] = (W_)&stg_ap_ppp_info; Sp[1] = (W_)ioAction; // apply the IO action to its two arguments above Sp[0] = (W_)&stg_enter_info; // get ready to run the IO action hunk ./rts/Interpreter.c 888 - // Note [unreg]: in unregisterised mode, the return - // convention for IO is different. The - // stg_noForceIO_info stack frame is necessary to - // account for this difference. // set the flag in the TSO to say that we are now // stopping at a breakpoint so that when we resume