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
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