On Fri, 14 Feb 2020 at 11:49, Ömer Sinan Ağacan
Hi Simon,
In this code: (slightly simplified)
StgPtr scavenge_PAP (StgPAP *pap) { evacuate(&pap->fun); return scavenge_PAP_payload (pap->fun, pap->payload, pap->n_args); }
StgPtr scavenge_PAP_payload (StgClosure *fun, StgClosure **payload, StgWord size) { const StgFunInfoTable *fun_info = get_fun_itbl(UNTAG_CONST_CLOSURE(fun)); StgPtr p = (StgPtr)payload;
switch (fun_info->f.fun_type) { case ARG_GEN_BIG: scavenge_large_bitmap(p, GET_FUN_LARGE_BITMAP(fun_info), size); p += size; break; ... } return p; }
Here the `size` argument in `scavenge_PAP_payload` is the number of arguments applied to the function in `pap->fun`. But when scavenging the function's bitmap we're using this number as the size of the bitmap which doesn't make sense to me, because I think size of the function's bitmap and size of the PAP's payload may be different.
"size" is an argument to scavenge_PAP_payload(), and when we call it we pass pap->n_args as the value, not the bitmap's size. Does that help? Cheers Simon
Or in other words I may have the same function used in many PAPs with different n_args, but that'd be buggy if this code is correct.
I haven't checked every single place where we build a PAP but for example the `NEW_PAP` macro uses the argument's (another PAP) function directly, without making any bitmap-related changes, but bumps n_args by one. If the code above is right, then this new PAP will be scavenged incorrectly.
Am I missing anything?
Thanks,
Ömer