Some cost centre stacks are not registered via registerCcsList()

In #15508 (closed) I observe that some closures have incorrect CCS field. To be able to catch this problem as early as possible I implemented a simple check:

static void
checkClosureProfSanity(const StgClosure *p)
{
    StgProfHeader prof_hdr = p->header.prof;
    CostCentreStack *ccs = prof_hdr.ccs;

    // For now just make sure the CCS is a registered CCS and not a pointer to
    // some random heap closure (happened before, see #15508).
    for (CostCentreStack *ccs_ = CCS_LIST; ccs_; ccs_ = ccs_->prevStack) {
        if (ccs == ccs_) {
            return;
        }
    }

    barf("CCS for closure %p is not registered: %p", (void*)p, (void*)ccs);
}

I call this on all closures before and after a GC. This assumes that all cost centre stacks are registered via registerCcsList(), however this currently does not hold. I was able to find two cases:

• base_GHCziIOziHandleziFD_CAFs_cc_ccs is never registered (there are probably

a few CCSs per module like this which are never registered)

• None of the dynamically allocated CCSs are registered.

My question is: am I misunderstanding how the CCS registry (CCS_LIST) is supposed to be used? I thought all CCSs should really be in that list, because the list is used when reporting. Not registering a CCS means not reporting it.

Trac metadata

Trac field	Value
Version	8.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Profiling
Test case
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Architecture