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GCHeap::NextObj fix #71113

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Jun 22, 2022
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22 changes: 19 additions & 3 deletions src/coreclr/gc/gc.cpp
Original file line number Diff line number Diff line change
Expand Up @@ -44526,9 +44526,25 @@ Object * GCHeap::NextObj (Object * object)
return NULL;
}

if ((nextobj < heap_segment_mem(hs)) ||
(nextobj >= heap_segment_allocated(hs) && hs != hp->ephemeral_heap_segment) ||
(nextobj >= hp->alloc_allocated))
if (nextobj < heap_segment_mem (hs))
{
return NULL;
}

uint8_t* saved_alloc_allocated = hp->alloc_allocated;
heap_segment* saved_ephemeral_heap_segment = hp->ephemeral_heap_segment;

// We still want to verify nextobj that lands between heap_segment_allocated and alloc_allocated
// on the ephemeral segment. In regions these 2 could be changed by another thread so we need
// to make sure they are still in sync by the time we check. If they are not in sync, we just
// bail which means we don't validate the next object during that small window and that's fine.
//
// We also miss validating nextobj if it's in the segment that just turned into the new ephemeral
// segment since we saved which is also a very small window and again that's fine.
if ((nextobj >= heap_segment_allocated (hs)) &&
((hs != saved_ephemeral_heap_segment) ||
!in_range_for_segment(saved_alloc_allocated, saved_ephemeral_heap_segment) ||
(nextobj >= saved_alloc_allocated)))
{
return NULL;
}
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