Record hidden ptr in layout #92
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@d-netto Can you review the PR? This PR just shows one way about how we can get the offsets of those 'hidden pointers', and it shows it is necessary for Julia to provide offsets of those pointers to GC impls. The actual implementation would be need to be discussed with Julia devs. The current implementation is not meant to be upstreamed. |
udesou
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* Add fields about hidden pointers in jl_datatype_layout_t * Record hidden pointer in layout * Move the new field to the end of the struct
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This PR records the hidden pointer offsets in
jl_datatype_layout_t. Hidden pointers are fields likeptr_or_offsetinjl_genericmemoryref_t, which is not recorded as a pointer but actually may be heap (internal) pointers.There might be other types of hidden pointers. Currently we assume the recorded hidden pointers are all like
ptr_or_offset-- a union of an internal pointer, or an integer.The current implementation adds
hiddenptrfieldstojl_typename_t, and specifically definehiddenptrfieldsforjl_genericmemoryref_t. This is not an ideal solution. I think a better solution would be to introduce a new type that represents a hidden pointer, and use the type for fields likeptr_or_offset. However, I am not familiar with Julia's type system, and didn't get it to work. The current approach usinghiddenptrfieldsis a workaround.