Hi all,
The LLVM discussion linked [0] happens to be us Sony folks, and it's
supporting the use-case Kyle described of automatic downcasting, i.e.
identifying the most-derived-class of an object from its vtable pointer.
Having to demangle the symbol table is a real pain (Tom, CC'd knows more)
especially with things like anonymous namespaces.
Right now the approach is to have a top-level nameless global variable with
the location set to the vtable address, and a DW_AT_specification linking
into the class definition:
0x00000082: DW_TAG_variable
DW_AT_specification (0x000000b6 "_vtable$")
DW_AT_alignment (8)
DW_AT_location (DW_OP_addrx 0x1)
[Then deeper into the DIE tree,]
0x0000008b: DW_TAG_structure_type
DW_AT_containing_type (0x00000034 "CBase")
DW_AT_calling_convention (DW_CC_pass_by_reference)
DW_AT_name ("CDerived")
DW_AT_decl_file ("vtables.cpp")
DW_AT_decl_line (6)
[...]
0x000000b6: DW_TAG_variable
DW_AT_name ("_vtable$")
DW_AT_type (0x00000081 "void *")
DW_AT_external (true)
DW_AT_declaration (true)
DW_AT_artificial (true)
DW_AT_accessibility (DW_ACCESS_private)
This works well enough for our own debugger use-cases; I agree with Cary
that it's hacky to rely on the name of a variable to signify important
information like this and an officially blessed way could help.
I've no opinion on the DW_AT_vtable_elem_location behaviours, although we
can consider it a separate issue.
[0] https://github.com/llvm/llvm-project/pull/130255
--
Thanks,
Jeremy
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