does lldb or the devtools debugger already use the calling_convention description on types, or would this require more work there? (relatedly, does clang generate this attribute already?)

is one struct guaranteed to always be passed the same?

Actually, instead of using DW_AT_location, I think the better approach here would be to add DW_AT_calling_convention to the struct entry itself. Normally DWARF relies on consumers knowing the ABI of any given type, but that attribute is explicitly designed to indicate whether a composite type is passed by reference or by value.

Note: adding this representation will require changing the spec at https://yurydelendik.github.io/webassembly-dwarf/ as some non-LLVM based tooling can also rely on it.