> Of the two problems discussed:
>
> 1. DW_TAG_LLVM_annotation not being able to denote annotations to
> non-pointed based types. clang currently ignores these instances.
>
> We discussed two possible options to deal with this:
> 1.1 To continue ignoring these cases in the front-end, keep the dwarf
> expressiveness limitation, and document it.
> 1.2 To change DW_TAG_LLVM_annotation so it behaves like a qualifier
> DIE (like const, volatile, etc.) so it can apply to any type.
Note that the non-pointed based types don't have to be basic types. The
limitation also impacts non-basic types that are not pointed to,
including pointer types themselves.
Therefore:
> : int * __tag1 * __tag2 h;
>
> - sparse
> + __tag1 applies to int*, __tag2 applies to int**
> : got int *[noderef] __tag1 *[addressable] [noderef] [toplevel] __tag2 h
> - clang
> + According to DWARF __tag1 applies to int*, no __tag2 (??).
> + According to BTF __tag1 applies to int*, no __tag2 (??).
> : DWARF
> : 0x00000023: DW_TAG_variable
> : DW_AT_name ("h")
> : DW_AT_type (0x0000002e "int **")
> :
> : 0x0000002e: DW_TAG_pointer_type
> : DW_AT_type (0x00000037 "int *")
> :
> : 0x00000033: DW_TAG_LLVM_annotation
> : DW_AT_name ("btf_type_tag")
> : DW_AT_const_value ("tag1")
> : BTF
> : [1] TYPE_TAG 'tag1' type_id=3
> : [2] PTR '(anon)' type_id=1
> : [3] PTR '(anon)' type_id=4
> : [4] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
> : [5] VAR 'h' type_id=2, linkage=global
> :
> : 'h' -> ptr -> 'tag1' -> ptr -> int
In the example above, `tag2' doesn't appear in neither DWARF nor BTF
because the type int** isn't pointed itself, and as Yonghong mentioned
in the call, the implementation of btf_type_tag in clang ignores these
cases.
