dwarf2-frame.c question for maintainers

[Martin M. Hunt]

I'm working on some dwarf2 fixes with kevinb.  In
dwarf2_build_frame_info(), Kevin added 
+unit.signed_addr_p = bfd_get_sign_extend_vma (unit.abfd);

This is useful for fixing several bugs where addresses needed to be
sign-extended.  However, I found that read_reg() also needs to
sign-extend its result.  Passing a pointer to the CU all the way down to
read_reg doesn't seem practical.

I don't have any understanding of the overall structure of this code or
where it is going. I can see several possibilities, including the
obvious one; using a global. So how do I solve this to get the patch
accepted?

Martin