Re: creating dwarf from scratch using dwarf_edit?

[Roland McGrath <roland at redhat dot com>]

> I was experimenting with creating a dwarf file from scrach using 
> dwarf_edit, but gut stuck when I was unable to figure out how to add an 
> attribute to a die.  So is that a use case that we don't care about, or 
> are the bits here and I just fail to see them?

That's the use case that I imagine dwarf_edit will eventually be for.
(It's probably not really useful otherwise.)  But it's not a priority
any time soon.  I didn't really think about the details of attr_value
construction too much.  If there are missing bits, we will add them.

> Snippet:
> 
>    dwarf_edit tst;
>    dwarf_edit::debug_info_entry cudie (DW_TAG_compile_unit);
>    dwarf_edit::compile_unit u (cudie);

I think:

	dwarf_edit::compile_unit u; // ()

should do the same.  But there is:

	dwarf_edit::compile_unit &u = tst.new_unit ();

for that (with less copying).

>    dwarf_edit::debug_info_entry x (DW_TAG_base_type);

For real use, we should probably add another entry point:

	dwarf_edit::debug_info_entry &x = u.new_entry (DW_TAG_base_type);

Or perhaps:
	
	x = u.new_entry (DW_TAG_base_type, u.children ().end ());

where you can pass an iterator to the specific insertion point.
(End would be the default, but you might use this to add an entry
between two existing ones.)

>    x.attributes () [DW_AT_name] = /* now what ? */;

I think the idea is:

	x.attributes () [DW_AT_name].source_file ().name () = "foo.c";

But I don't think that actually works.
Maybe this does it, but probably there are more wrinkles.

diff --git a/libdw/c++/dwarf_edit b/libdw/c++/dwarf_edit
index 00698b5..2fd7a5b 100644
--- a/libdw/c++/dwarf_edit
+++ b/libdw/c++/dwarf_edit
@@ -969,6 +969,8 @@ namespace elfutils
       template<typename flavor>
       inline flavor &variant () const
       {
+	if (_m_value == NULL)
+	  _m_value = new flavor;
 	flavor *p = dynamic_cast<flavor *> (_m_value);
 	if (p == NULL)
 	  throw std::runtime_error ("wrong value type");


Thanks,
Roland