scripts: Resolve DW_AT_abstract_origin during dwarf collection

Sometimes I feel like dwarf-info is designed to be as error-prone as
possible.

In this case, DW_AT_abstract_origin indicates that one dwarf entry
should inherit the attributes of another. If you don't know this, it's
easy to miss relevant dwarf entries due to missing name fields, etc.

Expanding DW_AT_abstract_origin lazily would be tricky due to how our
DwarfInfo class is structured, so instead I am just expanding
DW_AT_abstract_origins during collect_dwarf_info.

Note this doesn't handle recursive DW_AT_abstract_origins, but there is
at least an assert.

---

It does seem like DW_AT_abstract_origin is intended to be limited to
"Inline instances of inline subprograms" and "Out-of-line instances of
inline subprograms" according to the DWARF5 spec, but it's unclear if
this is a rule or suggestion...

This hasn't been an issue for existing scripts, but is needed from some
ongoing stack.py rework. Otherwise we don't find "out-of-line instances
of inline subprograms" (optimized functions?) correctly.

scripts/code.py

@@ -507,6 +507,18 @@ def collect_dwarf_info(obj_path, tags=None, *,
     if proc.returncode != 0:
         raise sp.CalledProcessError(proc.returncode, proc.args)
 
+    # resolve abstract origins
+    for entry in info.values():
+        if 'DW_AT_abstract_origin' in entry:
+            off = int(entry['DW_AT_abstract_origin'].strip('<>'), 0)
+            origin = info[off]
+            assert 'DW_AT_abstract_origin' not in origin, (
+                    "Recursive abstract origin?")
+
+            for k, v in origin.ats.items():
+                if k not in entry.ats:
+                    entry.ats[k] = v
+
     return DwarfInfo(info)
 
 def collect(obj_paths, *,