[lldb] [llvm] Add support for using foreign type units in .debug_names. (PR #87740)

[Greg Clayton via llvm-commits]

================
@@ -657,6 +657,42 @@ std::optional<uint64_t> DWARFDebugNames::Entry::getLocalTUOffset() const {
   return NameIdx->getLocalTUOffset(*Index);
 }
 
+std::optional<uint64_t>
+DWARFDebugNames::Entry::getForeignTUTypeSignature() const {
+  std::optional<uint64_t> Index = getLocalTUIndex();
+  const uint32_t NumLocalTUs = NameIdx->getLocalTUCount();
+  if (!Index || *Index < NumLocalTUs)
+    return std::nullopt; // Invalid TU index or TU index is for a local TU
+  // The foreign TU index is the TU index minus the number of local TUs.
+  const uint64_t ForeignTUIndex = *Index - NumLocalTUs;
+  if (ForeignTUIndex >= NameIdx->getForeignTUCount())
+    return std::nullopt; // Invalid foreign TU index.
+  return NameIdx->getForeignTUSignature(ForeignTUIndex);
+}
+
+std::optional<uint64_t>
+DWARFDebugNames::Entry::getForeignTUSkeletonCUOffset() const {
+  // Must have a DW_IDX_type_unit and it must be a foreign type unit.
+  if (!getForeignTUTypeSignature())
----------------
clayborg wrote:

Spec states:
```
6.1.1.4.2 List of CUs

The list of CUs immediately follows the header. Each entry in the list is an offset of the corresponding compilation unit in the .debug_info section. In the DWARF-32 format, a section offset is 4 bytes, while in the DWARF-64 format, a section offset is 8 bytes.

The total number of entries in the list is given by comp_unit_count. There must be at least one CU.
```

https://github.com/llvm/llvm-project/pull/87740