[llvm] [DWARFYAML] Implement debug_names support (PR #79666)

[James Henderson via llvm-commits]

================
@@ -691,6 +691,191 @@ Error DWARFYAML::emitDebugStrOffsets(raw_ostream &OS, const Data &DI) {
   return Error::success();
 }
 
+namespace {
+/// Emits the header for a DebugNames section.
+void emitDebugNamesHeader(raw_ostream &OS, bool IsLittleEndian,
+                          uint32_t NameCount, uint32_t AbbrevSize,
+                          uint32_t CombinedSizeOtherParts) {
+  StringRef AugmentationString = "LLVM0700";
+  auto TotalSize = CombinedSizeOtherParts + 5 * sizeof(uint32_t) +
+                   2 * sizeof(uint16_t) + sizeof(NameCount) +
+                   sizeof(AbbrevSize) + AugmentationString.size();
+  writeInteger(uint32_t(TotalSize), OS, IsLittleEndian); // Unit length
+
+  // Everything below is included in total size.
+  writeInteger(uint16_t(5), OS, IsLittleEndian); // Version
+  writeInteger(uint16_t(0), OS, IsLittleEndian); // Padding
+  writeInteger(uint32_t(1), OS, IsLittleEndian); // Compilation Unit count
+  writeInteger(uint32_t(0), OS, IsLittleEndian); // Local Type Unit count
+  writeInteger(uint32_t(0), OS, IsLittleEndian); // Foreign Type Unit count
+  writeInteger(uint32_t(0), OS, IsLittleEndian); // Bucket count
+  writeInteger(NameCount, OS, IsLittleEndian);
+  writeInteger(AbbrevSize, OS, IsLittleEndian);
+  writeInteger(uint32_t(AugmentationString.size()), OS, IsLittleEndian);
+  OS.write(AugmentationString.data(), AugmentationString.size());
+  return;
+}
+
+/// Emits the abbreviations for a DebugNames section.
+std::string
+emitDebugNamesAbbrev(ArrayRef<DWARFYAML::DebugNameAbbreviation> Abbrevs) {
+  std::string Data;
+  llvm::raw_string_ostream OS(Data);
+  for (const auto &Abbrev : Abbrevs) {
+    encodeULEB128(Abbrev.Code, OS);
+    encodeULEB128(Abbrev.Tag, OS);
+    for (auto [Idx, Form] : Abbrev.Indices) {
+      encodeULEB128(Idx, OS);
+      encodeULEB128(Form, OS);
+    }
+    encodeULEB128(0, OS);
+    encodeULEB128(0, OS);
+  }
+  encodeULEB128(0, OS);
+  return Data;
+}
+
+/// Emits a simple CU offsets list for a DebugNames section containing a single
+/// CU at offset 0.
+std::string emitDebugNamesCUOffsets(bool IsLittleEndian) {
+  std::string Data;
+  llvm::raw_string_ostream OS(Data);
+  writeInteger(uint32_t(0), OS, IsLittleEndian);
+  return Data;
+}
+
+/// Emits the "NameTable" for a DebugNames section; according to the spec, it
+/// consists of two arrays: an array of string offsets, followed immediately by
+/// an array of entry offsets. The string offsets are emitted in the order
+/// provided in `Entries`.
+std::string emitDebugNamesNameTable(
+    bool IsLittleEndian,
+    const std::map<uint32_t, std::vector<DWARFYAML::DebugNameEntry>> &Entries,
+    ArrayRef<uint32_t> EntryPoolOffsets) {
+  assert(Entries.size() == EntryPoolOffsets.size());
+
+  std::string Data;
+  llvm::raw_string_ostream OS(Data);
+
+  for (auto Strp : make_first_range(Entries))
+    writeInteger(Strp, OS, IsLittleEndian);
+  for (auto PoolOffset : EntryPoolOffsets)
+    writeInteger(uint32_t(PoolOffset), OS, IsLittleEndian);
+  return Data;
+}
+
+/// Groups entries based on their name (strp) code and returns a sorted map.
+std::map<uint32_t, std::vector<DWARFYAML::DebugNameEntry>>
+groupEntries(ArrayRef<DWARFYAML::DebugNameEntry> Entries) {
+  std::map<uint32_t, std::vector<DWARFYAML::DebugNameEntry>> Ans;
+  for (const auto &Entry : Entries)
----------------
jh7370 wrote:

Nit: Here and in many other places throughout this code, I think you're in violation of the LLVM coding standard on when to use `auto` - it's not immediately obvious looking purely at this loop that `Entry` is of type `DebugNameEntry`, so we should spell it out.

https://github.com/llvm/llvm-project/pull/79666