[lld] [lld][ELF] Implement merged .debug_names section. (PR #86508)

[Fangrui Song via llvm-commits]

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@@ -788,6 +792,125 @@ class RelroPaddingSection final : public SyntheticSection {
   void writeTo(uint8_t *buf) override {}
 };
 
+template <class ELFT> class DebugNamesSection final : public SyntheticSection {
+  // N.B. Everything in this class assumes that we are using DWARF32.
+  // If we move to DWARF64, most of this data will need to be re-sized,
+  // and the code that handles or manipulates it will need to be updated
+  // accordingly.
+
+public:
+  DebugNamesSection();
+  static DebugNamesSection *create();
+  void writeTo(uint8_t *buf) override;
+  size_t getSize() const override { return sectionSize; }
+  bool isNeeded() const override;
+
+  template <class RelTy>
+  void getNameRelocsImpl(InputSection *sec, ArrayRef<RelTy> rels,
+                         llvm::DenseMap<uint32_t, uint32_t> &relocs);
+
+  void getNameRelocs(InputSectionBase *base,
+                     llvm::DenseMap<uint32_t, uint32_t> &relocs);
+
+  struct Abbrev : public llvm::FoldingSetNode {
+    uint32_t code;
+    uint32_t tag;
+    SmallVector<llvm::DWARFDebugNames::AttributeEncoding, 2> attributes;
+
+    void Profile(llvm::FoldingSetNodeID &id) const;
+  };
+
+  struct AttrValueData {
+    uint32_t attrValue;
+    uint8_t attrSize;
+  };
+
+  struct IndexEntry {
+    uint32_t abbrevCode;
+    uint32_t poolOffset;
+    union {
+      int32_t parentOffset = -1;
+      IndexEntry *parentEntry;
+    };
+    SmallVector<AttrValueData, 3> attrValues;
+  };
+
+  struct NamedEntry {
+    const char *name;
+    uint32_t hashValue;
+    uint32_t stringOffsetOffset;
+    uint32_t entryOffset;
+    uint32_t relocatedEntryOffset;
+    // The index of the chunk that 'name' points into, for looking up
+    // relocation data for this string.
+    uint32_t chunkIdx;
+    SmallVector<std::unique_ptr<IndexEntry>, 0> indexEntries;
+  };
+
+  struct SectionOffsetLocs {
+    uint64_t stringOffsetsBase;
+    uint64_t entryOffsetsBase;
+    uint64_t entriesBase;
+  };
+
+  struct DebugNamesSectionData {
+    llvm::DWARFDebugNames::Header hdr;
+    llvm::DWARFDebugNames::DWARFDebugNamesOffsets locs;
+    SmallVector<uint32_t, 0> tuOffsets;
+    SmallVector<Abbrev, 0> abbrevTable;
+    SmallVector<uint32_t, 0> entryOffsets;
+    SmallVector<NamedEntry, 0> namedEntries;
+    uint16_t dwarfSize;
+    uint16_t hdrSize;
+  };
+
+  // Per-file data used, while reading in the data, to generate the merged
+  // section information.
+  struct DebugNamesInputChunk {
+    uint32_t baseCuOffsetIdx;
+    std::unique_ptr<llvm::DWARFDebugNames> debugNamesData;
+    std::unique_ptr<LLDDWARFSection> namesSection;
+    SmallVector<DebugNamesSectionData, 0> sectionsData;
+    SmallVector<uint32_t, 0> hashValues;
----------------
MaskRay wrote:

`hashValues` duplicates `hashValue` in entrys. I've removed this member in my branch to reduce memory usage.

https://github.com/llvm/llvm-project/pull/86508