[lld] [lld][ELF] Implement merged .debug_names section (PR #88092)

[Fangrui Song via llvm-commits]

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@@ -2711,6 +2714,581 @@ static uint32_t computeGdbHash(StringRef s) {
   return h;
 }
 
+// 4-byte alignment ensures that values in the hash lookup table and the name
+// table are aligned.
+DebugNamesBaseSection::DebugNamesBaseSection()
+    : SyntheticSection(0, SHT_PROGBITS, 4, ".debug_names") {}
+
+// Get the size of the .debug_names section header in bytes for DWARF32:
+static uint32_t getDebugNamesHeaderSize(uint32_t augmentationStringSize) {
+  return /* unit length */ 4 +
+         /* version */ 2 +
+         /* padding */ 2 +
+         /* CU count */ 4 +
+         /* TU count */ 4 +
+         /* Foreign TU count */ 4 +
+         /* Bucket Count */ 4 +
+         /* Name Count */ 4 +
+         /* Abbrev table size */ 4 +
+         /* Augmentation string size */ 4 +
+         /* Augmentation string */ augmentationStringSize;
+}
+
+void DebugNamesBaseSection::parse(
+    InputChunk &inputChunk, OutputChunk &chunk,
+    DWARFDataExtractor &namesExtractor, DataExtractor &strExtractor,
+    function_ref<SmallVector<uint32_t, 0>(
+        const DWARFDebugNames::Header &,
+        const DWARFDebugNames::DWARFDebugNamesOffsets &)>
+        readOffsets) {
+  const LLDDWARFSection namesSec = inputChunk.section;
+  DenseMap<uint32_t, IndexEntry *> offsetMap;
+  SmallVector<uint32_t, 0> entryOffsets;
+  for (const DWARFDebugNames::NameIndex &llvmNi : *inputChunk.llvmDebugNames) {
+    NameIndex &ni = inputChunk.nameIndices.emplace_back();
+    ni.hdr = llvmNi.getHeader();
+    if (ni.hdr.Format != DwarfFormat::DWARF32) {
+      errorOrWarn(toString(namesSec.sec) + Twine(": unsupported DWARF64"));
+      return;
+    }
+    if (ni.hdr.Version != 5) {
+      errorOrWarn(toString(namesSec.sec) + Twine(": unsupported version ") +
+                  Twine(ni.hdr.Version));
+      return;
+    }
+    const uint32_t dwarfSize =
+        dwarf::getDwarfOffsetByteSize(DwarfFormat::DWARF32);
+    const uint32_t hdrSize =
+        getDebugNamesHeaderSize(ni.hdr.AugmentationStringSize);
+    auto locs = findDebugNamesOffsets(hdrSize, ni.hdr);
+    if (locs.EntriesBase > namesExtractor.getData().size()) {
+      errorOrWarn(toString(namesSec.sec) +
+                  Twine(": index entry is out of bounds"));
+      return;
+    }
+
+    SmallVector<uint32_t, 0> entryOffsets = readOffsets(ni.hdr, locs);
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MaskRay wrote:

Good catch. I removed the unused one on 2746.

https://github.com/llvm/llvm-project/pull/88092