[lld] Write the PDB absolute path to the debug directory header

[zturner]

Summary

This matches the behavior of MSVC

[rnk]

lgtm

lld/COFF/Writer.cpp

81

Can we group this at the end with the other fields? That's more consistent with the rest of LLD, access labels be damned.

83

How about moving the public: label up here, since these are method overrides, so they are actually public.

lld/COFF/Writer.cpp

void writeTo(uint8_t *B) const override {
     }
   }
 
 private:
   const std::vector<Chunk *> &Records;
 };
 
 class CVDebugRecordChunk : public Chunk {
+  SmallString<128> PDBAbsPath;
+
   size_t getSize() const override {
-    return sizeof(codeview::DebugInfo) + Config->PDBPath.size() + 1;
+    return sizeof(codeview::DebugInfo) + PDBAbsPath.size() + 1;
   }
 
   void writeTo(uint8_t *B) const override {
     // Save off the DebugInfo entry to backfill the file signature (build id)
     // in Writer::writeBuildId
     DI = reinterpret_cast<codeview::DebugInfo *>(B + OutputSectionOff);
 
     DI->Signature.CVSignature = OMF::Signature::PDB70;
 
     // variable sized field (PDB Path)
     auto *P = reinterpret_cast<char *>(B + OutputSectionOff + sizeof(*DI));
-    if (!Config->PDBPath.empty())
-      memcpy(P, Config->PDBPath.data(), Config->PDBPath.size());
-    P[Config->PDBPath.size()] = '\0';
+    if (!PDBAbsPath.empty())
+      memcpy(P, PDBAbsPath.data(), PDBAbsPath.size());
+    P[PDBAbsPath.size()] = '\0';
   }
 
 public:
+  CVDebugRecordChunk() {
+    PDBAbsPath = Config->PDBPath;
+    if (!PDBAbsPath.empty())
+      llvm::sys::fs::make_absolute(PDBAbsPath);
+  }
+
   mutable codeview::DebugInfo *DI = nullptr;
 };
 
 // The writer writes a SymbolTable result to a file.
 class Writer {
 public:
   Writer(SymbolTable *T) : Symtab(T) {}
   void run();