[PDB] Improve our PDB OMF debug directory entry

In order to get dbghelp to load our pdb, we have to fill in the
PointerToRawData field as well as the AddressOfRawData field. One is the
file offset and the other is the RVA.

llvm-svn: 309900

lld/COFF/Chunks.h

@@ -82,7 +82,7 @@ public:
   // An output section has pointers to chunks in the section, and each
   // chunk has a back pointer to an output section.
   void setOutputSection(OutputSection *O) { Out = O; }
-  OutputSection *getOutputSection() { return Out; }
+  OutputSection *getOutputSection() const { return Out; }
 
   // Windows-specific.
   // Collect all locations that contain absolute addresses for base relocations.

lld/COFF/Writer.cpp

@@ -65,8 +65,9 @@ public:
       D->Type = COFF::IMAGE_DEBUG_TYPE_CODEVIEW;
       D->SizeOfData = Record->getSize();
       D->AddressOfRawData = Record->getRVA();
-      // TODO(compnerd) get the file offset
-      D->PointerToRawData = 0;
+      OutputSection *OS = Record->getOutputSection();
+      uint64_t Offs = OS->getFileOff() + (Record->getRVA() - OS->getRVA());
+      D->PointerToRawData = Offs;
 
       ++D;
     }