[NFC] Store signature symbol in ELFObjectFile

Signature symbols are relevant only for sections of type SHT_GROUP
and is best tracked at the level of ObjectFile.

Remove this member from ELFSection.

Addresses part of #629

Signed-off-by: Shankar Easwaran <seaswara@qti.qualcomm.com>

Author: quic-seaswara

include/eld/Input/ELFObjectFile.h

@@ -16,6 +16,7 @@
 namespace eld {
 
 class ELFSection;
+class LDSymbol;
 class TimingSection;
 class RelocMap;
 
@@ -119,6 +120,20 @@ class ELFObjectFile : public ELFFileBase {
   llvm::ArrayRef<std::string>
   getSectionAnnotations(const ELFSection &S) const;
 
+  void setSectionSignatureSymbol(const ELFSection &S, LDSymbol *Sym) {
+    if (Sym)
+      SignatureSymbolForGroupSections[&S] = Sym;
+    else
+      SignatureSymbolForGroupSections.erase(&S);
+  }
+
+  LDSymbol *getSectionSignatureSymbol(const ELFSection &S) const {
+    auto It = SignatureSymbolForGroupSections.find(&S);
+    if (It == SignatureSymbolForGroupSections.end())
+      return nullptr;
+    return It->second;
+  }
+
 private:
   eld::ELFSection *LLVMBCSection = nullptr;
   eld::TimingSection *TimingSection = nullptr;
@@ -138,6 +153,8 @@ class ELFObjectFile : public ELFFileBase {
   std::unordered_map<const ELFSection *, InputFile *> OldInputFileBySection;
   std::unordered_map<const ELFSection *, llvm::SmallVector<std::string, 1>>
       SectionAnnotationsBySection;
+  std::unordered_map<const ELFSection *, LDSymbol *>
+      SignatureSymbolForGroupSections;
 };
 
 } // namespace eld

include/eld/Readers/ELFSection.h

@@ -204,9 +204,16 @@ class ELFSection : public ELFSectionBase {
 
   void setPaddr(size_t A);
 
-  void setSymbol(LDSymbol *S) { Symbol = S; }
+  void setSignatureSymbol(LDSymbol *S) {
+    auto *ObjFile = llvm::dyn_cast_or_null<ELFObjectFile>(getInputFile());
+    assert(ObjFile && "Section symbol must be stored on an ELFObjectFile");
+    ObjFile->setSectionSignatureSymbol(*this, S);
+  }
 
-  LDSymbol *getSymbol() const { return Symbol; }
+  LDSymbol *getSignatureSymbol() const {
+    auto *ObjFile = llvm::dyn_cast_or_null<ELFObjectFile>(getInputFile());
+    return ObjFile ? ObjFile->getSectionSignatureSymbol(*this) : nullptr;
+  }
 
   llvm::ArrayRef<const ELFSection *> getGroupSections() const {
     auto *ObjFile = llvm::dyn_cast_or_null<ELFObjectFile>(getInputFile());
@@ -320,8 +327,6 @@ class ELFSection : public ELFSectionBase {
   uint64_t Offset = ~uint64_t(0);
   uint64_t Addr = InvalidAddr;
 
-  LDSymbol *Symbol = nullptr;
-
   /// FIXME: These can probably be moved out
   bool Wanted = false;
   bool WantedInOutput = false;

lib/Object/ObjectBuilder.cpp

@@ -141,7 +141,7 @@ ELFSection *ObjectBuilder::mergeSection(GNULDBackend &PGnuldBackend,
       // Add all the input sections that were part of the group
       for (auto *GroupSection : CurInputSection->getGroupSections())
         Target->addSectionsToGroup(GroupSection);
-      Target->setSymbol(CurInputSection->getSymbol());
+      Target->setSignatureSymbol(CurInputSection->getSignatureSymbol());
       if (!CurInputSection->getOutputSection())
         CurInputSection->setOutputSection(Target->getOutputSection());
       return Target;

lib/Readers/RelocELFReader.cpp

@@ -294,7 +294,7 @@ eld::Expected<bool> RelocELFReader<ELFT>::readOneGroup(ELFSection *S) {
   // FIXME: Return an error instead!
   if (!signatureSymbol)
     return false;
-  S->setSymbol(signatureSymbol->resolveInfo()->outSymbol());
+  S->setSignatureSymbol(signatureSymbol->resolveInfo()->outSymbol());
   return true;
 }
 

lib/Writers/ELFObjectWriter.cpp

@@ -751,7 +751,8 @@ uint64_t ELFObjectWriter::getSectLink(const ELFSection *S) const {
 /// getSectInfo - compute ElfXX_Shdr::sh_info
 uint64_t ELFObjectWriter::getSectInfo(ELFSection *CurSection) const {
   if (CurSection->isGroupKind())
-    return ThisModule.getBackend().getSymbolIdx(CurSection->getSymbol());
+    return ThisModule.getBackend().getSymbolIdx(
+        CurSection->getSignatureSymbol());
 
   if (llvm::ELF::SHT_SYMTAB == CurSection->getType() ||
       llvm::ELF::SHT_DYNSYM == CurSection->getType())