[ELF] - Handle EhInputSection Live bit in MarkLive.cpp

[grimar]

Summary

I suggest to so this refactoring change. Since MarkLive.cpp is
the place where we set Live flags for other sections, it looks correct
to do that there.
Benefit is that we stop spreading GC logic outsize of MarkLive.cpp.

[ruiu]

LGTM

lld/trunk/ELF/InputSection.cpp

void InputSection::replace(InputSection *Other) {
   Other->Repl = this->Repl;
   Other->Live = false;
 }
 
 template <class ELFT>
 EhInputSection::EhInputSection(ObjFile<ELFT> *F,
                                const typename ELFT::Shdr *Header,
                                StringRef Name)
-    : InputSectionBase(F, Header, Name, InputSectionBase::EHFrame) {
-  // Mark .eh_frame sections as live by default because there are
-  // usually no relocations that point to .eh_frames. Otherwise,
-  // the garbage collector would drop all .eh_frame sections.
-  this->Live = true;
-}
+    : InputSectionBase(F, Header, Name, InputSectionBase::EHFrame) {}
 
 SyntheticSection *EhInputSection::getParent() const {
   return cast_or_null<SyntheticSection>(Parent);
 }
 
 // Returns the index of the first relocation that points to a region between
 // Begin and Begin+Size.
 template <class IntTy, class RelTy>

lld/trunk/ELF/MarkLive.cpp

template <class ELFT> static void doGcSections() {
   // file can interrupt other ELF file's symbols at runtime.
   for (Symbol *S : Symtab->getSymbols())
     if (S->includeInDynsym())
       MarkSymbol(S);
 
   // Preserve special sections and those which are specified in linker
   // script KEEP command.
   for (InputSectionBase *Sec : InputSections) {
-    // .eh_frame is always marked as live now, but also it can reference to
-    // sections that contain personality. We preserve all non-text sections
-    // referred by .eh_frame here.
-    if (auto *EH = dyn_cast_or_null<EhInputSection>(Sec))
+    // Mark .eh_frame sections as live because there are usually no relocations
+    // that point to .eh_frames. Otherwise, the garbage collector would drop
+    // all of them. We also want to preserve personality routines and LSDA
+    // referenced by .eh_frame sections, so we scan them for that here.
+    if (auto *EH = dyn_cast_or_null<EhInputSection>(Sec)) {
+      EH->Live = true;
       scanEhFrameSection<ELFT>(*EH, Enqueue);
+    }
+
     if (Sec->Flags & SHF_LINK_ORDER)
       continue;
     if (isReserved<ELFT>(Sec) || Script->shouldKeep(Sec))
       Enqueue(Sec, 0);
     else if (isValidCIdentifier(Sec->Name)) {
       CNamedSections[Saver.save("__start_" + Sec->Name)].push_back(Sec);
       CNamedSections[Saver.save("__stop_" + Sec->Name)].push_back(Sec);
     }