[LLD][ELF] Refactor CreateThunks to extract the iteration through InputSections.

[peter.smith]

Summary

In preparation for inserting Thunks into InputSectionDescription::Sections extract the loop that finds InputSections that may have calls that need Thunks. This isn't much benefit now but this will be useful when we have to extract the InputSectionDescriptions::Sections from the Script commands.

This is patch 2 of 3 of converting createThunks() to insert into InputSectionDescriptions.

[ruiu]

LGTM

ELF/Relocations.h

 
 class ThunkCreator {
 public:
   // Return true if Thunks have been added to OutputSections
   bool createThunks(ArrayRef<OutputSection *> OutputSections);
 
 private:
   void mergeThunks();
-  ThunkSection *getOSThunkSec(ThunkSection *&TS, OutputSection *OS);
+  ThunkSection *getOSThunkSec(OutputSection *OS);
   ThunkSection *getISThunkSec(InputSection *IS, OutputSection *OS);
+  void forEachExecInputSection(
+      ArrayRef<OutputSection *> OutputSections,
+      std::function<void(OutputSection *, InputSection *)> Fn);
   std::pair<Thunk *, bool> getThunk(SymbolBody &Body, uint32_t Type);
 
   // Track Symbols that already have a Thunk
   llvm::DenseMap<SymbolBody *, Thunk *> ThunkedSymbols;
 
   // Track InputSections that have a ThunkSection placed in front
   llvm::DenseMap<InputSection *, ThunkSection *> ThunkedSections;
 
   // Track the ThunksSections that need to be inserted into an OutputSection
   std::map<std::vector<InputSection *> *, std::vector<ThunkSection *>>
       ThunkSections;
+
+  // The ThunkSection for this vector of InputSections
+  ThunkSection *CurTS;
 };
 
 // Return a int64_t to make sure we get the sign extension out of the way as
 // early as possible.
 template <class ELFT>
 static inline int64_t getAddend(const typename ELFT::Rel &Rel) {
   return 0;
 }
 template <class ELFT>
 static inline int64_t getAddend(const typename ELFT::Rela &Rel) {
   return Rel.r_addend;
 }
 }
 }
 
 #endif

ELF/Relocations.cpp

for (auto &KV : ThunkSections) {
     std::merge(ISR->begin(), ISR->end(), Thunks.begin(), Thunks.end(),
                std::back_inserter(Tmp), MergeCmp);
     OutputSection *OS = Thunks.front()->getParent();
     OS->Sections = std::move(Tmp);
     OS->assignOffsets();
   }
 }
 
-ThunkSection *ThunkCreator::getOSThunkSec(ThunkSection *&TS,
-                                          OutputSection *OS) {
-  if (TS == nullptr) {
+ThunkSection *ThunkCreator::getOSThunkSec(OutputSection *OS) {
+  if (CurTS == nullptr) {
     uint32_t Off = 0;
     for (auto *IS : OS->Sections) {
       Off = IS->OutSecOff + IS->getSize();
       if ((IS->Flags & SHF_EXECINSTR) == 0)
         break;
     }
-    TS = make<ThunkSection>(OS, Off);
-    ThunkSections[&OS->Sections].push_back(TS);
+    CurTS = make<ThunkSection>(OS, Off);
+    ThunkSections[&OS->Sections].push_back(CurTS);
   }
-  return TS;
+  return CurTS;
 }
 
 ThunkSection *ThunkCreator::getISThunkSec(InputSection *IS, OutputSection *OS) {
   ThunkSection *TS = ThunkedSections.lookup(IS);
   if (TS)
     return TS;
   auto *TOS = IS->getParent();
   TS = make<ThunkSection>(TOS, IS->OutSecOff);
   ThunkSections[&TOS->Sections].push_back(TS);
   ThunkedSections[IS] = TS;
   return TS;
 }
 
 std::pair<Thunk *, bool> ThunkCreator::getThunk(SymbolBody &Body,
                                                 uint32_t Type) {
   auto res = ThunkedSymbols.insert({&Body, nullptr});
   if (res.second)
     res.first->second = addThunk(Type, Body);
   return std::make_pair(res.first->second, res.second);
 }
 
+// Call Fn on every executable InputSection accessed via the linker script
+// InputSectionDescription::Sections.
+void ThunkCreator::forEachExecInputSection(
+    ArrayRef<OutputSection *> OutputSections,
+    std::function<void(OutputSection *, InputSection *)> Fn) {
+  for (OutputSection *OS : OutputSections) {
+    if (!(OS->Flags & SHF_ALLOC) || !(OS->Flags & SHF_EXECINSTR))
+      continue;
+    CurTS = nullptr;
+    for (InputSection *IS : OS->Sections)
+      Fn(OS, IS);
+  }
+}
+
 // Process all relocations from the InputSections that have been assigned
 // to OutputSections and redirect through Thunks if needed.
 //
 // createThunks must be called after scanRelocs has created the Relocations for
 // each InputSection. It must be called before the static symbol table is
 // finalized. If any Thunks are added to an OutputSection the output section
 // offsets of the InputSections will change.
 //
 // FIXME: All Thunks are assumed to be in range of the relocation. Range
 // extension Thunks are not yet supported.
 bool ThunkCreator::createThunks(ArrayRef<OutputSection *> OutputSections) {
   // Create all the Thunks and insert them into synthetic ThunkSections. The
   // ThunkSections are later inserted back into the OutputSection.
 
   // We separate the creation of ThunkSections from the insertion of the
   // ThunkSections back into the OutputSection as ThunkSections are not always
   // inserted into the same OutputSection as the caller.
-  for (OutputSection *OS : OutputSections) {
-    ThunkSection *OSTS = nullptr;
-    for (InputSection *IS : OS->Sections) {
+  forEachExecInputSection(
+      OutputSections, [=](OutputSection *OS, InputSection *IS) {
         for (Relocation &Rel : IS->Relocations) {
           SymbolBody &Body = *Rel.Sym;
           if (!Target->needsThunk(Rel.Expr, Rel.Type, IS->File, Body))
             continue;
           Thunk *T;
           bool IsNew;
           std::tie(T, IsNew) = getThunk(Body, Rel.Type);
           if (IsNew) {
             // Find or create a ThunkSection for the new Thunk
             ThunkSection *TS;
             if (auto *TIS = T->getTargetInputSection())
               TS = getISThunkSec(TIS, OS);
             else
-            TS = getOSThunkSec(OSTS, OS);
+              TS = getOSThunkSec(OS);
             TS->addThunk(T);
           }
           // Redirect relocation to Thunk, we never go via the PLT to a Thunk
           Rel.Sym = T->ThunkSym;
           Rel.Expr = fromPlt(Rel.Expr);
         }
-    }
-  }
+      });
 
   // Merge all created synthetic ThunkSections back into OutputSection
   mergeThunks();
   return !ThunkSections.empty();
 }
 
 template void elf::scanRelocations<ELF32LE>(InputSectionBase &);
 template void elf::scanRelocations<ELF32BE>(InputSectionBase &);
 template void elf::scanRelocations<ELF64LE>(InputSectionBase &);
 template void elf::scanRelocations<ELF64BE>(InputSectionBase &);