[BOLT] Relocation support for non-allocatable sections.

Summary:
Relocations can be created for non-allocatable (aka Note) sections.

To start using this for debug info, the emission has to be moved
earlier in the pipeline for relocation processing to kick in.

(cherry picked from FBD4835204)

bolt/DWARFRewriter.cpp

@@ -396,9 +396,8 @@ void RewriteInstance::updateFunctionRanges() {
 }
 
 void RewriteInstance::generateDebugRanges() {
-  using RangeType = enum { RANGES, ARANGES };
-  for (int IntRT = RANGES; IntRT <= ARANGES; ++IntRT) {
-    RangeType RT = static_cast<RangeType>(IntRT);
+  enum { RANGES, ARANGES };
+  for (auto RT = RANGES + 0; RT <= ARANGES; ++RT) {
     const char *SectionName = (RT == RANGES) ? ".debug_ranges"
                                              : ".debug_aranges";
     SmallVector<char, 16> RangesBuffer;

bolt/RewriteInstance.cpp

@@ -455,27 +455,21 @@ uint8_t *ExecutableFileMemoryManager::recordNoteSection(
                << " with size " << Size << ", alignment " << Alignment
                << " at 0x"
                << Twine::utohexstr(reinterpret_cast<uint64_t>(Data)) << '\n');
-  if (SectionName == ".debug_line") {
     // We need to make a copy of the section contents if we'll need it for
-    // a future reference.
-    uint8_t *DataCopy = new uint8_t[Size];
-    memcpy(DataCopy, Data, Size);
-    NoteSectionInfo[SectionName] =
-      SectionInfo(reinterpret_cast<uint64_t>(DataCopy),
-                  Size,
-                  Alignment,
-                  /*IsCode=*/false,
-                  /*IsReadOnly=*/true,
-                  /*IsLocal=*/false,
-                  0,
-                  0,
-                  SectionID);
-    return DataCopy;
-  } else {
-    DEBUG(dbgs() << "BOLT-DEBUG: ignoring section " << SectionName
-                 << " in recordNoteSection()\n");
-    return nullptr;
-  }
+  // a future reference. RuntimeDyld will not allocate the space forus.
+  uint8_t *DataCopy = new uint8_t[Size];
+  memcpy(DataCopy, Data, Size);
+  NoteSectionInfo[SectionName] =
+    SectionInfo(reinterpret_cast<uint64_t>(DataCopy),
+                Size,
+                Alignment,
+                /*IsCode=*/false,
+                /*IsReadOnly=*/true,
+                /*IsLocal=*/false,
+                0,
+                0,
+                SectionID);
+  return DataCopy;
 }
 
 bool ExecutableFileMemoryManager::finalizeMemory(std::string *ErrMsg) {
@@ -2105,14 +2099,11 @@ void RewriteInstance::emitFunctions() {
     Streamer->EmitLabel(BC->Ctx->getOrCreateSymbol("__hot_end"));
   }
 
-  if (opts::Relocs) {
-    emitDataSections(Streamer.get());
-  }
-
-
   if (opts::UpdateDebugSections)
     updateDebugLineInfoForNonSimpleFunctions();
 
+  emitDataSections(Streamer.get());
+
   // Relocate .eh_frame to .eh_frame_old.
   if (EHFrameSection.getObject() != nullptr) {
     relocateEHFrameSection();
@@ -2401,16 +2392,22 @@ void RewriteInstance::emitDataSection(MCStreamer *Streamer, SectionRef Section,
     SectionName = Name;
   else
     Section.getName(SectionName);
+
+  const auto SectionFlags = ELFSectionRef(Section).getFlags();
+  const auto SectionType = ELFSectionRef(Section).getType();
   auto *ELFSection = BC->Ctx->getELFSection(SectionName,
-                                            ELF::SHT_PROGBITS,
-                                            ELF::SHF_WRITE | ELF::SHF_ALLOC);
+                                            SectionType,
+                                            SectionFlags);
+
   StringRef SectionContents;
   Section.getContents(SectionContents);
 
   Streamer->SwitchSection(ELFSection);
   Streamer->EmitValueToAlignment(Section.getAlignment());
 
-  DEBUG(dbgs() << "BOLT-DEBUG: emitting section " << SectionName << '\n');
+  DEBUG(dbgs() << "BOLT-DEBUG: emitting "
+               << (SectionFlags & ELF::SHF_ALLOC ? "" : "non-")
+               << "allocatable data section " << SectionName << '\n');
 
   auto SRI = BC->SectionRelocations.find(Section);
   if (SRI == BC->SectionRelocations.end()) {
@@ -2634,7 +2631,7 @@ void RewriteInstance::rewriteNoteSections() {
       // Write section extension.
       Address = SI.AllocAddress;
       if (Address) {
-        DEBUG(dbgs() << "BOLT: " << (Size ? "appending" : "writing")
+        DEBUG(dbgs() << "BOLT-DEBUG: " << (Size ? "appending" : "writing")
                      << " contents to section "
                      << *SectionName << '\n');
         OS.write(reinterpret_cast<const char *>(Address), SI.Size);

bolt/RewriteInstance.h

@@ -384,7 +384,7 @@ class RewriteInstance {
                                        bool IsSimple);
 private:
 
-  /// If we are updating debug info, these are the section we need to overwrite.
+  /// When updating debug info, these are the sections we overwrite.
   static constexpr const char *DebugSectionsToOverwrite[] = {
     ".debug_aranges",
     ".debug_line",