[BOLT][NFC] Check section contents before registering it

[Amir]

Summary

Address fuzzer crash on malformed input:

BOLT-ERROR: cannot get section contents for .dynsym: The end of the file was unexpectedly encountered.

[rafauler]

LGTM

bolt/include/bolt/Rewrite/RewriteInstance.h

private:
   using ELF64LEPhdrTy = object::ELF64LEFile::Elf_Phdr;
 
   /// Populate array of binary functions and other objects of interest
   /// from meta data in the file.
   void discoverFileObjects();
 
   /// Read info from special sections. E.g. eh_frame and .gcc_except_table
   /// for exception and stack unwinding information.
-  void readSpecialSections();
+  Error readSpecialSections();
 
   /// Adjust supplied command-line options based on input data.
   void adjustCommandLineOptions();
 
   /// Process runtime relocations.
   void processDynamicRelocations();
 
   /// Process input relocations.

bolt/lib/Rewrite/RewriteInstance.cpp

Error RewriteInstance::run() {
   outs() << "BOLT-INFO: Target architecture: "
          << Triple::getArchTypeName(
                 (llvm::Triple::ArchType)InputFile->getArch())
          << "\n";
   outs() << "BOLT-INFO: BOLT version: " << BoltRevision << "\n";
 
   if (Error E = discoverStorage())
     return E;
-  readSpecialSections();
+  if (Error E = readSpecialSections())
+    return E;
   adjustCommandLineOptions();
   discoverFileObjects();
 
   preprocessProfileData();
 
   // Skip disassembling if we have a translation table and we are running an
   // aggregation job.
   if (opts::AggregateOnly && BAT->enabledFor(InputFile)) {

 
 ArrayRef<uint8_t> RewriteInstance::getLSDAData() {
   return ArrayRef<uint8_t>(LSDASection->getData(),
                            LSDASection->getContents().size());
 }
 
 uint64_t RewriteInstance::getLSDAAddress() { return LSDASection->getAddress(); }
 
-void RewriteInstance::readSpecialSections() {
+Error RewriteInstance::readSpecialSections() {
   NamedRegionTimer T("readSpecialSections", "read special sections",
                      TimerGroupName, TimerGroupDesc, opts::TimeRewrite);
 
   bool HasTextRelocations = false;
   bool HasDebugInfo = false;
 
   // Process special sections.
   for (const SectionRef &Section : InputFile->sections()) {
     Expected<StringRef> SectionNameOrErr = Section.getName();
     check_error(SectionNameOrErr.takeError(), "cannot get section name");
     StringRef SectionName = *SectionNameOrErr;
 
     // Only register sections with names.
     if (!SectionName.empty()) {
+      if (Error E = Section.getContents().takeError())
+        return E;
       BC->registerSection(Section);
       LLVM_DEBUG(
           dbgs() << "BOLT-DEBUG: registering section " << SectionName << " @ 0x"
                  << Twine::utohexstr(Section.getAddress()) << ":0x"
                  << Twine::utohexstr(Section.getAddress() + Section.getSize())
                  << "\n");
       if (isDebugSection(SectionName))
         HasDebugInfo = true;
Error RewriteInstance::readSpecialSections() {
   parseBuildID();
   if (Optional<std::string> FileBuildID = getPrintableBuildID())
     BC->setFileBuildID(*FileBuildID);
 
   parseSDTNotes();
 
   // Read .dynamic/PT_DYNAMIC.
   readELFDynamic();
+  return Error::success();
 }
 
 void RewriteInstance::adjustCommandLineOptions() {
   if (BC->isAArch64() && !BC->HasRelocations)
     errs() << "BOLT-WARNING: non-relocation mode for AArch64 is not fully "
               "supported\n";
 
   if (RuntimeLibrary *RtLibrary = BC->getRuntimeLibrary())