[Object/ELF] Ensure preconditions are satisfied.

[davide]

Summary

Also, clarify a comment while at it.

[• rafael]

The comment part is fine.

I am not sure how much more useful asserts are than segmentation faults. How about passing in const references? That way ubsan should be able to catch it as soon as an invalid reference is constructed (I think).

[davide]

r248032 fixes the comment, I would like to think about changing to const references a little bit more. Abandoning this for now.

include/llvm/Object/ELF.h

public:
   ErrorOr<ArrayRef<Elf_Word>> getSHNDXTable(const Elf_Shdr &Section) const;
 
   void VerifyStrTab(const Elf_Shdr *sh) const;
 
   StringRef getRelocationTypeName(uint32_t Type) const;
   void getRelocationTypeName(uint32_t Type,
                              SmallVectorImpl<char> &Result) const;
 
-  /// \brief Get the symbol table section and symbol for a given relocation.
+  /// \brief Get the symbol for a given relocation.
   template <class RelT>
   const Elf_Sym *getRelocationSymbol(const RelT *Rel,
                                      const Elf_Shdr *SymTab) const;
 
   ELFFile(StringRef Object, std::error_code &EC);
 
   bool isMipsELF64() const {
     return Header->e_machine == ELF::EM_MIPS &&
void ELFFile<ELFT>::getRelocationTypeName(uint32_t Type,
   }
 }
 
 template <class ELFT>
 template <class RelT>
 const typename ELFFile<ELFT>::Elf_Sym *
 ELFFile<ELFT>::getRelocationSymbol(const RelT *Rel,
                                    const Elf_Shdr *SymTab) const {
+  assert(Rel && "Invalid relocation");
+  assert(SymTab && "Invalid symbol table");
   uint32_t Index = Rel->getSymbol(isMips64EL());
   if (Index == 0)
     return nullptr;
   return getEntry<Elf_Sym>(SymTab, Index);
 }
 
 template <class ELFT>
 uint64_t ELFFile<ELFT>::getNumSections() const {