[ELF] - Do not crash when unable to parse ELF object file.

[grimar]

Summary

createELFObj() may call error(...), for example when file is too short.
In that case header is not set and following line lead to crash:

EMachine = ELFObj.getHeader()->e_machine;

Patch fixes the issue.

[grimar]

ELF/InputFiles.cpp

60

I wonder may be we can just make this fatal() ?
It is not called when file not found, but only when there is something wrong with it.

[ruiu]

ELF/InputFiles.cpp

73–74

This seems very weird. HasError should be used at major checkpoints, and we shouldn't have so many checkpoints. It is on the other hand called for every instantiation of the class.

[grimar]

ELF/InputFiles.cpp

73–74

What about my comment above about switching error -> fatal in createELFObj() then ?
This should be consistent with latest ELF parsing hardening as we use fatal for broken objects and
createELFObj() now call error() even if ELF is broken, what I think is the only possible reason for fail.

[ruiu]

ELF/InputFiles.cpp

73–74

That's probably better. We shouldn't do too much to try to recover from unrecoverable errors.

[grimar]

• Addressed review comments.

[ruiu]

LGTM

[• rafael]

LGTM

ELF/Error.h

 void error(std::error_code EC, const Twine &Prefix);
 
 template <typename T> void error(const ErrorOr<T> &V, const Twine &Prefix) {
   error(V.getError(), Prefix);
 }
 
 LLVM_ATTRIBUTE_NORETURN void fatal(const Twine &Msg);
 LLVM_ATTRIBUTE_NORETURN void fatal(const Twine &Msg, const Twine &Prefix);
+LLVM_ATTRIBUTE_NORETURN void fatal(std::error_code EC, const Twine &Prefix);
 
 template <class T> T check(ErrorOr<T> E) {
   if (auto EC = E.getError())
     fatal(EC.message());
   return std::move(*E);
 }
 
 template <class T> T check(Expected<T> E) {

ELF/Error.cpp

void elf::fatal(const Twine &Msg) {
   *ErrorOS << Msg << "\n";
   exit(1);
 }
 
 void elf::fatal(const Twine &Msg, const Twine &Prefix) {
   fatal(Prefix + ": " + Msg);
 }
 
+void elf::fatal(std::error_code EC, const Twine &Prefix) {
+  fatal(Prefix + ": " + EC.message());
+}
+
 } // namespace lld

ELF/InputFiles.cpp

if (!F->ArchiveName.empty())
     return (F->ArchiveName + "(" + F->getName() + ")").str();
   return F->getName();
 }
 
 template <class ELFT> static ELFFile<ELFT> createELFObj(MemoryBufferRef MB) {
   std::error_code EC;
   ELFFile<ELFT> F(MB.getBuffer(), EC);
   if (EC)
-    error(EC, "failed to read " + MB.getBufferIdentifier());
+    fatal(EC, "failed to read " + MB.getBufferIdentifier());
   return F;
 }
 
 template <class ELFT> static ELFKind getELFKind() {
   if (ELFT::TargetEndianness == support::little)
     return ELFT::Is64Bits ? ELF64LEKind : ELF32LEKind;
   return ELFT::Is64Bits ? ELF64BEKind : ELF32BEKind;
 }
 
 template <class ELFT>
 ELFFileBase<ELFT>::ELFFileBase(Kind K, MemoryBufferRef MB)
     : InputFile(K, MB), ELFObj(createELFObj<ELFT>(MB)) {
   EKind = getELFKind<ELFT>();
   EMachine = ELFObj.getHeader()->e_machine;
 }
 
 template <class ELFT>
 typename ELFT::SymRange ELFFileBase<ELFT>::getElfSymbols(bool OnlyGlobals) {
   if (!Symtab)
     return Elf_Sym_Range(nullptr, nullptr);
   Elf_Sym_Range Syms = ELFObj.symbols(Symtab);
   uint32_t NumSymbols = std::distance(Syms.begin(), Syms.end());

test/ELF/invalid/too-short.s

+# REQUIRES: x86
+
+## too-short.elf file is a truncated ELF.
+# RUN: not ld.lld %S/Inputs/too-short.elf -o %t 2>&1 | FileCheck %s
+# CHECK: failed to read