[obj2yaml] Don't crash for input files without symbol table

Summary: Previously we would dereference Symtab without checking for null.

Reviewers: davide, atanasyan, rafael

Reviewed By: davide, atanasyan

Differential Revision: https://reviews.llvm.org/D38080

llvm-svn: 313970

llvm/test/tools/obj2yaml/missing_symtab.test

@@ -0,0 +1,5 @@
+# RUN: obj2yaml %S/Inputs/crt1.o | FileCheck %s
+# test that we don't crash when passed object files without a symbol table
+# CHECK-LABEL: FileHeader:
+# CHECK-LABEL: Sections:
+# CHECK-LABEL: Symbols:

llvm/tools/obj2yaml/elf2yaml.cpp

@@ -188,6 +188,8 @@ template <class ELFT> ErrorOr<ELFYAML::Object *> ELFDumper<ELFT>::dump() {
   }
 
   // Dump symbols
+  if (!Symtab)
+    return Y.release(); // if the symbol table is missing return early
   auto StrTableOrErr = Obj.getStringTableForSymtab(*Symtab);
   if (!StrTableOrErr)
     return errorToErrorCode(StrTableOrErr.takeError());