[llvm/Object] - Add a test for "empty string table" error.

[grimar]

Summary

This error was never tested. In this patch I improved
the error message, added the test case and also simplified
the code that processes a similar error right below.

[MaskRay]

test/Object/invalid.test

611 ↗

(On Diff #212156)

not empty -> empty?

llvm/trunk/include/llvm/Object/ELF.h

return createError("invalid sh_type for string table section " +
                        ": expected SHT_STRTAB, but got " +
                        object::getELFSectionTypeName(getHeader()->e_machine,
                                                      Section->sh_type));
   auto V = getSectionContentsAsArray<char>(Section);
   if (!V)
     return V.takeError();
   ArrayRef<char> Data = *V;
   if (Data.empty())
-    // TODO: this error is untested.
-    return createError("empty string table");
+    return createError("SHT_STRTAB string table section " +
+                       getSecIndexForError(this, Section) + " is empty");
   if (Data.back() != '\0')
-    return createError(object::getELFSectionTypeName(getHeader()->e_machine,
-                                                     Section->sh_type) +
-                       " string table section " +
+    return createError("SHT_STRTAB string table section " +
                        getSecIndexForError(this, Section) +
                        " is non-null terminated");
   return StringRef(Data.begin(), Data.size());
 }
 
 template <class ELFT>
 Expected<ArrayRef<typename ELFT::Word>>
 ELFFile<ELFT>::getSHNDXTable(const Elf_Shdr &Section) const {

llvm/trunk/test/Object/invalid.test

  
 --- !ELF
 FileHeader:
   Class:    ELFCLASS64
   Data:     ELFDATA2LSB
   Type:     ET_REL
   Machine:  EM_X86_64
   SHOffset: 0xffffffffffffffff
+
+## Check that llvm-objdump reports an error when it tries to dump a
+## symbol name and .strtab is empty.
+
+# RUN: yaml2obj %s --docnum=29 -o %t29
+# RUN: not llvm-objdump -syms %t29 2>&1 | FileCheck -DFILE=%t29 --check-prefix=STRTAB-EMPTY2 %s
+
+# STRTAB-EMPTY2: error: '[[FILE]]': SHT_STRTAB string table section [index 1] is empty
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_DYN
+  Machine: EM_X86_64
+Sections:
+  - Name: .strtab
+    Type: SHT_STRTAB
+    Content: ""
+Symbols:
+  - Name: foo