[ELF.h] - Check the case when e_shstrndx=SHN_XINDEX, but the corresponding sh_link is broken.

When e_shstrndx is equal to SHN_XINDEX,
the index of the section string table section should
be taken from the sh_link field of the section
header at index 0.

If sh_link is broken, e.g. contains an index that is
larger than number of sections, then error is reported.

This error message was untested before.

Differential revision: https://reviews.llvm.org/D65391

llvm-svn: 368139

include/llvm/Object/ELF.h

@@ -465,7 +465,6 @@ ELFFile<ELFT>::getSectionStringTable(Elf_Shdr_Range Sections) const {
 
   if (!Index) // no section string table.
     return "";
-  // TODO: Test a case when the sh_link of the section with index 0 is broken.
   if (Index >= Sections.size())
     return createError("section header string table index " + Twine(Index) +
                        " does not exist");

test/Object/invalid.test

@@ -652,3 +652,23 @@ Sections:
 DynamicSymbols:
   - Name:    foo
     Binding: STB_GLOBAL
+
+## Check the case when e_shstrndx == SHN_XINDEX, but null section's sh_link contains
+## the index of a section header string table that is larger than the number of the sections.
+
+# RUN: yaml2obj --docnum=31 %s -o %t31
+# RUN: not llvm-objcopy %t31 2>&1 | FileCheck %s -DFILE=%t31 --check-prefix=INVALID-SHSTRTAB-INDEX
+
+# INVALID-SHSTRTAB-INDEX: error: section header string table index 255 does not exist
+
+--- !ELF
+FileHeader:
+  Class:    ELFCLASS64
+  Data:     ELFDATA2LSB
+  Type:     ET_REL
+  Machine:  EM_X86_64
+## SHN_XINDEX == 0xffff.
+  SHStrNdx: 0xffff
+Sections:
+  - Type: SHT_NULL
+    Link: 0xff