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

[grimar]

Summary

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.

This is almost the same as D65388, but now the code
in ELF.h is tested.

[MaskRay]

should be taken from zero section sh_link field

the sh_link field of the section header at index 0?

test/Object/invalid.test

610 ↗

(On Diff #212143)

null section -> the section header at index 0

[grimar]

• Addressed comments.

James, since this is independent from D65388,
are you OK to land it?

[grimar]

Ping. James?

[jhenderson]

LGTM, with nits fixed. Sorry, last week was very busy. Just working through my backlog now.

test/Object/invalid.test

632 ↗

(On Diff #212584)

contains the index of a
larger than the number

[grimar]

In D65391#1616494, @jhenderson wrote:

LGTM, with nits fixed. Sorry, last week was very busy. Just working through my backlog now.

No worries, thanks for review!

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

 Expected<StringRef>
 ELFFile<ELFT>::getSectionStringTable(Elf_Shdr_Range Sections) const {
   uint32_t Index = getHeader()->e_shstrndx;
   if (Index == ELF::SHN_XINDEX)
     Index = Sections[0].sh_link;
 
   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");
   return getStringTable(&Sections[Index]);
 }
 
 template <class ELFT> ELFFile<ELFT>::ELFFile(StringRef Object) : Buf(Object) {}
 

llvm/trunk/test/Object/invalid.test

Sections:
   - Name:    .gnu.version
     Type:    SHT_GNU_versym
     EntSize: 0x0000000000000003
     Entries: [ ]
 ## Needed to trigger creation of .dynsym.
 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