[ELF] - Make checks in ObjectFile<ELFT>::getSection() stricter.

[grimar]

Summary

One of the change we made in the past was:

" // STT_SECTION symbols can be

// associated with SHT_REL[A]/SHT_SYMTAB/SHT_STRTAB sections.
// In this case it is fine for section to be null here as we
// do not allocate sections of these types."

This patch makes the check for null section stricter, so it is only allowed for STT_SECTION symbols now.
I did it because testcase that contains local unnamed symbol crashes without that check in:

template <class ELFT>
static bool shouldKeepInSymtab(InputSectionBase<ELFT> *Sec, StringRef SymName,
                               const SymbolBody &B) {
...
  return !(Sec->getSectionHdr()->sh_flags & SHF_MERGE); // HERE, because Sec is null
}

[ruiu]

ELF/InputFiles.cpp

370

This code seems a bit too dense. I'd relax it like this.

if (Index >= Sections.size())
  fatal(getFilename(this) + ": invalid section index: " + Twine(Index));
InputSectionBase<ELFT> *S = Sections[Index];

// We found that GNU assembler 2.17.50 [FreeBSD] 2007-07-03
// could generate broken objects. STT_SECTION symbols can be
// associated with SHT_REL[A]/SHT_SYMTAB/SHT_STRTAB sections.
// In this case it is fine for section to be null here as we
// do not allocate sections of these types.
if (!S) {
  if (Sym.getType() == STT_SECTION)
    return;
  fatal(getFilename(this) + ": invalid section index: " + Twine(Index));
}

if (S == &InputSectionBase<ELFT>::Discarded)
  return S;
return S->Repl;

[grimar]

• Addressed review comments.

[ruiu]

LGTM

ELF/InputFiles.cpp

370

Add a blank line before this line.

[grimar]

r283426

ELF/InputFiles.cpp

 }
 
 template <class ELFT>
 InputSectionBase<ELFT> *
 elf::ObjectFile<ELFT>::getSection(const Elf_Sym &Sym) const {
   uint32_t Index = this->getSectionIndex(Sym);
   if (Index == 0)
     return nullptr;
-  if (Index >= Sections.size())
-    fatal(getFilename(this) + ": invalid section index: " + Twine(Index));
-  InputSectionBase<ELFT> *S = Sections[Index];
   // We found that GNU assembler 2.17.50 [FreeBSD] 2007-07-03
   // could generate broken objects. STT_SECTION symbols can be
   // associated with SHT_REL[A]/SHT_SYMTAB/SHT_STRTAB sections.
   // In this case it is fine for section to be null here as we
   // do not allocate sections of these types.
+  if (Index >= Sections.size() ||
+      (!Sections[Index] && Sym.getType() != STT_SECTION))
+    fatal(getFilename(this) + ": invalid section index: " + Twine(Index));
+  InputSectionBase<ELFT> *S = Sections[Index];
   if (!S || S == &InputSectionBase<ELFT>::Discarded)
     return S;
   return S->Repl;
 }
 
 template <class ELFT>
 SymbolBody *elf::ObjectFile<ELFT>::createSymbolBody(const Elf_Sym *Sym) {
   int Binding = Sym->getBinding();

test/ELF/invalid/invalid-elf.test

 # RUN: not ld.lld %p/Inputs/binding.elf -o %t2 2>&1 | \
 # RUN:   FileCheck --check-prefix=INVALID-BINDING %s
 # INVALID-BINDING: unexpected binding
 
 # RUN: not ld.lld %p/Inputs/section-index.elf -o %t2 2>&1 | \
 # RUN:   FileCheck --check-prefix=INVALID-SECTION-INDEX-LLD %s
 # INVALID-SECTION-INDEX-LLD: invalid section index
 
+## section-index2.elf has local symbol with incorrect section index.
+# RUN: not ld.lld %p/Inputs/section-index2.elf -o %t2 2>&1 | \
+# RUN:   FileCheck --check-prefix=INVALID-SECTION-INDEX-LLD %s
+
 # RUN: not ld.lld %p/Inputs/shstrndx.so -o %t2 2>&1 | \
 # RUN:   FileCheck --check-prefix=INVALID-SECTION-INDEX %s
 # INVALID-SECTION-INDEX: Invalid section index
 
 # RUN: not ld.lld %p/Inputs/multiple-eh-relocs.elf -o %t2 2>&1 | \
 # RUN:   FileCheck --check-prefix=INVALID-EH-RELOCS %s
 # INVALID-EH-RELOCS: multiple relocation sections to .eh_frame are not supported
 
 .long foo