[llvm-readobj] - Do not fail to dump the object which has wrong type of .shstrtab.

[grimar]

Summary

Imagine we have object that has .shstrtab with type != SHT_STRTAB.
In this case, we fail to dump the object, though GNU readelf dumps it without
any issues and warnings.

This patch fixes that. It adds a code to ELFDumper.cpp which is based on the implementation of getSectionName from the ELF.h:

https://github.com/llvm-mirror/llvm/blob/master/include/llvm/Object/ELF.h#L608
https://github.com/llvm-mirror/llvm/blob/master/include/llvm/Object/ELF.h#L431
https://github.com/llvm-mirror/llvm/blob/master/include/llvm/Object/ELF.h#L539

The difference is that all non critical errors are ommitted what allows us to
improve the dumping on a tool side. Also, this opens a road for a follow-up that
should allow us to dump the section headers, but drop the section names in case if .shstrtab is completely absent and/or broken.

[jhenderson]

tools/llvm-readobj/ELFDumper.cpp

3012 ↗

(On Diff #204525)

Could this call reportError(Twine) at least? Ideally, I'd prefer it if it called a function that included the file name too. I think there's one in llvm-readobj.cpp that would be useful: reportError(StringRef Input, Error Err). I don't see a reason that this couldn't be exposed to the rest of llvm-readobj.

[grimar]

• Addressed review comments.
• Fixed compilation with GCC.
• Added 2 lines of code to fix the Object/no-section-header-string-table.test

(It is needed for no section string table case, it matches the existent behavior).

tools/llvm-readobj/ELFDumper.cpp

3012 ↗

(On Diff #204525)

I changed to reportError(Twine). It looks a bit problematic to get a file name here and I am not sure it is very useful to do this change right now, because actually, I think we do not need this error at all here. I introduced it to minimize the change of the existent logic (i.e. we already had this fatal error at deeper levels), but I think getSectionName actually should never fail and terminate the proccess. It probably might return a Error instead or a pair of section name + warning message, or something else, but idea is that if we can`t get the section name because of any reason we should probably continue dumping and just show something like <section name unknown> instead of the section name.

[jhenderson]

LGTM.

tools/llvm-readobj/ELFDumper.cpp

3012 ↗

(On Diff #204525)

The easiest way would be to pass in ELFObjectFile rather than ELFFile, I think, but maybe that doesn't make sense.

llvm/trunk/test/tools/llvm-readobj/elf-wrong-shstrtab-type.test

+## wrong-shstrtab-type.elf-x86-64 contains .shstrtab section which has SHT_PROGBITS type.
+## Check we do not fail to dump the section headers in this case.
+
+# RUN: llvm-readobj -S %p/Inputs/wrong-shstrtab-type.elf-x86-64 | FileCheck %s --check-prefix LLVM
+# RUN: llvm-readelf -S %p/Inputs/wrong-shstrtab-type.elf-x86-64 | FileCheck %s --check-prefix GNU
+
+# LLVM:      Name: .shstrtab
+# LLVM-NEXT: Type: SHT_PROGBITS
+
+# GNU: [Nr] Name      Type
+# GNU: [ 3] .shstrtab PROGBITS

llvm/trunk/tools/llvm-readobj/ELFDumper.cpp

case SHT_GNU_versym:
     return "VERSYM";
   default:
     return getSectionTypeOffsetString(Type);
   }
   return "";
 }
 
 template <class ELFT>
+static StringRef getSectionName(const typename ELFT::Shdr &Sec,
+                                const ELFFile<ELFT> &Obj,
+                                ArrayRef<typename ELFT::Shdr> Sections) {
+  uint32_t Index = Obj.getHeader()->e_shstrndx;
+  if (Index == ELF::SHN_XINDEX)
+    Index = Sections[0].sh_link;
+  if (!Index) // no section string table.
+    return "";
+  if (Index >= Sections.size())
+    reportError("invalid section index");
+  StringRef Data = toStringRef(unwrapOrError(
+      Obj.template getSectionContentsAsArray<uint8_t>(&Sections[Index])));
+  return unwrapOrError(Obj.getSectionName(&Sec, Data));
+}
+
+template <class ELFT>
 void GNUStyle<ELFT>::printSectionHeaders(const ELFO *Obj) {
   unsigned Bias = ELFT::Is64Bits ? 0 : 8;
   ArrayRef<Elf_Shdr> Sections = unwrapOrError(Obj->sections());
   OS << "There are " << to_string(Sections.size())
      << " section headers, starting at offset "
      << "0x" << to_hexString(Obj->getHeader()->e_shoff, false) << ":\n\n";
   OS << "Section Headers:\n";
   Field Fields[11] = {
       {"[Nr]", 2},        {"Name", 7},        {"Type", 25},
       {"Address", 41},    {"Off", 58 - Bias}, {"Size", 65 - Bias},
       {"ES", 72 - Bias},  {"Flg", 75 - Bias}, {"Lk", 79 - Bias},
       {"Inf", 82 - Bias}, {"Al", 86 - Bias}};
   for (auto &F : Fields)
     printField(F);
   OS << "\n";
 
   size_t SectionIndex = 0;
   for (const Elf_Shdr &Sec : Sections) {
     Fields[0].Str = to_string(SectionIndex);
-    Fields[1].Str = unwrapOrError(Obj->getSectionName(&Sec));
+    Fields[1].Str = getSectionName(Sec, *Obj, Sections);
     Fields[2].Str =
         getSectionTypeString(Obj->getHeader()->e_machine, Sec.sh_type);
     Fields[3].Str =
         to_string(format_hex_no_prefix(Sec.sh_addr, ELFT::Is64Bits ? 16 : 8));
     Fields[4].Str = to_string(format_hex_no_prefix(Sec.sh_offset, 6));
     Fields[5].Str = to_string(format_hex_no_prefix(Sec.sh_size, 6));
     Fields[6].Str = to_string(format_hex_no_prefix(Sec.sh_entsize, 2));
     Fields[7].Str = getGNUFlags(Sec.sh_flags);
void LLVMStyle<ELFT>::printRelocation(const ELFO *Obj, Elf_Rela Rel,
   }
 }
 
 template <class ELFT>
 void LLVMStyle<ELFT>::printSectionHeaders(const ELFO *Obj) {
   ListScope SectionsD(W, "Sections");
 
   int SectionIndex = -1;
-  for (const Elf_Shdr &Sec : unwrapOrError(Obj->sections())) {
-    ++SectionIndex;
-
-    StringRef Name = unwrapOrError(Obj->getSectionName(&Sec));
-
+  ArrayRef<Elf_Shdr> Sections = unwrapOrError(Obj->sections());
+  for (const Elf_Shdr &Sec : Sections) {
+    StringRef Name = getSectionName(Sec, *Obj, Sections);
     DictScope SectionD(W, "Section");
-    W.printNumber("Index", SectionIndex);
+    W.printNumber("Index", ++SectionIndex);
     W.printNumber("Name", Name, Sec.sh_name);
     W.printHex(
         "Type",
         object::getELFSectionTypeName(Obj->getHeader()->e_machine, Sec.sh_type),
         Sec.sh_type);
     std::vector<EnumEntry<unsigned>> SectionFlags(std::begin(ElfSectionFlags),
                                                   std::end(ElfSectionFlags));
     switch (Obj->getHeader()->e_machine) {