[llvm-readobj] - Do not report invalid amount of sections.

[grimar]

Summary

When output style is GNU and amount of sections is >= SHN_LORESERVE,
llvm-readobj reports zero number of sections instead of actual value.

The patch fixes that.

[grimar]

• Cosmetic change.

[jhenderson]

LGTM.

test/tools/llvm-readobj/many-sections.s

 ## many-sections.elf-x86_64 is a file that was generated to simulate
 ## an object with more than ~65k sections. When an ELF object
 ## has SHN_LORESERVE (0xff00) or more sections, its e_shnum field
 ## should be zero and sh_size of the section header at index 0 is used
 ## to store the value. If the section name string table section index is
 ## greater than or equal to SHN_LORESERVE, then e_shstrndx field
 ## should have the value of SHN_XINDEX and sh_link of the section header
 ## at index 0 is used to store the value.
 ##
 ## many-sections.elf-x86_64 has few sections to save disk
 ## space, but its e_shnum, e_shstrndx, sh_size and sh_link fields are set
 ## according to the above description, so that we can test the dumper.
 
-# RUN: llvm-readobj -file-headers -elf-output-style GNU \
+# RUN: llvm-readobj -file-headers -sections -elf-output-style GNU \
 # RUN:   %p/Inputs/many-sections.elf-x86_64 | FileCheck %s --check-prefix=GNU1
 # GNU1: Number of section headers:         0 (5)
 # GNU1: Section header string table index: 65535 (3)
+# GNU1: There are 5 section headers, starting at offset 0xb8
 
 # RUN: llvm-readobj -file-headers -elf-output-style LLVM \
 # RUN:   %p/Inputs/many-sections.elf-x86_64 | FileCheck %s --check-prefix=LLVM1
 # LLVM1: SectionHeaderCount: 0 (5)
 # LLVM1: StringTableSectionIndex: 65535 (3)
 
 ## many-sections-stripped.elf-x86_64 is many-sections.elf-x86_64 with
 ## e_shoff field set to zero, but not e_shstrndx, to show that

tools/llvm-readobj/ELFDumper.cpp

template <class ELFT> void GNUStyle<ELFT>::printSections(const ELFO *Obj) {
 
   if (ELFT::Is64Bits) {
     Bias = 0;
     Width = 16;
   } else {
     Bias = 8;
     Width = 8;
   }
-  OS << "There are " << to_string(Obj->getHeader()->e_shnum)
+
+  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";
 
-  for (const Elf_Shdr &Sec : unwrapOrError(Obj->sections())) {
+  for (const Elf_Shdr &Sec : Sections) {
     Number = to_string(SectionIndex);
     Fields[0].Str = Number;
     Fields[1].Str = unwrapOrError(Obj->getSectionName(&Sec));
     Type = getSectionTypeString(Obj->getHeader()->e_machine, Sec.sh_type);
     Fields[2].Str = Type;
     Address = to_string(format_hex_no_prefix(Sec.sh_addr, Width));
     Fields[3].Str = Address;
     Offset = to_string(format_hex_no_prefix(Sec.sh_offset, 6));