[ELFYAML] Fix handling SHT_NOBITS sections by obj2yaml/yaml2obj tools

SHT_NOBITS sections do not have content in an object file. Now yaml2obj
tool does not accept `Content` field for such sections, and obj2yaml
tool does not attempt to read the section content from a file.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241350 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Object/ELFYAML.h

@@ -85,7 +85,13 @@ struct SectionOrType {
 };
 
 struct Section {
-  enum class SectionKind { Group, RawContent, Relocation, MipsABIFlags };
+  enum class SectionKind {
+    Group,
+    RawContent,
+    Relocation,
+    NoBits,
+    MipsABIFlags
+  };
   SectionKind Kind;
   StringRef Name;
   ELF_SHT Type;
@@ -106,6 +112,14 @@ struct RawContentSection : Section {
   }
 };
 
+struct NoBitsSection : Section {
+  llvm::yaml::Hex64 Size;
+  NoBitsSection() : Section(SectionKind::NoBits) {}
+  static bool classof(const Section *S) {
+    return S->Kind == SectionKind::NoBits;
+  }
+};
+
 struct Group : Section {
   // Members of a group contain a flag and a list of section indices
   // that are part of the group.

lib/Object/ELFYAML.cpp

@@ -627,6 +627,11 @@ static void sectionMapping(IO &IO, ELFYAML::RawContentSection &Section) {
   IO.mapOptional("Size", Section.Size, Hex64(Section.Content.binary_size()));
 }
 
+static void sectionMapping(IO &IO, ELFYAML::NoBitsSection &Section) {
+  commonSectionMapping(IO, Section);
+  IO.mapRequired("Size", Section.Size);
+}
+
 static void sectionMapping(IO &IO, ELFYAML::RelocationSection &Section) {
   commonSectionMapping(IO, Section);
   IO.mapOptional("Relocations", Section.Relocations);
@@ -682,6 +687,11 @@ void MappingTraits<std::unique_ptr<ELFYAML::Section>>::mapping(
       Section.reset(new ELFYAML::Group());
     groupSectionMapping(IO, *cast<ELFYAML::Group>(Section.get()));
     break;
+  case ELF::SHT_NOBITS:
+    if (!IO.outputting())
+      Section.reset(new ELFYAML::NoBitsSection());
+    sectionMapping(IO, *cast<ELFYAML::NoBitsSection>(Section.get()));
+    break;
   case ELF::SHT_MIPS_ABIFLAGS:
     if (!IO.outputting())
       Section.reset(new ELFYAML::MipsABIFlags());

test/Object/obj2yaml.test

@@ -234,7 +234,7 @@ ELF-MIPSEL-NEXT:   - Name:            .bss
 ELF-MIPSEL-NEXT:     Type:            SHT_NOBITS
 ELF-MIPSEL-NEXT:     Flags:           [ SHF_WRITE, SHF_ALLOC ]
 ELF-MIPSEL-NEXT:     AddressAlign:    0x0000000000000004
-ELF-MIPSEL-NEXT:     Content:         48656C6C
+ELF-MIPSEL-NEXT:     Size:            0x0000000000000004
 ELF-MIPSEL-NEXT:   - Name:            .mdebug.abi32
 ELF-MIPSEL-NEXT:     Type:            SHT_PROGBITS
 ELF-MIPSEL-NEXT:     AddressAlign:    0x0000000000000001
@@ -324,7 +324,7 @@ ELF-MIPS64EL-NEXT:   - Name:            .bss
 ELF-MIPS64EL-NEXT:     Type:            SHT_NOBITS
 ELF-MIPS64EL-NEXT:     Flags:           [ SHF_WRITE, SHF_ALLOC ]
 ELF-MIPS64EL-NEXT:     AddressAlign:    0x0000000000000010
-ELF-MIPS64EL-NEXT:     Content:         ''
+ELF-MIPS64EL-NEXT:     Size:            0x0000000000000000
 ELF-MIPS64EL-NEXT:   - Name:            .MIPS.options
 ELF-MIPS64EL-NEXT:     Type:            SHT_MIPS_OPTIONS
 ELF-MIPS64EL-NEXT:     Flags:           [ SHF_ALLOC ]

test/Object/yaml2obj-elf-rel-noref.yaml

@@ -32,7 +32,7 @@ Sections:
     Type:            SHT_NOBITS
     Flags:           [ SHF_WRITE, SHF_ALLOC ]
     AddressAlign:    0x0000000000000001
-    Content:         ''
+    Size:            0
   - Name:            .ARM.attributes
     Type:            SHT_ARM_ATTRIBUTES
     AddressAlign:    0x0000000000000001

tools/obj2yaml/elf2yaml.cpp

@@ -40,6 +40,7 @@ class ELFDumper {
   ErrorOr<ELFYAML::RelocationSection *> dumpRelaSection(const Elf_Shdr *Shdr);
   ErrorOr<ELFYAML::RawContentSection *>
   dumpContentSection(const Elf_Shdr *Shdr);
+  ErrorOr<ELFYAML::NoBitsSection *> dumpNoBitsSection(const Elf_Shdr *Shdr);
   ErrorOr<ELFYAML::Group *> dumpGroup(const Elf_Shdr *Shdr);
   ErrorOr<ELFYAML::MipsABIFlags *> dumpMipsABIFlags(const Elf_Shdr *Shdr);
 
@@ -104,6 +105,13 @@ ErrorOr<ELFYAML::Object *> ELFDumper<ELFT>::dump() {
       Y->Sections.push_back(std::unique_ptr<ELFYAML::Section>(G.get()));
       break;
     }
+    case ELF::SHT_NOBITS: {
+      ErrorOr<ELFYAML::NoBitsSection *> S = dumpNoBitsSection(&Sec);
+      if (std::error_code EC = S.getError())
+        return EC;
+      Y->Sections.push_back(std::unique_ptr<ELFYAML::Section>(S.get()));
+      break;
+    }
     default: {
       ErrorOr<ELFYAML::RawContentSection *> S = dumpContentSection(&Sec);
       if (std::error_code EC = S.getError())
@@ -304,6 +312,18 @@ ELFDumper<ELFT>::dumpContentSection(const Elf_Shdr *Shdr) {
   return S.release();
 }
 
+template <class ELFT>
+ErrorOr<ELFYAML::NoBitsSection *>
+ELFDumper<ELFT>::dumpNoBitsSection(const Elf_Shdr *Shdr) {
+  auto S = make_unique<ELFYAML::NoBitsSection>();
+
+  if (std::error_code EC = dumpCommonSection(Shdr, *S))
+    return EC;
+  S->Size = Shdr->sh_size;
+
+  return S.release();
+}
+
 template <class ELFT>
 ErrorOr<ELFYAML::Group *> ELFDumper<ELFT>::dumpGroup(const Elf_Shdr *Shdr) {
   auto S = make_unique<ELFYAML::Group>();

tools/yaml2obj/yaml2elf.cpp

@@ -241,6 +241,8 @@ bool ELFState<ELFT>::initSectionHeaders(std::vector<Elf_Shdr> &SHeaders,
     } else if (auto S = dyn_cast<ELFYAML::MipsABIFlags>(Sec.get())) {
       if (!writeSectionContent(SHeader, *S, CBA))
         return false;
+    } else if (isa<ELFYAML::NoBitsSection>(Sec.get())) {
+      // SHT_NOBITS section does not have content so nothing to do here.
     } else
       llvm_unreachable("Unknown section type");