[yaml2obj] - Map section names to chunks for each ELFYAML::ProgramHeader early. NFCI.

[grimar]

Summary

Each ELFYAML::ProgramHeader currently contains a list of section names
included. We are trying to map them to Fill/Sections very late,
though we can create such mapping early, in initProgramHeaders.

The benefit is that with such change it is possible to access mapped
chunks earlier (for example during writing section content) and have
simpler code.

(I am working on a patch to allocate a file space for no-bits sections
if there are non-nobits sections in a segment that follows them. It needs
such change to avoid code duplication).

[MaskRay]

LGTM.

[jhenderson]

LGTM, with one suggestion.

llvm/include/llvm/ObjectYAML/ELFYAML.h

503–506

Up to you, but maybe:

Optional<llvm::yaml::Hex64> Offset;

std::vector<SectionName> Sections;
// This vector is parallel to Sections and contains corresponding chunks.
std::vector<Chunk *> Chunks;

[grimar]

llvm/include/llvm/ObjectYAML/ELFYAML.h

503–506

OK.

llvm/include/llvm/ObjectYAML/ELFYAML.h

struct FileHeader {
   Optional<llvm::yaml::Hex16> SHNum;
   Optional<llvm::yaml::Hex16> SHStrNdx;
 };
 
 struct SectionName {
   StringRef Section;
 };
 
-struct ProgramHeader {
-  ELF_PT Type;
-  ELF_PF Flags;
-  llvm::yaml::Hex64 VAddr;
-  llvm::yaml::Hex64 PAddr;
-  Optional<llvm::yaml::Hex64> Align;
-  Optional<llvm::yaml::Hex64> FileSize;
-  Optional<llvm::yaml::Hex64> MemSize;
-  Optional<llvm::yaml::Hex64> Offset;
-  std::vector<SectionName> Sections;
-};
-
 struct Symbol {
   StringRef Name;
   ELF_STT Type;
   StringRef Section;
   Optional<ELF_SHN> Index;
   ELF_STB Binding;
   llvm::yaml::Hex64 Value;
   llvm::yaml::Hex64 Size;
struct MipsABIFlags : Section {
 
   MipsABIFlags() : Section(ChunkKind::MipsABIFlags) {}
 
   static bool classof(const Chunk *S) {
     return S->Kind == ChunkKind::MipsABIFlags;
   }
 };
 
+struct ProgramHeader {
+  ELF_PT Type;
+  ELF_PF Flags;
+  llvm::yaml::Hex64 VAddr;
+  llvm::yaml::Hex64 PAddr;
+  Optional<llvm::yaml::Hex64> Align;
+  Optional<llvm::yaml::Hex64> FileSize;
+  Optional<llvm::yaml::Hex64> MemSize;
+  Optional<llvm::yaml::Hex64> Offset;
+
+  std::vector<SectionName> Sections;
+  // This vector is parallel to Sections and contains corresponding chunks.
+  std::vector<Chunk *> Chunks;
+};
+
 struct Object {
   FileHeader Header;
   std::vector<ProgramHeader> ProgramHeaders;
 
   // An object might contain output section descriptions as well as
   // custom data that does not belong to any section.
   std::vector<std::unique_ptr<Chunk>> Chunks;
 

llvm/lib/ObjectYAML/ELFEmitter.cpp

void ELFState<ELFT>::writeELFHeader(ContiguousBlobAccumulator &CBA, raw_ostream &OS) {
   Header.e_shstrndx = Doc.Header.SHStrNdx ? (uint16_t)*Doc.Header.SHStrNdx
                                           : SN2I.get(".shstrtab");
 
   OS.write((const char *)&Header, sizeof(Header));
 }
 
 template <class ELFT>
 void ELFState<ELFT>::initProgramHeaders(std::vector<Elf_Phdr> &PHeaders) {
-  for (const auto &YamlPhdr : Doc.ProgramHeaders) {
+  DenseMap<StringRef, ELFYAML::Fill *> NameToFill;
+  for (const std::unique_ptr<ELFYAML::Chunk> &D : Doc.Chunks)
+    if (auto S = dyn_cast<ELFYAML::Fill>(D.get()))
+      NameToFill[S->Name] = S;
+
+  std::vector<ELFYAML::Section *> Sections = Doc.getSections();
+  for (ELFYAML::ProgramHeader &YamlPhdr : Doc.ProgramHeaders) {
     Elf_Phdr Phdr;
     zero(Phdr);
     Phdr.p_type = YamlPhdr.Type;
     Phdr.p_flags = YamlPhdr.Flags;
     Phdr.p_vaddr = YamlPhdr.VAddr;
     Phdr.p_paddr = YamlPhdr.PAddr;
     PHeaders.push_back(Phdr);
+
+    // Map Sections list to corresponding chunks.
+    for (const ELFYAML::SectionName &SecName : YamlPhdr.Sections) {
+      if (ELFYAML::Fill *Fill = NameToFill.lookup(SecName.Section)) {
+        YamlPhdr.Chunks.push_back(Fill);
+        continue;
+      }
+
+      unsigned Index;
+      if (SN2I.lookup(SecName.Section, Index)) {
+        YamlPhdr.Chunks.push_back(Sections[Index]);
+        continue;
+      }
+
+      reportError("unknown section or fill referenced: '" + SecName.Section +
+                  "' by program header");
+    }
   }
 }
 
 template <class ELFT>
 unsigned ELFState<ELFT>::toSectionIndex(StringRef S, StringRef LocSec,
                                         StringRef LocSym) {
   unsigned Index;
   if (SN2I.lookup(S, Index) || to_integer(S, Index))

 template <class ELFT> void ELFState<ELFT>::reportError(const Twine &Msg) {
   ErrHandler(Msg);
   HasError = true;
 }
 
 template <class ELFT>
 std::vector<Fragment>
 ELFState<ELFT>::getPhdrFragments(const ELFYAML::ProgramHeader &Phdr,
-                                 ArrayRef<typename ELFT::Shdr> SHeaders) {
-  DenseMap<StringRef, ELFYAML::Fill *> NameToFill;
-  for (const std::unique_ptr<ELFYAML::Chunk> &D : Doc.Chunks)
-    if (auto S = dyn_cast<ELFYAML::Fill>(D.get()))
-      NameToFill[S->Name] = S;
-
+                                 ArrayRef<Elf_Shdr> SHeaders) {
   std::vector<Fragment> Ret;
-  for (const ELFYAML::SectionName &SecName : Phdr.Sections) {
-    unsigned Index;
-    if (SN2I.lookup(SecName.Section, Index)) {
-      const typename ELFT::Shdr &H = SHeaders[Index];
-      Ret.push_back({H.sh_offset, H.sh_size, H.sh_type, H.sh_addralign});
-      continue;
-    }
-
-    if (ELFYAML::Fill *Fill = NameToFill.lookup(SecName.Section)) {
-      Ret.push_back({*Fill->Offset, Fill->Size, llvm::ELF::SHT_PROGBITS,
+  for (const ELFYAML::Chunk *C : Phdr.Chunks) {
+    if (const ELFYAML::Fill *F = dyn_cast<ELFYAML::Fill>(C)) {
+      Ret.push_back({*F->Offset, F->Size, llvm::ELF::SHT_PROGBITS,
                      /*ShAddrAlign=*/1});
       continue;
     }
 
-    reportError("unknown section or fill referenced: '" + SecName.Section +
-                "' by program header");
+    const ELFYAML::Section *S = cast<ELFYAML::Section>(C);
+    const Elf_Shdr &H = SHeaders[SN2I.get(S->Name)];
+    Ret.push_back({H.sh_offset, H.sh_size, H.sh_type, H.sh_addralign});
   }
-
   return Ret;
 }
 
 template <class ELFT>
 void ELFState<ELFT>::setProgramHeaderLayout(std::vector<Elf_Phdr> &PHeaders,
                                             std::vector<Elf_Shdr> &SHeaders) {
   uint32_t PhdrIdx = 0;
   for (auto &YamlPhdr : Doc.ProgramHeaders) {