[yaml2obj] - Add a way to describe content of the SHT_GNU_verneed section with "Content".

There is no way to set raw content for SHT_GNU_verneed section.
This patch implements it.

Differential revision: https://reviews.llvm.org/D70816

include/llvm/ObjectYAML/ELFYAML.h

@@ -324,7 +324,8 @@ struct VerneedEntry {
 };
 
 struct VerneedSection : Section {
-  std::vector<VerneedEntry> VerneedV;
+  Optional<yaml::BinaryRef> Content;
+  Optional<std::vector<VerneedEntry>> VerneedV;
   llvm::yaml::Hex64 Info;
 
   VerneedSection() : Section(ChunkKind::Verneed) {}

lib/ObjectYAML/ELFEmitter.cpp

@@ -1036,15 +1036,24 @@ void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
   typedef typename ELFT::Vernaux Elf_Vernaux;
 
   auto &OS = CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
+  SHeader.sh_info = Section.Info;
+
+  if (Section.Content) {
+    SHeader.sh_size = writeContent(OS, Section.Content, None);
+    return;
+  }
+
+  if (!Section.VerneedV)
+    return;
 
   uint64_t AuxCnt = 0;
-  for (size_t I = 0; I < Section.VerneedV.size(); ++I) {
-    const ELFYAML::VerneedEntry &VE = Section.VerneedV[I];
+  for (size_t I = 0; I < Section.VerneedV->size(); ++I) {
+    const ELFYAML::VerneedEntry &VE = (*Section.VerneedV)[I];
 
     Elf_Verneed VerNeed;
     VerNeed.vn_version = VE.Version;
     VerNeed.vn_file = DotDynstr.getOffset(VE.File);
-    if (I == Section.VerneedV.size() - 1)
+    if (I == Section.VerneedV->size() - 1)
       VerNeed.vn_next = 0;
     else
       VerNeed.vn_next =
@@ -1069,9 +1078,8 @@ void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
     }
   }
 
-  SHeader.sh_size = Section.VerneedV.size() * sizeof(Elf_Verneed) +
+  SHeader.sh_size = Section.VerneedV->size() * sizeof(Elf_Verneed) +
                     AuxCnt * sizeof(Elf_Vernaux);
-  SHeader.sh_info = Section.Info;
 }
 
 template <class ELFT>
@@ -1344,10 +1352,12 @@ template <class ELFT> void ELFState<ELFT>::finalizeStrings() {
   // add strings to .dynstr section.
   for (const ELFYAML::Chunk *Sec : Doc.getSections()) {
     if (auto VerNeed = dyn_cast<ELFYAML::VerneedSection>(Sec)) {
-      for (const ELFYAML::VerneedEntry &VE : VerNeed->VerneedV) {
-        DotDynstr.add(VE.File);
-        for (const ELFYAML::VernauxEntry &Aux : VE.AuxV)
-          DotDynstr.add(Aux.Name);
+      if (VerNeed->VerneedV) {
+        for (const ELFYAML::VerneedEntry &VE : *VerNeed->VerneedV) {
+          DotDynstr.add(VE.File);
+          for (const ELFYAML::VernauxEntry &Aux : VE.AuxV)
+            DotDynstr.add(Aux.Name);
+        }
       }
     } else if (auto VerDef = dyn_cast<ELFYAML::VerdefSection>(Sec)) {
       if (VerDef->Entries)

lib/ObjectYAML/ELFYAML.cpp

@@ -1086,7 +1086,8 @@ static void sectionMapping(IO &IO, ELFYAML::SymverSection &Section) {
 static void sectionMapping(IO &IO, ELFYAML::VerneedSection &Section) {
   commonSectionMapping(IO, Section);
   IO.mapRequired("Info", Section.Info);
-  IO.mapRequired("Dependencies", Section.VerneedV);
+  IO.mapOptional("Dependencies", Section.VerneedV);
+  IO.mapOptional("Content", Section.Content);
 }
 
 static void sectionMapping(IO &IO, ELFYAML::RelocationSection &Section) {
@@ -1427,6 +1428,13 @@ StringRef MappingTraits<std::unique_ptr<ELFYAML::Chunk>>::validate(
     return {};
   }
 
+  if (const auto *VD = dyn_cast<ELFYAML::VerneedSection>(C.get())) {
+    if (VD->VerneedV && VD->Content)
+      return "SHT_GNU_verneed: \"Dependencies\" and \"Content\" can't be used "
+             "together";
+    return {};
+  }
+
   return {};
 }
 

test/tools/yaml2obj/ELF/verneed-section.yaml

@@ -1,7 +1,7 @@
 ## Check we are able to handle SHT_GNU_verneed sections.
 
-# RUN: yaml2obj %s -o %t
-# RUN: llvm-readobj -V %t | FileCheck %s
+# RUN: yaml2obj --docnum=1 %s -o %t1
+# RUN: llvm-readobj -V %t1 | FileCheck %s
 
 # CHECK:      VersionRequirements [
 # CHECK-NEXT:   Dependency {
@@ -82,3 +82,77 @@ Sections:
 DynamicSymbols:
   - Name:    f1
     Binding: STB_GLOBAL
+
+## Check we can use "Content" to describe the content.
+
+# RUN: yaml2obj --docnum=2 %s -o %t2
+# RUN: llvm-readobj --sections --section-data %t2 | FileCheck %s --check-prefix=CONTENT
+
+# CONTENT:      Name: .gnu.version_r
+# CONTENT-NEXT: Type: SHT_GNU_verneed
+# CONTENT-NEXT: Flags [ (0x2)
+# CONTENT-NEXT:   SHF_ALLOC (0x2)
+# CONTENT-NEXT: ]
+# CONTENT-NEXT: Address: 0x0
+# CONTENT-NEXT: Offset: 0x40
+# CONTENT-NEXT: Size: 3
+# CONTENT-NEXT: Link: 0
+# CONTENT-NEXT: Info: 1
+# CONTENT-NEXT: AddressAlignment: 0
+# CONTENT-NEXT: EntrySize: 0
+# CONTENT-NEXT: SectionData (
+# CONTENT-NEXT:   0000: 112233
+# CONTENT-NEXT: )
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_EXEC
+  Machine: EM_X86_64
+Sections:
+  - Name:    .gnu.version_r
+    Type:    SHT_GNU_verneed
+    Flags:   [ SHF_ALLOC ]
+    Info:    0x1
+    Content: "112233"
+
+## Check we can omit "Content" and "Dependencies" fields to produce an empty SHT_GNU_verneed section.
+
+# RUN: yaml2obj --docnum=3 %s -o %t3
+# RUN: llvm-readelf --sections %t3 | FileCheck %s --check-prefix=NO-PROPS
+
+# NO-PROPS: [Nr] Name           Type    Address          Off    Size
+# NO-PROPS: [ 1] .gnu.version_r VERNEED 0000000000000000 000040 000000
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_EXEC
+  Machine: EM_X86_64
+Sections:
+  - Name:  .gnu.version_r
+    Type:  SHT_GNU_verneed
+    Flags: [ SHF_ALLOC ]
+    Info:  0x0
+
+## Check we can't use both "Dependencies" and "Content" together.
+
+# RUN: not yaml2obj --docnum=4 %s 2>&1 | FileCheck %s --check-prefix=BOTH
+
+# BOTH: error: SHT_GNU_verneed: "Dependencies" and "Content" can't be used together
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_EXEC
+  Machine: EM_X86_64
+Sections:
+  - Name:         .gnu.version_r
+    Type:         SHT_GNU_verneed
+    Flags:        [ SHF_ALLOC ]
+    Info:         0x0
+    Content:      ""
+    Dependencies: []

tools/obj2yaml/elf2yaml.cpp

@@ -993,6 +993,8 @@ ELFDumper<ELFT>::dumpVerneedSection(const Elf_Shdr *Shdr) {
   if (!StringTableOrErr)
     return StringTableOrErr.takeError();
 
+  S->VerneedV.emplace();
+
   llvm::ArrayRef<uint8_t> Data = *Contents;
   const uint8_t *Buf = Data.data();
   while (Buf) {
@@ -1019,7 +1021,7 @@ ELFDumper<ELFT>::dumpVerneedSection(const Elf_Shdr *Shdr) {
       BufAux = Vernaux->vna_next ? BufAux + Vernaux->vna_next : nullptr;
     }
 
-    S->VerneedV.push_back(Entry);
+    S->VerneedV->push_back(Entry);
     Buf = Verneed->vn_next ? Buf + Verneed->vn_next : nullptr;
   }