[yaml2obj] - Add NBucket and NChain fields for the SHT_HASH section.

These fields allows to override nchain and nbucket fields of a SHT_HASH section.

Differential revision: https://reviews.llvm.org/D76834

llvm/include/llvm/ObjectYAML/ELFYAML.h

@@ -282,6 +282,11 @@ struct HashSection : Section {
   Optional<std::vector<uint32_t>> Bucket;
   Optional<std::vector<uint32_t>> Chain;
 
+  // The following members are used to override section fields.
+  // This is useful for creating invalid objects.
+  Optional<llvm::yaml::Hex64> NBucket;
+  Optional<llvm::yaml::Hex64> NChain;
+
   HashSection() : Section(ChunkKind::Hash) {}
 
   static bool classof(const Chunk *S) { return S->Kind == ChunkKind::Hash; }

llvm/lib/ObjectYAML/ELFEmitter.cpp

@@ -1065,10 +1065,13 @@ void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
     return;
   }
 
-  support::endian::write<uint32_t>(OS, Section.Bucket->size(),
-                                   ELFT::TargetEndianness);
-  support::endian::write<uint32_t>(OS, Section.Chain->size(),
-                                   ELFT::TargetEndianness);
+  support::endian::write<uint32_t>(
+      OS, Section.NBucket.getValueOr(llvm::yaml::Hex64(Section.Bucket->size())),
+      ELFT::TargetEndianness);
+  support::endian::write<uint32_t>(
+      OS, Section.NChain.getValueOr(llvm::yaml::Hex64(Section.Chain->size())),
+      ELFT::TargetEndianness);
+
   for (uint32_t Val : *Section.Bucket)
     support::endian::write<uint32_t>(OS, Val, ELFT::TargetEndianness);
   for (uint32_t Val : *Section.Chain)

llvm/lib/ObjectYAML/ELFYAML.cpp

@@ -1091,6 +1091,13 @@ static void sectionMapping(IO &IO, ELFYAML::HashSection &Section) {
   IO.mapOptional("Bucket", Section.Bucket);
   IO.mapOptional("Chain", Section.Chain);
   IO.mapOptional("Size", Section.Size);
+
+  // obj2yaml does not dump these fields. They can be used to override nchain
+  // and nbucket values for creating broken sections.
+  assert(!IO.outputting() ||
+         (!Section.NBucket.hasValue() && !Section.NChain.hasValue()));
+  IO.mapOptional("NChain", Section.NChain);
+  IO.mapOptional("NBucket", Section.NBucket);
 }
 
 static void sectionMapping(IO &IO, ELFYAML::NoteSection &Section) {

llvm/test/tools/yaml2obj/ELF/hash-section.yaml

@@ -276,3 +276,39 @@ Sections:
     Type: SHT_HASH
     Size: 0x1
     Chain: [ 1 ]
+
+## Check we can override "nbucket" and "nchain" values of a SHT_HASH section using "NBucket"
+## and "NChain" tags. Check that the section size is unaffected when we do this.
+
+# RUN: yaml2obj --docnum=14 %s -o %t14
+# RUN: llvm-readobj --sections --section-data %t14 | FileCheck %s --check-prefix=OVERRIDE
+
+# OVERRIDE:      Name: .hash
+# OVERRIDE-NEXT: Type: SHT_HASH
+# OVERRIDE-NEXT: Flags [
+# OVERRIDE-NEXT: ]
+# OVERRIDE-NEXT: Address: 0x0
+# OVERRIDE-NEXT: Offset: 0x34
+# OVERRIDE-NEXT: Size: 28
+# OVERRIDE-NEXT: Link: 0
+# OVERRIDE-NEXT: Info: 0
+# OVERRIDE-NEXT: AddressAlignment: 0
+# OVERRIDE-NEXT: EntrySize: 0
+# OVERRIDE-NEXT: SectionData (
+# OVERRIDE-NEXT:   0000: AA000000 BB000000 01000000 02000000
+# OVERRIDE-NEXT:   0010: 03000000 04000000 05000000
+# OVERRIDE-NEXT: )
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS32
+  Data:    ELFDATA2LSB
+  Type:    ET_DYN
+  Machine: EM_386
+Sections:
+  - Name:   .hash
+    Type:   SHT_HASH
+    Bucket: [ 1, 2 ]
+    Chain:  [ 3, 4, 5 ]
+    NBucket: 0xAA
+    NChain:  0xBB