[yaml2obj][elf2yaml] - Add a support for the `EntSize` field for `SHT_HASH` sections.

[grimar]

Summary

Specification for SHT_HASH table says (https://refspecs.linuxbase.org/elf/gabi4+/ch5.dynamic.html#hash)
that it contains Elf32_Word entries for both 32/64 bit objects.

Currently both GNU linkers and LLD sets the sh_entsize field to 4.

At the same time, yaml2obj ignores the EntSize field for SHT_HASH sections.
This patch fixes this and also adds a support for obj2yaml: it will not
dump this field when the sh_entsize contains the default value (4).

[MaskRay]

LGTM.

llvm/lib/ObjectYAML/ELFEmitter.cpp

 void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
                                          const ELFYAML::HashSection &Section,
                                          ContiguousBlobAccumulator &CBA) {
   unsigned Link = 0;
   if (Section.Link.empty() && !ExcludedSectionHeaders.count(".dynsym") &&
       SN2I.lookup(".dynsym", Link))
     SHeader.sh_link = Link;
 
+  if (Section.EntSize)
+    SHeader.sh_entsize = *Section.EntSize;
+  else
+    SHeader.sh_entsize = sizeof(typename ELFT::Word);
+
   if (Section.Content || Section.Size) {
     SHeader.sh_size = writeContent(CBA, Section.Content, Section.Size);
     return;
   }
 
   CBA.write<uint32_t>(
       Section.NBucket.getValueOr(llvm::yaml::Hex64(Section.Bucket->size())),
       ELFT::TargetEndianness);

llvm/test/tools/obj2yaml/ELF/hash-section.yaml

##         Section size is less than (2 * nbucket + nchain) * 4.
   - Name:    .truncated
     Type:    SHT_HASH
     Content: '01000000020000000300000004000000'
 ## Case 4: nbucket == 1, nchain == 2.
 ##         Section size is greater than (2 * nbucket + nchain) * 4.
   - Name:    .oversized
     Type:    SHT_HASH
     Content: '0100000002000000030000000400000000'
+
+## Check how we dump the "EntSize" field. When the sh_entsize is 4,
+## we don't print it, because it is the default value for the SHT_HASH section.
+
+# RUN: yaml2obj --docnum=3 %s -o %t3
+# RUN: obj2yaml %t3 | FileCheck %s --check-prefix=ENT-SIZE
+
+# ENT-SIZE:      - Name:    .hash.entsize.0
+# ENT-SIZE-NEXT:   Type:    SHT_HASH
+# ENT-SIZE-NEXT:   EntSize: 0x0000000000000000
+# ENT-SIZE-NEXT:   Content: ''
+# ENT-SIZE-NEXT: - Name:    .hash.entsize.4.default
+# ENT-SIZE-NEXT:   Type:    SHT_HASH
+# ENT-SIZE-NEXT:   Content: ''
+# ENT-SIZE-NEXT: - Name:    .hash.entsize.255
+# ENT-SIZE-NEXT:   Type:    SHT_HASH
+# ENT-SIZE-NEXT:   EntSize: 0x00000000000000FF
+# ENT-SIZE-NEXT:   Content: ''
+
+--- !ELF
+FileHeader:
+  Class: ELFCLASS32
+  Data:  ELFDATA2LSB
+  Type:  ET_DYN
+Sections:
+  - Name:    .hash.entsize.0
+    Type:    SHT_HASH
+    EntSize: 0
+    Size:    0
+  - Name:    .hash.entsize.4.default
+    Type:    SHT_HASH
+    EntSize: 4
+    Size:    0
+  - Name:    .hash.entsize.255
+    Type:    SHT_HASH
+    EntSize: 255
+    Size:    0

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

 ## Check how yaml2obj produces SHT_HASH sections.
 
 ## Check we can describe a SHT_HASH section using the "Content" tag.
+## Check default values of section fields.
 
 # RUN: yaml2obj --docnum=1 %s -o %t1
-# RUN: llvm-readobj --sections --section-data %t1 | FileCheck %s --check-prefix=CONTENT
+# RUN: llvm-readobj --sections --section-data %t1 | \
+# RUN:   FileCheck %s -DENTSIZE=4 --check-prefix=CONTENT
 
 # CONTENT:      Name: .hash
 # CONTENT-NEXT: Type: SHT_HASH
 # CONTENT-NEXT: Flags [
 # CONTENT-NEXT: ]
 # CONTENT-NEXT: Address: 0x0
 # CONTENT-NEXT: Offset: 0x44
 # CONTENT-NEXT: Size: 20
 # CONTENT-NEXT: Link: 1
 # CONTENT-NEXT: Info: 0
 # CONTENT-NEXT: AddressAlignment: 0
-# CONTENT-NEXT: EntrySize: 0
+# CONTENT-NEXT: EntrySize: [[ENTSIZE]]{{$}}
 # CONTENT-NEXT: SectionData (
 # CONTENT-NEXT:   0000: 01000000 02000000 03000000 04000000
 # CONTENT-NEXT:   0010: 05000000
 # CONTENT-NEXT: )
 
 --- !ELF
 FileHeader:
   Class: ELFCLASS32
   Data:  ELFDATA2LSB
   Type:  ET_DYN
 Sections:
 ## SHT_HASH is linked to dynamic symbol table by default.
   - Name: .dynsym
     Type: SHT_DYNSYM
   - Name:    .hash
     Type:    SHT_HASH
     Content: '0100000002000000030000000400000005000000'
+    EntSize: [[ENTSIZE=<none>]]
+
+## Check we can set an arbitrary entry size for the SHT_HASH section.
+
+# RUN: yaml2obj --docnum=1 -DENTSIZE=0xFF %s -o %t1.entsize
+# RUN: llvm-readobj --sections --section-data %t1.entsize | \
+# RUN:   FileCheck %s -DENTSIZE=255 --check-prefix=CONTENT
 
 ## Check we can describe a SHT_HASH section using "Bucket" and "Chain" tags.
 
 # RUN: yaml2obj --docnum=2 %s -o %t2
 # RUN: llvm-readobj --sections --section-data %t2 | FileCheck %s --check-prefix=BUCKET-CHAIN
 
 # BUCKET-CHAIN:      Name: .hash
 # BUCKET-CHAIN:      Size:

 # 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: EntrySize: 4
 # OVERRIDE-NEXT: SectionData (
 # OVERRIDE-NEXT:   0000: AA000000 BB000000 01000000 02000000
 # OVERRIDE-NEXT:   0010: 03000000 04000000 05000000
 # OVERRIDE-NEXT: )
 
 --- !ELF
 FileHeader:
   Class: ELFCLASS32

llvm/test/tools/yaml2obj/ELF/section-headers-exclude.yaml

Excluded:
     - Name: .symtab
 
 ## Case H: check we do not link SHT_HASH/SHT_GNU_HASH sections with .dynsym
 ##         implicitly when the latter is excluded.
 # RUN: yaml2obj %s --docnum=16 -o %t8
 # RUN: llvm-readelf %t8 --section-headers | FileCheck %s --check-prefix=LINK-HASH
 
 # LINK-HASH:      [Nr] Name      Type     Address          Off    Size   ES Flg Lk Inf Al
-# LINK-HASH:      [ 1] .hash     HASH     0000000000000000 000040 000000 00      0   0  0
+# LINK-HASH:      [ 1] .hash     HASH     0000000000000000 000040 000000 04      0   0  0
 # LINK-HASH-NEXT: [ 2] .gnu_hash GNU_HASH 0000000000000000 000040 000000 00      0   0  0
 
 --- !ELF
 FileHeader:
   Class: ELFCLASS64
   Data:  ELFDATA2LSB
   Type:  ET_DYN
 Sections:

llvm/tools/obj2yaml/elf2yaml.cpp

static unsigned getDefaultShEntSize(ELFYAML::ELF_SHT SecType,
   case ELF::SHT_REL:
     return sizeof(typename ELFT::Rel);
   case ELF::SHT_RELA:
     return sizeof(typename ELFT::Rela);
   case ELF::SHT_RELR:
     return sizeof(typename ELFT::Relr);
   case ELF::SHT_DYNAMIC:
     return sizeof(typename ELFT::Dyn);
+  case ELF::SHT_HASH:
+    return sizeof(typename ELFT::Word);
   default:
     if (SecName == ".debug_str")
       return 1;
     return 0;
   }
 }
 
 template <class ELFT>