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

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`).

Differential revision: https://reviews.llvm.org/D88652

Author: Georgii Rymar

llvm/lib/ObjectYAML/ELFEmitter.cpp

@@ -1396,6 +1396,11 @@ void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
       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;

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

@@ -74,3 +74,40 @@ Sections:
   - 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

@@ -1,9 +1,11 @@
 ## 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
@@ -15,7 +17,7 @@
 # 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
@@ -33,6 +35,13 @@ Sections:
   - 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.
 
@@ -280,7 +289,7 @@ Sections:
 # 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

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

@@ -406,7 +406,7 @@ SectionHeaderTable:
 # 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

llvm/tools/obj2yaml/elf2yaml.cpp

@@ -659,6 +659,8 @@ static unsigned getDefaultShEntSize(ELFYAML::ELF_SHT SecType,
     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;