[yaml2obj] - Add a way to set sh_entsize for relocation sections.

We are missing ability to override the sh_entsize field for
SHT_REL[A] sections. It would be useful for writing test cases.

Differential revision: https://reviews.llvm.org/D73621

Author: Georgii Rymar

llvm/lib/ObjectYAML/ELFEmitter.cpp

@@ -796,8 +796,12 @@ void ELFState<ELFT>::writeSectionContent(
          "Section type is not SHT_REL nor SHT_RELA");
 
   bool IsRela = Section.Type == llvm::ELF::SHT_RELA;
-  SHeader.sh_entsize = IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
-  SHeader.sh_size = SHeader.sh_entsize * Section.Relocations.size();
+  if (Section.EntSize)
+    SHeader.sh_entsize = *Section.EntSize;
+  else
+    SHeader.sh_entsize = IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
+  SHeader.sh_size = (IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel)) *
+                    Section.Relocations.size();
 
   // For relocation section set link to .symtab by default.
   unsigned Link = 0;

llvm/test/tools/yaml2obj/ELF/reloc-sec-entry-size.yaml

@@ -0,0 +1,73 @@
+## Test how yaml2obj sets values for sh_entsize fields of relocation sections.
+
+# RUN: yaml2obj --docnum=1 %s -o %t64
+# RUN: llvm-readelf --sections %t64 | FileCheck %s --check-prefix=ELF64
+
+# RUN: yaml2obj --docnum=2 %s -o %t32
+# RUN: llvm-readelf --sections %t32 | FileCheck %s --check-prefix=ELF32
+
+# ELF64: Name          Type Address          Off    Size   ES
+# ELF64: .rela.default RELA 0000000000000000 000040 000000 18
+# ELF64: .rel.default  REL  0000000000000000 000040 000000 10
+# ELF64: .relr.default RELR 0000000000000000 000040 000000 08
+# ELF64: .rela.custom  RELA 0000000000000000 000040 000000 ff
+# ELF64: .rel.custom   REL  0000000000000000 000040 000000 ff
+# ELF64: .relr.custom  RELR 0000000000000000 000040 000000 ff
+
+# ELF32: Name          Type  Address  Off    Size   ES
+# ELF32: .rela.default RELA  00000000 000034 000000 0c
+# ELF32: .rel.default  REL   00000000 000034 000000 08
+# ELF32: .relr.default RELR  00000000 000034 000000 04
+# ELF32: .rela.custom  RELA  00000000 000034 000000 ff
+# ELF32: .rel.custom   REL   00000000 000034 000000 ff
+# ELF32: .relr.custom  RELR  00000000 000034 000000 ff
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_X86_64
+Sections:
+## Check default sh_entsize field values.
+  - Name: .rela.default
+    Type: SHT_RELA
+  - Name: .rel.default
+    Type: SHT_REL
+  - Name: .relr.default
+    Type: SHT_RELR
+## Check we can set sh_entsize fields to arbitrary values.
+  - Name:    .rela.custom
+    Type:    SHT_RELA
+    EntSize: 0xFF
+  - Name:    .rel.custom
+    Type:    SHT_REL
+    EntSize: 0xFF
+  - Name:    .relr.custom
+    Type:    SHT_RELR
+    EntSize: 0xFF
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS32
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_386
+Sections:
+## Check default sh_entsizes field values.
+  - Name: .rela.default
+    Type: SHT_RELA
+  - Name: .rel.default
+    Type: SHT_REL
+  - Name: .relr.default
+    Type: SHT_RELR
+## Check we can set sh_entsize fields to arbitrary values.
+  - Name:    .rela.custom
+    Type:    SHT_RELA
+    EntSize: 0xFF
+  - Name:    .rel.custom
+    Type:    SHT_REL
+    EntSize: 0xFF
+  - Name:    .relr.custom
+    Type:    SHT_RELR
+    EntSize: 0xFF