[yaml2obj] - Add a support for changing EntSize.

[grimar]

Summary

I was trying to add a test case for LLD and found that it
is impossible to set sh_entsize via yaml.
The patch implements the missing part.

I am sorry, I do not know who is an appropriate reviewer for that,
so added people who seem were involved in recent changes to yaml2obj.

[jhenderson]

tools/yaml2obj/yaml2elf.cpp

464–466

What if a user explicitly requests EntSize 0? I would expect that to override the defaults as much as 1 does.

[grimar]

tools/yaml2obj/yaml2elf.cpp

464–466

Interesting case, but should we support it right how?

[jhenderson]

tools/yaml2obj/yaml2elf.cpp

464–466

I don't think it's any different a case to EntSize 1, 2 etc in a SHT_RELR/DYNAMIC etc section.

We could avoid it by using the explicit value only when the section type doesn't imply it, but I'd rather keep the explicit version.

[grimar]

• Addressed review comments.

[jhenderson]

LGTM with one nit.

test/tools/yaml2obj/elf-ent-size.yaml

25

I'm not sure you want this line here at all. Just start the CHECK sequence with the next line.

[grimar]

Thanks, James!

include/llvm/ObjectYAML/ELFYAML.h

struct Section {
   SectionKind Kind;
   StringRef Name;
   ELF_SHT Type;
   ELF_SHF Flags;
   llvm::yaml::Hex64 Address;
   StringRef Link;
   StringRef Info;
   llvm::yaml::Hex64 AddressAlign;
+  Optional<llvm::yaml::Hex64> EntSize;
 
   Section(SectionKind Kind) : Kind(Kind) {}
   virtual ~Section();
 };
 struct RawContentSection : Section {
   yaml::BinaryRef Content;
   llvm::yaml::Hex64 Size;
 

lib/ObjectYAML/ELFYAML.cpp

 
 static void commonSectionMapping(IO &IO, ELFYAML::Section &Section) {
   IO.mapOptional("Name", Section.Name, StringRef());
   IO.mapRequired("Type", Section.Type);
   IO.mapOptional("Flags", Section.Flags, ELFYAML::ELF_SHF(0));
   IO.mapOptional("Address", Section.Address, Hex64(0));
   IO.mapOptional("Link", Section.Link, StringRef());
   IO.mapOptional("AddressAlign", Section.AddressAlign, Hex64(0));
+  IO.mapOptional("EntSize", Section.EntSize);
   IO.mapOptional("Info", Section.Info, StringRef());
 }
 
 static void sectionMapping(IO &IO, ELFYAML::RawContentSection &Section) {
   commonSectionMapping(IO, Section);
   IO.mapOptional("Content", Section.Content);
   IO.mapOptional("Size", Section.Size, Hex64(Section.Content.binary_size()));
 }

test/tools/yaml2obj/elf-ent-size.yaml

+# RUN: yaml2obj %s -o %t
+# RUN: llvm-readobj -sections %t | FileCheck %s
+
+!ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  OSABI:           ELFOSABI_FREEBSD
+  Type:            ET_REL
+  Machine:         EM_X86_64
+Sections:
+  - Type:            SHT_PROGBITS
+    Name:            .strings
+    Flags:           [ SHF_ALLOC, SHF_MERGE, SHF_STRINGS ]
+    AddressAlign:    0x04
+    Content:         "FFFFFFFFFFFFFFFF"
+    EntSize:         0x1
+  - Name:            .mydynamic
+    Type:            SHT_DYNAMIC
+    EntSize:         0x0
+
+
+## Check we were able to set entry size for .strings and .mydynamic
+# CHECK:      Section {
+# CHECK:        Index: 1
+# CHECK-NEXT:   Name: .strings
+# CHECK-NEXT:   Type: SHT_PROGBITS
+# CHECK-NEXT:   Flags [
+# CHECK-NEXT:     SHF_ALLOC
+# CHECK-NEXT:     SHF_MERGE
+# CHECK-NEXT:     SHF_STRINGS
+# CHECK-NEXT:   ]
+# CHECK-NEXT:   Address:
+# CHECK-NEXT:   Offset:
+# CHECK-NEXT:   Size:
+# CHECK-NEXT:   Link:
+# CHECK-NEXT:   Info:
+# CHECK-NEXT:   AddressAlignment:
+# CHECK-NEXT:   EntrySize: 1
+# CHECK-NEXT: }
+# CHECK-NEXT: Section {
+# CHECK-NEXT:   Index:
+# CHECK-NEXT:   Name: .mydynamic
+# CHECK-NEXT:   Type: SHT_DYNAMIC
+# CHECK-NEXT:   Flags [
+# CHECK-NEXT:   ]
+# CHECK-NEXT:   Address:
+# CHECK-NEXT:   Offset:
+# CHECK-NEXT:   Size:
+# CHECK-NEXT:   Link:
+# CHECK-NEXT:   Info:
+# CHECK-NEXT:   AddressAlignment:
+# CHECK-NEXT:   EntrySize: 0
+# CHECK-NEXT: }

tools/yaml2obj/yaml2elf.cpp

ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
                                     ContiguousBlobAccumulator &CBA) {
   assert(Section.Size >= Section.Content.binary_size() &&
          "Section size and section content are inconsistent");
   raw_ostream &OS =
       CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
   Section.Content.writeAsBinary(OS);
   for (auto i = Section.Content.binary_size(); i < Section.Size; ++i)
     OS.write(0);
-  if (Section.Type == llvm::ELF::SHT_RELR)
+  if (Section.EntSize)
+    SHeader.sh_entsize = *Section.EntSize;
+  else if (Section.Type == llvm::ELF::SHT_RELR)
     SHeader.sh_entsize = sizeof(Elf_Relr);
   else if (Section.Type == llvm::ELF::SHT_DYNAMIC)
     SHeader.sh_entsize = sizeof(Elf_Dyn);
   else
     SHeader.sh_entsize = 0;
   SHeader.sh_size = Section.Size;
 }