[yaml2obj] - Allow producing ELFDATANONE ELFs

[grimar]

Summary

I need this to remove a binary from LLD test suite.
The patch also simplifies the code a bit.

[grimar]

That is not enough it seems. Planning change.

[grimar]

This is fine as is. Just LLD side requires a slightly more complex test than I expected initially.
It is: https://reviews.llvm.org/D59085

[jhenderson]

What about support for other invalid data encodings e.g. 3, 4 etc?

lib/ObjectYAML/ELFYAML.cpp

235–236 ↗

(On Diff #189667)

I'd completely rewrite the first part of the sentence, up to the comma as "ELFDATANONE is an invalid data encoding, ..."
"because want" -> "because we want"
Remove the quotes around "invalid"

test/tools/yaml2obj/elf-header-data.yaml

1 ↗

(On Diff #189667)

Please name this test after ELFDATANONE, e.g. elfdatanone.yaml or elf-header-elfdatanone.aml etc?

6 ↗

(On Diff #189667)

What about llvm-objdump? I'm guessing they all rely on the same Object library, so all get the error from the same place?

Perhaps a better test is to show using something like od that the byte at EI_DATA is 0?

[grimar]

In D59082#1421321, @jhenderson wrote:

What about support for other invalid data encodings e.g. 3, 4 etc?

I do not have a use case for that, so I am not sure it is worth to think about that atm.

[grimar]

• Addressed review comments.

test/tools/yaml2obj/elf-header-data.yaml

6 ↗

(On Diff #189667)

What about llvm-objdump? I'm guessing they all rely on the same Object library, so all get the error from the same place?

Yes.

Perhaps a better test is to show using something like od that the byte at EI_DATA is 0?

Done, thanks for the hint about od!

[jhenderson]

test/tools/yaml2obj/elf-header-elfdatanone.yaml

1 ↗

(On Diff #189687)

YAML -> "YAML file" or "YAML input"

[jhenderson]

LGTM, with one nit.

llvm/lib/ObjectYAML/ELFYAML.cpp

#define ECase(X) IO.enumCase(Value, #X, ELF::X)
   ECase(ELFCLASS32);
   ECase(ELFCLASS64);
 #undef ECase
 }
 
 void ScalarEnumerationTraits<ELFYAML::ELF_ELFDATA>::enumeration(
     IO &IO, ELFYAML::ELF_ELFDATA &Value) {
 #define ECase(X) IO.enumCase(Value, #X, ELF::X)
-  // Since the semantics of ELFDATANONE is "invalid", just don't accept it
-  // here.
+  // ELFDATANONE is an invalid data encoding, but we accept it because
+  // we want to be able to produce invalid binaries for the tests.
+  ECase(ELFDATANONE);
   ECase(ELFDATA2LSB);
   ECase(ELFDATA2MSB);
 #undef ECase
 }
 
 void ScalarEnumerationTraits<ELFYAML::ELF_ELFOSABI>::enumeration(
     IO &IO, ELFYAML::ELF_ELFOSABI &Value) {
 #define ECase(X) IO.enumCase(Value, #X, ELF::X)

llvm/test/tools/yaml2obj/elf-header-elfdatanone.yaml

+## We have a YAML file describing an invalid data type.
+## Check we are able to produce the invalid binary.
+
+# RUN: yaml2obj %s -o %t.o
+
+## Check that EI_DATA field is ELFDATANONE(0)
+# RUN:   od -b %t.o +5 | FileCheck %s
+# CHECK: 0000005 000
+
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATANONE
+  Type:            ET_REL
+  Machine:         EM_X86_64

llvm/tools/yaml2obj/yaml2elf.cpp

 void ELFState<ELFT>::initELFHeader(Elf_Ehdr &Header) {
   using namespace llvm::ELF;
   zero(Header);
   Header.e_ident[EI_MAG0] = 0x7f;
   Header.e_ident[EI_MAG1] = 'E';
   Header.e_ident[EI_MAG2] = 'L';
   Header.e_ident[EI_MAG3] = 'F';
   Header.e_ident[EI_CLASS] = ELFT::Is64Bits ? ELFCLASS64 : ELFCLASS32;
-  bool IsLittleEndian = ELFT::TargetEndianness == support::little;
-  Header.e_ident[EI_DATA] = IsLittleEndian ? ELFDATA2LSB : ELFDATA2MSB;
+  Header.e_ident[EI_DATA] = Doc.Header.Data;
   Header.e_ident[EI_VERSION] = EV_CURRENT;
   Header.e_ident[EI_OSABI] = Doc.Header.OSABI;
   Header.e_ident[EI_ABIVERSION] = Doc.Header.ABIVersion;
   Header.e_type = Doc.Header.Type;
   Header.e_machine = Doc.Header.Machine;
   Header.e_version = EV_CURRENT;
   Header.e_entry = Doc.Header.Entry;
   Header.e_phoff = sizeof(Header);