[yaml2obj] Make e_phoff and e_phentsize 0 if there are no program headers

Summary: It says [[ http://www.sco.com/developers/gabi/latest/ch4.eheader.html | here ]] that if there are no program headers than e_phoff should be 0, but currently it is always set after the header. GNU's `readelf` (but not `llvm-readelf`) complains about this: `readelf: Warning: possibly corrupt ELF header - it has a non-zero program header offset, but no program headers`.

Reviewers: jhenderson, grimar, MaskRay, rupprecht

Reviewed By: jhenderson, grimar, MaskRay

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D67054

llvm-svn: 371162

Author: abrachet

llvm/lib/ObjectYAML/ELFEmitter.cpp

@@ -224,10 +224,10 @@ void ELFState<ELFT>::writeELFHeader(ContiguousBlobAccumulator &CBA, raw_ostream
   Header.e_machine = Doc.Header.Machine;
   Header.e_version = EV_CURRENT;
   Header.e_entry = Doc.Header.Entry;
-  Header.e_phoff = sizeof(Header);
+  Header.e_phoff = Doc.ProgramHeaders.size() ? sizeof(Header) : 0;
   Header.e_flags = Doc.Header.Flags;
   Header.e_ehsize = sizeof(Elf_Ehdr);
-  Header.e_phentsize = sizeof(Elf_Phdr);
+  Header.e_phentsize = Doc.ProgramHeaders.size() ? sizeof(Elf_Phdr) : 0;
   Header.e_phnum = Doc.ProgramHeaders.size();
 
   Header.e_shentsize =

llvm/test/tools/yaml2obj/elf-no-phdrs.yaml

@@ -0,0 +1,15 @@
+## Check that e_phoff and e_phentsize are set to 0 when there are no
+## program headers.
+
+# RUN: yaml2obj %s -o %t
+# RUN: llvm-readobj --file-headers %t | FileCheck %s
+
+# CHECK: ProgramHeaderOffset: 0x0{{$}}
+# CHECK: ProgramHeaderEntrySize: 0{{$}}
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_X86_64