[yaml2obj] - Allow overriding e_shentsize, e_shoff, e_shnum and e_shstrndx fields in the YAML.

This allows setting different values for e_shentsize, e_shoff, e_shnum
and e_shstrndx fields and is useful for producing broken inputs for various
test cases.

Differential revision: https://reviews.llvm.org/D63771

llvm-svn: 364517

llvm/include/llvm/ObjectYAML/ELFYAML.h

@@ -75,6 +75,11 @@ struct FileHeader {
   ELF_EM Machine;
   ELF_EF Flags;
   llvm::yaml::Hex64 Entry;
+
+  Optional<llvm::yaml::Hex16> SHEntSize;
+  Optional<llvm::yaml::Hex16> SHOffset;
+  Optional<llvm::yaml::Hex16> SHNum;
+  Optional<llvm::yaml::Hex16> SHStrNdx;
 };
 
 struct SectionName {

llvm/lib/ObjectYAML/ELFYAML.cpp

@@ -842,6 +842,11 @@ void MappingTraits<ELFYAML::FileHeader>::mapping(IO &IO,
   IO.mapRequired("Machine", FileHdr.Machine);
   IO.mapOptional("Flags", FileHdr.Flags, ELFYAML::ELF_EF(0));
   IO.mapOptional("Entry", FileHdr.Entry, Hex64(0));
+
+  IO.mapOptional("SHEntSize", FileHdr.SHEntSize);
+  IO.mapOptional("SHOffset", FileHdr.SHOffset);
+  IO.mapOptional("SHNum", FileHdr.SHNum);
+  IO.mapOptional("SHStrNdx", FileHdr.SHStrNdx);
 }
 
 void MappingTraits<ELFYAML::ProgramHeader>::mapping(

llvm/test/tools/yaml2obj/elf-header-sh-fields.yaml

@@ -0,0 +1,61 @@
+## In this test case we check that we can override the default values for
+## e_shentsize, e_shoff, e_shnum and e_shstrndx fields in the YAML.
+
+## First we check the default values.
+
+# RUN: yaml2obj --docnum=1 %s -o %t1
+# RUN: llvm-readelf --file-headers %t1 | FileCheck %s --check-prefix=DEFAULT
+
+# DEFAULT:   Start of section headers:          64 (bytes into file)
+# DEFAULT:   Size of section headers:           64 (bytes)
+# DEFAULT:   Number of section headers:         4
+# DEFAULT:   Section header string table index: 3
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_X86_64
+
+## Override 3 fields: e_shoff, e_shnum and e_shstrndx. Check the output.
+
+# RUN: yaml2obj --docnum=2 %s -o %t2
+# RUN: llvm-readelf --file-headers %t2 | FileCheck %s --check-prefix=CUSTOM
+
+# CUSTOM: Start of section headers:          2 (bytes into file)
+# CUSTOM: Size of section headers:           64 (bytes)
+# CUSTOM: Number of section headers:         3
+# CUSTOM: Section header string table index: 4
+
+--- !ELF
+FileHeader:
+  Class:     ELFCLASS64
+  Data:      ELFDATA2LSB
+  Type:      ET_REL
+  Machine:   EM_X86_64
+  SHEntSize: 64
+  SHOffset:  2
+  SHNum:     3
+  SHStrNdx:  4
+
+## Finally, we use the same YAML as above, but set e_shentsize to 1.
+## Check the result using raw output from 'od' because llvm-readelf
+## is unable to dump such headers.
+
+# RUN: yaml2obj --docnum=3 %s -o %t3
+# RUN: od -t x1 -v -j 0x3a -N 1 %t3 | FileCheck %s --check-prefix=NEWSIZE
+# RUN: od -t x1 -v -j 0x3a -N 1 %t2 | FileCheck %s --check-prefix=OLDSIZE
+# NEWSIZE: 0000072 01
+# OLDSIZE: 0000072 40
+
+--- !ELF
+FileHeader:
+  Class:     ELFCLASS64
+  Data:      ELFDATA2LSB
+  Type:      ET_REL
+  Machine:   EM_X86_64
+  SHEntSize: 1
+  SHOffset:  2
+  SHNum:     3
+  SHStrNdx:  4

llvm/tools/obj2yaml/elf2yaml.cpp

@@ -137,7 +137,9 @@ ELFDumper<ELFT>::getUniquedSymbolName(const Elf_Sym *Sym, StringRef StrTable,
 template <class ELFT> ErrorOr<ELFYAML::Object *> ELFDumper<ELFT>::dump() {
   auto Y = make_unique<ELFYAML::Object>();
 
-  // Dump header
+  // Dump header. We do not dump SHEntSize, SHOffset, SHNum and SHStrNdx field.
+  // When not explicitly set, the values are set by yaml2obj automatically
+  // and there is no need to dump them here.
   Y->Header.Class = ELFYAML::ELF_ELFCLASS(Obj.getHeader()->getFileClass());
   Y->Header.Data = ELFYAML::ELF_ELFDATA(Obj.getHeader()->getDataEncoding());
   Y->Header.OSABI = Obj.getHeader()->e_ident[ELF::EI_OSABI];

llvm/tools/yaml2obj/yaml2elf.cpp

@@ -208,12 +208,18 @@ void ELFState<ELFT>::initELFHeader(Elf_Ehdr &Header) {
   Header.e_ehsize = sizeof(Elf_Ehdr);
   Header.e_phentsize = sizeof(Elf_Phdr);
   Header.e_phnum = Doc.ProgramHeaders.size();
-  Header.e_shentsize = sizeof(Elf_Shdr);
+
+  Header.e_shentsize =
+      Doc.Header.SHEntSize ? (uint16_t)*Doc.Header.SHEntSize : sizeof(Elf_Shdr);
   // Immediately following the ELF header and program headers.
   Header.e_shoff =
-      sizeof(Header) + sizeof(Elf_Phdr) * Doc.ProgramHeaders.size();
-  Header.e_shnum = SN2I.size() + 1;
-  Header.e_shstrndx = SN2I.get(".shstrtab");
+      Doc.Header.SHOffset
+          ? (uint16_t)*Doc.Header.SHOffset
+          : sizeof(Header) + sizeof(Elf_Phdr) * Doc.ProgramHeaders.size();
+  Header.e_shnum =
+      Doc.Header.SHNum ? (uint16_t)*Doc.Header.SHNum : SN2I.size() + 1;
+  Header.e_shstrndx = Doc.Header.SHStrNdx ? (uint16_t)*Doc.Header.SHStrNdx
+                                          : SN2I.get(".shstrtab");
 }
 
 template <class ELFT>