[yaml2obj] - Allow setting st_value explicitly for Symbol.

In some cases it is useful to explicitly set symbol's st_name value.
For example, I am using it in a patch for LLD to remove the broken
binary from a test case and replace it with a YAML test.

Differential revision: https://reviews.llvm.org/D61180

llvm-svn: 360137

include/llvm/ObjectYAML/ELFYAML.h

@@ -95,6 +95,7 @@ struct ProgramHeader {
 
 struct Symbol {
   StringRef Name;
+  Optional<uint32_t> NameIndex;
   ELF_STT Type;
   StringRef Section;
   Optional<ELF_SHN> Index;

lib/ObjectYAML/ELFYAML.cpp

@@ -854,6 +854,7 @@ struct NormalizedOther {
 
 void MappingTraits<ELFYAML::Symbol>::mapping(IO &IO, ELFYAML::Symbol &Symbol) {
   IO.mapOptional("Name", Symbol.Name, StringRef());
+  IO.mapOptional("NameIndex", Symbol.NameIndex);
   IO.mapOptional("Type", Symbol.Type, ELFYAML::ELF_STT(0));
   IO.mapOptional("Section", Symbol.Section, StringRef());
   IO.mapOptional("Index", Symbol.Index);
@@ -867,12 +868,12 @@ void MappingTraits<ELFYAML::Symbol>::mapping(IO &IO, ELFYAML::Symbol &Symbol) {
 
 StringRef MappingTraits<ELFYAML::Symbol>::validate(IO &IO,
                                                    ELFYAML::Symbol &Symbol) {
-  if (Symbol.Index && Symbol.Section.data()) {
+  if (Symbol.Index && Symbol.Section.data())
     return "Index and Section cannot both be specified for Symbol";
-  }
-  if (Symbol.Index && *Symbol.Index == ELFYAML::ELF_SHN(ELF::SHN_XINDEX)) {
+  if (Symbol.Index && *Symbol.Index == ELFYAML::ELF_SHN(ELF::SHN_XINDEX))
     return "Large indexes are not supported";
-  }
+  if (Symbol.NameIndex && !Symbol.Name.empty())
+    return "Name and NameIndex cannot both be specified for Symbol";
   return StringRef();
 }
 

test/tools/yaml2obj/symbol-name.yaml

@@ -0,0 +1,37 @@
+## Check we are able to use integers as both
+## symbol name indices (st_name values) and symbol names.
+# RUN: yaml2obj --docnum=1 %s > %t
+# RUN: llvm-readobj --symbols %t | FileCheck %s
+
+# CHECK: Name: test (1)
+# CHECK: Name: test (1)
+# CHECK: Name: est (2)
+# CHECK: Name: 1 (8)
+# CHECK: Name: 2 (6)
+
+--- !ELF
+FileHeader:
+  Class:     ELFCLASS64
+  Data:      ELFDATA2LSB
+  Type:      ET_REL
+  Machine:   EM_X86_64
+Symbols:
+  - Name:      test
+  - NameIndex: 1
+  - NameIndex: 2
+  - Name:      1
+  - Name:      2
+
+## Check we do not allow specifying both Name and NameIndex at once.
+# RUN: not yaml2obj --docnum=2 %s 2>&1 | FileCheck %s --check-prefix=ERR
+# ERR: error: Name and NameIndex cannot both be specified for Symbol
+
+--- !ELF
+FileHeader:
+  Class:     ELFCLASS64
+  Data:      ELFDATA2LSB
+  Type:      ET_REL
+  Machine:   EM_X86_64
+Symbols:
+  - Name:      foo
+    NameIndex: 0

tools/yaml2obj/yaml2elf.cpp

@@ -468,8 +468,15 @@ void ELFState<ELFT>::addSymbols(ArrayRef<ELFYAML::Symbol> Symbols,
   for (const auto &Sym : Symbols) {
     Elf_Sym Symbol;
     zero(Symbol);
-    if (!Sym.Name.empty())
+
+    // If NameIndex, which contains the name offset, is explicitly specified, we
+    // use it. This is useful for preparing broken objects. Otherwise, we add
+    // the specified Name to the string table builder to get its offset.
+    if (Sym.NameIndex)
+      Symbol.st_name = *Sym.NameIndex;
+    else if (!Sym.Name.empty())
       Symbol.st_name = Strtab.getOffset(Sym.Name);
+
     Symbol.setBindingAndType(Sym.Binding, Sym.Type);
     if (!Sym.Section.empty()) {
       unsigned Index;