[yaml2obj] - Make DynamicSymbols to be Optional<> too.

We already have Symbols property to list regular symbols and
it is currently Optional<>. This patch makes DynamicSymbols to be optional
too. With this there is no need to define a dummy symbol anymore to trigger
creation of the .dynsym and it is now possible to define an empty .dynsym using
just the following line:

DynamicSymbols: []
(it is important to have when you do not want to have dynamic symbols,
but want to have a .dynsym)

Now the code is consistent and it helped to fix a bug: previously we
did not report an error when both Content/Size and an empty
Symbols/DynamicSymbols list were specified.

Differential revision: https://reviews.llvm.org/D70956

1 files changed, 21 insertions, 16 deletions

diff --git a/llvm/lib/ObjectYAML/ELFEmitter.cpp b/llvm/lib/ObjectYAML/ELFEmitter.cpp
index 37eeb01fb09..d2e6fdfea00 100644
--- a/llvm/lib/ObjectYAML/ELFEmitter.cpp
+++ b/llvm/lib/ObjectYAML/ELFEmitter.cpp
@@ -248,7 +248,7 @@ ELFState<ELFT>::ELFState(ELFYAML::Object &D, yaml::ErrorHandler EH)
     ImplicitSections.push_back(".symtab");
   ImplicitSections.insert(ImplicitSections.end(), {".strtab", ".shstrtab"});
 
-  if (!Doc.DynamicSymbols.empty())
+  if (Doc.DynamicSymbols)
     ImplicitSections.insert(ImplicitSections.end(), {".dynsym", ".dynstr"});
 
   // Insert placeholders for implicit sections that are not
@@ -562,21 +562,24 @@ void ELFState<ELFT>::initSymtabSectionHeader(Elf_Shdr &SHeader,
   ArrayRef<ELFYAML::Symbol> Symbols;
   if (IsStatic && Doc.Symbols)
     Symbols = *Doc.Symbols;
-  else if (!IsStatic)
-    Symbols = Doc.DynamicSymbols;
+  else if (!IsStatic && Doc.DynamicSymbols)
+    Symbols = *Doc.DynamicSymbols;
 
   ELFYAML::RawContentSection *RawSec =
       dyn_cast_or_null<ELFYAML::RawContentSection>(YAMLSec);
-  if (RawSec && !Symbols.empty() && (RawSec->Content || RawSec->Size)) {
-    if (RawSec->Content)
-      reportError("cannot specify both `Content` and " +
-                  (IsStatic ? Twine("`Symbols`") : Twine("`DynamicSymbols`")) +
-                  " for symbol table section '" + RawSec->Name + "'");
-    if (RawSec->Size)
-      reportError("cannot specify both `Size` and " +
-                  (IsStatic ? Twine("`Symbols`") : Twine("`DynamicSymbols`")) +
-                  " for symbol table section '" + RawSec->Name + "'");
-    return;
+  if (RawSec && (RawSec->Content || RawSec->Size)) {
+    bool HasSymbolsDescription =
+        (IsStatic && Doc.Symbols) || (!IsStatic && Doc.DynamicSymbols);
+    if (HasSymbolsDescription) {
+      StringRef Property = (IsStatic ? "`Symbols`" : "`DynamicSymbols`");
+      if (RawSec->Content)
+        reportError("cannot specify both `Content` and " + Property +
+                    " for symbol table section '" + RawSec->Name + "'");
+      if (RawSec->Size)
+        reportError("cannot specify both `Size` and " + Property +
+                    " for symbol table section '" + RawSec->Name + "'");
+      return;
+    }
   }
 
   zero(SHeader);
@@ -1334,7 +1337,8 @@ template <class ELFT> void ELFState<ELFT>::buildSymbolIndexes() {
 
   if (Doc.Symbols)
     Build(*Doc.Symbols, SymN2I);
-  Build(Doc.DynamicSymbols, DynSymN2I);
+  if (Doc.DynamicSymbols)
+    Build(*Doc.DynamicSymbols, DynSymN2I);
 }
 
 template <class ELFT> void ELFState<ELFT>::finalizeStrings() {
@@ -1345,8 +1349,9 @@ template <class ELFT> void ELFState<ELFT>::finalizeStrings() {
   DotStrtab.finalize();
 
   // Add the dynamic symbol names to .dynstr section.
-  for (const ELFYAML::Symbol &Sym : Doc.DynamicSymbols)
-    DotDynstr.add(ELFYAML::dropUniqueSuffix(Sym.Name));
+  if (Doc.DynamicSymbols)
+    for (const ELFYAML::Symbol &Sym : *Doc.DynamicSymbols)
+      DotDynstr.add(ELFYAML::dropUniqueSuffix(Sym.Name));
 
   // SHT_GNU_verdef and SHT_GNU_verneed sections might also
   // add strings to .dynstr section.