Perform symbol binding for .symver versioned symbols

Summary:
In a .symver assembler directive like:
.symver name, name2@@nodename
"name2@@nodename" should get the same symbol binding as "name".

While the ELF object writer is updating the symbol binding for .symver
aliases before emitting the object file, not doing so when the module
inline assembly is handled by the RecordStreamer is causing the wrong
behavior in *LTO mode.

E.g. when "name" is global, "name2@@nodename" must also be marked as
global. Otherwise, the symbol is skipped when iterating over the LTO
InputFile symbols (InputFile::Symbol::shouldSkip). So, for example,
when performing any *LTO via the gold-plugin, the versioned symbol
definition is not recorded by the plugin and passed back to the
linker. If the object was in an archive, and there were no other symbols
needed from that object, the object would not be included in the final
link and references to the versioned symbol are undefined.

The llvm-lto2 tests added will give an error about an unused symbol
resolution without the fix.

Reviewers: rafael, pcc

Reviewed By: pcc

Subscribers: mehdi_amini, llvm-commits

Differential Revision: https://reviews.llvm.org/D30485

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@297332 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 106 insertions, 6 deletions

diff --git a/lib/Object/ModuleSymbolTable.cpp b/lib/Object/ModuleSymbolTable.cpp
index 90488007ff5..21709b5c223 100644
--- a/lib/Object/ModuleSymbolTable.cpp
+++ b/lib/Object/ModuleSymbolTable.cpp
@@ -50,20 +50,95 @@ void ModuleSymbolTable::addModule(Module *M) {
   for (GlobalAlias &GA : M->aliases())
     SymTab.push_back(&GA);
 
-  CollectAsmSymbols(Triple(M->getTargetTriple()), M->getModuleInlineAsm(),
-                    [this](StringRef Name, BasicSymbolRef::Flags Flags) {
-                      SymTab.push_back(new (AsmSymbols.Allocate())
-                                           AsmSymbol(Name, Flags));
-                    });
+  CollectAsmSymbols(*M, [this](StringRef Name, BasicSymbolRef::Flags Flags) {
+    SymTab.push_back(new (AsmSymbols.Allocate()) AsmSymbol(Name, Flags));
+  });
+}
+
+// Ensure ELF .symver aliases get the same binding as the defined symbol
+// they alias with.
+static void handleSymverAliases(const Module &M, RecordStreamer &Streamer) {
+  if (Streamer.symverAliases().empty())
+    return;
+
+  // The name in the assembler will be mangled, but the name in the IR
+  // might not, so we first compute a mapping from mangled name to GV.
+  Mangler Mang;
+  SmallString<64> MangledName;
+  StringMap<const GlobalValue *> MangledNameMap;
+  auto GetMangledName = [&](const GlobalValue &GV) {
+    if (!GV.hasName())
+      return;
+
+    MangledName.clear();
+    MangledName.reserve(GV.getName().size() + 1);
+    Mang.getNameWithPrefix(MangledName, &GV, /*CannotUsePrivateLabel=*/false);
+    MangledNameMap[MangledName] = &GV;
+  };
+  for (const Function &F : M)
+    GetMangledName(F);
+  for (const GlobalVariable &GV : M.globals())
+    GetMangledName(GV);
+  for (const GlobalAlias &GA : M.aliases())
+    GetMangledName(GA);
+
+  // Walk all the recorded .symver aliases, and set up the binding
+  // for each alias.
+  for (auto &Symver : Streamer.symverAliases()) {
+    const MCSymbol *Aliasee = Symver.first;
+    MCSymbolAttr Attr = MCSA_Invalid;
+
+    // First check if the aliasee binding was recorded in the asm.
+    RecordStreamer::State state = Streamer.getSymbolState(Aliasee);
+    switch (state) {
+    case RecordStreamer::Global:
+    case RecordStreamer::DefinedGlobal:
+      Attr = MCSA_Global;
+      break;
+    case RecordStreamer::UndefinedWeak:
+    case RecordStreamer::DefinedWeak:
+      Attr = MCSA_Weak;
+      break;
+    default:
+      break;
+    }
+
+    // If we don't have a symbol attribute from assembly, then check if
+    // the aliasee was defined in the IR.
+    if (Attr == MCSA_Invalid) {
+      const auto *GV = M.getNamedValue(Aliasee->getName());
+      if (!GV) {
+        auto MI = MangledNameMap.find(Aliasee->getName());
+        if (MI != MangledNameMap.end())
+          GV = MI->second;
+        else
+          continue;
+      }
+      if (GV->hasExternalLinkage())
+        Attr = MCSA_Global;
+      else if (GV->hasLocalLinkage())
+        Attr = MCSA_Local;
+      else if (GV->isWeakForLinker())
+        Attr = MCSA_Weak;
+    }
+    if (Attr == MCSA_Invalid)
+      continue;
+
+    // Set the detected binding on each alias with this aliasee.
+    for (auto &Alias : Symver.second)
+      Streamer.EmitSymbolAttribute(Alias, Attr);
+  }
 }
 
 void ModuleSymbolTable::CollectAsmSymbols(
-    const Triple &TT, StringRef InlineAsm,
+    const Module &M,
     function_ref<void(StringRef, BasicSymbolRef::Flags)> AsmSymbol) {
+  StringRef InlineAsm = M.getModuleInlineAsm();
   if (InlineAsm.empty())
     return;
 
   std::string Err;
+  const Triple TT(M.getTargetTriple());
   const Target *T = TargetRegistry::lookupTarget(TT.str(), Err);
   assert(T && T->hasMCAsmParser());
 
@@ -106,6 +181,8 @@ void ModuleSymbolTable::CollectAsmSymbols(
   if (Parser->Run(false))
     return;
 
+  handleSymverAliases(M, Streamer);
+
   for (auto &KV : Streamer) {
     StringRef Key = KV.first();
     RecordStreamer::State Value = KV.second;
diff --git a/lib/Object/RecordStreamer.cpp b/lib/Object/RecordStreamer.cpp
index da99b3fea00..8be6d0b60cf 100644
--- a/lib/Object/RecordStreamer.cpp
+++ b/lib/Object/RecordStreamer.cpp
@@ -110,3 +110,8 @@ void RecordStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                                       unsigned ByteAlignment) {
   markDefined(*Symbol);
 }
+
+void RecordStreamer::emitELFSymverDirective(MCSymbol *Alias,
+                                            const MCSymbol *Aliasee) {
+  SymverAliasMap[Aliasee].push_back(Alias);
+}
diff --git a/lib/Object/RecordStreamer.h b/lib/Object/RecordStreamer.h
index c795dbb2e43..c3bd5b09a9b 100644
--- a/lib/Object/RecordStreamer.h
+++ b/lib/Object/RecordStreamer.h
@@ -20,6 +20,10 @@ public:
 
 private:
   StringMap<State> Symbols;
+  // Map of aliases created by .symver directives, saved so we can update
+  // their symbol binding after parsing complete. This maps from each
+  // aliasee to its list of aliases.
+  DenseMap<const MCSymbol *, std::vector<MCSymbol *>> SymverAliasMap;
   void markDefined(const MCSymbol &Symbol);
   void markGlobal(const MCSymbol &Symbol, MCSymbolAttr Attribute);
   void markUsed(const MCSymbol &Symbol);
@@ -38,6 +42,20 @@ public:
                     unsigned ByteAlignment) override;
   void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                         unsigned ByteAlignment) override;
+  /// Record .symver aliases for later processing.
+  void emitELFSymverDirective(MCSymbol *Alias,
+                              const MCSymbol *Aliasee) override;
+  /// Return the map of .symver aliasee to associated aliases.
+  DenseMap<const MCSymbol *, std::vector<MCSymbol *>> &symverAliases() {
+    return SymverAliasMap;
+  }
+  /// Get the state recorded for the given symbol.
+  State getSymbolState(const MCSymbol *Sym) {
+    auto SI = Symbols.find(Sym->getName());
+    if (SI == Symbols.end())
+      return NeverSeen;
+    return SI->second;
+  }
 };
 }
 #endif