[GCC] Attribute ifunc support in clang

This patch add support for GCC attribute((ifunc("resolver"))) for
targets that use ELF as object file format. In general ifunc is a
special kind of function alias with type @gnu_indirect_function. LLVM
patch http://reviews.llvm.org/D15525

Differential Revision: http://reviews.llvm.org/D15524

llvm-svn: 265917

1 files changed, 100 insertions, 21 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 7e522f2..e4ae5bb 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -274,20 +274,21 @@ void CodeGenModule::applyGlobalValReplacements() {
 
 // This is only used in aliases that we created and we know they have a
 // linear structure.
-static const llvm::GlobalObject *getAliasedGlobal(const llvm::GlobalAlias &GA) {
-  llvm::SmallPtrSet<const llvm::GlobalAlias*, 4> Visited;
-  const llvm::Constant *C = &GA;
+static const llvm::GlobalObject *getAliasedGlobal(
+    const llvm::GlobalIndirectSymbol &GIS) {
+  llvm::SmallPtrSet<const llvm::GlobalIndirectSymbol*, 4> Visited;
+  const llvm::Constant *C = &GIS;
   for (;;) {
     C = C->stripPointerCasts();
     if (auto *GO = dyn_cast<llvm::GlobalObject>(C))
       return GO;
     // stripPointerCasts will not walk over weak aliases.
-    auto *GA2 = dyn_cast<llvm::GlobalAlias>(C);
-    if (!GA2)
+    auto *GIS2 = dyn_cast<llvm::GlobalIndirectSymbol>(C);
+    if (!GIS2)
       return nullptr;
-    if (!Visited.insert(GA2).second)
+    if (!Visited.insert(GIS2).second)
       return nullptr;
-    C = GA2->getAliasee();
+    C = GIS2->getIndirectSymbol();
   }
 }
 
@@ -299,20 +300,35 @@ void CodeGenModule::checkAliases() {
   DiagnosticsEngine &Diags = getDiags();
   for (const GlobalDecl &GD : Aliases) {
     const auto *D = cast<ValueDecl>(GD.getDecl());
-    const AliasAttr *AA = D->getAttr<AliasAttr>();
+    SourceLocation Location;
+    bool IsIFunc = D->hasAttr<IFuncAttr>();
+    if (const Attr *A = D->getDefiningAttr())
+      Location = A->getLocation();
+    else
+      llvm_unreachable("Not an alias or ifunc?");
     StringRef MangledName = getMangledName(GD);
     llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
-    auto *Alias = cast<llvm::GlobalAlias>(Entry);
+    auto *Alias  = cast<llvm::GlobalIndirectSymbol>(Entry);
     const llvm::GlobalValue *GV = getAliasedGlobal(*Alias);
     if (!GV) {
       Error = true;
-      Diags.Report(AA->getLocation(), diag::err_cyclic_alias);
+      Diags.Report(Location, diag::err_cyclic_alias) << IsIFunc;
     } else if (GV->isDeclaration()) {
       Error = true;
-      Diags.Report(AA->getLocation(), diag::err_alias_to_undefined);
+      Diags.Report(Location, diag::err_alias_to_undefined)
+          << IsIFunc << IsIFunc;
+    } else if (IsIFunc) {
+      // Check resolver function type.
+      llvm::FunctionType *FTy = dyn_cast<llvm::FunctionType>(
+          GV->getType()->getPointerElementType());
+      assert(FTy);
+      if (!FTy->getReturnType()->isPointerTy())
+        Diags.Report(Location, diag::err_ifunc_resolver_return);
+      if (FTy->getNumParams())
+        Diags.Report(Location, diag::err_ifunc_resolver_params);
     }
 
-    llvm::Constant *Aliasee = Alias->getAliasee();
+    llvm::Constant *Aliasee = Alias->getIndirectSymbol();
     llvm::GlobalValue *AliaseeGV;
     if (auto CE = dyn_cast<llvm::ConstantExpr>(Aliasee))
       AliaseeGV = cast<llvm::GlobalValue>(CE->getOperand(0));
@@ -323,7 +339,7 @@ void CodeGenModule::checkAliases() {
       StringRef AliasSection = SA->getName();
       if (AliasSection != AliaseeGV->getSection())
         Diags.Report(SA->getLocation(), diag::warn_alias_with_section)
-            << AliasSection;
+            << AliasSection << IsIFunc << IsIFunc;
     }
 
     // We have to handle alias to weak aliases in here. LLVM itself disallows
@@ -331,13 +347,13 @@ void CodeGenModule::checkAliases() {
     // compatibility with gcc we implement it by just pointing the alias
     // to its aliasee's aliasee. We also warn, since the user is probably
     // expecting the link to be weak.
-    if (auto GA = dyn_cast<llvm::GlobalAlias>(AliaseeGV)) {
+    if (auto GA = dyn_cast<llvm::GlobalIndirectSymbol>(AliaseeGV)) {
       if (GA->isInterposable()) {
-        Diags.Report(AA->getLocation(), diag::warn_alias_to_weak_alias)
-            << GV->getName() << GA->getName();
+        Diags.Report(Location, diag::warn_alias_to_weak_alias)
+            << GV->getName() << GA->getName() << IsIFunc;
         Aliasee = llvm::ConstantExpr::getPointerBitCastOrAddrSpaceCast(
-            GA->getAliasee(), Alias->getType());
-        Alias->setAliasee(Aliasee);
+            GA->getIndirectSymbol(), Alias->getType());
+        Alias->setIndirectSymbol(Aliasee);
       }
     }
   }
@@ -347,7 +363,7 @@ void CodeGenModule::checkAliases() {
   for (const GlobalDecl &GD : Aliases) {
     StringRef MangledName = getMangledName(GD);
     llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
-    auto *Alias = cast<llvm::GlobalAlias>(Entry);
+    auto *Alias = dyn_cast<llvm::GlobalIndirectSymbol>(Entry);
     Alias->replaceAllUsesWith(llvm::UndefValue::get(Alias->getType()));
     Alias->eraseFromParent();
   }
@@ -1538,6 +1554,10 @@ void CodeGenModule::EmitGlobal(GlobalDecl GD) {
   if (Global->hasAttr<AliasAttr>())
     return EmitAliasDefinition(GD);
 
+  // IFunc like an alias whose value is resolved at runtime by calling resolver.
+  if (Global->hasAttr<IFuncAttr>())
+    return emitIFuncDefinition(GD);
+
   // If this is CUDA, be selective about which declarations we emit.
   if (LangOpts.CUDA) {
     if (LangOpts.CUDAIsDevice) {
@@ -2901,7 +2921,7 @@ void CodeGenModule::EmitAliasDefinition(GlobalDecl GD) {
   StringRef MangledName = getMangledName(GD);
 
   if (AA->getAliasee() == MangledName) {
-    Diags.Report(AA->getLocation(), diag::err_cyclic_alias);
+    Diags.Report(AA->getLocation(), diag::err_cyclic_alias) << 0;
     return;
   }
 
@@ -2932,7 +2952,7 @@ void CodeGenModule::EmitAliasDefinition(GlobalDecl GD) {
 
   if (Entry) {
     if (GA->getAliasee() == Entry) {
-      Diags.Report(AA->getLocation(), diag::err_cyclic_alias);
+      Diags.Report(AA->getLocation(), diag::err_cyclic_alias) << 0;
       return;
     }
 
@@ -2969,6 +2989,65 @@ void CodeGenModule::EmitAliasDefinition(GlobalDecl GD) {
   setAliasAttributes(D, GA);
 }
 
+void CodeGenModule::emitIFuncDefinition(GlobalDecl GD) {
+  const auto *D = cast<ValueDecl>(GD.getDecl());
+  const IFuncAttr *IFA = D->getAttr<IFuncAttr>();
+  assert(IFA && "Not an ifunc?");
+
+  StringRef MangledName = getMangledName(GD);
+
+  if (IFA->getResolver() == MangledName) {
+    Diags.Report(IFA->getLocation(), diag::err_cyclic_alias) << 1;
+    return;
+  }
+
+  // Report an error if some definition overrides ifunc.
+  llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
+  if (Entry && !Entry->isDeclaration()) {
+    GlobalDecl OtherGD;
+    if (lookupRepresentativeDecl(MangledName, OtherGD) &&
+        DiagnosedConflictingDefinitions.insert(GD).second) {
+      Diags.Report(D->getLocation(), diag::err_duplicate_mangled_name);
+      Diags.Report(OtherGD.getDecl()->getLocation(),
+                   diag::note_previous_definition);
+    }
+    return;
+  }
+
+  Aliases.push_back(GD);
+
+  llvm::Type *DeclTy = getTypes().ConvertTypeForMem(D->getType());
+  llvm::Constant *Resolver =
+      GetOrCreateLLVMFunction(IFA->getResolver(), DeclTy, GD,
+                              /*ForVTable=*/false);
+  llvm::GlobalIFunc *GIF =
+      llvm::GlobalIFunc::create(DeclTy, 0, llvm::Function::ExternalLinkage,
+                                "", Resolver, &getModule());
+  if (Entry) {
+    if (GIF->getResolver() == Entry) {
+      Diags.Report(IFA->getLocation(), diag::err_cyclic_alias) << 1;
+      return;
+    }
+    assert(Entry->isDeclaration());
+
+    // If there is a declaration in the module, then we had an extern followed
+    // by the ifunc, as in:
+    //   extern int test();
+    //   ...
+    //   int test() __attribute__((ifunc("resolver")));
+    //
+    // Remove it and replace uses of it with the ifunc.
+    GIF->takeName(Entry);
+
+    Entry->replaceAllUsesWith(llvm::ConstantExpr::getBitCast(GIF,
+                                                          Entry->getType()));
+    Entry->eraseFromParent();
+  } else
+    GIF->setName(MangledName);
+
+  SetCommonAttributes(D, GIF);
+}
+
 llvm::Function *CodeGenModule::getIntrinsic(unsigned IID,
                                             ArrayRef<llvm::Type*> Tys) {
   return llvm::Intrinsic::getDeclaration(&getModule(), (llvm::Intrinsic::ID)IID,