[CodeGen] Emit a CoreFoundation link guard when @available is used

After r297760, __isOSVersionAtLeast in compiler-rt loads the CoreFoundation
symbols at runtime. This means that `@available` will always fail when used in a
binary without a linked CoreFoundation.

This commit forces Clang to emit a reference to a CoreFoundation symbol when
`@available` is used to ensure that linking will fail when CoreFoundation isn't
linked with the build product.

rdar://31039592

Differential Revision: https://reviews.llvm.org/D30977

llvm-svn: 298588

3 files changed, 38 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CGObjC.cpp b/clang/lib/CodeGen/CGObjC.cpp
index 4954a0d1238..4af5af93248 100644
--- a/clang/lib/CodeGen/CGObjC.cpp
+++ b/clang/lib/CodeGen/CGObjC.cpp
@@ -3416,4 +3416,37 @@ CodeGenFunction::EmitBuiltinAvailable(ArrayRef<llvm::Value *> Args) {
   return Builder.CreateICmpNE(CallRes, llvm::Constant::getNullValue(Int32Ty));
 }
 
+void CodeGenModule::emitAtAvailableLinkGuard() {
+  if (!IsOSVersionAtLeastFn)
+    return;
+  // @available requires CoreFoundation only on Darwin.
+  if (!Target.getTriple().isOSDarwin())
+    return;
+  // Add -framework CoreFoundation to the linker commands. We still want to
+  // emit the core foundation reference down below because otherwise if
+  // CoreFoundation is not used in the code, the linker won't link the
+  // framework.
+  auto &Context = getLLVMContext();
+  llvm::Metadata *Args[2] = {llvm::MDString::get(Context, "-framework"),
+                             llvm::MDString::get(Context, "CoreFoundation")};
+  LinkerOptionsMetadata.push_back(llvm::MDNode::get(Context, Args));
+  // Emit a reference to a symbol from CoreFoundation to ensure that
+  // CoreFoundation is linked into the final binary.
+  llvm::FunctionType *FTy =
+      llvm::FunctionType::get(Int32Ty, {VoidPtrTy}, false);
+  llvm::Constant *CFFunc =
+      CreateRuntimeFunction(FTy, "CFBundleGetVersionNumber");
+
+  llvm::FunctionType *CheckFTy = llvm::FunctionType::get(VoidTy, {}, false);
+  llvm::Function *CFLinkCheckFunc = cast<llvm::Function>(CreateBuiltinFunction(
+      CheckFTy, "__clang_at_available_requires_core_foundation_framework"));
+  CFLinkCheckFunc->setLinkage(llvm::GlobalValue::LinkOnceAnyLinkage);
+  CFLinkCheckFunc->setVisibility(llvm::GlobalValue::HiddenVisibility);
+  CodeGenFunction CGF(*this);
+  CGF.Builder.SetInsertPoint(CGF.createBasicBlock("", CFLinkCheckFunc));
+  CGF.EmitNounwindRuntimeCall(CFFunc, llvm::Constant::getNullValue(VoidPtrTy));
+  CGF.Builder.CreateUnreachable();
+  addCompilerUsedGlobal(CFLinkCheckFunc);
+}
+
 CGObjCRuntime::~CGObjCRuntime() {}
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index ca1850e1043..89ee7fc74c3 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -414,6 +414,7 @@ void CodeGenModule::Release() {
     CoverageMapping->emit();
   if (CodeGenOpts.SanitizeCfiCrossDso)
     CodeGenFunction(*this).EmitCfiCheckFail();
+  emitAtAvailableLinkGuard();
   emitLLVMUsed();
   if (SanStats)
     SanStats->finish();
diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index 1d59230c2c2..5c9dd965e85 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -1286,6 +1286,10 @@ private:
   /// Emit any vtables which we deferred and still have a use for.
   void EmitDeferredVTables();
 
+  /// Emit a dummy function that reference a CoreFoundation symbol when
+  /// @available is used on Darwin.
+  void emitAtAvailableLinkGuard();
+
   /// Emit the llvm.used and llvm.compiler.used metadata.
   void emitLLVMUsed();