[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

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() {}

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();

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();
 

clang/test/CodeGenObjC/availability-cf-link-guard.m

@@ -0,0 +1,45 @@
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.11 -emit-llvm -o - %s | FileCheck --check-prefixes=CHECK,CHECK_LINK_OPT %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.11 -emit-llvm -o - -D USE_BUILTIN %s | FileCheck --check-prefixes=CHECK,CHECK_LINK_OPT %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.11 -emit-llvm -o - -D DEF_CF %s | FileCheck --check-prefixes=CHECK_CF,CHECK_LINK_OPT %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.12 -emit-llvm -o - %s | FileCheck --check-prefix=CHECK_NO_GUARD %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux -emit-llvm -o - %s | FileCheck --check-prefix=CHECK_NO_GUARD %s
+
+#ifdef DEF_CF
+struct CFBundle;
+typedef struct CFBundle *CFBundleRef;
+unsigned CFBundleGetVersionNumber(CFBundleRef bundle);
+// CHECK_CF: declare i32 @CFBundleGetVersionNumber(%struct.CFBundle*)
+// CHECK_CF: @__clang_at_available_requires_core_foundation_framework
+// CHECK_CF-NEXT: call {{.*}}@CFBundleGetVersionNumber
+#endif
+
+void use_at_available() {
+#ifdef DEF_CF
+  CFBundleGetVersionNumber(0);
+#endif
+#ifdef USE_BUILTIN
+  if (__builtin_available(macos 10.12, *))
+    ;
+#else
+  if (@available(macos 10.12, *))
+    ;
+#endif
+}
+
+// CHECK: @llvm.compiler.used{{.*}}@__clang_at_available_requires_core_foundation_framework
+
+// CHECK: declare i32 @CFBundleGetVersionNumber(i8*)
+
+// CHECK-LABEL: linkonce hidden void @__clang_at_available_requires_core_foundation_framework
+// CHECK: call i32 @CFBundleGetVersionNumber(i8* null)
+// CHECK-NEXT: unreachable
+
+// CHECK_NO_GUARD-NOT: __clang_at_available_requires_core_foundation_framework
+// CHECK_NO_GUARD-NOT: CFBundleGetVersionNumber
+
+// CHECK_LINK_OPT: !"Linker Options", ![[OPTS:[0-9]+]]
+// CHECK_LINK_OPT: ![[OPTS]] = !{![[FRAMEWORK:[0-9]+]]
+// CHECK_LINK_OPT: ![[FRAMEWORK]] = !{!"-framework", !"CoreFoundation"}
+
+// CHECK_NO_GUARD-NOT: "Linker Options"
+// CHECK_NO_GUARD-NOT: CoreFoundation