[cfi] Emit __cfi_check stub in the frontend.
Previously __cfi_check was created in LTO optimization pipeline, which
means LLD has no way of knowing about the existence of this symbol
without rescanning the LTO output object. As a result, LLD fails to
export __cfi_check, even when given --export-dynamic-symbol flag.
llvm-svn: 299806
diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index 38eb345..c412456 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -2783,6 +2783,24 @@
EmitBlock(Cont);
}
+// Emit a stub for __cfi_check function so that the linker knows about this
+// symbol in LTO mode.
+void CodeGenFunction::EmitCfiCheckStub() {
+ llvm::Module *M = &CGM.getModule();
+ auto &Ctx = M->getContext();
+ llvm::Function *F = llvm::Function::Create(
+ llvm::FunctionType::get(VoidTy, {Int64Ty, Int8PtrTy, Int8PtrTy}, false),
+ llvm::GlobalValue::WeakAnyLinkage, "__cfi_check", M);
+ llvm::BasicBlock *BB = llvm::BasicBlock::Create(Ctx, "entry", F);
+ // FIXME: consider emitting an intrinsic call like
+ // call void @llvm.cfi_check(i64 %0, i8* %1, i8* %2)
+ // which can be lowered in CrossDSOCFI pass to the actual contents of
+ // __cfi_check. This would allow inlining of __cfi_check calls.
+ llvm::CallInst::Create(
+ llvm::Intrinsic::getDeclaration(M, llvm::Intrinsic::trap), "", BB);
+ llvm::ReturnInst::Create(Ctx, nullptr, BB);
+}
+
// This function is basically a switch over the CFI failure kind, which is
// extracted from CFICheckFailData (1st function argument). Each case is either
// llvm.trap or a call to one of the two runtime handlers, based on
diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index ee85e30..3321bc8 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -3524,6 +3524,9 @@
/// "trap-func-name" if specified.
llvm::CallInst *EmitTrapCall(llvm::Intrinsic::ID IntrID);
+ /// \brief Emit a stub for the cross-DSO CFI check function.
+ void EmitCfiCheckStub();
+
/// \brief Emit a cross-DSO CFI failure handling function.
void EmitCfiCheckFail();
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 479a390..6bc7d4f 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -406,8 +406,10 @@
EmitDeferredUnusedCoverageMappings();
if (CoverageMapping)
CoverageMapping->emit();
- if (CodeGenOpts.SanitizeCfiCrossDso)
+ if (CodeGenOpts.SanitizeCfiCrossDso) {
CodeGenFunction(*this).EmitCfiCheckFail();
+ CodeGenFunction(*this).EmitCfiCheckStub();
+ }
emitAtAvailableLinkGuard();
emitLLVMUsed();
if (SanStats)