[PATCH] D31796: [cfi] Emit __cfi_check stub in the frontend

[Evgeniy Stepanov via Phabricator via llvm-commits]

eugenis created this revision.
Herald added a subscriber: mehdi_amini.

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.


Repository:
  rL LLVM

https://reviews.llvm.org/D31796

Files:
  lib/CodeGen/CGExpr.cpp
  lib/CodeGen/CodeGenFunction.h
  lib/CodeGen/CodeGenModule.cpp
  test/CodeGen/cfi-check-fail.c


Index: test/CodeGen/cfi-check-fail.c
===================================================================
--- test/CodeGen/cfi-check-fail.c
+++ test/CodeGen/cfi-check-fail.c
@@ -72,3 +72,7 @@
 
 // CHECK: [[CONT5]]:
 // CHECK:   ret void
+
+// CHECK: define weak void @__cfi_check(i64, i8*, i8*)
+// CHECK-NOT: }
+// CHECK: ret void
Index: lib/CodeGen/CodeGenModule.cpp
===================================================================
--- lib/CodeGen/CodeGenModule.cpp
+++ 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)
Index: lib/CodeGen/CodeGenFunction.h
===================================================================
--- lib/CodeGen/CodeGenFunction.h
+++ lib/CodeGen/CodeGenFunction.h
@@ -3524,6 +3524,9 @@
   /// "trap-func-name" if specified.
   llvm::CallInst *EmitTrapCall(llvm::Intrinsic::ID IntrID);
 
+  /// \brief Emit a empty stub for the cross-DSO CFI check function.
+  void EmitCfiCheckStub();
+
   /// \brief Emit a cross-DSO CFI failure handling function.
   void EmitCfiCheckFail();
 
Index: lib/CodeGen/CGExpr.cpp
===================================================================
--- lib/CodeGen/CGExpr.cpp
+++ lib/CodeGen/CGExpr.cpp
@@ -2783,6 +2783,15 @@
   EmitBlock(Cont);
 }
 
+void CodeGenFunction::EmitCfiCheckStub() {
+  auto &Ctx = CGM.getModule().getContext();
+  llvm::Function *F = llvm::Function::Create(
+      llvm::FunctionType::get(VoidTy, {Int64Ty, Int8PtrTy, Int8PtrTy}, false),
+      llvm::GlobalValue::WeakAnyLinkage, "__cfi_check", &CGM.getModule());
+  llvm::BasicBlock *BB = llvm::BasicBlock::Create(Ctx, "entry", F);
+  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
@@ -2864,6 +2873,7 @@
   }
 
   FinishFunction();
+
   // The only reference to this function will be created during LTO link.
   // Make sure it survives until then.
   CGM.addUsedGlobal(F);


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