[PATCH] D115015: CodeGen: Strip exception specifications from function types in CFI type names.

Peter Collingbourne via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Thu Dec 2 17:46:10 PST 2021

pcc created this revision.
pcc added a reviewer: eugenis.
pcc requested review of this revision.
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With C++17 the exception specification has been made part of the
function type, and therefore part of mangled type names.

However, it's valid to convert function pointers with an exception
specification to function pointers with the same argument and return
types but without an exception specification, which means that e.g. a
function of type "void () noexcept" can be called through a pointer
of type "void ()". We must therefore consider the two types to be
compatible for CFI purposes.

We can do this by stripping the exception specification before mangling
the type name, which is what this patch does.

  rG LLVM Github Monorepo



Index: clang/test/CodeGenCXX/cfi-icall-noexcept.cpp
--- /dev/null
+++ clang/test/CodeGenCXX/cfi-icall-noexcept.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux -fsanitize=cfi-icall -emit-llvm -std=c++17 -o - %s | FileCheck %s
+// Tests that exception specifiers are stripped when forming the
+// mangled CFI type name.
+void f() noexcept {}
+// CHECK: define{{.*}} void @_Z1fv({{.*}} !type [[TS1:![0-9]+]] !type [[TS2:![0-9]+]]
+// CHECK: [[TS1]] = !{i64 0, !"_ZTSFvvE"}
+// CHECK: [[TS2]] = !{i64 0, !"_ZTSFvvE.generalized"}
Index: clang/lib/CodeGen/CodeGenModule.cpp
--- clang/lib/CodeGen/CodeGenModule.cpp
+++ clang/lib/CodeGen/CodeGenModule.cpp
@@ -6398,6 +6398,11 @@
 llvm::Metadata *
 CodeGenModule::CreateMetadataIdentifierImpl(QualType T, MetadataTypeMap &Map,
                                             StringRef Suffix) {
+  if (auto *FnType = T->getAs<FunctionProtoType>())
+    T = getContext().getFunctionType(
+        FnType->getReturnType(), FnType->getParamTypes(),
+        FnType->getExtProtoInfo().withExceptionSpec(EST_None));
   llvm::Metadata *&InternalId = Map[T.getCanonicalType()];
   if (InternalId)
     return InternalId;

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