[CodeGen][CFI] Generalize transparent union parameters (llvm#158193)

vitalybuka · lntue · web-flow · commit 004f209199d5 · 2025-09-13T02:18:58.000Z
According GCC documentation transparent union
calling convention is the same as the type of the
first member of the union.

C++ ignores attribute.

Note, it does not generalize args of function pointer args.
It's unnecessary with pointer generalization.
It will be fixed in followup patch.

---------

Co-authored-by: lntue &lt;lntue@google.com&gt;
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -2339,13 +2339,26 @@ llvm::ConstantInt *CodeGenModule::CreateCrossDsoCfiTypeId(llvm::Metadata *MD) {
   return llvm::ConstantInt::get(Int64Ty, llvm::MD5Hash(MDS->getString()));
 }
 
+static QualType GeneralizeTransparentUnion(QualType Ty) {
+  const RecordType *UT = Ty->getAsUnionType();
+  if (!UT)
+    return Ty;
+  const RecordDecl *UD = UT->getOriginalDecl()->getDefinitionOrSelf();
+  if (!UD->hasAttr<TransparentUnionAttr>())
+    return Ty;
+  for (const auto *it : UD->fields()) {
+    return it->getType();
+  }
+  return Ty;
+}
+
 // If `GeneralizePointers` is true, generalizes types to a void pointer with the
 // qualifiers of the originally pointed-to type, e.g. 'const char *' and 'char *
 // const *' generalize to 'const void *' while 'char *' and 'const char **'
 // generalize to 'void *'.
 static QualType GeneralizeType(ASTContext &Ctx, QualType Ty,
                                bool GeneralizePointers) {
-  // TODO: Add other generalizations.
+  Ty = GeneralizeTransparentUnion(Ty);
 
   if (!GeneralizePointers || !Ty->isPointerType())
     return Ty;
diff --git a/clang/test/CodeGen/cfi-icall-generalize.c b/clang/test/CodeGen/cfi-icall-generalize.c
@@ -22,14 +22,14 @@ union Union {
 
 // CHECK: define{{.*}} void @uni({{.*}} !type [[TYPE2:![0-9]+]] !type [[TYPE2_GENERALIZED:![0-9]+]]
 void uni(void (*fn)(union Union), union Union arg1) {
-  // UNGENERALIZED: call i1 @llvm.type.test(ptr {{.*}}, metadata !"_ZTSFv5UnionE")
-  // GENERALIZED: call i1 @llvm.type.test(ptr {{.*}}, metadata !"_ZTSFv5UnionE.generalized")
+  // UNGENERALIZED: call i1 @llvm.type.test(ptr {{.*}}, metadata !"_ZTSFvPcE")
+  // GENERALIZED: call i1 @llvm.type.test(ptr {{.*}}, metadata !"_ZTSFvPvE.generalized")
     fn(arg1);
 }
 
 // CHECK: [[TYPE]] = !{i64 0, !"_ZTSFPPiPKcPS2_E"}
 // CHECK: [[TYPE_GENERALIZED]] = !{i64 0, !"_ZTSFPvPKvS_E.generalized"}
 
-// CHECK: [[TYPE2]] = !{i64 0, !"_ZTSFvPFv5UnionES_E"}
-// CHECK: [[TYPE2_GENERALIZED]] = !{i64 0, !"_ZTSFvPv5UnionE.generalized"}
+// CHECK: [[TYPE2]] = !{i64 0, !"_ZTSFvPFv5UnionEPcE"}
+// CHECK: [[TYPE2_GENERALIZED]] = !{i64 0, !"_ZTSFvPvS_E.generalized"}
 
diff --git a/clang/test/CodeGen/cfi-icall-normalize2.c b/clang/test/CodeGen/cfi-icall-normalize2.c
@@ -32,12 +32,12 @@ union Union {
 void uni(void (*fn)(union Union), union Union arg1) {
     // CHECK-LABEL: define{{.*}}uni
     // CHECK-SAME: {{.*}}!type ![[TYPE4:[0-9]+]] !type !{{[0-9]+}}
-    // CHECK: call i1 @llvm.type.test({{i8\*|ptr}} {{%f|%0}}, metadata !"_ZTSFv5UnionE.normalized")
+    // CHECK: call i1 @llvm.type.test({{i8\*|ptr}} {{%f|%0}}, metadata !"_ZTSFvPu2i8E.normalized")
     fn(arg1);
 }
 
 // CHECK: ![[TYPE1]] = !{i64 0, !"_ZTSFvPFvu3i32ES_E.normalized"}
 // CHECK: ![[TYPE2]] = !{i64 0, !"_ZTSFvPFvu3i32S_ES_S_E.normalized"}
 // CHECK: ![[TYPE3]] = !{i64 0, !"_ZTSFvPFvu3i32S_S_ES_S_S_E.normalized"}
-// CHECK: ![[TYPE4]] = !{i64 0, !"_ZTSFvPFv5UnionES_E.normalized"}
+// CHECK: ![[TYPE4]] = !{i64 0, !"_ZTSFvPFv5UnionEPu2i8E.normalized"}
 
diff --git a/clang/test/CodeGen/kcfi-generalize.c b/clang/test/CodeGen/kcfi-generalize.c
@@ -33,8 +33,8 @@ union Union {
 
 // CHECK: define{{.*}} void @uni({{.*}} !kcfi_type [[TYPE4:![0-9]+]]
 void uni(void (*fn)(union Union), union Union arg1) {
-  // UNGENERALIZED: call {{.*}} [ "kcfi"(i32 -1037059548) ]
-  // GENERALIZED: call {{.*}} [ "kcfi"(i32 422130955) ]
+  // UNGENERALIZED: call {{.*}} [ "kcfi"(i32 -587217045) ]
+  // GENERALIZED: call {{.*}} [ "kcfi"(i32 2139530422) ]
     fn(arg1);
 }
 
@@ -44,6 +44,5 @@ void uni(void (*fn)(union Union), union Union arg1) {
 // UNGENERALIZED: [[TYPE3]] = !{i32 874141567}
 // GENERALIZED: [[TYPE3]] = !{i32 954385378}
 
-// UNGENERALIZED: [[TYPE4]] = !{i32 981319178}
-// GENERALIZED: [[TYPE4]] = !{i32 -1599950473}
-
+// UNGENERALIZED: [[TYPE4]] = !{i32 -1619636625}
+// GENERALIZED: [[TYPE4]] = !{i32 -125078496}
diff --git a/clang/test/CodeGen/kcfi-normalize.c b/clang/test/CodeGen/kcfi-normalize.c
@@ -1,5 +1,5 @@
-// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fsanitize=kcfi -fsanitize-cfi-icall-experimental-normalize-integers -o - %s | FileCheck %s
-// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fsanitize=kcfi -fsanitize-cfi-icall-experimental-normalize-integers -x c++ -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fsanitize=kcfi -fsanitize-cfi-icall-experimental-normalize-integers -o - %s | FileCheck %s --check-prefixes=CHECK,C
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fsanitize=kcfi -fsanitize-cfi-icall-experimental-normalize-integers -x c++ -o - %s | FileCheck %s --check-prefixes=CHECK,CPP
 #if !__has_feature(kcfi)
 #error Missing kcfi?
 #endif
@@ -36,13 +36,14 @@ union Union {
 void uni(void (*fn)(union Union), union Union arg1) {
     // CHECK-LABEL: define{{.*}}uni
     // CHECK-SAME: {{.*}}!kcfi_type ![[TYPE4:[0-9]+]]
-    // CHECK: call void %0(ptr %1) [ "kcfi"(i32 -1430221633) ]
+    // C: call void %0(ptr %1) [ "kcfi"(i32 1819770848) ]
+    // CPP: call void %0(ptr %1) [ "kcfi"(i32 -1430221633) ]
     fn(arg1);
 }
 
 // CHECK: ![[#]] = !{i32 4, !"cfi-normalize-integers", i32 1}
 // CHECK: ![[TYPE1]] = !{i32 -1143117868}
 // CHECK: ![[TYPE2]] = !{i32 -460921415}
 // CHECK: ![[TYPE3]] = !{i32 -333839615}
-// CHECK: ![[TYPE4]] = !{i32 1766237188}
-
+// C: ![[TYPE4]] = !{i32 -650530463}
+// CPP: ![[TYPE4]] = !{i32 1766237188}
