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[CodeGen][CFI] Generalize transparent union in args of args of functions #158194

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[CodeGen][CFI] Generalize transparent union in args of args of functions #158194

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[𝘀𝗽𝗿] initial version
vitalybuka Sep 12, 2025
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16 changes: 13 additions & 3 deletions clang/lib/CodeGen/CodeGenModule.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2352,6 +2352,9 @@ static QualType GeneralizeTransparentUnion(QualType Ty) {
return Ty;
}

static QualType GeneralizeFunctionType(ASTContext &Ctx, QualType Ty,
bool GeneralizePointers);

// Generalize pointer 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
Expand All @@ -2360,12 +2363,19 @@ static QualType GeneralizeType(ASTContext &Ctx, QualType Ty,
bool GeneralizePointers) {
Ty = GeneralizeTransparentUnion(Ty);

if (!GeneralizePointers || !Ty->isPointerType())
if (!Ty->isPointerType())
return Ty;

QualType PTy = Ty->getPointeeType();
if (PTy->getAs<FunctionProtoType>() || PTy->getAs<FunctionNoProtoType>())
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@pcc pcc Sep 12, 2025

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I guess this is not the only way you can end up with a function type. E.g. pointer to pointer to function, reference to pointer to function, etc.

What do you think about doing this in the mangler? E.g. add a call to a hook near the top of void CXXNameMangler::mangleType(QualType T) and supply a hook that does the transparent_union generalization from here.

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@vitalybuka vitalybuka Sep 12, 2025

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Mangler is too late, if we have pointer generalization, it should apply to pointers form transparent union

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@pcc pcc Sep 12, 2025

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The hook could also do the pointer generalization, no?

Ty = Ctx.getPointerType(
GeneralizeFunctionType(Ctx, PTy, GeneralizePointers));

if (!GeneralizePointers)
return Ty;

return Ctx.getPointerType(
QualType(Ctx.VoidTy)
.withCVRQualifiers(Ty->getPointeeType().getCVRQualifiers()));
QualType(Ctx.VoidTy).withCVRQualifiers(PTy.getCVRQualifiers()));
}

// Apply type generalization to a FunctionType's return and argument types
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2 changes: 1 addition & 1 deletion clang/test/CodeGen/cfi-icall-generalize.c
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Expand Up @@ -30,6 +30,6 @@ void uni(void (*fn)(union Union), union Union arg1) {
// CHECK: [[TYPE]] = !{i64 0, !"_ZTSFPPiPKcPS2_E"}
// CHECK: [[TYPE_GENERALIZED]] = !{i64 0, !"_ZTSFPvPKvS_E.generalized"}

// CHECK: [[TYPE2]] = !{i64 0, !"_ZTSFvPFv5UnionEPcE"}
// CHECK: [[TYPE2]] = !{i64 0, !"_ZTSFvPFvPcES_E"}
// CHECK: [[TYPE2_GENERALIZED]] = !{i64 0, !"_ZTSFvPvS_E.generalized"}

2 changes: 1 addition & 1 deletion clang/test/CodeGen/cfi-icall-normalize2.c
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Expand Up @@ -39,5 +39,5 @@ void uni(void (*fn)(union Union), union Union 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, !"_ZTSFvPFv5UnionEPu2i8E.normalized"}
// CHECK: ![[TYPE4]] = !{i64 0, !"_ZTSFvPFvPu2i8ES0_E.normalized"}

2 changes: 1 addition & 1 deletion clang/test/CodeGen/kcfi-generalize.c
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Expand Up @@ -44,5 +44,5 @@ void uni(void (*fn)(union Union), union Union arg1) {
// UNGENERALIZED: [[TYPE3]] = !{i32 874141567}
// GENERALIZED: [[TYPE3]] = !{i32 954385378}

// UNGENERALIZED: [[TYPE4]] = !{i32 -1619636625}
// UNGENERALIZED: [[TYPE4]] = !{i32 -1954865805}
// GENERALIZED: [[TYPE4]] = !{i32 -125078496}
2 changes: 1 addition & 1 deletion clang/test/CodeGen/kcfi-normalize.c
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Expand Up @@ -45,5 +45,5 @@ void uni(void (*fn)(union Union), union Union arg1) {
// CHECK: ![[TYPE1]] = !{i32 -1143117868}
// CHECK: ![[TYPE2]] = !{i32 -460921415}
// CHECK: ![[TYPE3]] = !{i32 -333839615}
// C: ![[TYPE4]] = !{i32 -650530463}
// C: ![[TYPE4]] = !{i32 1186327125}
// CPP: ![[TYPE4]] = !{i32 1766237188}
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