[Clang][Sema] Add -Wcast-function-type-strict

[samitolvanen]

Summary

Clang supports indirect call Control-Flow Integrity (CFI) sanitizers
(e.g. -fsanitize=cfi-icall), which enforce an exact type match between
a function pointer and the target function. Unfortunately, Clang
doesn't provide diagnostics that would help developers avoid function
type casts that lead to runtime CFI failures. -Wcast-function-type,
while helpful, only warns about ABI incompatibility, which isn't
sufficient with CFI.

Add -Wcast-function-type-strict, which checks for a strict type
compatibility in function type casts and helps warn about casts that
can potentially lead to CFI failures.

[samitolvanen]

Any thoughts about adding a stricter version of -Wcast-function-type to make it easier to catch potential CFI issues? I also considered also gating this behind -fsanitize=cfi-icall/kcfi, but having a separate warning flag would be more consistent.

[nickdesaulniers]

SGTM; please make a note of this new diagnostic flag in clang/docs/ReleaseNotes.rst under Improvements to Clang's diagnostics.

clang/include/clang/Basic/DiagnosticSemaKinds.td

8698

I don't think we need a new group for a warning that only contains one diagnostic kind?

[samitolvanen]

Added a release note.

clang/include/clang/Basic/DiagnosticSemaKinds.td

8698

I don't think we need a new group for a warning that only contains one diagnostic kind?

I might have misunderstood something, but we seem to have plenty of groups with only one diagnostic kind. Is there a way to add a new warning flag without adding a diagnostic group? Most users of -Wcast-function-type wouldn't want to enable the stricter version, so I would prefer to keep this separate.

I did notice that some warnings don't define the group in DiagnosticGroups.td, but specify it directly here. For example, InGroup<DiagGroup<"argument-outside-range">>. I'm not sure if there are any benefits in doing so.

[aaron.ballman]

clang/include/clang/Basic/DiagnosticSemaKinds.td

8698

Typically we only define a group in DiagnosticGroups.td when the group is going to be used by more than one diagnostic, otherwise we prefer using InGroup<DiagGroup<"whatever">> to form one-off diagnostic groups.

However, in this case, I am wondering if we want to add CastFunctionTypeStrict to be a subgroup of CastFunctionType so that users who enable -Wcast-function-type get the stricter checking by default, but still have a way to disable the stricter checking if it's too noisy for them?

clang/lib/Sema/SemaCast.cpp

1095–1097

Coding style nit.

1185–1186

Same elsewhere (the type isn't spelled out in the initialization, so we prefer using an explicit type).

clang/test/Sema/warn-cast-function-type-strict.c

2

Do we need to use the triple here, or can we make this test target agnostic?

clang/test/SemaCXX/warn-cast-function-type-strict.cpp

2

Same question about triples here.

33

You should use // style comments here, this is a C++ test file anyway.

[kees]

clang/include/clang/Basic/DiagnosticSemaKinds.td

8698

However, in this case, I am wondering if we want to add CastFunctionTypeStrict to be a subgroup of CastFunctionType so that users who enable -Wcast-function-type get the stricter checking by default, but still have a way to disable the stricter checking if it's too noisy for them?

I'd be for that. It'll be very noisy for the Linux kernel, but they are all instances we need to fix.

cc @nathanchance

[nathanchance]

clang/include/clang/Basic/DiagnosticSemaKinds.td

8698

However, in this case, I am wondering if we want to add CastFunctionTypeStrict to be a subgroup of CastFunctionType so that users who enable -Wcast-function-type get the stricter checking by default, but still have a way to disable the stricter checking if it's too noisy for them?

I'd be for that. It'll be very noisy for the Linux kernel, but they are all instances we need to fix.

cc @nathanchance

Right, it would be quite noisy but we have already built an escape hatch for this type of scenario. We can just do what we have done for other warnings and disable it for "normal" builds to avoid disrupting the configurations with -Werror enabled (especially since we are not the only ones testing with tip of tree LLVM) then turn it on for W=1 so that the build bots will catch new instances of the warnings while we clean up the other ones. I think such a diff would just look like:

diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index 6ae482158bc4..52bd7df84fd6 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -64,6 +64,7 @@ KBUILD_CFLAGS += -Wno-sign-compare
 KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast)
 KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare
 KBUILD_CFLAGS += $(call cc-disable-warning, unaligned-access)
+KBUILD_CFLAGS += $(call cc-disable-warning, cast-function-type-strict)
 endif

 endif

then that can just be reverted when we have all the instances cleaned up. It would be nice to get a game plan together for tackling all these because they appear to be quite numerous.

[aaron.ballman]

clang/include/clang/Basic/DiagnosticSemaKinds.td

8698

Do we think this will be onerously chatty for C code bases in general? My intuition is that it will be reasonable -- folks who have enabled this warning want to know when they're type casting function pointers in odd ways. Looking at some test cases, I actually think this will behave more like users expect. e.g., https://godbolt.org/z/cWGecK1KG

clang/test/Sema/warn-cast-function-type-strict.c

31

Some other test cases I think we should try out:

typedef int (f8)(int *);
typedef int (f9)(const int);
typedef int (f10)(int);

int foo(int array[static 12]);
int bar(int i);
const int baz(int i);

f8 *h = (f8 *)foo; // Should be okay, types are the same after adjustment
f9 *i = (f9 *)bar; // Should be okay, types are the same after adjustment
f10 *j = (f10 *)baz; // Should be okay, types are the same after adjustment

[samitolvanen]

Moved CastFunctionTypeStrict to a subgroup of CastFunctionType, addressed other feedback, and updated tests.

clang/include/clang/Basic/DiagnosticSemaKinds.td

8698

Do we think this will be onerously chatty for C code bases in general? My intuition is that it will be reasonable -- folks who have enabled this warning want to know when they're type casting function pointers in odd ways.

This produces 1500+ new warnings in the kernel, but yes, I believe these are warnings we expected to see already with -Wcast-function-type. Nathan's suggestion to disable the strict warning without W=1 sounds reasonable to me.

clang/test/Sema/warn-cast-function-type-strict.c

2

I don't think it's needed. This was copied from the -Wcast-function-type test.

31

The first two seem to be OK, the last one does produce a warning here:

cast from 'const int (*)(int)' to 'f10 *' (aka 'int (*)(int)') converts to incompatible function type

[aaron.ballman]

clang/docs/ReleaseNotes.rst

311–313

clang/test/Sema/warn-cast-function-type-strict.c

31

Oh yeah, that's right, the C standard is pretty weird here. The return type is required to be compatible (aka same type in this case) per C2x 6.7.6.3p14, and int and const int are not compatible types (C2x 6.7.3p11). However, the qualifier on the return type is useless because it's stripped when the function is called (C2x 6.5.2.2p5, 6.8.6.4p3, 6.5.16p3, 6.3.2.1p2).

Compilers are wildly inconsistent about this: https://godbolt.org/z/hc6ordGeM

clang/test/SemaCXX/warn-cast-function-type-strict.cpp

2

You should remove the -x c++ from the RUN line still.

clang/test/SemaCXX/warn-cast-function-type.cpp

1

[samitolvanen]

Addressed feedback.

[aaron.ballman]

LGTM assuming precommit CI doesn't find any surprises, thank you for this!

[nickdesaulniers]

Please get the patch disabling this warning for the kernel in flight before landing this. It's going to make a lot of CI red due to kernel builds enabling -Werror.

[samitolvanen]

In D134831#3827730, @nickdesaulniers wrote:

Please get the patch disabling this warning for the kernel in flight before landing this.

Agreed. @nathanchance do you want to send the patch above to LKML?

[nathanchance]

In D134831#3827790, @samitolvanen wrote:

In D134831#3827730, @nickdesaulniers wrote:

Please get the patch disabling this warning for the kernel in flight before landing this.

Agreed. @nathanchance do you want to send the patch above to LKML?

I can send it on Monday, as I am offline today (or at least not at a computer lol). If you want to move on it quicker, feel free to draft a commit message and slap my Suggested-by on it.

[samitolvanen]

In D134831#3827861, @nathanchance wrote:

If you want to move on it quicker, feel free to draft a commit message and slap my Suggested-by on it.

https://lore.kernel.org/all/[e-mail]/

[nickdesaulniers]

Please consider waiting until the warning flag has started propagating to branches of stable, at least to whatever branch -Werror is first enabled in.

[samitolvanen]

In D134831#3838373, @nickdesaulniers wrote:

Please consider waiting until the warning flag has started propagating to branches of stable, at least to whatever branch -Werror is first enabled in.

Yes, I'm planning to wait until the kernel patch lands in stable branches. Greg picked up the patch this morning, so it should be in the next batch of stable releases.

[samitolvanen]

The patch to disable this warning in Linux without W=1 is now in all supported stable kernels (https://lwn.net/Articles/912498/), so I'll commit this later today.

[inglorion]

Is this intended to warn on code that casts a function taking a pointer to some non-void type to a function that takes a void*?

void set(void (*g)(int*)) {
  f = (void(*)(void*)) g;
}

gives me

warning: cast from 'void (*)(int *)' to 'void (*)(void *)' converts to incompatible function type [-Wcast-function-type-strict]

I didn't see this mentioned in the diff description, comments, or test. Is the behavior intentional? Are these types actually incompatible?

[samitolvanen]

In D134831#4137408, @inglorion wrote:

Is this intended to warn on code that casts a function taking a pointer to some non-void type to a function that takes a void*?

Yes, this is intended to warn if the function types don't match.

I didn't see this mentioned in the diff description, comments, or test. Is the behavior intentional? Are these types actually incompatible?

As far as the language is concerned, the types are not incompatible, but calling the function pointer would trip -fsanitize=cfi checking, which this warning is meant to catch. If your program is not using CFI, you may want to consider disabling the -strict warning.

[inglorion]

Thanks for the reply!

FWIW, this warning is triggered by code which uses glib, which contains a number of function(some_type*) to function(void*) casts, for example here: https://github.com/GNOME/glib/blob/339aaa3719757614af61f427b66a46893e6dc760/glib/glib-autocleanups.h#L47, which expands to function pointer casts here: https://github.com/GNOME/glib/blob/339aaa3719757614af61f427b66a46893e6dc760/glib/gmacros.h#L1360

I imagine glib is reasonably commonly used, so this might cause some build failures (we're seeing some in ChromiumOS). Not sure if that's enough to affect the choice of having this on or off by default when -Wcast-function-type is in effect, but I thought I would provide the data point.

[aaron.ballman]

In D134831#4141842, @samitolvanen wrote:

In D134831#4137408, @inglorion wrote:

Is this intended to warn on code that casts a function taking a pointer to some non-void type to a function that takes a void*?

Yes, this is intended to warn if the function types don't match.

I didn't see this mentioned in the diff description, comments, or test. Is the behavior intentional? Are these types actually incompatible?

As far as the language is concerned, the types are not incompatible, <snip>

As far as C and C++ are concerned, those types *are* incompatible.

C2x 6.7.6.3p14: For two function types to be compatible, both shall specify compatible return types. Moreover, the parameter type lists shall agree in the number of parameters and in use of the final ellipsis; corresponding parameters shall have compatible types. In the determination of type compatibility and of a composite type, each parameter declared with function or array type is taken as having the adjusted type and each parameter declared with qualified type is taken as having the unqualified version of its declared type.

6.7.6.1p2: For two pointer types to be compatible, both shall be identically qualified and both shall be pointers to compatible types.

6.2.7p1: Two types are compatible types if they are the same. Additional rules for determining whether two types are compatible are described in <snip>

void * and int * are not compatible types, so the function parameter lists are not compatible, so the function types are not compatible.

(Similar is in C++, though the specification mechanics are different.)

clang/docs/ReleaseNotes.rst

- Clang now correctly diagnoses index that refers past the last possible element
   of FAM-like arrays.
 - Clang now correctly diagnoses a warning when defercencing a void pointer in C mode.
   This fixes `Issue 53631 <https://github.com/llvm/llvm-project/issues/53631>`_
 - Clang will now diagnose an overload set where a candidate has a constraint that
   refers to an expression with a previous error as nothing viable, so that it
   doesn't generate strange cascading errors, particularly in cases where a
   subsuming constraint fails, which would result in a less-specific overload to
   be selected.
 - Add a fix-it hint for the ``-Wdefaulted-function-deleted`` warning to
   explicitly delete the function.
 - Fixed an accidental duplicate diagnostic involving the declaration of a
   function definition without a prototype which is preceded by a static
   declaration of the function with a prototype. Fixes
   `Issue 58181 <https://github.com/llvm/llvm-project/issues/58181>`_.
 - Copy-elided initialization of lock scopes is now handled differently in
   ``-Wthread-safety-analysis``: annotations on the move constructor are no
   longer taken into account, in favor of annotations on the function returning
   the lock scope by value. This could result in new warnings if code depended
   on the previous undocumented behavior. As a side effect of this change,
   constructor calls outside of initializer expressions are no longer ignored,
   which can result in new warnings (or make existing warnings disappear).
 - The wording of diagnostics regarding arithmetic on fixed-sized arrays and
   pointers is improved to include the type of the array and whether it's cast
   to another type. This should improve comprehension for why an index is
   out-of-bounds.
 - Clang now correctly points to the problematic parameter for the ``-Wnonnull``
   warning. This fixes
   `Issue 58273 <https://github.com/llvm/llvm-project/issues/58273>`_.
+- Introduced ``-Wcast-function-type-strict`` to warn about function type mismatches
+  in casts that may result in runtime indirect call `Control-Flow Integrity (CFI)
+  <https://clang.llvm.org/docs/ControlFlowIntegrity.html>`_ failures. This diagnostic
+  is grouped under ``-Wcast-function-type`` as it identifies a more strict set of
+  potentially problematic function type casts.
 
 Non-comprehensive list of changes in this release
 -------------------------------------------------
 - It's now possible to set the crash diagnostics directory through
   the environment variable ``CLANG_CRASH_DIAGNOSTICS_DIR``.
   The ``-fcrash-diagnostics-dir`` flag takes precedence.
 - When using header modules, inclusion of a private header and violations of
   the `use-declaration rules

clang/include/clang/Basic/DiagnosticGroups.td

 def ObjCReceiver : DiagGroup<"receiver-expr">;
 def OperatorNewReturnsNull : DiagGroup<"new-returns-null">;
 def OverlengthStrings : DiagGroup<"overlength-strings">;
 def OverloadedVirtual : DiagGroup<"overloaded-virtual">;
 def PrivateExtern : DiagGroup<"private-extern">;
 def SelTypeCast : DiagGroup<"cast-of-sel-type">;
 def FunctionDefInObjCContainer : DiagGroup<"function-def-in-objc-container">;
 def BadFunctionCast : DiagGroup<"bad-function-cast">;
-def CastFunctionType : DiagGroup<"cast-function-type">;
+def CastFunctionTypeStrict : DiagGroup<"cast-function-type-strict">;
+def CastFunctionType : DiagGroup<"cast-function-type", [CastFunctionTypeStrict]>;
 def ObjCPropertyImpl : DiagGroup<"objc-property-implementation">;
 def ObjCPropertyNoAttribute : DiagGroup<"objc-property-no-attribute">;
 def ObjCPropertyAssignOnObjectType : DiagGroup<"objc-property-assign-on-object-type">;
 def ObjCProtocolQualifiers : DiagGroup<"objc-protocol-qualifiers">;
 def ObjCMissingSuperCalls : DiagGroup<"objc-missing-super-calls">;
 def ObjCDesignatedInit : DiagGroup<"objc-designated-initializers">;
 def ObjCRetainBlockProperty : DiagGroup<"objc-noncopy-retain-block-property">;
 def ObjCReadonlyPropertyHasSetter : DiagGroup<"objc-readonly-with-setter-property">;

clang/include/clang/Basic/DiagnosticSemaKinds.td

 def note_change_calling_conv_fixit : Note<
   "consider defining %0 with the '%1' calling convention">;
 def warn_bad_function_cast : Warning<
   "cast from function call of type %0 to non-matching type %1">,
   InGroup<BadFunctionCast>, DefaultIgnore;
 def warn_cast_function_type : Warning<
   "cast %diff{from $ to $ |}0,1converts to incompatible function type">,
   InGroup<CastFunctionType>, DefaultIgnore;
+def warn_cast_function_type_strict : Warning<warn_cast_function_type.Text>,
+  InGroup<CastFunctionTypeStrict>, DefaultIgnore;
 def err_cast_pointer_to_non_pointer_int : Error<
   "pointer cannot be cast to type %0">;
 def err_nullptr_cast : Error<
   "cannot cast an object of type %select{'nullptr_t' to %1|%1 to 'nullptr_t'}0"
 >;
 def err_cast_to_bfloat16 : Error<"cannot type-cast to __bf16">;
 def err_cast_from_bfloat16 : Error<"cannot type-cast from __bf16">;
 def err_typecheck_expect_scalar_operand : Error<

clang/lib/Sema/SemaCast.cpp

static bool argTypeIsABIEquivalent(QualType SrcType, QualType DestType,
   if (SrcType->isIntegralType(Context) && DestType->isIntegralType(Context))
     if (Context.getTypeInfoInChars(SrcType).Width ==
         Context.getTypeInfoInChars(DestType).Width)
       return true;
 
   return Context.hasSameUnqualifiedType(SrcType, DestType);
 }
 
-static bool checkCastFunctionType(Sema &Self, const ExprResult &SrcExpr,
+static unsigned int checkCastFunctionType(Sema &Self, const ExprResult &SrcExpr,
                                           QualType DestType) {
-  if (Self.Diags.isIgnored(diag::warn_cast_function_type,
-                           SrcExpr.get()->getExprLoc()))
-    return true;
+  unsigned int DiagID = 0;
+  const unsigned int DiagList[] = {diag::warn_cast_function_type_strict,
+                                   diag::warn_cast_function_type};
+  for (auto ID : DiagList) {
+    if (!Self.Diags.isIgnored(ID, SrcExpr.get()->getExprLoc())) {
+      DiagID = ID;
+      break;
+    }
+  }
+  if (!DiagID)
+    return 0;
 
   QualType SrcType = SrcExpr.get()->getType();
   const FunctionType *SrcFTy = nullptr;
   const FunctionType *DstFTy = nullptr;
   if (((SrcType->isBlockPointerType() || SrcType->isFunctionPointerType()) &&
        DestType->isFunctionPointerType()) ||
       (SrcType->isMemberFunctionPointerType() &&
        DestType->isMemberFunctionPointerType())) {
     SrcFTy = SrcType->getPointeeType()->castAs<FunctionType>();
     DstFTy = DestType->getPointeeType()->castAs<FunctionType>();
   } else if (SrcType->isFunctionType() && DestType->isFunctionReferenceType()) {
     SrcFTy = SrcType->castAs<FunctionType>();
     DstFTy = DestType.getNonReferenceType()->castAs<FunctionType>();
   } else {
-    return true;
+    return 0;
   }
   assert(SrcFTy && DstFTy);
 
+  if (Self.Context.hasSameType(SrcFTy, DstFTy))
+    return 0;
+
+  // For strict checks, ensure we have an exact match.
+  if (DiagID == diag::warn_cast_function_type_strict)
+    return DiagID;
+
   auto IsVoidVoid = [](const FunctionType *T) {
     if (!T->getReturnType()->isVoidType())
       return false;
     if (const auto *PT = T->getAs<FunctionProtoType>())
       return !PT->isVariadic() && PT->getNumParams() == 0;
     return false;
   };
 
   // Skip if either function type is void(*)(void)
   if (IsVoidVoid(SrcFTy) || IsVoidVoid(DstFTy))
-    return true;
+    return 0;
 
   // Check return type.
   if (!argTypeIsABIEquivalent(SrcFTy->getReturnType(), DstFTy->getReturnType(),
                               Self.Context))
-    return false;
+    return DiagID;
 
   // Check if either has unspecified number of parameters
   if (SrcFTy->isFunctionNoProtoType() || DstFTy->isFunctionNoProtoType())
-    return true;
+    return 0;
 
   // Check parameter types.
 
   const auto *SrcFPTy = cast<FunctionProtoType>(SrcFTy);
   const auto *DstFPTy = cast<FunctionProtoType>(DstFTy);
 
   // In a cast involving function types with a variable argument list only the
   // types of initial arguments that are provided are considered.
   unsigned NumParams = SrcFPTy->getNumParams();
   unsigned DstNumParams = DstFPTy->getNumParams();
   if (NumParams > DstNumParams) {
     if (!DstFPTy->isVariadic())
-      return false;
+      return DiagID;
     NumParams = DstNumParams;
   } else if (NumParams < DstNumParams) {
     if (!SrcFPTy->isVariadic())
-      return false;
+      return DiagID;
   }
 
   for (unsigned i = 0; i < NumParams; ++i)
     if (!argTypeIsABIEquivalent(SrcFPTy->getParamType(i),
                                 DstFPTy->getParamType(i), Self.Context))
-      return false;
+      return DiagID;
 
-  return true;
+  return 0;
 }
 
 /// CheckReinterpretCast - Check that a reinterpret_cast\<DestType\>(SrcExpr) is
 /// valid.
 /// Refer to C++ 5.2.10 for details. reinterpret_cast is typically used in code
 /// like this:
 /// char *bytes = reinterpret_cast\<char*\>(int_ptr);
 void CastOperation::CheckReinterpretCast() {
if (tcr != TC_Success && msg != 0) {
     }
   }
 
   if (isValidCast(tcr)) {
     if (Self.getLangOpts().allowsNonTrivialObjCLifetimeQualifiers())
       checkObjCConversion(Sema::CCK_OtherCast);
     DiagnoseReinterpretUpDownCast(Self, SrcExpr.get(), DestType, OpRange);
 
-    if (!checkCastFunctionType(Self, SrcExpr, DestType))
-      Self.Diag(OpRange.getBegin(), diag::warn_cast_function_type)
+    if (unsigned DiagID = checkCastFunctionType(Self, SrcExpr, DestType))
+      Self.Diag(OpRange.getBegin(), DiagID)
           << SrcExpr.get()->getType() << DestType << OpRange;
   } else {
     SrcExpr = ExprError();
   }
 }
 
 
 /// CheckStaticCast - Check that a static_cast\<DestType\>(SrcExpr) is valid.
if (SrcExpr.get()->getType() == Self.Context.OverloadTy) {
                       OpRange, SrcExpr.get(), DestType, ListInitialization);
     }
   }
 
   if (isValidCast(tcr)) {
     if (Kind == CK_BitCast)
       checkCastAlign();
 
-    if (!checkCastFunctionType(Self, SrcExpr, DestType))
-      Self.Diag(OpRange.getBegin(), diag::warn_cast_function_type)
+    if (unsigned DiagID = checkCastFunctionType(Self, SrcExpr, DestType))
+      Self.Diag(OpRange.getBegin(), DiagID)
           << SrcExpr.get()->getType() << DestType << OpRange;
 
   } else {
     SrcExpr = ExprError();
   }
 }
 
 /// DiagnoseBadFunctionCast - Warn whenever a function call is cast to a
else if (!Self.CheckObjCARCUnavailableWeakConversion(DestType, SrcType)) {
       Self.Diag(SrcExpr.get()->getBeginLoc(),
                 diag::err_arc_convesion_of_weak_unavailable)
           << 1 << SrcType << DestType << SrcExpr.get()->getSourceRange();
       SrcExpr = ExprError();
       return;
     }
   }
 
-  if (!checkCastFunctionType(Self, SrcExpr, DestType))
-    Self.Diag(OpRange.getBegin(), diag::warn_cast_function_type)
-        << SrcType << DestType << OpRange;
+  if (unsigned DiagID = checkCastFunctionType(Self, SrcExpr, DestType))
+    Self.Diag(OpRange.getBegin(), DiagID) << SrcType << DestType << OpRange;
 
   if (isa<PointerType>(SrcType) && isa<PointerType>(DestType)) {
     QualType SrcTy = cast<PointerType>(SrcType)->getPointeeType();
     QualType DestTy = cast<PointerType>(DestType)->getPointeeType();
 
     const RecordDecl *SrcRD = SrcTy->getAsRecordDecl();
     const RecordDecl *DestRD = DestTy->getAsRecordDecl();
 

clang/test/Sema/warn-cast-function-type-strict.c

+// RUN: %clang_cc1 %s -fsyntax-only -Wcast-function-type -verify
+// RUN: %clang_cc1 %s -fsyntax-only -Wcast-function-type-strict -verify
+
+
+int t(int array[static 12]);
+int u(int i);
+const int v(int i);
+int x(long);
+
+typedef int (f1)(long);
+typedef int (f2)(void*);
+typedef int (f3)();
+typedef void (f4)();
+typedef void (f5)(void);
+typedef int (f6)(long, int);
+typedef int (f7)(long,...);
+typedef int (f8)(int *);
+typedef int (f9)(const int);
+typedef int (f10)(int);
+
+f1 *a;
+f2 *b;
+f3 *c;
+f4 *d;
+f5 *e;
+f6 *f;
+f7 *g;
+f8 *h;
+f9 *i;
+f10 *j;
+
+void foo(void) {
+  a = (f1 *)x;
+  b = (f2 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f2 *' (aka 'int (*)(void *)') converts to incompatible function type}} */
+  c = (f3 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f3 *' (aka 'int (*)()') converts to incompatible function type}} */
+  d = (f4 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f4 *' (aka 'void (*)()') converts to incompatible function type}} */
+  e = (f5 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f5 *' (aka 'void (*)(void)') converts to incompatible function type}} */
+  f = (f6 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f6 *' (aka 'int (*)(long, int)') converts to incompatible function type}} */
+  g = (f7 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f7 *' (aka 'int (*)(long, ...)') converts to incompatible function type}} */
+  h = (f8 *)t;
+  i = (f9 *)u;
+  j = (f10 *)v; /* expected-warning {{cast from 'const int (*)(int)' to 'f10 *' (aka 'int (*)(int)') converts to incompatible function type}} */
+}

clang/test/Sema/warn-cast-function-type.c

-// RUN: %clang_cc1 -x c %s -fsyntax-only -Wcast-function-type -triple x86_64-- -verify
+// RUN: %clang_cc1 %s -fsyntax-only -Wcast-function-type -Wno-cast-function-type-strict -verify
 
 int x(long);
 
 typedef int (f1)(long);
 typedef int (f2)(void*);
 typedef int (f3)();
 typedef void (f4)();
 typedef void (f5)(void);

clang/test/SemaCXX/warn-cast-function-type-strict.cpp

+// RUN: %clang_cc1 %s -fblocks -fsyntax-only -Wcast-function-type -verify
+// RUN: %clang_cc1 %s -fblocks -fsyntax-only -Wcast-function-type-strict -verify
+
+int x(long);
+
+typedef int (f1)(long);
+typedef int (f2)(void*);
+typedef int (f3)(...);
+typedef void (f4)(...);
+typedef void (f5)(void);
+typedef int (f6)(long, int);
+typedef int (f7)(long,...);
+typedef int (&f8)(long, int);
+
+f1 *a;
+f2 *b;
+f3 *c;
+f4 *d;
+f5 *e;
+f6 *f;
+f7 *g;
+
+struct S
+{
+  void foo (int*);
+  void bar (int);
+};
+
+typedef void (S::*mf)(int);
+
+void foo() {
+  a = (f1 *)x;
+  b = (f2 *)x; // expected-warning {{cast from 'int (*)(long)' to 'f2 *' (aka 'int (*)(void *)') converts to incompatible function type}}
+  b = reinterpret_cast<f2 *>(x); // expected-warning {{cast from 'int (*)(long)' to 'f2 *' (aka 'int (*)(void *)') converts to incompatible function type}}
+  c = (f3 *)x; // expected-warning {{cast from 'int (*)(long)' to 'f3 *' (aka 'int (*)(...)') converts to incompatible function type}}
+  d = (f4 *)x; // expected-warning {{cast from 'int (*)(long)' to 'f4 *' (aka 'void (*)(...)') converts to incompatible function type}}
+  e = (f5 *)x; // expected-warning {{cast from 'int (*)(long)' to 'f5 *' (aka 'void (*)()') converts to incompatible function type}}
+  f = (f6 *)x; // expected-warning {{cast from 'int (*)(long)' to 'f6 *' (aka 'int (*)(long, int)') converts to incompatible function type}}
+  g = (f7 *)x; // expected-warning {{cast from 'int (*)(long)' to 'f7 *' (aka 'int (*)(long, ...)') converts to incompatible function type}}
+
+  mf p1 = (mf)&S::foo; // expected-warning {{cast from 'void (S::*)(int *)' to 'mf' (aka 'void (S::*)(int)') converts to incompatible function type}}
+
+  f8 f2 = (f8)x; // expected-warning {{cast from 'int (long)' to 'f8' (aka 'int (&)(long, int)') converts to incompatible function type}}
+  (void)f2;
+
+  int (^y)(long);
+  f = (f6 *)y; // expected-warning {{cast from 'int (^)(long)' to 'f6 *' (aka 'int (*)(long, int)') converts to incompatible function type}}
+}

clang/test/SemaCXX/warn-cast-function-type.cpp

-// RUN: %clang_cc1 -x c++ %s -fblocks -fsyntax-only -Wcast-function-type -triple x86_64-- -verify
+// RUN: %clang_cc1 %s -fblocks -fsyntax-only -Wcast-function-type -Wno-cast-function-type-strict -verify
 
 int x(long);
 
 typedef int (f1)(long);
 typedef int (f2)(void*);
 typedef int (f3)(...);
 typedef void (f4)(...);
 typedef void (f5)(void);
struct S
   void foo (int*);
   void bar (int);
 };
 
 typedef void (S::*mf)(int);
 
 void foo() {
   a = (f1 *)x;
-  b = (f2 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f2 *' (aka 'int (*)(void *)') converts to incompatible function type}} */
-  b = reinterpret_cast<f2 *>(x); /* expected-warning {{cast from 'int (*)(long)' to 'f2 *' (aka 'int (*)(void *)') converts to incompatible function type}} */
+  b = (f2 *)x; // expected-warning {{cast from 'int (*)(long)' to 'f2 *' (aka 'int (*)(void *)') converts to incompatible function type}}
+  b = reinterpret_cast<f2 *>(x); // expected-warning {{cast from 'int (*)(long)' to 'f2 *' (aka 'int (*)(void *)') converts to incompatible function type}}
   c = (f3 *)x;
-  d = (f4 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f4 *' (aka 'void (*)(...)') converts to incompatible function type}} */
+  d = (f4 *)x; // expected-warning {{cast from 'int (*)(long)' to 'f4 *' (aka 'void (*)(...)') converts to incompatible function type}}
   e = (f5 *)x;
-  f = (f6 *)x; /* expected-warning {{cast from 'int (*)(long)' to 'f6 *' (aka 'int (*)(long, int)') converts to incompatible function type}} */
+  f = (f6 *)x; // expected-warning {{cast from 'int (*)(long)' to 'f6 *' (aka 'int (*)(long, int)') converts to incompatible function type}}
   g = (f7 *)x;
 
-  mf p1 = (mf)&S::foo; /* expected-warning {{cast from 'void (S::*)(int *)' to 'mf' (aka 'void (S::*)(int)') converts to incompatible function type}} */
+  mf p1 = (mf)&S::foo; // expected-warning {{cast from 'void (S::*)(int *)' to 'mf' (aka 'void (S::*)(int)') converts to incompatible function type}}
 
-  f8 f2 = (f8)x; /* expected-warning {{cast from 'int (long)' to 'f8' (aka 'int (&)(long, int)') converts to incompatible function type}} */
+  f8 f2 = (f8)x; // expected-warning {{cast from 'int (long)' to 'f8' (aka 'int (&)(long, int)') converts to incompatible function type}}
   (void)f2;
 
   int (^y)(long);
-  f = (f6 *)y; /* expected-warning {{cast from 'int (^)(long)' to 'f6 *' (aka 'int (*)(long, int)') converts to incompatible function type}} */
+  f = (f6 *)y; // expected-warning {{cast from 'int (^)(long)' to 'f6 *' (aka 'int (*)(long, int)') converts to incompatible function type}}
 }