Diagnose problematic uses of constructor/destructor attribute (#67360)

Functions with these attributes will be automatically called before
`main()` or after `main()` exits gracefully, which means the functions
should not accept arguments or have a returned value (nothing can
provide an argument to the call in these cases, and nothing can use the
returned value), nor should they be allowed on a non-static member
function or consteval function in C++. We allow 'int' as a return type for
the function due to finding a significant amount of historical code using
`int(void)` as a signature.

Additionally, these reuse the same priority logic as the init_priority
attribute which explicitly reserved priorty values <= 100 or > 65535. So
we now diagnose use of reserved priorities the same as we do for the
init_priority attribute.

Author: AaronBallman

clang/docs/ReleaseNotes.rst

@@ -171,6 +171,11 @@ Attribute Changes in Clang
   automatic diagnostic to use parameters of types that the format style
   supports but that are never the result of default argument promotion, such as
   ``float``. (`#59824: <https://github.com/llvm/llvm-project/issues/59824>`_)
+- The ``constructor`` and ``destructor`` attributes now diagnose when:
+  - the priority is not between 101 and 65535, inclusive,
+  - the function it is applied to accepts arguments or has a non-void return
+    type, or
+  - the function it is applied to is a non-static member function (C++).
 
 Improvements to Clang's diagnostics
 -----------------------------------

clang/include/clang/Basic/AttrDocs.td

@@ -7251,8 +7251,10 @@ after returning from ``main()`` or when the ``exit()`` function has been
 called. Note, ``quick_exit()``, ``_Exit()``, and ``abort()`` prevent a function
 marked ``destructor`` from being called.
 
-The constructor or destructor function should not accept any arguments and its
-return type should be ``void``.
+The constructor or destructor function cannot accept any arguments and its
+return type should be ``void``, ``int``, or ``unsigned int``. The latter two
+types are supported for historical reasons. In C++ language modes, the function
+cannot be marked ``consteval``, nor can it be a non-static member function.
 
 The attributes accept an optional argument used to specify the priority order
 in which to execute constructor and destructor functions. The priority is

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -2864,6 +2864,8 @@ def warn_cxx11_compat_constexpr_body_multiple_return : Warning<
   InGroup<CXXPre14Compat>, DefaultIgnore;
 def note_constexpr_body_previous_return : Note<
   "previous return statement is here">;
+def err_ctordtor_attr_consteval : Error<
+  "%0 attribute cannot be applied to a 'consteval' function">;
 
 // C++20 function try blocks in constexpr
 def ext_constexpr_function_try_block_cxx20 : ExtWarn<
@@ -3176,6 +3178,11 @@ def err_alignas_underaligned : Error<
   "requested alignment is less than minimum alignment of %1 for type %0">;
 def warn_aligned_attr_underaligned : Warning<err_alignas_underaligned.Summary>,
   InGroup<IgnoredAttributes>;
+def err_ctor_dtor_attr_on_non_void_func : Error<
+  "%0 attribute can only be applied to a function which accepts no arguments "
+  "and has a 'void' or 'int' return type">;
+def err_ctor_dtor_member_func : Error<
+  "%0 attribute cannot be applied to a member function">;
 def err_attribute_sizeless_type : Error<
   "%0 attribute cannot be applied to sizeless type %1">;
 def err_attribute_argument_n_type : Error<

clang/lib/Sema/SemaDeclAttr.cpp

@@ -2352,26 +2352,78 @@ static void handleUnusedAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
   D->addAttr(::new (S.Context) UnusedAttr(S.Context, AL));
 }
 
-static void handleConstructorAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
-  uint32_t priority = ConstructorAttr::DefaultPriority;
+static bool diagnoseInvalidPriority(Sema &S, uint32_t Priority,
+                                    const ParsedAttr &A,
+                                    SourceLocation PriorityLoc) {
+  constexpr uint32_t ReservedPriorityLower = 101, ReservedPriorityUpper = 65535;
+
+  // Only perform the priority check if the attribute is outside of a system
+  // header. Values <= 100 are reserved for the implementation, and libc++
+  // benefits from being able to specify values in that range. Values > 65535
+  // are reserved for historical reasons.
+  if ((Priority < ReservedPriorityLower || Priority > ReservedPriorityUpper) &&
+      !S.getSourceManager().isInSystemHeader(A.getLoc())) {
+    S.Diag(A.getLoc(), diag::err_attribute_argument_out_of_range)
+        << PriorityLoc << A << ReservedPriorityLower << ReservedPriorityUpper;
+    A.setInvalid();
+    return true;
+  }
+  return false;
+}
+
+template <typename CtorDtorAttr>
+static void handleCtorDtorAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
+  uint32_t Priority = CtorDtorAttr::DefaultPriority;
   if (S.getLangOpts().HLSL && AL.getNumArgs()) {
     S.Diag(AL.getLoc(), diag::err_hlsl_init_priority_unsupported);
     return;
   }
-  if (AL.getNumArgs() &&
-      !checkUInt32Argument(S, AL, AL.getArgAsExpr(0), priority))
-    return;
 
-  D->addAttr(::new (S.Context) ConstructorAttr(S.Context, AL, priority));
-}
+  // If we're given an argument for the priority, check that it's valid.
+  if (AL.getNumArgs()) {
+    if (!checkUInt32Argument(S, AL, AL.getArgAsExpr(0), Priority))
+      return;
 
-static void handleDestructorAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
-  uint32_t priority = DestructorAttr::DefaultPriority;
-  if (AL.getNumArgs() &&
-      !checkUInt32Argument(S, AL, AL.getArgAsExpr(0), priority))
+    // Ensure the priority is in a reasonable range.
+    if (diagnoseInvalidPriority(S, Priority, AL,
+                                AL.getArgAsExpr(0)->getExprLoc()))
+      return;
+  }
+
+  // Ensure the function we're attaching to is something that is sensible to
+  // automatically call before or after main(); it should accept no arguments.
+  // In theory, a void return type is the only truly safe return type (consider
+  // that calling conventions may place returned values in a hidden pointer
+  // argument passed to the function that will not be present when called
+  // automatically). However, there is a significant amount of existing code
+  // which uses an int return type. So we will accept void, int, and
+  // unsigned int return types. Any other return type, or a non-void parameter
+  // list is treated as an error because it's a form of type system
+  // incompatibility. The function also cannot be a member function. We allow
+  // K&R C functions because that's a difficult edge case where it depends on
+  // how the function is defined as to whether it does or does not expect
+  // arguments.
+  const auto *FD = cast<FunctionDecl>(D);
+  QualType RetTy = FD->getReturnType();
+  if (!(RetTy->isVoidType() ||
+        RetTy->isSpecificBuiltinType(BuiltinType::UInt) ||
+        RetTy->isSpecificBuiltinType(BuiltinType::Int)) ||
+      (FD->hasPrototype() && FD->getNumParams() != 0)) {
+    S.Diag(AL.getLoc(), diag::err_ctor_dtor_attr_on_non_void_func)
+        << AL << FD->getSourceRange();
     return;
+  } else if (const auto *MD = dyn_cast<CXXMethodDecl>(FD);
+             MD && MD->isInstance()) {
+    S.Diag(AL.getLoc(), diag::err_ctor_dtor_member_func)
+        << AL << FD->getSourceRange();
+    return;
+  } else if (FD->isConsteval()) {
+    S.Diag(AL.getLoc(), diag::err_ctordtor_attr_consteval)
+        << AL << FD->getSourceRange();
+    return;
+  }
 
-  D->addAttr(::new (S.Context) DestructorAttr(S.Context, AL, priority));
+  D->addAttr(CtorDtorAttr::Create(S.Context, Priority, AL));
 }
 
 template <typename AttrTy>
@@ -3888,16 +3940,9 @@ static void handleInitPriorityAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
     return;
   }
 
-  // Only perform the priority check if the attribute is outside of a system
-  // header. Values <= 100 are reserved for the implementation, and libc++
-  // benefits from being able to specify values in that range.
-  if ((prioritynum < 101 || prioritynum > 65535) &&
-      !S.getSourceManager().isInSystemHeader(AL.getLoc())) {
-    S.Diag(AL.getLoc(), diag::err_attribute_argument_out_of_range)
-        << E->getSourceRange() << AL << 101 << 65535;
-    AL.setInvalid();
+  if (diagnoseInvalidPriority(S, prioritynum, AL, E->getExprLoc()))
     return;
-  }
+
   D->addAttr(::new (S.Context) InitPriorityAttr(S.Context, AL, prioritynum));
 }
 
@@ -8930,13 +8975,13 @@ ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D, const ParsedAttr &AL,
     handlePassObjectSizeAttr(S, D, AL);
     break;
   case ParsedAttr::AT_Constructor:
-      handleConstructorAttr(S, D, AL);
+    handleCtorDtorAttr<ConstructorAttr>(S, D, AL);
     break;
   case ParsedAttr::AT_Deprecated:
     handleDeprecatedAttr(S, D, AL);
     break;
   case ParsedAttr::AT_Destructor:
-      handleDestructorAttr(S, D, AL);
+    handleCtorDtorAttr<DestructorAttr>(S, D, AL);
     break;
   case ParsedAttr::AT_EnableIf:
     handleEnableIfAttr(S, D, AL);

clang/test/CodeGen/PowerPC/aix-destructor-attribute.c

@@ -12,9 +12,8 @@
 // RUN:     -fno-use-cxa-atexit -fregister-global-dtors-with-atexit < %s | \
 // RUN:   FileCheck --check-prefix=REGISTER %s
 
-int bar(void) __attribute__((destructor(100)));
+int bar(void) __attribute__((destructor(101)));
 int bar2(void) __attribute__((destructor(65535)));
-int bar3(int) __attribute__((destructor(65535)));
 
 int bar(void) {
   return 1;
@@ -24,16 +23,12 @@ int bar2(void) {
   return 2;
 }
 
-int bar3(int a) {
-  return a;
-}
-
-// NO-REGISTER: @llvm.global_dtors = appending global [3 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 100, ptr @bar, ptr null }, { i32, ptr, ptr } { i32 65535, ptr @bar2, ptr null }, { i32, ptr, ptr } { i32 65535, ptr @bar3, ptr null }]
+// NO-REGISTER: @llvm.global_dtors = appending global [2 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 101, ptr @bar, ptr null }, { i32, ptr, ptr } { i32 65535, ptr @bar2, ptr null }]
 
-// REGISTER: @llvm.global_ctors = appending global [2 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 100, ptr @__GLOBAL_init_100, ptr null }, { i32, ptr, ptr } { i32 65535, ptr @__GLOBAL_init_65535, ptr null }]
-// REGISTER: @llvm.global_dtors = appending global [2 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 100, ptr @__GLOBAL_cleanup_100, ptr null }, { i32, ptr, ptr } { i32 65535, ptr @__GLOBAL_cleanup_65535, ptr null }]
+// REGISTER: @llvm.global_ctors = appending global [2 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 101, ptr @__GLOBAL_init_101, ptr null }, { i32, ptr, ptr } { i32 65535, ptr @__GLOBAL_init_65535, ptr null }]
+// REGISTER: @llvm.global_dtors = appending global [2 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 101, ptr @__GLOBAL_cleanup_101, ptr null }, { i32, ptr, ptr } { i32 65535, ptr @__GLOBAL_cleanup_65535, ptr null }]
 
-// REGISTER: define internal void @__GLOBAL_init_100() [[ATTR:#[0-9]+]] {
+// REGISTER: define internal void @__GLOBAL_init_101() [[ATTR:#[0-9]+]] {
 // REGISTER: entry:
 // REGISTER:   %0 = call i32 @atexit(ptr @bar)
 // REGISTER:   ret void
@@ -42,11 +37,10 @@ int bar3(int a) {
 // REGISTER: define internal void @__GLOBAL_init_65535() [[ATTR:#[0-9]+]] {
 // REGISTER: entry:
 // REGISTER:   %0 = call i32 @atexit(ptr @bar2)
-// REGISTER:   %1 = call i32 @atexit(ptr @bar3)
 // REGISTER:   ret void
 // REGISTER: }
 
-// REGISTER: define internal void @__GLOBAL_cleanup_100() [[ATTR:#[0-9]+]] {
+// REGISTER: define internal void @__GLOBAL_cleanup_101() [[ATTR:#[0-9]+]] {
 // REGISTER: entry:
 // REGISTER:   %0 = call i32 @unatexit(ptr @bar)
 // REGISTER:   %needs_destruct = icmp eq i32 %0, 0
@@ -62,20 +56,11 @@ int bar3(int a) {
 
 // REGISTER: define internal void @__GLOBAL_cleanup_65535() [[ATTR:#[0-9]+]] {
 // REGISTER: entry:
-// REGISTER:   %0 = call i32 @unatexit(ptr @bar3)
+// REGISTER:   %0 = call i32 @unatexit(ptr @bar2)
 // REGISTER:   %needs_destruct = icmp eq i32 %0, 0
-// REGISTER:   br i1 %needs_destruct, label %destruct.call, label %unatexit.call
+// REGISTER:   br i1 %needs_destruct, label %destruct.call, label %destruct.end
 
 // REGISTER: destruct.call:
-// REGISTER:   call void @bar3()
-// REGISTER:   br label %unatexit.call
-
-// REGISTER: unatexit.call:
-// REGISTER:   %1 = call i32 @unatexit(ptr @bar2)
-// REGISTER:   %needs_destruct1 = icmp eq i32 %1, 0
-// REGISTER:   br i1 %needs_destruct1, label %destruct.call2, label %destruct.end
-
-// REGISTER: destruct.call2:
 // REGISTER:   call void @bar2()
 // REGISTER:   br label %destruct.end
 

clang/test/CodeGenCXX/aix-destructor-attribute.cpp

@@ -17,9 +17,8 @@ struct test {
   ~test();
 } t;
 
-int bar() __attribute__((destructor(100)));
+int bar() __attribute__((destructor(101)));
 int bar2() __attribute__((destructor(65535)));
-int bar3(int) __attribute__((destructor(65535)));
 
 int bar() {
   return 1;
@@ -29,17 +28,13 @@ int bar2() {
   return 2;
 }
 
-int bar3(int a) {
-  return a;
-}
-
 // NO-REGISTER: @llvm.global_ctors = appending global [1 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 65535, ptr @_GLOBAL__sub_I__, ptr null }]
-// NO-REGISTER: @llvm.global_dtors = appending global [4 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 100, ptr @_Z3barv, ptr null }, { i32, ptr, ptr } { i32 65535, ptr @_Z4bar2v, ptr null }, { i32, ptr, ptr } { i32 65535, ptr @_Z4bar3i, ptr null }, { i32, ptr, ptr } { i32 65535, ptr @_GLOBAL__D_a, ptr null }]
+// NO-REGISTER: @llvm.global_dtors = appending global [3 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 101, ptr @_Z3barv, ptr null }, { i32, ptr, ptr } { i32 65535, ptr @_Z4bar2v, ptr null }, { i32, ptr, ptr } { i32 65535, ptr @_GLOBAL__D_a, ptr null }]
 
-// REGISTER: @llvm.global_ctors = appending global [3 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 65535, ptr @_GLOBAL__sub_I__, ptr null }, { i32, ptr, ptr } { i32 100, ptr @__GLOBAL_init_100, ptr null }, { i32, ptr, ptr } { i32 65535, ptr @__GLOBAL_init_65535, ptr null }]
-// REGISTER: @llvm.global_dtors = appending global [3 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 65535, ptr @_GLOBAL__D_a, ptr null }, { i32, ptr, ptr } { i32 100, ptr @__GLOBAL_cleanup_100, ptr null }, { i32, ptr, ptr } { i32 65535, ptr @__GLOBAL_cleanup_65535, ptr null }]
+// REGISTER: @llvm.global_ctors = appending global [3 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 65535, ptr @_GLOBAL__sub_I__, ptr null }, { i32, ptr, ptr } { i32 101, ptr @__GLOBAL_init_101, ptr null }, { i32, ptr, ptr } { i32 65535, ptr @__GLOBAL_init_65535, ptr null }]
+// REGISTER: @llvm.global_dtors = appending global [3 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 65535, ptr @_GLOBAL__D_a, ptr null }, { i32, ptr, ptr } { i32 101, ptr @__GLOBAL_cleanup_101, ptr null }, { i32, ptr, ptr } { i32 65535, ptr @__GLOBAL_cleanup_65535, ptr null }]
 
-// REGISTER: define internal void @__GLOBAL_init_100() [[ATTR:#[0-9]+]] {
+// REGISTER: define internal void @__GLOBAL_init_101() [[ATTR:#[0-9]+]] {
 // REGISTER: entry:
 // REGISTER:   %0 = call i32 @atexit(ptr @_Z3barv)
 // REGISTER:   ret void
@@ -48,11 +43,10 @@ int bar3(int a) {
 // REGISTER: define internal void @__GLOBAL_init_65535() [[ATTR:#[0-9]+]] {
 // REGISTER: entry:
 // REGISTER:   %0 = call i32 @atexit(ptr @_Z4bar2v)
-// REGISTER:   %1 = call i32 @atexit(ptr @_Z4bar3i)
 // REGISTER:   ret void
 // REGISTER: }
 
-// REGISTER: define internal void @__GLOBAL_cleanup_100() [[ATTR:#[0-9]+]] {
+// REGISTER: define internal void @__GLOBAL_cleanup_101() [[ATTR:#[0-9]+]] {
 // REGISTER: entry:
 // REGISTER:   %0 = call i32 @unatexit(ptr @_Z3barv)
 // REGISTER:   %needs_destruct = icmp eq i32 %0, 0
@@ -68,20 +62,11 @@ int bar3(int a) {
 
 // REGISTER: define internal void @__GLOBAL_cleanup_65535() [[ATTR:#[0-9]+]] {
 // REGISTER: entry:
-// REGISTER:   %0 = call i32 @unatexit(ptr @_Z4bar3i)
+// REGISTER:   %0 = call i32 @unatexit(ptr @_Z4bar2v)
 // REGISTER:   %needs_destruct = icmp eq i32 %0, 0
-// REGISTER:   br i1 %needs_destruct, label %destruct.call, label %unatexit.call
+// REGISTER:   br i1 %needs_destruct, label %destruct.call, label %destruct.end
 
 // REGISTER: destruct.call:
-// REGISTER:   call void @_Z4bar3i()
-// REGISTER:   br label %unatexit.call
-
-// REGISTER: unatexit.call:
-// REGISTER:   %1 = call i32 @unatexit(ptr @_Z4bar2v)
-// REGISTER:   %needs_destruct1 = icmp eq i32 %1, 0
-// REGISTER:   br i1 %needs_destruct1, label %destruct.call2, label %destruct.end
-
-// REGISTER: destruct.call2:
 // REGISTER:   call void @_Z4bar2v()
 // REGISTER:   br label %destruct.end