[attributes] Add an attribute for server routines in Mach kernel and extensions.

The new __attribute__ ((mig_server_routine)) is going to be used for annotating
Mach Interface Generator (MIG) callback functions as such, so that additional
static analysis could be applied to their implementations. It can also be
applied to regular functions behavior of which is supposed to be identical to
that of a MIG server routine.

Differential Revision: https://reviews.llvm.org/D58365

llvm-svn: 354530

clang/include/clang/Basic/Attr.td

@@ -1300,6 +1300,12 @@ def MayAlias : InheritableAttr {
   let Documentation = [Undocumented];
 }
 
+def MIGServerRoutine : InheritableAttr {
+  let Spellings = [Clang<"mig_server_routine">];
+  let Subjects = SubjectList<[Function, ObjCMethod, Block]>;
+  let Documentation = [MIGConventionDocs];
+}
+
 def MSABI : DeclOrTypeAttr {
   let Spellings = [GCC<"ms_abi">];
 //  let Subjects = [Function, ObjCMethod];

clang/include/clang/Basic/AttrDocs.td

@@ -4095,3 +4095,24 @@ Likewise, when applied to a strong local variable, that variable becomes
 
 When compiled without ``-fobjc-arc``, this attribute is ignored.
 }]; }
+
+def MIGConventionDocs : Documentation {
+  let Category = DocCatType;
+  let Content = [{
+  The Mach Interface Generator release-on-success convention dictates
+functions that follow it to only release arguments passed to them when they
+return "success" (a ``kern_return_t`` error code that indicates that
+no errors have occured). Otherwise the release is performed by the MIG client
+that called the function. The annotation ``__attribute__((mig_server_routine))``
+is applied in order to specify which functions are expected to follow the
+convention. This allows the Static Analyzer to find bugs caused by violations of
+that convention. The attribute would normally appear on the forward declaration
+of the actual server routine in the MIG server header, but it may also be
+added to arbitrary functions that need to follow the same convention - for
+example, a user can add them to auxiliary functions called by the server routine
+that have their return value of type ``kern_return_t`` unconditionally returned
+from the routine. The attribute can be applied to C++ methods, and in this case
+it will be automatically applied to overrides if the method is virtual. The
+attribute can also be written using C++11 syntax: ``[[mig::server_routine]]``.
+}];
+}

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -8706,6 +8706,11 @@ def err_opencl_builtin_expected_type : Error<
 def ext_opencl_ext_vector_type_rgba_selector: ExtWarn<
   "vector component name '%0' is an OpenCL version 2.2 feature">,
   InGroup<OpenCLUnsupportedRGBA>;
+
+// MIG routine annotations.
+def warn_mig_server_routine_does_not_return_kern_return_t : Warning<
+  "'mig_server_routine' attribute only applies to routines that return a kern_return_t">,
+  InGroup<IgnoredAttributes>;
 } // end of sema category
 
 let CategoryName = "OpenMP Issue" in {

clang/lib/Sema/SemaDeclAttr.cpp

@@ -6458,6 +6458,28 @@ static void handleFortifyStdLib(Sema &S, Decl *D, const ParsedAttr &AL) {
       AL.getAttributeSpellingListIndex()));
 }
 
+static void handleMIGServerRoutineAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
+  // Check that the return type is a `typedef int kern_return_t` or a typedef
+  // around it, because otherwise MIG convention checks make no sense.
+  // BlockDecl doesn't store a return type, so it's annoying to check,
+  // so let's skip it for now.
+  if (!isa<BlockDecl>(D)) {
+    QualType T = getFunctionOrMethodResultType(D);
+    bool IsKernReturnT = false;
+    while (const auto *TT = T->getAs<TypedefType>()) {
+      IsKernReturnT = (TT->getDecl()->getName() == "kern_return_t");
+      T = TT->desugar();
+    }
+    if (!IsKernReturnT || T.getCanonicalType() != S.getASTContext().IntTy) {
+      S.Diag(D->getBeginLoc(),
+             diag::warn_mig_server_routine_does_not_return_kern_return_t);
+      return;
+    }
+  }
+
+  handleSimpleAttribute<MIGServerRoutineAttr>(S, D, AL);
+}
+
 //===----------------------------------------------------------------------===//
 // Top Level Sema Entry Points
 //===----------------------------------------------------------------------===//
@@ -7191,6 +7213,10 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
   case ParsedAttr::AT_FortifyStdLib:
     handleFortifyStdLib(S, D, AL);
     break;
+
+  case ParsedAttr::AT_MIGServerRoutine:
+    handleMIGServerRoutineAttr(S, D, AL);
+    break;
   }
 }
 

clang/test/Misc/pragma-attribute-supported-attributes-list.test

@@ -61,6 +61,7 @@
 // CHECK-NEXT: InternalLinkage (SubjectMatchRule_variable, SubjectMatchRule_function, SubjectMatchRule_record)
 // CHECK-NEXT: LTOVisibilityPublic (SubjectMatchRule_record)
 // CHECK-NEXT: Lockable (SubjectMatchRule_record)
+// CHECK-NEXT: MIGServerRoutine (SubjectMatchRule_function)
 // CHECK-NEXT: MSStruct (SubjectMatchRule_record)
 // CHECK-NEXT: MicroMips (SubjectMatchRule_function)
 // CHECK-NEXT: MinSize (SubjectMatchRule_function, SubjectMatchRule_objc_method)

clang/test/Sema/attr-mig.c

@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+typedef int kern_return_t;
+#define KERN_SUCCESS 0
+
+__attribute__((mig_server_routine)) kern_return_t var = KERN_SUCCESS; // expected-warning{{'mig_server_routine' attribute only applies to functions, Objective-C methods, and blocks}}
+
+__attribute__((mig_server_routine)) void foo_void(); // expected-warning{{'mig_server_routine' attribute only applies to routines that return a kern_return_t}}
+__attribute__((mig_server_routine)) int foo_int(); // expected-warning{{'mig_server_routine' attribute only applies to routines that return a kern_return_t}}
+
+__attribute__((mig_server_routine)) kern_return_t bar_extern(); // no-warning
+__attribute__((mig_server_routine)) kern_return_t bar_forward(); // no-warning
+
+__attribute__((mig_server_routine)) kern_return_t bar_definition() { // no-warning
+  return KERN_SUCCESS;
+}
+
+kern_return_t bar_forward() { // no-warning
+  return KERN_SUCCESS;
+}
+
+__attribute__((mig_server_routine(123))) kern_return_t bar_with_argument(); // expected-error{{'mig_server_routine' attribute takes no arguments}}

clang/test/Sema/attr-mig.cpp

@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+typedef int kern_return_t;
+typedef kern_return_t IOReturn;
+#define KERN_SUCCESS 0
+#define kIOReturnSuccess KERN_SUCCESS
+
+class MyServer {
+public:
+  virtual __attribute__((mig_server_routine)) IOReturn externalMethod();
+  virtual __attribute__((mig_server_routine)) void anotherMethod(); // expected-warning{{'mig_server_routine' attribute only applies to routines that return a kern_return_t}}
+  virtual __attribute__((mig_server_routine)) int yetAnotherMethod(); // expected-warning{{'mig_server_routine' attribute only applies to routines that return a kern_return_t}}
+  [[clang::mig_server_routine]] virtual IOReturn cppAnnotatedMethod();
+  [[clang::mig_server_routine("arg")]] virtual IOReturn cppAnnotatedMethodWithInvalidArgs(); // expected-error{{'mig_server_routine' attribute takes no arguments}}
+  [[clang::mig_server_routine]] virtual int cppInvalidAnnotatedMethod(); // expected-warning{{'mig_server_routine' attribute only applies to routines that return a kern_return_t}}
+};
+
+IOReturn MyServer::externalMethod() {
+  return kIOReturnSuccess;
+}

clang/test/Sema/attr-mig.m

@@ -0,0 +1,31 @@
+// RUN: %clang_cc1 -fsyntax-only -fblocks -verify %s
+
+typedef int kern_return_t;
+#define KERN_SUCCESS 0
+
+@interface NSObject
+@end
+
+@interface I: NSObject
+- (kern_return_t)foo __attribute__((mig_server_routine)); // no-warning
+- (void) bar_void __attribute__((mig_server_routine)); // expected-warning{{'mig_server_routine' attribute only applies to routines that return a kern_return_t}}
+- (int) bar_int __attribute__((mig_server_routine)); // expected-warning{{'mig_server_routine' attribute only applies to routines that return a kern_return_t}}
+@end
+
+@implementation I
+- (kern_return_t)foo {
+  kern_return_t (^block)() = ^ __attribute__((mig_server_routine)) { // no-warning
+    return KERN_SUCCESS;
+  };
+
+  // FIXME: Warn that this block doesn't return a kern_return_t.
+  void (^invalid_block)() = ^ __attribute__((mig_server_routine)) {};
+
+  return block();
+}
+- (void)bar_void {
+}
+- (int)bar_int {
+  return 0;
+}
+@end