Support function attribute patchable_function_entry

This feature is generic. Make it applicable for AArch64 and X86 because
the backend has only implemented NOP insertion for AArch64 and X86.

Reviewed By: nickdesaulniers, aaron.ballman

Differential Revision: https://reviews.llvm.org/D72221

clang/include/clang/Basic/Attr.td

@@ -683,6 +683,15 @@ def XRayLogArgs : InheritableAttr {
   let Documentation = [XRayDocs];
 }
 
+def PatchableFunctionEntry
+    : InheritableAttr,
+      TargetSpecificAttr<TargetArch<["aarch64", "x86", "x86_64"]>> {
+  let Spellings = [GCC<"patchable_function_entry">];
+  let Subjects = SubjectList<[Function, ObjCMethod]>;
+  let Args = [UnsignedArgument<"Count">, DefaultIntArgument<"Offset", 0>];
+  let Documentation = [PatchableFunctionEntryDocs];
+}
+
 def TLSModel : InheritableAttr {
   let Spellings = [GCC<"tls_model">];
   let Subjects = SubjectList<[TLSVar], ErrorDiag>;

clang/include/clang/Basic/AttrDocs.td

@@ -3988,6 +3988,18 @@ If a function has neither of these attributes, they become subject to the XRay h
   }];
 }
 
+def PatchableFunctionEntryDocs : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+``__attribute__((patchable_function_entry(N,M)))`` is used to generate M NOPs
+before the function entry and N-M NOPs after the function entry. This attribute
+takes precedence over the command line option ``-fpatchable-function-entry=N,M``.
+``M`` defaults to 0 if omitted.
+
+Currently, only M=0 is supported.
+}];
+}
+
 def TransparentUnionDocs : Documentation {
   let Category = DocCatDecl;
   let Content = [{

clang/lib/CodeGen/CodeGenFunction.cpp

@@ -799,8 +799,8 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
           FD->getBody()->getStmtClass() == Stmt::CoroutineBodyStmtClass)
         SanOpts.Mask &= ~SanitizerKind::Null;
 
-  // Apply xray attributes to the function (as a string, for now)
   if (D) {
+    // Apply xray attributes to the function (as a string, for now)
     if (const auto *XRayAttr = D->getAttr<XRayInstrumentAttr>()) {
       if (CGM.getCodeGenOpts().XRayInstrumentationBundle.has(
               XRayInstrKind::Function)) {
@@ -819,6 +819,12 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
             "xray-instruction-threshold",
             llvm::itostr(CGM.getCodeGenOpts().XRayInstructionThreshold));
     }
+
+    if (const auto *Attr = D->getAttr<PatchableFunctionEntryAttr>()) {
+      // Attr->getStart is currently ignored.
+      Fn->addFnAttr("patchable-function-entry",
+                    std::to_string(Attr->getCount()));
+    }
   }
 
   // Add no-jump-tables value.

clang/lib/Sema/SemaDeclAttr.cpp

@@ -4915,6 +4915,25 @@ static void handleXRayLogArgsAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
                  XRayLogArgsAttr(S.Context, AL, ArgCount.getSourceIndex()));
 }
 
+static void handlePatchableFunctionEntryAttr(Sema &S, Decl *D,
+                                             const ParsedAttr &AL) {
+  uint32_t Count = 0, Offset = 0;
+  if (!checkUInt32Argument(S, AL, AL.getArgAsExpr(0), Count, 0, true))
+    return;
+  if (AL.getNumArgs() == 2) {
+    Expr *Arg = AL.getArgAsExpr(1);
+    if (!checkUInt32Argument(S, AL, Arg, Offset, 1, true))
+      return;
+    if (Offset) {
+      S.Diag(getAttrLoc(AL), diag::err_attribute_argument_out_of_range)
+          << &AL << 0 << 0 << Arg->getBeginLoc();
+      return;
+    }
+  }
+  D->addAttr(::new (S.Context)
+                 PatchableFunctionEntryAttr(S.Context, AL, Count, Offset));
+}
+
 static bool ArmMveAliasValid(unsigned BuiltinID, StringRef AliasName) {
   if (AliasName.startswith("__arm_"))
     AliasName = AliasName.substr(6);
@@ -7396,6 +7415,10 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
     handleXRayLogArgsAttr(S, D, AL);
     break;
 
+  case ParsedAttr::AT_PatchableFunctionEntry:
+    handlePatchableFunctionEntryAttr(S, D, AL);
+    break;
+
   // Move semantics attribute.
   case ParsedAttr::AT_Reinitializes:
     handleSimpleAttribute<ReinitializesAttr>(S, D, AL);

clang/test/CodeGen/patchable-function-entry.c

@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 -triple aarch64 -emit-llvm %s -o - | FileCheck %s
+
+// CHECK: define void @f0() #0
+__attribute__((patchable_function_entry(0))) void f0() {}
+
+// CHECK: define void @f00() #0
+__attribute__((patchable_function_entry(0, 0))) void f00() {}
+
+// CHECK: define void @f2() #1
+__attribute__((patchable_function_entry(2))) void f2() {}
+
+// CHECK: define void @f20() #1
+__attribute__((patchable_function_entry(2, 0))) void f20() {}
+
+// CHECK: define void @f20decl() #1
+__attribute__((patchable_function_entry(2, 0))) void f20decl();
+void f20decl() {}
+
+/// M in patchable_function_entry(N,M) is currently ignored.
+// CHECK: attributes #0 = { {{.*}} "patchable-function-entry"="0"
+// CHECK: attributes #1 = { {{.*}} "patchable-function-entry"="2"

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

@@ -128,6 +128,7 @@
 // CHECK-NEXT: Owner (SubjectMatchRule_record_not_is_union)
 // CHECK-NEXT: ParamTypestate (SubjectMatchRule_variable_is_parameter)
 // CHECK-NEXT: PassObjectSize (SubjectMatchRule_variable_is_parameter)
+// CHECK-NEXT: PatchableFunctionEntry (SubjectMatchRule_function, SubjectMatchRule_objc_method)
 // CHECK-NEXT: Pointer (SubjectMatchRule_record_not_is_union)
 // CHECK-NEXT: ReleaseHandle (SubjectMatchRule_variable_is_parameter)
 // CHECK-NEXT: RenderScriptKernel (SubjectMatchRule_function)

clang/test/Sema/patchable-function-entry-attr.c

@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -triple aarch64 -fsyntax-only -verify %s
+
+// expected-error@+1 {{'patchable_function_entry' attribute takes at least 1 argument}}
+__attribute__((patchable_function_entry)) void f();
+
+// expected-error@+1 {{'patchable_function_entry' attribute takes no more than 2 arguments}}
+__attribute__((patchable_function_entry(0, 0, 0))) void f();
+
+// expected-error@+1 {{'patchable_function_entry' attribute requires a non-negative integral compile time constant expression}}
+__attribute__((patchable_function_entry(-1))) void f();
+
+int i;
+// expected-error@+1 {{'patchable_function_entry' attribute requires parameter 0 to be an integer constant}}
+__attribute__((patchable_function_entry(i))) void f();
+
+// expected-error@+1 {{'patchable_function_entry' attribute requires integer constant between 0 and 0 inclusive}}
+__attribute__((patchable_function_entry(1, 1))) void f();

clang/test/Sema/patchable-function-entry-attr.cpp

@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -triple aarch64 -fsyntax-only -verify=silence %s
+// RUN: %clang_cc1 -triple i386 -fsyntax-only -verify=silence %s
+// RUN: %clang_cc1 -triple x86_64 -fsyntax-only -verify=silence %s
+// RUN: %clang_cc1 -triple ppc64le -fsyntax-only -verify %s
+
+// silence-no-diagnostics
+
+// expected-warning@+1 {{unknown attribute 'patchable_function_entry' ignored}}
+[[gnu::patchable_function_entry(0)]] void f();