[clang] Implement -fptrauth-auth-traps. (#102417)

This provides -fptrauth-auth-traps, which at the frontend level only
controls the addition of the "ptrauth-auth-traps" function attribute.

The attribute in turn controls various aspects of backend codegen, by
providing the guarantee that every "auth" operation generated will trap
on failure.

This can either be delegated to the hardware (if AArch64 FPAC is known
to be available), in which case this attribute doesn't change codegen.
Otherwise, if FPAC isn't available, this asks the backend to emit
additional instructions to check and trap on auth failure.

Author: ahmedbougacha

clang/include/clang/Basic/PointerAuthOptions.h

@@ -166,6 +166,9 @@ struct PointerAuthOptions {
   /// Should return addresses be authenticated?
   bool ReturnAddresses = false;
 
+  /// Do authentication failures cause a trap?
+  bool AuthTraps = false;
+
   /// Do indirect goto label addresses need to be authenticated?
   bool IndirectGotos = false;
 

clang/lib/CodeGen/CodeGenFunction.cpp

@@ -884,6 +884,8 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
     Fn->addFnAttr("ptrauth-returns");
   if (CodeGenOpts.PointerAuth.FunctionPointers)
     Fn->addFnAttr("ptrauth-calls");
+  if (CodeGenOpts.PointerAuth.AuthTraps)
+    Fn->addFnAttr("ptrauth-auth-traps");
   if (CodeGenOpts.PointerAuth.IndirectGotos)
     Fn->addFnAttr("ptrauth-indirect-gotos");
 

clang/lib/Frontend/CompilerInvocation.cpp

@@ -1510,16 +1510,17 @@ void CompilerInvocation::setDefaultPointerAuthOptions(
           Discrimination::Constant, InitFiniPointerConstantDiscriminator);
     }
   }
-  Opts.IndirectGotos = LangOpts.PointerAuthIndirectGotos;
   Opts.ReturnAddresses = LangOpts.PointerAuthReturns;
+  Opts.AuthTraps = LangOpts.PointerAuthAuthTraps;
+  Opts.IndirectGotos = LangOpts.PointerAuthIndirectGotos;
 }
 
 static void parsePointerAuthOptions(PointerAuthOptions &Opts,
                                     const LangOptions &LangOpts,
                                     const llvm::Triple &Triple,
                                     DiagnosticsEngine &Diags) {
-  if (!LangOpts.PointerAuthCalls && !LangOpts.PointerAuthIndirectGotos &&
-      !LangOpts.PointerAuthReturns)
+  if (!LangOpts.PointerAuthCalls && !LangOpts.PointerAuthReturns &&
+      !LangOpts.PointerAuthAuthTraps && !LangOpts.PointerAuthIndirectGotos)
     return;
 
   CompilerInvocation::setDefaultPointerAuthOptions(Opts, LangOpts, Triple);

clang/test/CodeGen/ptrauth-function-attributes.c

@@ -8,6 +8,9 @@
 // RUN: %clang_cc1 -triple arm64-apple-ios   -fptrauth-returns -emit-llvm %s -o - | FileCheck %s --check-prefixes=ALL,RETS
 // RUN: %clang_cc1 -triple aarch64-linux-gnu -fptrauth-returns -emit-llvm %s -o - | FileCheck %s --check-prefixes=ALL,RETS
 
+// RUN: %clang_cc1 -triple arm64-apple-ios   -fptrauth-auth-traps -emit-llvm %s -o - | FileCheck %s --check-prefixes=ALL,TRAPS
+// RUN: %clang_cc1 -triple aarch64-linux-gnu -fptrauth-auth-traps -emit-llvm %s -o - | FileCheck %s --check-prefixes=ALL,TRAPS
+
 // RUN: %clang_cc1 -triple arm64-apple-ios   -fptrauth-indirect-gotos -emit-llvm %s -o - | FileCheck %s --check-prefixes=ALL,GOTOS
 // RUN: %clang_cc1 -triple aarch64-linux-gnu -fptrauth-indirect-gotos -emit-llvm %s -o - | FileCheck %s --check-prefixes=ALL,GOTOS
 
@@ -19,6 +22,8 @@ void test() {
 
 // RETS: attributes #0 = {{{.*}} "ptrauth-returns" {{.*}}}
 
+// TRAPS: attributes #0 = {{{.*}} "ptrauth-auth-traps" {{.*}}}
+
 // GOTOS: attributes #0 = {{{.*}} "ptrauth-indirect-gotos" {{.*}}}
 
 // OFF-NOT: attributes {{.*}} "ptrauth-