[clang] Wire -fptrauth-returns to "ptrauth-returns" fn attribute. (#102416)

We already ended up with -fptrauth-returns, the feature macro, the lang
opt, and the actual backend lowering.

The only part left is threading it all through PointerAuthOptions, to
drive the addition of the "ptrauth-returns" attribute to generated
functions.
While there, do minor cleanup on ptrauth-function-attributes.c.

This also adds ptrauth_key_return_address to ptrauth.h.

3 files changed, 11 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index af20155..4dc57d0 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -880,6 +880,8 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
 
   // Add pointer authentication attributes.
   const CodeGenOptions &CodeGenOpts = CGM.getCodeGenOpts();
+  if (CodeGenOpts.PointerAuth.ReturnAddresses)
+    Fn->addFnAttr("ptrauth-returns");
   if (CodeGenOpts.PointerAuth.FunctionPointers)
     Fn->addFnAttr("ptrauth-calls");
   if (CodeGenOpts.PointerAuth.IndirectGotos)
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 4dbb13f..4370342 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1511,13 +1511,15 @@ void CompilerInvocation::setDefaultPointerAuthOptions(
     }
   }
   Opts.IndirectGotos = LangOpts.PointerAuthIndirectGotos;
+  Opts.ReturnAddresses = LangOpts.PointerAuthReturns;
 }
 
 static void parsePointerAuthOptions(PointerAuthOptions &Opts,
                                     const LangOptions &LangOpts,
                                     const llvm::Triple &Triple,
                                     DiagnosticsEngine &Diags) {
-  if (!LangOpts.PointerAuthCalls && !LangOpts.PointerAuthIndirectGotos)
+  if (!LangOpts.PointerAuthCalls && !LangOpts.PointerAuthIndirectGotos &&
+      !LangOpts.PointerAuthReturns)
     return;
 
   CompilerInvocation::setDefaultPointerAuthOptions(Opts, LangOpts, Triple);
diff --git a/clang/lib/Headers/ptrauth.h b/clang/lib/Headers/ptrauth.h
index 6cbdccf..d489a67 100644
--- a/clang/lib/Headers/ptrauth.h
+++ b/clang/lib/Headers/ptrauth.h
@@ -28,6 +28,12 @@ typedef enum {
   /* A process-specific key which can be used to sign data pointers. */
   ptrauth_key_process_dependent_data = ptrauth_key_asdb,
 
+  /* The key used to sign return addresses on the stack.
+     The extra data is based on the storage address of the return address.
+     On AArch64, that is always the storage address of the return address + 8
+     (or, in other words, the value of the stack pointer on function entry) */
+  ptrauth_key_return_address = ptrauth_key_process_dependent_code,
+
   /* The key used to sign C function pointers.
      The extra data is always 0. */
   ptrauth_key_function_pointer = ptrauth_key_process_independent_code,