[ARM][clang] Option b-key must not affect __ARM_FEATURE_PAC_DEFAULT

[stuij]

Summary

When using -mbranch-protection=pac-ret+b-key, macro __ARM_FEATURE_PAC_DEFAULT
should still have the value corresponding to a-key, because b-key is only valid
for AArch64.

This patch is part of a series that adds support for the PACBTI-M extension of
the Armv8.1-M architecture, as detailed here:

https://community.arm.com/arm-community-blogs/b/architectures-and-processors-blog/posts/armv8-1-m-pointer-authentication-and-branch-target-identification-extension

The PACBTI-M specification can be found in the Armv8-M Architecture Reference
Manual:

https://developer.arm.com/documentation/ddi0553/latest

The following people contributed to this patch:

• Victor Campos

[stuij]

tickling the commit so the buildbot picks up the dependency

[stuij]

another tickle

[danielkiss]

I think rejecting\warning the b-key from the command line maybe a more developer friendly way.

[stuij]

@danielkiss Yes that needs to be addressed, but we are doing that in another patch that will (hopefully) cover all permutations of architecture and branch protection values on both the cmdline and as function attributes.

So this patch is just about not having logic in the ARM code that shouldn't be there.

[danielkiss]

In D115140#3176800, @stuij wrote:

@danielkiss Yes that needs to be addressed, but we are doing that in another patch that will (hopefully) cover all permutations of architecture and branch protection values on both the cmdline and as function attributes.

sound good, Thanks!

LGTM.

[stuij]

rebasing

clang/lib/Basic/Targets/ARM.cpp

 //===--- ARM.cpp - Implement ARM target feature support -------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
if (HasBFloat16) {
     Builder.defineMacro("__ARM_FEATURE_BF16_VECTOR_ARITHMETIC", "1");
     Builder.defineMacro("__ARM_BF16_FORMAT_ALTERNATIVE", "1");
   }
 
   if (Opts.BranchTargetEnforcement)
     Builder.defineMacro("__ARM_FEATURE_BTI_DEFAULT", "1");
 
   if (Opts.hasSignReturnAddress()) {
-    unsigned Value = Opts.isSignReturnAddressWithAKey() ? 1 : 2;
+    unsigned Value = 1;
     if (Opts.isSignReturnAddressScopeAll())
       Value |= 1 << 2;
     Builder.defineMacro("__ARM_FEATURE_PAC_DEFAULT", Twine(Value));
   }
 
   switch (ArchKind) {
   default:
     break;

clang/test/Preprocessor/arm-target-features.c

 
 // RUN: %clang -target arm-none-none-eabi -march=armv7-m -mfpu=softvfp -x c -E -dM %s -o - | FileCheck --check-prefix=CHECK-SOFTVFP %s
 // CHECK-SOFTVFP-NOT: #define __ARM_FP 0x
 
 // Test Armv8.1-M PACBTI
 // RUN: %clang -target arm-arm-none-eabi -march=armv8.1-m.main -x c -E -dM %s -o - | FileCheck --check-prefixes=CHECK-NOBTI,CHECK-NOPAC %s
 // RUN: %clang -target arm-arm-none-eabi -march=armv8.1-m.main -mbranch-protection=bti -x c -E -dM %s -o - | FileCheck --check-prefixes=CHECK-BTI,CHECK-NOPAC %s
 // RUN: %clang -target arm-arm-none-eabi -march=armv8.1-m.main -mbranch-protection=pac-ret -x c -E -dM %s -o - | FileCheck --check-prefixes=CHECK-PAC,CHECK-NOBTI %s
-// RUN: %clang -target arm-arm-none-eabi -march=armv8.1-m.main -mbranch-protection=pac-ret+b-key -x c -E -dM %s -o - | FileCheck --check-prefixes=CHECK-PAC-BKEY,CHECK-NOBTI %s
+// RUN: %clang -target arm-arm-none-eabi -march=armv8.1-m.main -mbranch-protection=pac-ret+b-key -x c -E -dM %s -o - | FileCheck --check-prefixes=CHECK-PAC,CHECK-NOBTI %s
 // RUN: %clang -target arm-arm-none-eabi -march=armv8.1-m.main -mbranch-protection=pac-ret+leaf -x c -E -dM %s -o - | FileCheck --check-prefixes=CHECK-PAC-LEAF,CHECK-NOBTI %s
-// RUN: %clang -target arm-arm-none-eabi -march=armv8.1-m.main -mbranch-protection=pac-ret+b-key+leaf -x c -E -dM %s -o - | FileCheck --check-prefixes=CHECK-PAC-BKEY-LEAF,CHECK-NOBTI %s
+// RUN: %clang -target arm-arm-none-eabi -march=armv8.1-m.main -mbranch-protection=pac-ret+b-key+leaf -x c -E -dM %s -o - | FileCheck --check-prefixes=CHECK-PAC-LEAF,CHECK-NOBTI %s
 // RUN: %clang -target arm-arm-none-eabi -march=armv8.1-m.main -mbranch-protection=bti+pac-ret -x c -E -dM %s -o - | FileCheck --check-prefixes=CHECK-PAC,CHECK-BTI %s
-// RUN: %clang -target arm-arm-none-eabi -march=armv8.1-m.main -mbranch-protection=bti+pac-ret+b-key -x c -E -dM %s -o - | FileCheck --check-prefixes=CHECK-PAC-BKEY,CHECK-BTI %s
+// RUN: %clang -target arm-arm-none-eabi -march=armv8.1-m.main -mbranch-protection=bti+pac-ret+b-key -x c -E -dM %s -o - | FileCheck --check-prefixes=CHECK-PAC,CHECK-BTI %s
 // RUN: %clang -target arm-arm-none-eabi -march=armv8.1-m.main -mbranch-protection=bti+pac-ret+leaf -x c -E -dM %s -o - | FileCheck --check-prefixes=CHECK-PAC-LEAF,CHECK-BTI %s
-// RUN: %clang -target arm-arm-none-eabi -march=armv8.1-m.main -mbranch-protection=bti+pac-ret+b-key+leaf -x c -E -dM %s -o - | FileCheck --check-prefixes=CHECK-PAC-BKEY-LEAF,CHECK-BTI %s
+// RUN: %clang -target arm-arm-none-eabi -march=armv8.1-m.main -mbranch-protection=bti+pac-ret+b-key+leaf -x c -E -dM %s -o - | FileCheck --check-prefixes=CHECK-PAC-LEAF,CHECK-BTI %s
 // CHECK-NOBTI-NOT: #define __ARM_FEATURE_BTI_DEFAULT
 // CHECK-NOPAC-NOT: #define __ARM_FEATURE_PAC_DEFAULT
 // CHECK-BTI: #define __ARM_FEATURE_BTI_DEFAULT 1
 // CHECK-PAC: #define __ARM_FEATURE_PAC_DEFAULT 1
-// CHECK-PAC-BKEY: #define __ARM_FEATURE_PAC_DEFAULT 2
 // CHECK-PAC-LEAF: #define __ARM_FEATURE_PAC_DEFAULT 5
-// CHECK-PAC-BKEY-LEAF: #define __ARM_FEATURE_PAC_DEFAULT 6
 
 // RUN: %clang -target arm-arm-none-eabi -march=armv8.1-m.main -x c -E -dM %s -o - | FileCheck --check-prefixes=CHECK-NOBTI-EXT,CHECK-NOPAC-EXT %s
 // RUN: %clang -target arm-arm-none-eabi -march=armv7-m+pacbti -x c -E -dM %s -o - | FileCheck --check-prefixes=CHECK-PACBTI-EXT %s
 // CHECK-NOBTI-EXT-NOT: #define __ARM_FEATURE_BTI 1
 // CHECK-NOPAC-EXT-NOT: #define __ARM_FEATURE_PAUTH 1
 // CHECK-PACBTI-EXT: #define __ARM_FEATURE_BTI 1
 // CHECK-PACBTI-EXT: #define __ARM_FEATURE_PAUTH 1