[llvm] [arm64e][cfi] .cfi_negate_ra_state is irrelevant for Mach-O platforms (PR #203076)

[Jon Roelofs via llvm-commits]

https://github.com/jroelofs created https://github.com/llvm/llvm-project/pull/203076

The arm64e unwinder on Mach-O platforms always assumes saved LR's have been signed with a pacibsp, and does not support mixed signed and un-signed frames. Since the unwinder behaves the same whether the directive is present, it is better to avoid emitting it in the first place. This aligns with the behavior of AppleClang.

rdar://178084701

>From aa53f10ed97aa6dc108b57c2c7f5f4f69745df06 Mon Sep 17 00:00:00 2001
From: Jon Roelofs <jonathan_roelofs at apple.com>
Date: Tue, 9 Jun 2026 16:21:36 -0700
Subject: [PATCH] [arm64e][cfi] .cfi_negate_ra_state is irrelevant for Mach-O
 platforms

The arm64e unwinder on Mach-O platforms always assumes saved LR's have been
signed with a pacibsp, and does not support mixed signed and un-signed frames.
Since the unwinder behaves the same whether the directive is present, it is
better to avoid emitting it in the first place. This aligns with the behavior of
AppleClang.

rdar://178084701
---
 llvm/lib/Target/AArch64/AArch64FrameLowering.cpp    | 10 +++++++---
 llvm/lib/Target/AArch64/AArch64PointerAuth.cpp      |  7 +++++--
 llvm/test/CodeGen/AArch64/arm64e-tail-call-autib.ll |  2 --
 3 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
index 2c68e379205ce..2fd8872dfccd1 100644
--- a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
@@ -728,9 +728,13 @@ void AArch64FrameLowering::resetCFIToInitialState(
   CFIBuilder.buildDefCFA(AArch64::SP, 0);
 
   // Flip the RA sign state.
-  if (MFI.shouldSignReturnAddress(MF))
-    MFI.branchProtectionPAuthLR() ? CFIBuilder.buildNegateRAStateWithPC()
-                                  : CFIBuilder.buildNegateRAState();
+  if (MFI.shouldSignReturnAddress(MF)) {
+    if (MFI.branchProtectionPAuthLR()) {
+      CFIBuilder.buildNegateRAStateWithPC();
+    } else if (!MF.getTarget().getTargetTriple().isOSBinFormatMachO()) {
+      CFIBuilder.buildNegateRAState();
+    }
+  }
 
   // Shadow call stack uses X18, reset it.
   if (MFI.needsShadowCallStackPrologueEpilogue(MF))
diff --git a/llvm/lib/Target/AArch64/AArch64PointerAuth.cpp b/llvm/lib/Target/AArch64/AArch64PointerAuth.cpp
index 252bd696665db..3c0ed248fc28a 100644
--- a/llvm/lib/Target/AArch64/AArch64PointerAuth.cpp
+++ b/llvm/lib/Target/AArch64/AArch64PointerAuth.cpp
@@ -82,8 +82,11 @@ static void emitPACCFI(MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
   auto &MFnI = *MF.getInfo<AArch64FunctionInfo>();
 
   CFIInstBuilder CFIBuilder(MBB, MBBI, Flags);
-  MFnI.branchProtectionPAuthLR() ? CFIBuilder.buildNegateRAStateWithPC()
-                                 : CFIBuilder.buildNegateRAState();
+  if (MFnI.branchProtectionPAuthLR()) {
+    CFIBuilder.buildNegateRAStateWithPC();
+  } else if (!MF.getTarget().getTargetTriple().isOSBinFormatMachO()) {
+    CFIBuilder.buildNegateRAState();
+  }
 }
 
 void AArch64PointerAuthImpl::signLR(MachineFunction &MF,
diff --git a/llvm/test/CodeGen/AArch64/arm64e-tail-call-autib.ll b/llvm/test/CodeGen/AArch64/arm64e-tail-call-autib.ll
index 47e6abb6312c8..707bf229c3787 100644
--- a/llvm/test/CodeGen/AArch64/arm64e-tail-call-autib.ll
+++ b/llvm/test/CodeGen/AArch64/arm64e-tail-call-autib.ll
@@ -13,7 +13,6 @@ define swifttailcc void @test_async_tail_call(ptr swiftasync %ctx) "ptrauth-retu
 ; CHECK-LABEL: test_async_tail_call:
 ; CHECK:       ; %bb.0:
 ; CHECK-NEXT:    pacibsp
-; CHECK-NEXT:    .cfi_negate_ra_state
 ; CHECK-NEXT:    orr x29, x29, #0x1000000000000000
 ; CHECK-NEXT:    sub sp, sp, #48
 ; CHECK-NEXT:    stp x29, x30, [sp, #16] ; 16-byte Folded Spill
@@ -57,7 +56,6 @@ define swifttailcc void @test_no_fpdiff_tail_call(ptr swiftasync %ctx) "ptrauth-
 ; CHECK-LABEL: test_no_fpdiff_tail_call:
 ; CHECK:       ; %bb.0:
 ; CHECK-NEXT:    pacibsp
-; CHECK-NEXT:    .cfi_negate_ra_state
 ; CHECK-NEXT:    orr x29, x29, #0x1000000000000000
 ; CHECK-NEXT:    sub sp, sp, #32
 ; CHECK-NEXT:    stp x29, x30, [sp, #16] ; 16-byte Folded Spill