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

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-aarch64

Author: Jon Roelofs (jroelofs)

<details>
<summary>Changes</summary>

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

---
Full diff: https://github.com/llvm/llvm-project/pull/203076.diff


3 Files Affected:

- (modified) llvm/lib/Target/AArch64/AArch64FrameLowering.cpp (+7-3) 
- (modified) llvm/lib/Target/AArch64/AArch64PointerAuth.cpp (+5-2) 
- (modified) llvm/test/CodeGen/AArch64/arm64e-tail-call-autib.ll (-2) 


``````````diff
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

``````````

</details>


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