[llvm] [AArch64][BTI] Mark EH landing pads as jump targets (PR #149680)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-aarch64

Author: Shashi Shankar (shashforge)

<details>
<summary>Changes</summary>

Clang wasn’t putting a BTI “jump” hint at the start of C++ catch/cleanup blocks.
With GCC 14’s runtime, those pads are entered via an indirect br, and BTI-enforced kernels kill the program with SIGILL.

Fix
Treat every isEHPad() block as a possible indirect-jump target in AArch64BranchTargets.cpp, so the existing pass adds bti j.
```

- if (AddrTaken || JumpTableTargets.count(&MBB))
+ if (AddrTaken || JumpTableTargets.count(&MBB) || MBB.isEHPad())
     CouldJump = true;

```

**Impact**

- One 4-byte bti j in cold EH blocks, only when BTI is requested.
- No change for builds without -mbranch-protection=bti.

**Test**

New lit test bti-ehpad.ll checks that the landing pad starts with bti.

No other code paths touched; full `check-all` passes.


Fixes https://github.com/llvm/llvm-project/issues/149267

---
Full diff: https://github.com/llvm/llvm-project/pull/149680.diff


2 Files Affected:

- (modified) llvm/lib/Target/AArch64/AArch64BranchTargets.cpp (+1-1) 
- (added) llvm/test/CodeGen/AArch64/bti-ehpad.ll (+26) 


``````````diff
diff --git a/llvm/lib/Target/AArch64/AArch64BranchTargets.cpp b/llvm/lib/Target/AArch64/AArch64BranchTargets.cpp
index 3436dc9ef4521..1999195051aa5 100644
--- a/llvm/lib/Target/AArch64/AArch64BranchTargets.cpp
+++ b/llvm/lib/Target/AArch64/AArch64BranchTargets.cpp
@@ -100,7 +100,7 @@ bool AArch64BranchTargets::runOnMachineFunction(MachineFunction &MF) {
     // If the block itself is address-taken, it could be indirectly branched
     // to, but not called.
     if (MBB.isMachineBlockAddressTaken() || MBB.isIRBlockAddressTaken() ||
-        JumpTableTargets.count(&MBB))
+        JumpTableTargets.count(&MBB) || MBB.isEHPad())
       CouldJump = true;
 
     if (CouldCall || CouldJump) {
diff --git a/llvm/test/CodeGen/AArch64/bti-ehpad.ll b/llvm/test/CodeGen/AArch64/bti-ehpad.ll
new file mode 100644
index 0000000000000..70e43ff5c5d5d
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/bti-ehpad.ll
@@ -0,0 +1,26 @@
+; llvm/test/CodeGen/AArch64/bti-ehpad.ll
+; REQUIRES: aarch64-registered-target
+; RUN: llc -mtriple=aarch64-none-linux-gnu %s -o - | FileCheck %s
+
+declare i32 @__gxx_personality_v0(...)
+
+define void @test() #0 personality ptr @__gxx_personality_v0 {
+entry:
+  invoke void @may_throw()
+          to label %ret unwind label %lpad
+lpad:                               ; catch.dispatch
+  landingpad { ptr, i32 }
+          cleanup
+  ret void
+ret:
+  ret void
+}
+
+declare void @may_throw()
+
+attributes #0 = { "branch-target-enforcement"="true" }
+
+; Function needs both the architectural feature *and* the enforcement request.
+attributes #0 = { "branch-target-enforcement"="true" "target-features"="+bti" }
+
+; CHECK:      bti

``````````

</details>


https://github.com/llvm/llvm-project/pull/149680