[clang] [llvm] [ARM][KCFI] Add backend support for Kernel Control-Flow Integrity (PR #163698)

[Sami Tolvanen via cfe-commits]

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@@ -12007,6 +12011,49 @@ static void genTPLoopBody(MachineBasicBlock *TpLoopBody,
       .add(predOps(ARMCC::AL));
 }
 
+bool ARMTargetLowering::supportKCFIBundles() const {
+  // KCFI is only supported in ARM mode, not Thumb mode
+  return !Subtarget->isThumb();
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samitolvanen wrote:

This seems fine for the Linux kernel, but we have existing (firmware) KCFI users who [mix ARM and Thumb code](https://github.com/llvm/llvm-project/issues?q=is%3Aissue%20kcfi%20thumb). This would completely break that use case, correct?

https://github.com/llvm/llvm-project/pull/163698