[llvm] [BPF] Handle unreachable with a kfunc call (PR #131731)

[via llvm-commits]

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@@ -22,6 +22,8 @@ class BPFTargetMachine;
 class InstructionSelector;
 class PassRegistry;
 
+static const char *BPF_UNREACHABLE = "bpf_unreachable";
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yonghong-song wrote:

In kernel, all our kfuncs do not have `__` prefix so I don't know whether we could use `__bpf_unreachable` or not. I still prefer to use `bpf_unreachable` as this is BPF backend only and the code is expected to be used by kernel. It is unlikely we have conflict with other symbols in a bpf program.

https://github.com/llvm/llvm-project/pull/131731