[compiler-rt] [libcxx] [libcxxabi] [libunwind] [runtimes][PAC] Harden unwinding when possible (PR #143230)

[Daniil Kovalev via llvm-commits]

kovdan01 wrote:

> > * Fix personality pointer authentication on non-Apple targets: [[runtimes][PAC] Harden unwinding when possible #143230 (comment)](https://github.com/llvm/llvm-project/pull/143230#discussion_r2318636296)
> 
> I'm not sure what's going on in this diff as it does not appear related to changes in this PR? Is it just a general issue that already exists?

@ojhunt Well, I'd rather say that it's not an issue that already exists, it's just missing functionality - libunwind does not support ptrauth-hardened personality pointer, and this is true for both signed personality pointer on Apple and Linux. We just have different signing schemes, and the signing scheme on Linux is defined in this PR: #119361

If you prefer not to include support for signed personality on Linux, I would be happy to submit support for that as a follow-up PR as soon as this one is merged (since logic for Linux is similar to logic for Apple, we just have different discriminators). But, if we take this approach, let's at least add a TODO note mentioning that signed personality now only works for Apple's arm64e, and support for Linux will be implemented in future.

Probably, we can use smth like this:

```
#if __has_feature(ptrauth_calls) // as discussed in discord, let's replace that with some macro for calls+returns
        if (personality) {
#if __APPLE__
          const auto discriminator = ptrauth_blend_discriminator(
              &cieInfo->personality, __ptrauth_unwind_cie_info_personality_disc);
          void *signedPtr = ptrauth_auth_and_resign(
              (void *)personality, ptrauth_key_function_pointer, resultAddr,
              ptrauth_key_function_pointer, discriminator);
          personality = (pint_t)signedPtr;
#else
#error "Signed personality function pointer is not supported for non-Apple targets"
// TODO: Implement support for Linux. The signing scheme of personality pointer
// differ for Linux and Apple targets. For Linux targets, the signing scheme is
// defined in https://github.com/llvm/llvm-project/pull/119361
#endif
        }
#endif
```

Which approach do you prefer? Is it applying the suggestion from commit https://github.com/llvm/llvm-project/commit/e2f8b9d3859eff96442ce04662aefb40debbef3f or postponing the Linux support and using the code snippet like above?

I'm OK with both, just please let me know which is more comfortable for you.


https://github.com/llvm/llvm-project/pull/143230