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

[Oliver Hunt via llvm-commits]

ojhunt wrote:

> > I _think_ doing it as a follow up makes sense: it's not a matter of me not wanting to do this for linux, it's that I cannot test it at all. Doing it as a follow up would also give you the constants block to put the definition rather than having it just slotted in the code. I've found moving to the constant blocks to be incredibly useful for being able to see where/how they cross ABI boundaries.
> 
> @ojhunt Thanks! So could you please adopt the code snippet from my previous comment to make things explicitly unsupported for Linux?
> 
> And also I kindly ask you to fix p.4 from [#143230 (comment)](https://github.com/llvm/llvm-project/pull/143230#issuecomment-3249013139) (we've already discussed that in Discord). Please let me know if you need any help.
> 
> A couple of things are on my side:
> 
> 1. Compile a local pac-ret-enabled toolchain. This would allow you to fix p.3 from the same comment. I'll let you know when it's ready.

In _principle_ I could set up this configuration right? (Obviously not actually test it, but in principle at least be able to verify it builds before pushing the update)

> 2. Look through other comments in this PR (they have lower priority since they are not related to any runtime/compile-time failures). I'll highlight the ones which I think are worth fixing in scope of this PR (if any).
> 
> Please let me know if I've missed smth or if you have any objections on this plan.

GH makes finding these things so utterly miserable. I hate it so very much.



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