[llvm] [BOLT] Gadget scanner: detect non-protected indirect calls (PR #131899)

[Jacob Bramley via llvm-commits]

jacobbramley wrote:

> I'm not fully sure if @jacobbramley still wanted to see some changes before merging this patch?

The only thing bothering me is the `-fno-plt`/RELRO stuff. I couldn't work out how to get Clang to generate the problematic sequences, though, and there might not even be a compiler that supports forward-edge PAuth _and_ responds to `-fno-plt`. Given how much work is likely to be required to handle it in BOLT, it probably makes more sense to merge this first accept some (unlikely) false positives. I don't know this project well enough to make a judgement there, but it would seem a reasonable approach.

The other outstanding threads are about `isIndirectCall` but I think we all agree to handle that in the other PR.

LGTM, thanks!

https://github.com/llvm/llvm-project/pull/131899