Re: [PATCH] x86/Kconfig: make CFI_AUTO_DEFAULT depend on !RUST

[Miguel Ojeda]

On Thu, Apr 10, 2025 at 4:08 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> Maybe I've been living in C/C++ land for too long, but you either expose
> a full language feature and then everybody can use it, runtime,
> libraries and user code alike, or you don't.

I find it unlikely that C++ stdlibs happen to build and work properly
with compilers they are not tested for. Say, MS' STL with GCC or
libc++ with MSVC.

At the very least, you need to agree on builtins or `#ifdef` stuff
manually for magic bits, and you need to avoid to rely on any compiler
detail (or bug... :) anywhere (say, the non-conforming template
behavior from old MSVC), and so on. So you need an active effort to
make it work, I would expect.

And with new complex features like modules, I find it even more
unlikely the first implementations of a compiler's stdlib would happen
to work on the first implementation of the feature of another
compiler...

Now, it is true that Rust's `core` uses a lot of internal features,
precisely because they don't expect to be built by anything else that
the current (and current - 1) compiler, so they actually take
advantage of that.

It would perhaps be nice to split the "really requires magic" in
`core` from the rest somehow. In this case it wouldn't have helped
though, since the formatting machinery still uses builtins last time I
looked.

Relatedly, GCC Rust's goal is to build an old `core` at the moment, so
that they have a fixed set of things to solve.

Cheers,
Miguel