On Tuesday, 3 June 2025 13:13:10 Brasilia Standard Time Frederick Virchanza
Gotham via Std-Proposals wrote:
> So . . . . before the type-erasure takes place, we would have to record
> this secret number somewhere.

Before any of that, you need to describe the objective for this. What problem
is this solving? What this casting allow that isn't allowed today? Are there
other ways of solving the same problem? How have programs coped with this.

Time and again you come up with a solution in search of a problem. You're
putting the cart ahead of the oxen: you've discovered a technique through low-
level programming and are struggling to find a motivation to have it
standardised.

> I think I'll build an aarch64 cross-compiler to run on my x86_64 computer
> and put it inside a chroot jail with Qemu and see about getting Possibility
> No. 2 working.

Download the SDK & toolchain from Yocto Project.
https://www.yoctoproject.org/development/releases/ ->
https://downloads.yoctoproject.org/releases/yocto/yocto-5.2/toolchain/x86_64/

Download the "cortexa57" non-minimal non-ext (extensible) toolchain.

It'll install a GTCC cross-compiler, a sysroot, and qemu-aarch64. Whether qemu
supports the ARMv8.3 authenticated pointer instructions, I have no clue. As
for Clang, I don't know if Yocto/Poky have it, but your regular Clang can
target the sysroot by passing the relevant --target and --sysroot options.

-- 
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
  Principal Engineer - Intel Platform & System Engineering