Update toolchain to 2025-04-27

[Rahix]

Some floating point intrinsics were added in this newer version which helps on systems where these intrinsics are not provided by avr-gcc.

Cc: @Patryk27

[Rahix]

@Patryk27, can you check the CI failures please? Looks like there was a panicking code-path left in one of the intrinsics if I interpret this correctly?

[Patryk27]

Okie, will check! 🦀

[Patryk27]

Status: not really a bug, it's the same case as rust-lang/rust#139737 (comment).

tl;dr sometimes for unreachable code paths LLVM inserts a special kind of panic-instruction - e.g. on x86 this:

#[inline(never)]
pub fn foo() {
    unsafe {
        core::hint::unreachable_unchecked();
    }
}

... gets compiled into:

playground::foo:
	ud2

... with ud2 being this sort of hardware-level panic / abort instruction.

There's no ud2 equivalent for AVR, so LLVM just inserts a call to a function called abort, expecting for user to define what should happen then (we might loop {}, write something to uart, blink leds etc.). Notably, this is different from #[panic_handler], because panic!() is a Rust-specific construct, while trapping (aborting) is much more low-level (there's no &PanicInfo available etc.).

Overall:

So tl;dr not a bug - at the same time, I understand that 99% of people don't want to be bothered with this, "do whatever" will work just fine for them; I think we might be able to get the best of both worlds (provide a default function, but allow to overwrite it) by utilizing weak symbols (we'd create a weak fn abort() within compiler-builtins).

I'll experiment and report back.

[Patryk27]

Ok, seems we're ready!

I've checked nightly-2025-04-27 and the examples build on my machine now 🙂

[Rahix]

Very nice, thanks you!!