alloc_error_handler does not link using stable rust

[miladfarca]

Hello,
We maintain Node.js runtime and the Chromium V8 JS engine on IBM platforms. V8 has introduced Rust as a dependency in order to support Temporal. Unlike Chromium upstream we do not use nightly versions of Rust and can only rely on stable builds of rustc. So far we have been using version 1.84 and these alloc handlers have been compiling fine for us:
https://chromium.googlesource.com/chromium/src/build/+/refs/heads/main/rust/allocator/lib.rs#111

But since version 1.88 we get these link errors:

ld.lld: error: undefined symbol: __rustc::__rust_alloc_error_handler_should_panic
ld.lld: error: undefined symbol: __rustc::__rust_alloc_error_handler

I'm assuming they are related to this change: #127173
I have tried exporting the symbols it's complaining about as such but it still can't find them:

#[export_name = "__rustc::__rust_alloc_error_handler_should_panic"]
pub extern "C" fn __rust_alloc_error_handler_should_panic() -> u8 {
    oom_should_panic_impl()
}

#[export_name = "__rustc::__rust_alloc_error_handler"]
pub extern "C" fn __rust_alloc_error_handler(_size: usize, _align: usize) {
    unsafe { ffi::alloc_error_handler_impl() }
}

I know the proper way is to use #[rustc_std_internal_symbol] but that's not available in stable rust versions.

Is this a bug? Is there no way we can fix this with stable Rust? I have seen similar issues being reported upstream, i.e bazelbuild/rules_rust#3459

[miladfarca]

/cc @bjorn3

[bjorn3]

__rustc::__rust_alloc_error_handler_should_panic is the demangled name. The full mangled name contains a version dependent hash. Only #[rustc_std_internal_symbol] works to get the right symbol name. If you want to use stable rustc, you will have to use the special env var to make rustc behave like nightly rustc. In either case this can and will break in the future as I'm making changes towards hopefully getting direct linking of rlibs working on stable at some point. Currently the only stable way to use rust in a C project are building a staticlib or cdylib, which bundles all rust dependencies and includes the allocator shim that defines these symbols you are missing.

[miladfarca]

Thank you for the information.

I'm making changes towards hopefully getting direct linking of rlibs working on stable at some point.

So does this mean my patch above will eventually work as is with stable rust? Sounds like we need to stick to rust 1.84 until this is resolved?

[bjorn3]

So does this mean my patch above will eventually work as is with stable rust?

I hope it will eventually not be necessary at all.

Sounds like we need to stick to rust 1.84 until this is resolved?

I don't think that is a good idea. It is probably going to take several years if at all before this is solved.

[miladfarca]

Thank you. Since we are currently dependent on the way Chromium packages rlibs do you think export RUSTC_BOOTSTRAP=1 is an acceptable workaround?

[bjorn3]

If you can control exactly which rustc version you get built with then yes. If you have a minimum supported rustc version, but not a maximum supported rustc version, I would recommend against it.

[miladfarca]

Thank you for the information, I'll close this issue for now then.