rustc emits an unexpected `_rdl` symbols for WASM with `lto=true`

[ok-ul-ch]

It seems that 7a01c7f introduced an issue with lto + WASM + global allocator

Details

rustc emits an unexpected _rdl symbol for WASM (no_std) with lto=true, which imports unavailable external functions:

...
(import "env" "_RNvCs3SlB0nJ74mU_7___rustc9___rdl_oom" (func $_RNvCs3SlB0nJ74mU_7___rustc9___rdl_oom (;0;) (type 0)))
...

This behavior is not observed with lto=false OR the latest stable Rust (1.89)

Cargo.toml

[package]
name = "issue-wasm-lto"
edition = "2024"

[lib]
crate-type = ["cdylib"]

[profile.release]
lto = true

[dependencies]
dlmalloc = { version = "*", features = ["global"] }

lib.rs

#![no_std]
extern crate alloc;

#[panic_handler]
fn panic(_info: &core::panic::PanicInfo) -> ! {
    core::arch::wasm32::unreachable();
}

#[global_allocator]
static ALLOC: dlmalloc::GlobalDlmalloc = dlmalloc::GlobalDlmalloc;

#[unsafe(no_mangle)]
pub extern "C" fn test_sum(size: usize) -> usize {
    // Allocate smth
    alloc::vec::Vec::with_capacity(size).iter().sum()
}

build with

cargo +nightly build --target=wasm32-unknown-unknown --release
wasm-tools print target/wasm32-unknown-unknown/release/issue_wasm_lto.wasm  > issue_wasm_lto.wat

Version it worked on

rustc 1.91.0-nightly (c8ca44c98 2025-08-10)

Version with regression

rustc 1.91.0-nightly (af00ff2ce 2025-09-04)

[lqd]

cc @bjorn3

[bjorn3]

In #145955 I made those exported by LTO (exported_symbols_for_lto), but the linker should still hide them the same way they are hidden for non-LTO builds as they weren't added to exported_symbols_for_non_proc_macro and thus no --export argument will be passed to wasm-ld. In any case it should be hidden by LTO again if #146232 gets merged.