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Remove extra indirection from statics with linkage? #156468

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Remove extra indirection from statics with linkage?#156468
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A-linkageArea: linking into static, shared libraries and binariesF-linkage#![feature(linkage)]`needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging

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@RalfJung
RalfJung
opened on May 11, 2026

I just learned from @bjorn3 that the way we represent statics with linkage, such as #[linkage = "extern_weak"], is kind of strange:

unsafe extern "C" {
    #[linkage = "extern_weak"]
    static test_symbol_that_does_not_exist: Option<unsafe extern "C" fn()>;
}

Here, test_symbol_that_does_not_exist will actually be a global variable local to this module that points to the weak symbol.

Now that we have the &raw address-of operator, we could avoid this extra indirection. Whether we should, I do not know.
Cc @bjorn3 @nikic @chorman0773

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  1. rustbot
    added
    needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging
    on May 11, 2026
  2. bjorn3
    added
    A-linkageArea: linking into static, shared libraries and binaries
    F-linkage#![feature(linkage)]`
    on May 11, 2026

  3. chorman0773 commented on May 12, 2026

    @chorman0773
    chorman0773
    on May 12, 2026
    Contributor

    Note that this replacement isn't possible for functions, only statics (since &raw const fn doesn't work). Otherwise, yeah, I agree that the added level of indirection is unneeded (and personally, not something I'd want to use).

  4. RalfJung commented on May 12, 2026

    @RalfJung
    RalfJung
    on May 12, 2026
    MemberAuthor

    As @bjorn3 mentioned on Zulip, it's possible, just awkward: you'd do something like

    unsafe extern "C" {
    #[linkage = "extern_weak"]
    static weak_fn: ();
}

let fn_ptr: Option<fn(i32) -> i32> = transmute(&raw const weak_fn);
// ...

  5. bjorn3 commented on May 12, 2026

    @bjorn3
    bjorn3
    on May 12, 2026
    Member

    Targets where function pointers are larger than data pointers would be an issue, but the (unstable) std::marker::FnPtr::addr method would truncate on those targets too.

  6. chorman0773 commented on May 12, 2026

    @chorman0773
    chorman0773
    on May 12, 2026
    Contributor

    That also loses the ability to use the definition safely.

  7. bjorn3
    marked Specifying linkage on externs silently removes indirection #31508 as a duplicate of this issue on Oct 8, 2026
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