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Rollup merge of #145724 - folkertdev:track-caller-drop-no-mangle, r=fee1-dead

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the `#[track_caller]` shim should not inherit `#[no_mangle]`

fixes https://github.com/rust-lang/rust/issues/143162

builds on https://github.com/rust-lang/rust/pull/143293 which introduced a mechanism to strip attributes from shims.

cc `@Jules-Bertholet` `@workingjubilee` `@bjorn3`

---

Summary:

This PR fixes an interaction between `#[track_caller]`, `#[no_mangle]`, and casting to a function pointer.

A function annotated with `#[track_caller]` internally has a hidden extra argument for the panic location. The `#[track_caller]` attribute is only allowed on `extern "Rust"` functions. When a function is annotated with both `#[no_mangle]` and `#[track_caller]`, the exported symbol has the signature that includes the extra panic location argument. This works on stable rust today:

```rust
extern "Rust" {
    #[track_caller]
    fn rust_track_caller_ffi_test_tracked() -> &'static Location<'static>;
}

mod provides {
    use std::panic::Location;
    #[track_caller] // UB if we did not have this!
    #[no_mangle]
    fn rust_track_caller_ffi_test_tracked() -> &'static Location<'static> {
        Location::caller()
    }
}
```

When a `#[track_caller]` function is converted to a function pointer, a shim is added to drop the additional argument. So this is a valid program:

```rust
#[track_caller]
fn foo() {}

fn main() {
    let f = foo as fn();
    f();
}
```

The issue arises when `foo` is additionally annotated with `#[no_mangle]`, the generated shim currently inherits this attribute, also exporting a symbol named `foo`, but one without the hidden panic location argument. The linker rightfully complains about a duplicate symbol.

The solution of this PR is to have the generated shim drop the `#[no_mangle]` attribute.
This commit is contained in:
Matthias Krüger
2025-10-18 08:08:36 +02:00
committed by GitHub
parent b46db5c6b7 9db778155e
commit a5d38ede1d
6 changed files with 69 additions and 12 deletions
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5
compiler/rustc_mir_transform/src/inline.rs
View File

@@ -245,7 +245,7 @@ impl<'tcx> Inliner<'tcx> for ForceInliner<'tcx> {
fn on_inline_failure(&self, callsite: &CallSite<'tcx>, reason: &'static str) {
let tcx = self.tcx();
let InlineAttr::Force { attr_span, reason: justification } =
tcx.codegen_fn_attrs(callsite.callee.def_id()).inline
tcx.codegen_instance_attrs(callsite.callee.def).inline
else {
bug!("called on item without required inlining");
};
@@ -603,7 +603,8 @@ fn try_inlining<'tcx, I: Inliner<'tcx>>(
let tcx = inliner.tcx();
check_mir_is_available(inliner, caller_body, callsite.callee)?;
let callee_attrs = tcx.codegen_fn_attrs(callsite.callee.def_id());
let callee_attrs = tcx.codegen_instance_attrs(callsite.callee.def);
let callee_attrs = callee_attrs.as_ref();
check_inline::is_inline_valid_on_fn(tcx, callsite.callee.def_id())?;
check_codegen_attributes(inliner, callsite, callee_attrs)?;
inliner.check_codegen_attributes_extra(callee_attrs)?;