rust_eh_personality exported by cdylibs

[bjorn3]

I tried this:

$ echo | rustc - --crate-type cdylib
$ bingrep librust_out.so
[...]
Dyn Syms(13):
               Addr   Bind       Type        Symbol                            Size     Section     Other
[...]
              1300    GLOBAL     FUNC        rust_eh_personality               0x2e5    .text(11)   0x0
[...]

I expected to see this happen: No symbols are exported as there are no #[no_mangle] symbols in the crate source.

Instead, this happened: rust_eh_personality is exported. This means that different rustc versions could potentially interfere with unwinding of code compiled by the other rustc version by overriding this symbol.

Meta

rustc --version --verbose:

rustc 1.59.0-nightly (91a0600a5 2021-12-18)
binary: rustc
commit-hash: 91a0600a5c22b9d159e3c57526af83e71d1120f8
commit-date: 2021-12-18
host: x86_64-unknown-linux-gnu
release: 1.59.0-nightly
LLVM version: 13.0.0

and

rustc 1.56.0 (09c42c458 2021-10-18)
binary: rustc
commit-hash: 09c42c45858d5f3aedfa670698275303a3d19afa
commit-date: 2021-10-18
host: x86_64-unknown-linux-gnu
release: 1.56.0
LLVM version: 13.0.0

[bjorn3]

Weak lang items should be marked with #[rustc_std_internal_symbol] already which should hide it from cdylibs:

rust/compiler/rustc_typeck/src/collect.rs

Lines 3230 to 3232 in f58d51b

	if tcx.is_weak_lang_item(id) {
	codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
	}

[petrochenkov]

Fixed in #95604.