Static items can result in references to unexported symbols

[bkoropoff]

Scenario

• Crate 1 contains a struct with an extern fn field
• Crate 1 contains a pub static item of that struct, with the field being initialized to a priv extern fn
• Crate 2 contains a static item of the same struct which is initialized to the static item in crate 1
• All crates are built as dylibs, and a program is linked against crate 2

Result

Crate 2 ends up referring directly to the priv extern fn in crate 1, which is not in the dynamic symbol table for the crate. The program fails to link.

Code

crate1.rs

pub struct Foo {
    pub foo: extern fn()
}

extern fn the_foo() {}

pub static FOO: Foo = Foo {
    foo: the_foo
};

crate2.rs

extern crate crate1;

pub static FOO2: crate1::Foo = crate1::FOO;

main.rs

extern crate crate2;

fn main() {
    (crate2::FOO2.foo)();
}

Makefile

CRATE1=$(shell rustc --crate-type=dylib --crate-file-name crate1.rs)
CRATE2=$(shell rustc --crate-type=dylib --crate-file-name crate2.rs)

all: main

$(CRATE1): crate1.rs
    rustc --crate-type=dylib $<

$(CRATE2): crate2.rs $(CRATE1)
    rustc --crate-type=dylib -L. $<

main: main.rs $(CRATE2)
    rustc -L. $<

clean:
    rm -f *.so main

.PHONY: clean all

Output

Excerpt of error:

....
note: .../rust-bug/libcrate2-c9f1a15a-0.0.so: error: undefined reference to 'the_foo::h33cb9568e97d6893haa::v0.0'