wrong link_name for msvc

[Dushistov]

Input C Header

extern void test(void);

Bindgen Invocation

    let mut bindings: Builder = bindgen::builder().header(c_file_path.to_str().unwrap());
    bindings = include_dirs.iter().fold(bindings, |acc, x| acc.clang_arg("-I".to_string() + x.as_ref().to_str().unwrap()));

    bindings = bindings
        .no_unstable_rust()
        .raw_line("#![allow(non_upper_case_globals, dead_code, non_camel_case_types, improper_ctypes)]")
        ;
    bindings = c_headers[1..].iter().fold(Ok(bindings), |acc: Result<Builder, String>, header| {
        let c_file_path = search_file_in_directory(include_dirs, header)
                               .map_err(|_| format!("Can not find {}", header))?;
        let c_file_str = c_file_path.to_str()
            .ok_or_else(|| format!("Invalid unicode in path to {}", header))?;
        Ok(acc.unwrap().clang_arg("-include").clang_arg(c_file_str))
    })?;
    
    let generated_bindings = bindings.generate().map_err(|_| "Failed to generate bindings".to_string())?;
    generated_bindings.write_to_file(output_rust).map_err(|err| err.to_string())?;

Actual Results

extern "C" {
    #[link_name = "_test"]
    pub fn test();
}

error LNK2019: unresolved external symbol __test

Expected Results

linking without any errors.

Hint the problem in two underscores instead of one,
looks like rustc (at least 1.16) smart enought to add "_" to names.
So if remove #[link_name = "_test"] all works fine,
but I can not find option to strip link_name from output.

[emilio]

Which clang version are you using?

You can workaround this with --distrust-clang-mangling

[Dushistov]

@emilio

Which clang version are you using?

C:\Users\IEUser\projects\link_name_bug\mylib-sys\src>clang --version
clang version 3.9.0 (branches/release_39)
Target: i686-pc-windows-msvc
Thread model: posix
InstalledDir: C:\Program Files\LLVM\bin

You can workaround this with --distrust-clang-mangling

I can not, with/without this option it generates the same:

C:\Users\IEUser\projects\link_name_bug\mylib-sys\src>bindgen --version
bindgen 0.22.1

C:\Users\IEUser\projects\link_name_bug\mylib-sys\src>bindgen test.h
/* automatically generated by rust-bindgen */

extern "C" {
    #[link_name = "_test"]
    pub fn test();
}

C:\Users\IEUser\projects\link_name_bug\mylib-sys\src>bindgen --distrust-clang-mangling test.h
/* automatically generated by rust-bindgen */

extern "C" {
    #[link_name = "_test"]
    pub fn test();
}

[emilio]

Whoopsies, that's my fault. Could you confirm it works with #579?

Also, I'm intrigued by this anyway, given we used to have this remove first underscore of the mangling thing also for windows (see https://github.com/servo/rust-bindgen/blob/master/src/ir/function.rs#L133), but it was removed because it seemed no longer necessary...

Does cd bindgen-integration && cargo test work for you now? and adding windows to that condition?

[Dushistov]

Could you confirm it works with #579?

Yes, with --distrust-clang-mangling and #579 it works

Does cd bindgen-integration && cargo test work for you now?

It works on my host machine (with linux) without #579,

and it failed on windows inside virtualbox with #579:

--- stderr
thread 'main' panicked at 'unsupported calling convention: 4', C:\Users\IEUser\p
rojects\rust-bindgen\src\ir\function.rs:109
note: Run with `RUST_BACKTRACE=1` for a backtrace.

[fitzgen]

I think all that is required to repro is this:

// bindgen-flags: -- --target i686-pc-windows-msvc
extern void test(void);

[fitzgen]

Duping this to #541 which is the same root issue but has more discussion.