Unsupported calling convention on i686-pc-windows-msvc

[tmccrmck]

I was investigating how easy it would be to create bindings for Windows 32-bit with different calling conventions and so I ran the example in the ./bindgen-integration directory.

System

> rustup show
Default host: x86_64-pc-windows-msvc

installed toolchains
--------------------

stable-i686-pc-windows-msvc
stable-x86_64-pc-windows-msvc (default)
nightly-i686-pc-windows-msvc
nightly-x86_64-pc-windows-msvc

active toolchain
----------------

stable-i686-pc-windows-msvc (directory override for 'C:\Repos\rust-bindgen\bindgen-integration')
rustc 1.15.1 (021bd294c 2017-02-08)


> clang -v
clang version 3.9.1 (branches/release_39)
Target: i686-pc-windows-msvc

Input C/C++ Header

#pragma once

class Test {
  int m_int;
  double m_double;
public:
  static const char* name();
  Test(int foo);
  Test(double foo);

  static const int COUNTDOWN[];
  static const int* COUNTDOWN_PTR;
  static const int* countdown();
};

namespace testing {

typedef Test TypeAlias;

} // namespace testing

typedef testing::TypeAlias TypeAlias;

Bindgen Invokation

let bindings = Builder::default()
        .no_unstable_rust()
        .enable_cxx_namespaces()
        .raw_line("pub use self::root::*;")
        .header("cpp/Test.h")
        .clang_arg("-x")
        .clang_arg("c++")
        .clang_arg("-std=c++11")
        .generate()
        .expect("Unable to generate bindings");

Actual Results

error: failed to run custom build command for `bindgen-integration v0.1.0 (file:///C:/Repos/rust-bindgen/bindgen-integration)`
process didn't exit successfully: `C:\Repos\rust-bindgen\bindgen-integration\target\debug\build\bindgen-integration-a1a8c12a2facefae\build-script-build` (exit code: 101)
--- stdout
TARGET = Some("i686-pc-windows-msvc")
OPT_LEVEL = Some("0")
TARGET = Some("i686-pc-windows-msvc")
HOST = Some("i686-pc-windows-msvc")
TARGET = Some("i686-pc-windows-msvc")
TARGET = Some("i686-pc-windows-msvc")
HOST = Some("i686-pc-windows-msvc")
CXX_i686-pc-windows-msvc = None
CXX_i686_pc_windows_msvc = None
HOST_CXX = None
CXX = None
TARGET = Some("i686-pc-windows-msvc")
HOST = Some("i686-pc-windows-msvc")
CXXFLAGS_i686-pc-windows-msvc = None
CXXFLAGS_i686_pc_windows_msvc = None
HOST_CXXFLAGS = None
CXXFLAGS = None
PROFILE = Some("debug")
running: "C:\\Program Files (x86)\\Microsoft Visual Studio 14.0\\VC\\bin\\amd64_x86\\cl.exe" "/nologo" "/MD" "/Z7" "/FoC:\\Repos\\rust-bindgen\\bindgen-integration\\target\\debug\\build\
\bindgen-integration-89b7af89d851f38d\\out\\cpp\\Test.o" "/c" "cpp/Test.cc"
ExitStatus(ExitStatus(0))
TARGET = Some("i686-pc-windows-msvc")
running: "C:\\Program Files (x86)\\Microsoft Visual Studio 14.0\\VC\\bin\\amd64_x86\\lib.exe" "/OUT:C:\\Repos\\rust-bindgen\\bindgen-integration\\target\\debug\\build\\bindgen-integratio
n-89b7af89d851f38d\\out\\libtest.a" "/nologo" "C:\\Repos\\rust-bindgen\\bindgen-integration\\target\\debug\\build\\bindgen-integration-89b7af89d851f38d\\out\\cpp\\Test.o"
ExitStatus(ExitStatus(0))
TARGET = Some("i686-pc-windows-msvc")
HOST = Some("i686-pc-windows-msvc")
TARGET = Some("i686-pc-windows-msvc")
TARGET = Some("i686-pc-windows-msvc")
HOST = Some("i686-pc-windows-msvc")
CXX_i686-pc-windows-msvc = None
CXX_i686_pc_windows_msvc = None
HOST_CXX = None
CXX = None
cargo:rustc-link-search=native=C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\atlmfc\lib\
cargo:rustc-link-lib=static=test
cargo:rustc-link-search=native=C:\Repos\rust-bindgen\bindgen-integration\target\debug\build\bindgen-integration-89b7af89d851f38d\out
TARGET = Some("i686-pc-windows-msvc")
cpp/Test.h:1:9: warning: #pragma once in main file [-Wpragma-once-outside-header], err: false

--- stderr
thread 'main' panicked at 'unsupported calling convention: 4', C:\Repos\rust-bindgen\src\ir\function.rs:103
note: Run with `RUST_BACKTRACE=1` for a backtrace.

Steps to reproduce

1. Install clang 3.9.1 for Windows 32-bit
2. > git clone https://github.com/servo/rust-bindgen.git
3. > cd rust-bindgen\bindgen-integration
4. > rustup override set stable-i686-pc-windows-msvc
5. > cargo build

[tmccrmck]

OK I wanted to isolate the problem so I could try with stdcall and cdecl so I removed nearly everything from the header:

#pragma once

class Test {
  int m_int;
  double m_double;
public:
  static const char* name();
};

And it compiles with this. But as soon as you try to use cargo test you get

  = note: bindgen_integration-2ef5a86ee87393d3.0.o : error LNK2019: unresolved external symbol _?name@Test@@SAPBDXZ referenced in function __ZN19bindgen_integration8bindings4root4Test4name17h1c2ec80b5b5613d1E
C:\Repos\rust-bindgen\bindgen-integration\target\debug\deps\bindgen_integration-2ef5a86ee87393d3.exe : fatal error LNK1120: 1 unresolved externals

Which just looks like a mangling problem.

[emilio]

I don't have a windows machine to test on, could you inspect the generated library to see which mangled names are being generated?

[froydnj]

The original issue here is that calling convention 4 is __thiscall, which is the default ABI for methods in MSVC. However, the packages bindgen is using (syntex_syntax) don't define anything for __thiscall.

@emilio is it feasible to just modify syntex_syntax here to define __thiscall, and then do the appropriate adjustments to bindgen?

[emilio]

@froydnj yeah, also, note that syntex_syntax is pretty much a clone of libsyntax in the rust compiler, so this should probably be upstreamed.

Is this blocking you in any meaningful way? If there's any workaround we can do in bindgen, happy to help. Perhaps making it a soft error may help for now.

[froydnj]

Is this blocking you in any meaningful way? If there's any workaround we can do in bindgen, happy to help. Perhaps making it a soft error may help for now.

Throwing a soft error here is hard, because we have to pass in /something/ for the calling convention. I guess we already have special cases for Obj-C method declarations, we could fake things up for C++ method declarations, and then cross fingers that nobody is actually bindgen'ing calls to C++ methods? That seems like a giant hack, though, with some definite footgun possibilities.

We can work around this in Stylo by simply not building Stylo for win32 for the time being.

[fitzgen]

All that is required to repro is this:

// bindgen-flags: -- --target=i686-pc-windows-msvc

class Foo {
  public:
    void test();
};

or with --target=i686-pc-win32 as well.