Rust FFI on Windows MSVC

.gitignore

/target/
**/*.rs.bk
Cargo.lock
*.exe
*.obj
exports.txt

README.md

Rust FFI: Calling a Rust function from a C program

Environment

• Windows 10 Home Edition (64 bit)
• Rust 1.20.0 stable (MSVC)
• Build Tools for Visual Studio 2017

C:\Users\tatsuya>rustc --version
rustc 1.20.0 (f3d6973f4 2017-08-27)

C:\Users\tatsuya>rustup run nightly rustc --version
rustc 1.22.0-nightly (277476c4f 2017-09-16)

C:\Users\tatsuya>link
Microsoft (R) Incremental Linker Version 14.11.25507.1
Copyright (C) Microsoft Corporation.  All rights reserved.
...

C:\Users\tatsuya>cl
Microsoft (R) C/C++ Optimizing Compiler Version 19.11.25507.1 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

usage: cl [ option... ] filename... [ /link linkoption... ]

Building and Running

cargo build --release does not emit an import library (.lib) but only creates .dll. To make the C++ compile (cl.ext) to link with the .dll, I had to create .lib from .dll using several commands like dumpbin and lib.

**********************************************************************
** Visual Studio 2017 Developer Command Prompt v15.0.26730.12
** Copyright (c) 2017 Microsoft Corporation
**********************************************************************
[vcvarsall.bat] Environment initialized for: 'x64'

C:\Program Files (x86)\Microsoft Visual Studio\2017\BuildTools>cd \Users\tatsuya\ffi

C:\Users\tatsuya\ffi>cargo build --release
   Compiling ffi v0.1.0 (file:///C:/Users/tatsuya/ffi)
    Finished release [optimized] target(s) in 0.51 secs

C:\Users\tatsuya\ffi>dir .\target\release
 Volume in drive C has no label.
 Volume Serial Number is 96D9-58A2

 Directory of C:\Users\tatsuya\ffi\target\release

2017/09/17  19:17    <DIR>          .
2017/09/17  19:17    <DIR>          ..
2017/09/17  19:17                 0 .cargo-lock
2017/09/17  19:17    <DIR>          .fingerprint
2017/09/17  19:17    <DIR>          build
2017/09/17  19:17    <DIR>          deps
2017/09/17  19:17    <DIR>          examples
2017/09/17  19:17                77 ffi.d
2017/09/17  19:17           111,616 ffi.dll
2017/09/17  19:17    <DIR>          incremental
2017/09/17  19:17    <DIR>          native
               3 File(s)        111,693 bytes
               8 Dir(s)  44,607,131,648 bytes free

C:\Users\tatsuya\ffi>dumpbin /Exports target\release\ffi.dll > exports.txt

C:\Users\tatsuya\ffi>echo LIBRARY FFI > ffi.def

C:\Users\tatsuya\ffi>echo EXPORTS >> ffi.def

C:\Users\tatsuya\ffi>for /f "skip=19 tokens=4" %A in (exports.txt) do echo %A >> ffi.def

...

C:\Users\tatsuya\ffi>type ffi.def
LIBRARY FFI
EXPORTS
__rdl_alloc
__rdl_alloc_excess
__rdl_alloc_zeroed
__rdl_dealloc
__rdl_grow_in_place
__rdl_oom
__rdl_realloc
__rdl_realloc_excess
__rdl_shrink_in_place
__rdl_usable_size
pow
rust_eh_personality

C:\Users\tatsuya\ffi>lib /Def:ffi.def /Out:target\release\ffi.lib /Machine:x64
Microsoft (R) Library Manager Version 14.11.25507.1
Copyright (C) Microsoft Corporation.  All rights reserved.
   Creating library target\release\ffi.lib and object target\release\ffi.exp

C:\Users\tatsuya\ffi>cl /EHsc c_src\main.c .\target\release\ffi.lib
Microsoft (R) C/C++ Optimizing Compiler Version 19.11.25507.1 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

main.c
Microsoft (R) Incremental Linker Version 14.11.25507.1
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:main.exe
main.obj
.\target\release\ffi.lib

C:\Users\tatsuya\ffi>set PATH=.\target\release;%PATH%

C:\Users\tatsuya\ffi>.\main.exe
100

Link Arguments

Maybe there is a way to emit .lib from MSVC?

C:\Users\tatsuya\ffi>set RUSTFLAGS=-Z print-link-args

C:\Users\tatsuya\ffi>cargo +nightly build --release
   Compiling ffi v0.1.0 (file:///C:/Users/tatsuya/ffi)
"C:\\Program Files (x86)\\Microsoft Visual Studio\\2017\\BuildTools\\VC\\Tools\\MSVC\\14.11.25503\\bin\\HostX64\\x64\\link.exe"
  "/NOLOGO"
  "/NXCOMPAT"
  "/LIBPATH:C:\\Users\\tatsuya\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib"
  "C:\\Users\\tatsuya\\ffi\\target\\release\\deps\\ffi.0.o"
  "/OUT:C:\\Users\\tatsuya\\ffi\\target\\release\\deps\\ffi.dll" 
  "/DEF:C:\\Users\\tatsuya\\AppData\\Local\\Temp\\rustc.WXmH6dixFUrY\\lib.def" 
  "C:\\Users\\tatsuya\\ffi\\target\\release\\deps\\ffi.crate.allocator.o"
  "/OPT:REF,ICF"
  "/DEBUG" 
  "/NATVIS:C:\\Users\\tatsuya\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\etc\\liballoc.natvis" 
  "/NATVIS:C:\\Users\\tatsuya\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\etc\\libcore.natvis" 
  "/LIBPATH:C:\\Users\\tatsuya\\ffi\\target\\release\\deps"
  "/LIBPATH:C:\\Users\\tatsuya\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib" 
  "C:\\Users\\tatsuya\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libstd-db6de5af2d0a9c77.rlib"
  "C:\\Users\\tatsuya\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\liballoc_system-01640051e83829a3.rlib"
  "C:\\Users\\tatsuya\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\librand-1691a4817e1014c0.rlib"
  "C:\\Users\\tatsuya\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libpanic_unwind-fe3db6e00272232d.rlib"
  "C:\\Users\\tatsuya\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\liblibc-1bcdb4f089768c3e.rlib"
  "C:\\Users\\tatsuya\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\liballoc-256d8904b26e3f9f.rlib"
  "C:\\Users\\tatsuya\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libstd_unicode-e1b478fb207a2cfd.rlib"
  "C:\\Users\\tatsuya\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libunwind-b58e94042876ce0c.rlib"
  "C:\\Users\\tatsuya\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libcore-3837fbddd99d1fca.rlib"
  "C:\\Users\\tatsuya\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libcompiler_builtins-b0347d25dae429a5.rlib"
  "advapi32.lib"
  "ws2_32.lib"
  "userenv.lib"
  "shell32.lib"
  "msvcrt.lib"
  "/DLL"
  "/IMPLIB:C:\\Users\\tatsuya\\ffi\\target\\release\\deps\\ffi.dll.lib"
    Finished release [optimized] target(s) in 0.64 secs

C:\Users\tatsuya\ffi>

c_src-main.c

#include <stdio.h>
#include <stdint.h>

int32_t
pow(int32_t n);

int
main()
{
    int32_t n = 10;
    int32_t ret;

    ret = pow(n);

    printf("%d\n", ret);
}

Cargo.toml

[package]
name = "ffi"
version = "0.1.0"
authors = ["Tatsuya Kawano <[email protected]>"]

[lib]
crate-type = ["cdylib"]

[dependencies]

src-rib.rs

#[no_mangle]
pub extern "C" fn pow(n: i32) -> i32 {
    n * n
}

cargo build --release does not emit an import library (.lib) but only creates .dll.

Does specifying crate-type = ["staticlib"] instead of "cdylib" help ?

Hi. Thank you for your comment. I forgot to update this Gist but I actually fixed the issue by submitting a pull request to the Cargo project:

• rust-lang/cargo#4570

I think the PR was merged for Cargo v0.23.0 (released on Nov 29, 2017).