How do I statically link a Haskell library with a Rust project?

Question

I’ve had no luck so far with linking a Haskell library to a Rust project. I’ve had a lot of errors, the latest being the recompile with -fPIC for ghc.

I’ve managed to get a functional example of dynamically linking — but have been unable to get it linked statically.

Attaching my current setup right now:

1. build.rs

   fn main() {
       println!("cargo:rustc-link-search=native=deps");
       println!("cargo:rustc-link-lib=static=tesths");
   }
   

2. src/main.rs

   extern "C" {
       pub fn addTwo(x: i32) -> i32;
       pub fn init();
       pub fn fin();
   }
   
   fn main() {
       println!("Hello, world!");
   }
   

3. src/haskell/Lib.hs

   module Lib where
   
   import Foreign.C.Types
   
   addTwo :: CInt -> CInt
   addTwo = (2 + )
   
   foreign export ccall addTwo :: CInt -> CInt
   

4. cwrapper.c

   #include <HsFFI.h>
   #ifdef __GLASGOW_HASKELL__
   #include "Lib_stub.h"
   #endif
   #include <stdio.h>
   
   void init(void) {
     static char *argv[] = {"libhs.so", 0}, **argv_ = argv;
     static int argc = 1;
   
     hs_init(&argc, &argv_);
   }
   
   void fin(void) { hs_exit(); }
   

I compile #4 with ghc -c -static -lHSrts -lffi cwrapper.c, getting cwrapper.o. Similarly, I compile #3 with ghc -c -static -fPIC -lffi Lib.hs and get object code for that as well.

Once that is done, I go ahead and archive the two with ar rcs libtesths.a Lib.o cwrapper.o.

On cargo build:

note: /usr/bin/ld: deps/libtesths.a(Lib.o):(.text+0x29): undefined reference to `newCAF'
          /usr/bin/ld: deps/libtesths.a(Lib.o):(.text+0x39): undefined reference to `stg_bh_upd_frame_info'
          /usr/bin/ld: deps/libtesths.a(Lib.o):(.text+0x48): undefined reference to `base_ForeignziCziTypes_zdfNumCInt_closure'
          /usr/bin/ld: deps/libtesths.a(Lib.o):(.text+0x4f): undefined reference to `stg_ap_p_info'
…

I’ve got a hunch that libHSrts isn’t being linked statically for some reason.

Update

I followed Shepmaster’s advice and successfully made a working example. But I’m having issues linking with my rust exec now.

I used stack with ghc-options: -staticlib -stubdir . and c-sources: cwrapper.c to build. When I try to build the rust project with cargo rustc — -C relocation-model=static:

/usr/bin/ld: deps/liba.a(Type.o): in function `integerzmwiredzmin_GHCziIntegerziType_zdwplusBigNatWord_info'
(.text.integerzmwiredzmin_GHCziIntegerziType_zdwplusBigNatWord_info+0x128): undefined reference to `__gmpn_add_1'
/usr/bin/ld: deps/liba.a(Type.o): in function
`integerzmwiredzmin_GHCziIntegerziType_zdwminusBigNatWord_info'
(.text.integerzmwiredzmin_GHCziIntegerziType_zdwminusBigNatWord_info+0xdf): undefined reference to `__gmpn_sub_1'
/usr/bin/ld: deps/liba.a(Type.o): in function `integerzmwiredzmin_GHCziIntegerziType_complementInteger_info'
(.text.integerzmwiredzmin_GHCziIntegerziType_complementInteger_info+0x138): undefined reference to `__gmpn_sub_1'
/usr/bin/ld: deps/liba.a(Type.o): in function `integerzmwiredzmin_GHCziIntegerziType_zdwtimesBigNatWord_info'
(.text.integerzmwiredzmin_GHCziIntegerziType_zdwtimesBigNatWord_info+0x158): undefined reference to `__gmpn_mul_1'

There is also mention of a wrappers.o. Any help is appreciated.

Update 2

I solved the gmp issues by setting build.rs to link libgmp as well. I have a different problem now, though.

note: /usr/bin/ld: deps/libhssource.a(Lib.o): in function `testFFI':
          (.text+0x88fd): multiple definition of `testFFI'; deps/libhssource.a(Lib.o):(.text+0x1b66): first defined here
          /usr/bin/ld: deps/libhssource.a(cwrapper.o): in function `init':
          cwrapper.c:(.text+0x0): multiple definition of `init'; deps/libhssource.a(cwrapper.o):cwrapper.c:(.text+0x0): first defined here
          /usr/bin/ld: deps/libhssource.a(cwrapper.o): in function `fin':
          cwrapper.c:(.text+0x20): multiple definition of `fin'; deps/libhssource.a(cwrapper.o):cwrapper.c:(.text+0x1a): first defined here
          collect2: error: ld returned 1 exit status

Update 3

This the final build command that does the trick:

cargo rustc -- -C relocation-model=static -Clink-arg=-Wl,--allow-multiple-definition

Using RUSTFLAGS will cause the build to crash because it builds all the dependencies with a static relocation model, which won’t work — in my case — for the rustversion crate. It will report a recompile with -fPIC error.

Answer 1

I compiled the Haskell library and C shim at once, passing the -staticlib flag:

ghc -c -staticlib Lib.hs cwrapper.c -o libtesths.a

I then called the functions:

extern "C" {
    pub fn addTwo(x: i32) -> i32;
    pub fn init();
    pub fn fin();
}

fn main() {
    unsafe {
        init();
        println!("{}", addTwo(40));
        fin();
    }
}

% cargo run -q
42

This worked for me on macOS 12.0.1 on an Apple Silicon processor using GHC 8.10.7.

If you are on x86_64 Linux, you may need to add RUSTFLAGS='-C relocation-model=static'.