Crosscompiling Rust from Fedora Linux host to Windows target does not find dependencies

Question

I run x86_64 Fedora Linux 31 host and want to compile some simplest rust code:

fn main() {
    println!("Hello, world!");
}

It compiles from the host to this host natively fine but when I try to cross compile it to either i686 or x86_64 windows it fails to compile.

I read stackoverflow (for example here) and googled the Internet trying to find out similar problem and how to solve it but with no profit.

I have installed all the targets necessary:

[pfemidi@pfemidi hello_cargo]$ rustup show
Default host: x86_64-unknown-linux-gnu
rustup home:  /home/pfemidi/.rustup

installed targets for active toolchain
--------------------------------------

i686-pc-windows-gnu
i686-unknown-linux-gnu
i686-unknown-linux-musl
x86_64-pc-windows-gnu
x86_64-unknown-linux-gnu
x86_64-unknown-linux-musl

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

stable-x86_64-unknown-linux-gnu (default)
rustc 1.39.0 (4560ea788 2019-11-04)

[pfemidi@pfemidi hello_cargo]$

I have installed as mingw32 as mingw64, this little test C++ code has been compiled as by mingw32 as mingw64 just fine and with no errors:

#include <iomanip>
#include <iostream>

int main() {
    std::cout << "Hello, world!" << std::endl;
    return 0;
}

I have added windows specific mingw linker and ar to my .cargo/config:

[target.i686-pc-windows-gnu]
linker = "i686-w64-mingw32-gcc"
ar = "i686-w64-mingw32-ar"

[target.x86_64-pc-windows-gnu]
linker = "x86_64-w64-mingw32-gcc"
ar = "x86_64-w64-mingw32-ar"

But when I run either

cargo build --release --target i686-pc-windows-gnu --verbose

or

cargo build --release --target x86_64-pc-windows-gnu --verbose

both complain "cannot find -lpthread":

[pfemidi@pfemidi hello_cargo]$ cargo build --release --target i686-pc-windows-gnu --verbose
   Compiling hello_cargo v0.1.0 (/home/pfemidi/mywork/rust/hello_cargo)
     Running `rustc --edition=2018 --crate-name hello_cargo src/main.rs --color always --crate-type bin --emit=dep-info,link -C opt-level=3 -C panic=abort -C metadata=3801b83c24480675 -C extra-filename=-3801b83c24480675 --out-dir /home/pfemidi/mywork/rust/hello_cargo/target/i686-pc-windows-gnu/release/deps --target i686-pc-windows-gnu -C ar=i686-w64-mingw32-ar -C linker=i686-w64-mingw32-gcc -L dependency=/home/r/mywork/rust/hello_cargo/target/i686-pc-windows-gnu/release/deps -L dependency=/home/r/mywork/rust/hello_cargo/target/release/deps`
error: linking with `i686-w64-mingw32-gcc` failed: exit code: 1
  |
  = note: "i686-w64-mingw32-gcc" "-Wl,--enable-long-section-names" "-fno-use-linker-plugin" "-Wl,--nxcompat" "-nostdlib" "-Wl,--large-address-aware" "/home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/crt2.o" "/home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/rsbegin.o" "-L" "/home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib" "/home/pfemidi/mywork/rust/hello_cargo/target/i686-pc-windows-gnu/release/deps/hello_cargo-3801b83c24480675.hello_cargo.ejabbyqy-cgu.0.rcgu.o" "/home/pfemidi/mywork/rust/hello_cargo/target/i686-pc-windows-gnu/release/deps/hello_cargo-3801b83c24480675.hello_cargo.ejabbyqy-cgu.1.rcgu.o" "/home/pfemidi/mywork/rust/hello_cargo/target/i686-pc-windows-gnu/release/deps/hello_cargo-3801b83c24480675.hello_cargo.ejabbyqy-cgu.10.rcgu.o" "/home/pfemidi/mywork/rust/hello_cargo/target/i686-pc-windows-gnu/release/deps/hello_cargo-3801b83c24480675.hello_cargo.ejabbyqy-cgu.11.rcgu.o" "/home/pfemidi/mywork/rust/hello_cargo/target/i686-pc-windows-gnu/release/deps/hello_cargo-3801b83c24480675.hello_cargo.ejabbyqy-cgu.12.rcgu.o" "/home/pfemidi/mywork/rust/hello_cargo/target/i686-pc-windows-gnu/release/deps/hello_cargo-3801b83c24480675.hello_cargo.ejabbyqy-cgu.2.rcgu.o" "/home/pfemidi/mywork/rust/hello_cargo/target/i686-pc-windows-gnu/release/deps/hello_cargo-3801b83c24480675.hello_cargo.ejabbyqy-cgu.3.rcgu.o" "/home/pfemidi/mywork/rust/hello_cargo/target/i686-pc-windows-gnu/release/deps/hello_cargo-3801b83c24480675.hello_cargo.ejabbyqy-cgu.4.rcgu.o" "/home/pfemidi/mywork/rust/hello_cargo/target/i686-pc-windows-gnu/release/deps/hello_cargo-3801b83c24480675.hello_cargo.ejabbyqy-cgu.5.rcgu.o" "/home/pfemidi/mywork/rust/hello_cargo/target/i686-pc-windows-gnu/release/deps/hello_cargo-3801b83c24480675.hello_cargo.ejabbyqy-cgu.6.rcgu.o" "/home/pfemidi/mywork/rust/hello_cargo/target/i686-pc-windows-gnu/release/deps/hello_cargo-3801b83c24480675.hello_cargo.ejabbyqy-cgu.7.rcgu.o" "/home/pfemidi/mywork/rust/hello_cargo/target/i686-pc-windows-gnu/release/deps/hello_cargo-3801b83c24480675.hello_cargo.ejabbyqy-cgu.8.rcgu.o" "/home/pfemidi/mywork/rust/hello_cargo/target/i686-pc-windows-gnu/release/deps/hello_cargo-3801b83c24480675.hello_cargo.ejabbyqy-cgu.9.rcgu.o" "-o" "/home/pfemidi/mywork/rust/hello_cargo/target/i686-pc-windows-gnu/release/deps/hello_cargo-3801b83c24480675.exe" "/home/pfemidi/mywork/rust/hello_cargo/target/i686-pc-windows-gnu/release/deps/hello_cargo-3801b83c24480675.3miif37looiovbes.rcgu.o" "-Wl,--gc-sections" "-nodefaultlibs" "-L" "/home/pfemidi/mywork/rust/hello_cargo/target/i686-pc-windows-gnu/release/deps" "-L" "/home/pfemidi/mywork/rust/hello_cargo/target/release/deps" "-L" "/home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib" "-Wl,--start-group" "-Wl,-Bstatic" "/home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/libstd-78187cf09a9bef6f.rlib" "/home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/libpanic_abort-699459bd9d6c1638.rlib" "/home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/libhashbrown-397a481a32803af5.rlib" "/home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/librustc_std_workspace_alloc-27eb482dce24475f.rlib" "/home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/libbacktrace-046a61f77fc212c5.rlib" "/home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/libbacktrace_sys-8c6fe5218eaa7203.rlib" "/home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/librustc_demangle-4d4d47417516248c.rlib" "/home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/libunwind-ef8ccbbd42d1b53f.rlib" "/home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/libcfg_if-bbe68dc13352b6cc.rlib" "/home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/liblibc-b6447d8e4c58855b.rlib" "/home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/liballoc-3890c13f15229667.rlib" "/home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/librustc_std_workspace_core-ceab434c37c7417c.rlib" "/home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/libcore-3b2fced4ccf446c5.rlib" "-Wl,--end-group" "/home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/libcompiler_builtins-7e358676639674ac.rlib" "-Wl,-Bdynamic" "-ladvapi32" "-lws2_32" "-luserenv" "-Wl,-Bstatic" "-lgcc_eh" "-lpthread" "-Wl,-Bdynamic" "-lmingwex" "-lmingw32" "-lgcc" "-lmsvcrt" "-lmsvcrt" "-luser32" "-lkernel32" "/home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/rsend.o"
  = note: /usr/lib/gcc/i686-w64-mingw32/9.2.1/../../../../i686-w64-mingw32/bin/ld: cannot find -lpthread
          collect2: error: ld returned 1 exit status


error: aborting due to previous error

error: could not compile `hello_cargo`.

Caused by:
  process didn't exit successfully: `rustc --edition=2018 --crate-name hello_cargo src/main.rs --color always --crate-type bin --emit=dep-info,link -C opt-level=3 -C panic=abort -C metadata=3801b83c24480675 -C extra-filename=-3801b83c24480675 --out-dir /home/pfemidi/mywork/rust/hello_cargo/target/i686-pc-windows-gnu/release/deps --target i686-pc-windows-gnu -C ar=i686-w64-mingw32-ar -C linker=i686-w64-mingw32-gcc -L dependency=/home/pfemidi/mywork/rust/hello_cargo/target/i686-pc-windows-gnu/release/deps -L dependency=/home/pfemidi/mywork/rust/hello_cargo/target/release/deps` (exit code: 1)
[pfemidi@pfemidi hello_cargo]$

Why? What else should I do to satisfy everything?

Answer 1

After a little thought I was able to solve the problem to cross compile projects in Rust from the Linux host to the Windows target without using cross and similar tools but simply by specifying specific target in the cargo. Of course testing and running the project will fail (if you have no any emulator like wine installed), but just creating the Windows target goes smoothly. BTW Rust was developed to be cross compiler initially and therefore having the full working project and passing all the tests in Linux one can be almost sure that a simple cross compilation of this project in Windows will not break it in any way.

Since I run Fedora Linux 31 all of the following applies to this distribution. But I do not think that there are significant differences among other Linux distributions. And I only consider pc-windows-gnu Rust targets, pc-windows-msvc targets are not of my interest.

First, make sure all the necessary MinGW packages for cross compilation are installed:

[pfemidi@pfemidi ~]$ rpm -qa | grep mingw | sort
mingw32-binutils-2.32-6.fc31.x86_64
mingw32-cpp-9.2.1-1.fc31.x86_64
mingw32-crt-6.0.0-2.fc31.noarch
mingw32-filesystem-110-1.fc31.noarch
mingw32-gcc-9.2.1-1.fc31.x86_64
mingw32-headers-6.0.0-2.fc31.noarch
mingw32-winpthreads-6.0.0-2.fc31.noarch
mingw32-winpthreads-static-6.0.0-2.fc31.noarch
mingw64-binutils-2.32-6.fc31.x86_64
mingw64-cpp-9.2.1-1.fc31.x86_64
mingw64-crt-6.0.0-2.fc31.noarch
mingw64-filesystem-110-1.fc31.noarch
mingw64-gcc-9.2.1-1.fc31.x86_64
mingw64-headers-6.0.0-2.fc31.noarch
mingw64-winpthreads-6.0.0-2.fc31.noarch
mingw64-winpthreads-static-6.0.0-2.fc31.noarch
mingw-binutils-generic-2.32-6.fc31.x86_64
mingw-filesystem-base-110-1.fc31.noarch
[pfemidi@pfemidi ~]$

Lets create the simplest project in the Rust language:

[pfemidi@pfemidi rust]$ cargo new foobar
     Created binary (application) `foobar` package
[pfemidi@pfemidi rust]$ cat foobar/src/main.rs 
fn main() {
    println!("Hello, world!");
}
[pfemidi@pfemidi rust]$

Create the .cargo directory with the config file in the project directory with the following contents:

[pfemidi@pfemidi rust]$ cd foobar
[pfemidi@pfemidi foobar]$ mkdir .cargo
[pfemidi@pfemidi foobar]$ cat > .cargo/config
[target.i686-pc-windows-gnu]
linker = "i686-w64-mingw32-gcc"
ar = "i686-w64-mingw32-ar"

[target.x86_64-pc-windows-gnu]
linker = "x86_64-w64-mingw32-gcc"
ar = "x86_64-w64-mingw32-ar"
[pfemidi@pfemidi foobar]$

This step is necessary so that when building Windows targets Rust uses not the linker from the default gcc installed but the MinGW linker.

Now try to build the project as the i686-pc-windows-gnu target:

[pfemidi@pfemidi foobar]$ cargo build --target i686-pc-windows-gnu
   Compiling foobar v0.1.0 (/home/pfemidi/mywork/rust/foobar)
error: linking with `i686-w64-mingw32-gcc` failed: exit code: 1
  |
  = note: "i686-w64-mingw32-gcc" "-Wl,--enable-long-section-names" "-fno-use-linker-plugin" "-Wl,--nxcompat" "-nostdlib"

...

  = note: /usr/lib/gcc/i686-w64-mingw32/9.2.1/../../../../i686-w64-mingw32/bin/ld: /home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/crt2.o:crtexe.c:(.text+0x75): undefined reference to `__onexitend'
          /usr/lib/gcc/i686-w64-mingw32/9.2.1/../../../../i686-w64-mingw32/bin/ld: /home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/crt2.o:crtexe.c:(.text+0x7a): undefined reference to `__onexitbegin'
          collect2: error: ld returned 1 exit status


error: aborting due to previous error

error: could not compile `foobar`.

To learn more, run the command again with --verbose.
[pfemidi@pfemidi foobar]$

Error! Got "undefined reference to __onexitend" and "undefined reference to __onexitbegin" in the crt2.o file. The fact is that Rust component for pc-windows-gnu target has been built with MinGW 6.3.0 but there is MinGW version 9.2.1 in Fedora Linux 31. So there is a difference in the CRT due compiler versions mismatch. Ok, lets copy crt2.o from Fedora Linux MinGW repository to the Rust directory for the i686-pc-windows-gnu component. And along with crt2.o we also copy dllcrt2.o, it is the entry point for dynamic libraries as crt2.o is for standalone executable files. Just in case, we save the original files:

[pfemidi@pfemidi foobar]$ cd ~/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/
[pfemidi@pfemidi lib]$ mv crt2.o crt2.o.ori
[pfemidi@pfemidi lib]$ mv dllcrt2.o dllcrt2.o.ori
[pfemidi@pfemidi lib]$ cp /usr/i686-w64-mingw32/sys-root/mingw/lib/crt2.o .
[pfemidi@pfemidi lib]$ cp /usr/i686-w64-mingw32/sys-root/mingw/lib/dllcrt2.o .
[pfemidi@pfemidi lib]$ cd -
/home/pfemidi/mywork/rust/foobar
[pfemidi@pfemidi foobar]$ 

Now try to build the project as the i686-pc-windows-gnu target again:

[pfemidi@pfemidi foobar]$ cargo build --target i686-pc-windows-gnu
   Compiling foobar v0.1.0 (/home/pfemidi/mywork/rust/foobar)
    Finished dev [unoptimized + debuginfo] target(s) in 0.19s
[pfemidi@pfemidi foobar]$ 

It worked!

Now try to do the same for x86_64-pc-windows-gnu target:

[pfemidi@pfemidi foobar]$ cargo build --target x86_64-pc-windows-gnu
   Compiling foobar v0.1.0 (/home/pfemidi/mywork/rust/foobar)
error: linking with `x86_64-w64-mingw32-gcc` failed: exit code: 1
  |
  = note: "x86_64-w64-mingw32-gcc" "-Wl,--enable-long-section-names" "-fno-use-linker-plugin" "-Wl,--nxcompat" "-nostdlib" "-m64"

...

  = note: /usr/lib/gcc/x86_64-w64-mingw32/9.2.1/../../../../x86_64-w64-mingw32/bin/ld: /home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-pc-windows-gnu/lib/crt2.o:crtexe.c:(.rdata$.refptr.__onexitbegin[.refptr.__onexitbegin]+0x0): undefined reference to `__onexitbegin'
          /usr/lib/gcc/x86_64-w64-mingw32/9.2.1/../../../../x86_64-w64-mingw32/bin/ld: /home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-pc-windows-gnu/lib/crt2.o:crtexe.c:(.rdata$.refptr.__onexitend[.refptr.__onexitend]+0x0): undefined reference to `__onexitend'
          collect2: error: ld returned 1 exit status


error: aborting due to previous error

error: could not compile `foobar`.

To learn more, run the command again with --verbose.
[pfemidi@pfemidi foobar]$ 

The error is exactly the same as for the i686-pc-windows-gnu target was noted before. Lets copy the files crt2.o and dllcrt2.o by analogy with the 32bit target above:

[pfemidi@pfemidi foobar]$ cd ~/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-pc-windows-gnu/lib/
[pfemidi@pfemidi lib]$ mv crt2.o crt2.o.ori
[pfemidi@pfemidi lib]$ mv dllcrt2.o dllcrt2.o.ori
[pfemidi@pfemidi lib]$ cp /usr/x86_64-w64-mingw32/sys-root/mingw/lib/crt2.o .
[pfemidi@pfemidi lib]$ cp /usr/x86_64-w64-mingw32/sys-root/mingw/lib/dllcrt2.o .
[pfemidi@pfemidi lib]$ cd -
/home/pfemidi/mywork/rust/foobar
[pfemidi@pfemidi foobar]$ 

And try to build the project as the x86_64-pc-windows-gnu target again:

[pfemidi@pfemidi foobar]$ cargo build --target x86_64-pc-windows-gnu
   Compiling foobar v0.1.0 (/home/pfemidi/mywork/rust/foobar)
    Finished dev [unoptimized + debuginfo] target(s) in 0.20s
[pfemidi@pfemidi foobar]$ 

Yes! It worked also! So now we can easily build targets for Windows using the standard cargo included in the Rust distribution! And for x86_64 targets this is completely true. But for x86 targets everything will be fine only until we use in our project any functions that panic (f.e. macro panic!, expect functions, etc.).

Lets add panic to our simple project:

[pfemidi@pfemidi foobar]$ cat src/main.rs 
fn main() {
    println!("Hello, world!");
    panic!("I'm panicked!");    // <-- here it is
}
[pfemidi@pfemidi foobar]$

Build it as x86_64 target:

[pfemidi@pfemidi foobar]$ cargo build --target x86_64-pc-windows-gnu
   Compiling foobar v0.1.0 (/home/pfemidi/mywork/rust/foobar)
    Finished dev [unoptimized + debuginfo] target(s) in 0.16s
[pfemidi@pfemidi foobar]$ 

It is going perfectly (and works just as well, I checked). Now try to do the same for the x86 target:

[pfemidi@pfemidi foobar]$ cargo build --target i686-pc-windows-gnu
   Compiling foobar v0.1.0 (/home/pfemidi/mywork/rust/foobar)
error: linking with `i686-w64-mingw32-gcc` failed: exit code: 1
  |
  = note: "i686-w64-mingw32-gcc" "-Wl,--enable-long-section-names" "-fno-use-linker-plugin" "-Wl,--nxcompat" "-nostdlib"

...

  = note: /usr/lib/gcc/i686-w64-mingw32/9.2.1/../../../../i686-w64-mingw32/bin/ld: /home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/libpanic_unwind-0c029c00da54fbf5.rlib(panic_unwind-0c029c00da54fbf5.panic_unwind.2hgzd7yq-cgu.0.rcgu.o): in function `ZN12panic_unwind3imp5panic17h03027a0e504502cdE':
          /rustc/73528e339aae0f17a15ffa49a8ac608f50c6cf14\/src\libpanic_unwind/gcc.rs:73: undefined reference to `_Unwind_RaiseException'
          /usr/lib/gcc/i686-w64-mingw32/9.2.1/../../../../i686-w64-mingw32/bin/ld: /home/pfemidi/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/libpanic_unwind-0c029c00da54fbf5.rlib(panic_unwind-0c029c00da54fbf5.panic_unwind.2hgzd7yq-cgu.0.rcgu.o): in function `rust_eh_unwind_resume':
          /rustc/73528e339aae0f17a15ffa49a8ac608f50c6cf14\/src\libpanic_unwind/gcc.rs:327: undefined reference to `_Unwind_Resume'
          collect2: error: ld returned 1 exit status


error: aborting due to previous error

error: could not compile `foobar`.

To learn more, run the command again with --verbose.
[pfemidi@pfemidi foobar]$

Oops! We got "undefined reference to _Unwind_RaiseException" and "undefined reference to _Unwind_Resume" in the libpanic_unwind module of the Rust standard library. But this problem is also solved, though not as simple as the previous one which is a mere replacement of CRT crt2.o and dllcrt2.o files.

For the stack unwinding Rust uses the dwarf method for 32bit Windows targets and seh method for 64bit Windows targets while MinGW from the standard Fedora Linux distribution uses the sjlj method for 32bit Windows targets and seh method for 64bit Windows targets (read about the difference here). Therefore 64bit targets are linked by MinGW linker without any problem but for 32bit ones there are no necessary symbols and object files to be linked correctly. To get these files and symbols it's necessary to rebuild MinGW with dwarf support instead of sjlj support by default for 32bit Windows targets.

I will not go into details on how to rebuild MinGW here, I will say only one thing: after MinGW is rebuilt with the dwarf stack unwinding instead of sjlj method you need to pick only one file called libgcc_eh.a from the MinGW just built and put it in the library directory for the Rust i686-pc-windows-gnu target. After doing that projects with any panic functions will build with no errors not only for 64bit Windows targets, but also for 32bit ones:

[pfemidi@pfemidi foobar]$ cd ~/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/i686-pc-windows-gnu/lib/
[pfemidi@pfemidi lib]$ cp ~/rpmbuild/BUILD/gcc-9.2.1-20190827/build_win32/i686-w64-mingw32/libgcc/libgcc_eh.a .
[pfemidi@pfemidi lib]$ cd -
/home/pfemidi/mywork/rust/foobar
[pfemidi@pfemidi foobar]$ cargo build --target i686-pc-windows-gnu
   Compiling foobar v0.1.0 (/home/pfemidi/mywork/rust/foobar)
    Finished dev [unoptimized + debuginfo] target(s) in 0.30s
[pfemidi@pfemidi foobar]$ 

Happy RUSTing! :-)

Answer 2

Cross-compiling isn't always easy as it sounds. I recommend to not invent your own wheel and use already tested solutions.

Currently "standard" way to do cross-compiling is to use cross, which is cargo wrapper that abstracts you away from details of cross-compilation.

Before installing cross you should install it's dependencies. How to do that exactly depends on your distribution.

After dependencies are ready you should install cross like this (assuming you have cargo).

$ cargo install cross

After that build works semi-magically

cross build --target x86_64-pc-windows-gnu