id = 2603
title = "Recent libslirp commit broke Qemu network stack: qemu and libslirp teams should settle on SOCKET handler type"
state = "closed"
created_at = "2024-10-01T17:06:01.697Z"
closed_at = "2025-02-06T09:08:12.850Z"
labels = ["Networking", "hostos: Windows", "kind::Feature Request"]
url = "https://gitlab.com/qemu-project/qemu/-/issues/2603"
host-os = "Fedora 40"
host-arch = "x86"
qemu-version = "9.1.0"
guest-os = "n/a"
guest-arch = "n/a"
description = """https://gitlab.freedesktop.org/slirp/libslirp/-/commit/72f85005a2307fd0961543e3cea861ad7a4d201e introduced regression causing QEMU compilation for Windows to error out due to missing 64-bit SOCKET handler pointer type.

```
x86_64-w64-mingw32-gcc -m64 ... -MD -MQ libcommon.a.p/net_slirp.c.obj -MF libcommon.a.p/net_slirp.c.obj.d -o libcommon.a.p/net_slirp.c.obj -c ../net/slirp.c
../net/slirp.c:289:25: error: initialization of 'void (*)(slirp_os_socket,  void *)' {aka 'void (*)(long long unsigned int,  void *)'} from incompatible pointer type 'void (*)(int,  void *)' [-Wincompatible-pointer-types]
  289 |     .register_poll_fd = net_slirp_register_poll_fd,
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~
../net/slirp.c:289:25: note: (near initialization for 'slirp_cb.register_poll_fd')
../net/slirp.c:290:27: error: initialization of 'void (*)(slirp_os_socket,  void *)' {aka 'void (*)(long long unsigned int,  void *)'} from incompatible pointer type 'void (*)(int,  void *)' [-Wincompatible-pointer-types]
  290 |     .unregister_poll_fd = net_slirp_unregister_poll_fd,
      |                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
../net/slirp.c:290:27: note: (near initialization for 'slirp_cb.unregister_poll_fd')
../net/slirp.c: In function 'net_slirp_poll_notify':
../net/slirp.c:367:28: error: passing argument 3 of 'slirp_pollfds_fill' from incompatible pointer type [-Wincompatible-pointer-types]
  367 |                            net_slirp_add_poll, poll->pollfds);
      |                            ^~~~~~~~~~~~~~~~~~
      |                            |
      |                            int (*)(int,  int,  void *)
In file included from ../net/slirp.c:41:
/home/cross-qemu-deps/include/slirp/libslirp.h:255:40: note: expected 'SlirpAddPollCb' {aka 'int (*)(long long unsigned int,  int,  void *)'} but argument is of type 'int (*)(int,  int,  void *)'
  255 |                         SlirpAddPollCb add_poll, void *opaque);
      |                         ~~~~~~~~~~~~~~~^~~~~~~~
```

Possible solution relying on cross-platform MACRO: https://handsonnetworkprogramming.com/articles/socket-function-return-value-windows-linux-macos/"""
reproduce = """1. Prepare cross-compilation build of qemu 9.1.0 using following steps (It's not necessary to set up a virtual machine if your main OS has good mingw repository, like Fedora, Arch linux, Manjaro. But if you're on Debian or Ubuntu, it's required):
2. Download official Fedora workstation 40 x86_64 ISO and install it to a virtual disk and boot that disk.
3. On Fedora, do:\\
   `wget https://download.qemu.org/qemu-9.1.0.tar.xz`\\
   ` tar xvJf qemu-9.1.0.tar.xz`\\
   ` cd qemu-9.1.0`
4. `sudo yum install git meson ninja-build python3-sphinx python3-sphinx_rtd_theme gcc mingw64-gcc mingw64-pkg-config mingw64-glib2`
5. `git clone https://gitlab.freedesktop.org/slirp/libslirp.git`
6. create file x86_64-w64-mingw32.txt in qemu-9.1.0 directory with the content as follows:

```
[binaries]
c = '/usr/bin/x86_64-w64-mingw32-gcc'
cpp = '/usr/bin/x86_64-w64-mingw32-g++'
ar = '/usr/bin/x86_64-w64-mingw32-ar'
strip = '/usr/bin/x86_64-w64-mingw32-strip'
pkg-config = '/usr/bin/x86_64-w64-mingw32-pkg-config'
exe_wrapper = 'wine'

[host_machine]
system = 'windows'
cpu_family = 'x86_64'
cpu = 'i686'
endian = 'little'
```

 7. Run 2 commands:

    `export CROSS_QEMU_DEPS="/home/cross-qemu-deps"`\\
    ` sudo mkdir -p $CROSS_QEMU_DEPS`
 8. Install libslirp so that future qemu binaries can have internet access via \\`-netdev user\\`\\
    \\
    `cd libslirp`\\
    \\
    ` meson setup --cross-file ../x86_64-w64-mingw32.txt --prefix "$CROSS_QEMU_DEPS" build-mingw/`\\
    ` meson compile -C build-mingw`\\
    ` cd build-mingw`\\
    ` ninja install`
 9. Set environment variables for cross-compilation\\
    \\
    ` sudo find / -type f -name '*.pc'` and make sure all mingw \\*.pc files live in /usr/x86_64-w64-mingw32/sys-root/mingw/lib/pkgconfig/. Correct this path in PKG_CONFIG_PATH if you see it was altered by mingw or package contributors.\\
    \\
    ` export PKG_CONFIG_PATH="/usr/x86_64-w64-mingw32/sys-root/mingw/lib/pkgconfig/:$PKG_CONFIG_PATH"`\\
    ` export PKG_CONFIG_LIBDIR="${CROSS_QEMU_DEPS}/lib/pkgconfig/:$PKG_CONFIG_LIBDIR"`\\
    ` export PKG_CONFIG_SYSROOT_DIR=""`
10. Configure Qemu makefile:\\
    \\
    `cd ../../`\\
    `./configure --cross-prefix=x86_64-w64-mingw32- --enable-slirp`\\
    \\
    and make sure you see this in the output of configure:\\
    `Compilation`\\
    `host CPU : x86_64`\\
    `host endianness : little`\\
    `C compiler : x86_64-w64-mingw32-gcc -m64`\\
    `Host C compiler : cc`
11. Cross-compile qemu: `` make -j`nproc` ``
12. Get the error `initialization of 'void (*)(slirp_os_socket,  void *)' {aka 'void (*)(long long unsigned int,  void *)'} from incompatible pointer type 'void (*)(int,  void *)'` as above."""
additional = """After having seen this bug, do these steps (revert to the commit right before the buggy one).

`    cd libslirp`\\
`    git reset --hard 5e97a93b`

`    meson setup --cross-file ../x86_64-w64-mingw32.txt --prefix "$CROSS_QEMU_DEPS" build-mingw/ --reconfigure`\\
`    meson compile -C build-mingw`\\
`    cd build-mingw`\\
`    ninja install`

``     cd ../../ ``\\
``     ./configure --cross-prefix=x86_64-w64-mingw32- --enable-slirp ``\\
``    make -j`nproc` ``

=\\> Cross-compilation comes to an end just fine, building all compilation targets without any errors."""