Linking against ffmpeg libs on Rust gives `vdp_device_create_x11` (libvdpau-dev missing?)

[guerlando]

I'm trying to link against ffmpeg libraries, in rust, and getting as the only error:

undefined reference to `vdp_device_create_x11'

Here's the libs linked:

fn main() {
    println!("cargo:rerun-if-changed=build.rs");
    println!("cargo:rustc-link-lib=static=z");
    println!("cargo:rustc-link-lib=dylib=dl");
    println!("cargo:rustc-link-lib=static=X11");
    println!("cargo:rustc-link-lib=dylib=vdpau");
    println!("cargo:rustc-link-lib=dylib=va");
    println!("cargo:rustc-link-lib=dylib=va-drm");
    println!("cargo:rustc-link-lib=dylib=va-x11");
    println!("cargo:rustc-link-lib=dylib=xcb");
}

On C++ I used to link with all these libs above + some for GTK and it worked. Don't know why it wont work now.

On errors when compiling c code with ffmpeg library - Stack Overflow it says that I should link against -lvdpau - libvdpau-dev

I tried adding

    println!("cargo:rustc-link-lib=dylib=vdpau-dev");

but I get

  = note: /usr/bin/ld: cannot find -lvdpau-dev

Even though I installed libvdpau-dev. Indeed,

ldconfig -p | grep vdpau
        libvdpau.so.1 (libc6,x86-64) => /lib/x86_64-linux-gnu/libvdpau.so.1
        libvdpau.so (libc6,x86-64) => /lib/x86_64-linux-gnu/libvdpau.so

Why libdpau-dev is missing? I'm on ubuntu 20, apt-get install -y libdpau-dev. Finny thing is that C++ compiles perfectly in this same docker container without any modifications and without libdpau-dev

[guerlando]

nm -D /lib/x86_64-linux-gnu/libvdpau.so | grep x11
0000000000001d50 T vdp_device_create_x11

[mbrubeck]

On Debian-based systems (including Ubuntu), every C library package has a separate dev package for headers and other development files. For example:

• libvdpau1 contains files needed at run time by programs that use VDPAU.
• libvdpau-dev contains files needed at build time when compiling programs that use VDPAU.

The correct linker argument is -lvdpau, and your build script that uses dylib=vdpau is correct.

I was not able to reproduce your link error, on Ubuntu 20.04. Can you provide a reproducible test case? I copied your build script into a new Cargo project, and installed the required packages:

sudo apt install libvdpau-dev libva-dev libx11-dev zlib1g-dev

Then I put the following code into main.rs:

extern {
    fn vdp_device_create_x11(
        display: *const u8,
        screen: i32,
        device: *const u8,
        get_proc_address: *const u8,
    )-> i32;
}

fn main() {
    unsafe {
        vdp_device_create_x11(0 as _, 0, 0 as _, 0 as _);
    }
}

The program builds successfully:

$ cargo build
   Compiling ff v0.1.0 (/home/mbrubeck/src/test/ff)
    Finished dev [unoptimized + debuginfo] target(s) in 0.47s

[mbrubeck]

Also, note that the order of the linker arguments is important. You might need to move the vdpau line below some other library that depends on it.

[guerlando]

I'll try to provide a minimal reproducible example. Meanwhile, here's a more detailed error:

note: /usr/bin/ld: /home/dev/orwell/liborwell_rust/target/debug/deps/libffmpeg_sys_next-109176c9182219d2.rlib(hwcontext_vdpau.o): in function `vdpau_device_create':
          hwcontext_vdpau.c:(.text+0x686): undefined reference to `vdp_device_create_x11'

The file hwcontext_vdpau.o is from ffmpeg: FFmpeg: libavutil/hwcontext_vdpau.c Source File

My theory of why it worked for your case but not mine is that in your case you link these libraries after the code that uses vdp_device_create_x11. In my case, I think it links my code against the libs I provided + ffmpeg libs. So maybe ffmpeg libs come after or before the libs I provided.

Well, since I'm linking against the project that links with ffmpeg, I think this is what's happening:

my_code is being linked against ffmpeg-sys-next crate + libs I provided. Where ffmpeg-sys-next crate contains the ffmpeg libs. I just don't know if the order is

ffmpeg-sys-next crate + libs I provided

or

libs I provided + ffmpeg-sys-next crate.

If ffmpeg needs vdp_device_create_x11, then vdp_device_create_x11 should come before ffmpeg or after?

Is it possible to control if the crate dependencies are linked after or before the libs I provided?

[mbrubeck]

@guerlando

Is it possible to control if the crate dependencies are linked after or before the libs I provided?

This might be possible by making your build script output its own link arguments for the FFMPEG libraries. I haven't found a way to test this yet.

Alternately, perhaps the ffmeg-sys-next crate could add an optional feature to link to libvdpau.

[guerlando]

no, actually the situation is like this:

MyRustLib + RustStaticLib{rust code + ffmpeg libs} + libvdpau + other system libs

I was talking about the linking order of these things. I think it's cargo that manages the linking of 2 rust crates or rust packages and it uses the linking arguments from lib.rs to link libvdpau + other system libs

[guerlando]

Running `rustc --crate-name liborwell_rust --edition=2018 src/main.rs --error-format=json --json=diagnostic-rendered-ansi --crate-type bin --emit=dep-info,link -Cembed-bitcode=no -C debuginfo=2 -C metadata=a40686dab33e6453 -C extra-filename=-a40686dab33e6453 --out-dir /home/dev/orwell/liborwell_rust/target/debug/deps -C incremental=/home/dev/orwell/liborwell_rust/target/debug/incremental -L dependency=/home/dev/orwell/liborwell_rust/target/debug/deps --extern ffmpeg_next=/home/dev/orwell/liborwell_rust/target/debug/deps/libffmpeg_next-c150275f8ec2ece5.rlib --extern liborwellprofile_protobuf_rust=/home/dev/orwell/liborwell_rust/target/debug/deps/libliborwellprofile_protobuf_rust-85a803bf8441d976.rlib --extern phf=/home/dev/orwell/liborwell_rust/target/debug/deps/libphf-0282e4d662343769.rlib --extern protobuf=/home/dev/orwell/liborwell_rust/target/debug/deps/libprotobuf-525fd12c456cb486.rlib -l static=z -l dylib=dl -l dylib=vdpau -l static=X11 -l dylib=va -l dylib=va-drm -l dylib=va-x11 -l dylib=xcb -L native=/home/dev/orwell/deps/ffmpeg/build/linux/x86_64/lib`

Looks like the ffmpeg libraries are the last thing passed to the compiler/linker: -L native=/home/dev/orwell/deps/ffmpeg/build/linux/x86_64/lib

rustc passed -L native=/home/dev/orwell/deps/ffmpeg/build/linux/x86_64/lib as its last flag. It comes after all the libs, including vdpau. Don't know, however, if it actually tries to link vdpau first then the ffmpeg libs.