Skia renderer with Linux backend

[igiona]

I'm trying to cross-compile a Slint application using the Linux backend and the Skia renderer.
Unfortunately, I get several errors.
The first

error: failed to run custom build command for `skia-bindings v0.78.2`
[...]
  [8/1528] compile ../../../../../../../../../../../../home/igiona/.cargo/registry/src/index.crates.io-6f17d22bba15001f/skia-bindings-0.78.2/skia/src/ports/SkFontConfigInterface.cpp
  FAILED: obj/src/ports/fontmgr_FontConfigInterface.SkFontConfigInterface.o
  clang++ -MD -MF obj/src/ports/fontmgr_FontConfigInterface.SkFontConfigInterface.o.d -DNDEBUG -DSK_CODEC_DECODES_BMP -DSK_CODEC_DECODES_WBMP -DSK_R32_SHIFT=16 -DSK_ENABLE_PRECOMPILE -DSK_GANESH -DSK_DISABLE_TRACING -DSK_USE_PERFETTO -DSK_GAMMA_APPLY_TO_A8 -DSK_ENABLE_AVX512_OPTS -DSKIA_IMPLEMENTATION=1 -DSK_TYPEFACE_FACTORY_FREETYPE -I../../../../../../../../../../../../home/igiona/.cargo/registry/src/index.crates.io-6f17d22bba15001f/skia-bindings-0.78.2/skia -Wno-attributes -ffp-contract=off -fstrict-aliasing -fPIC -fvisibility=hidden -march=armv7-a -mfpu=neon -mthumb -O3 -fdata-sections -ffunction-sections -I=/usr/include/freetype2 -I/usr/include/freetype2 -O3 -I/usr/armv7-linux-gnueabihf/include/c++/7/armv7-linux-gnueabihf -I/usr/armv7-linux-gnueabihf/include --target=armv7-unknown-linux-gnueabihf -std=c++17 -fvisibility-inlines-hidden -fno-exceptions -fno-rtti -c ../../../../../../../../../../../../home/igiona/.cargo/registry/src/index.crates.io-6f17d22bba15001f/skia-bindings-0.78.2/skia/src/ports/SkFontConfigInterface.cpp -o obj/src/ports/fontmgr_FontConfigInterface.SkFontConfigInterface.o
  In file included from ../../../../../../../../../../../../home/igiona/.cargo/registry/src/index.crates.io-6f17d22bba15001f/skia-bindings-0.78.2/skia/src/ports/SkFontConfigInterface.cpp:7:
  In file included from ../../../../../../../../../../../../home/igiona/.cargo/registry/src/index.crates.io-6f17d22bba15001f/skia-bindings-0.78.2/skia/include/ports/SkFontConfigInterface.h:11:
  In file included from ../../../../../../../../../../../../home/igiona/.cargo/registry/src/index.crates.io-6f17d22bba15001f/skia-bindings-0.78.2/skia/include/core/SkFontStyle.h:11:
  In file included from ../../../../../../../../../../../../home/igiona/.cargo/registry/src/index.crates.io-6f17d22bba15001f/skia-bindings-0.78.2/skia/include/core/SkTypes.h:21:
  In file included from ../../../../../../../../../../../../home/igiona/.cargo/registry/src/index.crates.io-6f17d22bba15001f/skia-bindings-0.78.2/skia/include/private/base/SkAssert.h:15:
  /usr/lib/gcc-cross/arm-linux-gnueabihf/11/../../../../include/c++/11/cstddef:49:10: fatal error: 'bits/c++config.h' file not found
     49 | #include <bits/c++config.h>
        |          ^~~~~~~~~~~~~~~~~~
  1 error generated.

[...]

This seems to me related to some kind of issues with sysroot or so.
I did not manage to pass sysroot to the C compiler though, or at least the error never changed.
I therefore tried to source the cross-compile environment file that Yocto generates along with the SDK, but then I stumble across another error:

error: failed to run custom build command for `skia-bindings v0.78.2`

[...]

  [1/1521] compile ../../../../../../../../../../../../home/igiona/.cargo/registry/src/index.crates.io-6f17d22bba15001f/skia-bindings-0.78.2/skia/src/ports/SkFontConfigInterface.cpp
  FAILED: obj/src/ports/fontmgr_FontConfigInterface.SkFontConfigInterface.o
  arm-org-linux-gnueabi-g++  -march=armv7ve -mthumb -mfpu=neon -mfloat-abi=hard -fstack-protector-strong  -O2 -D_FORTIFY_SOURCE=2 -Wformat -Wformat-security -Werror=format-security --sysroot=/home/igiona/sdks/lcd_sdk2/sysroots/armv7vet2hf-neon-org-linux-gnueabi -MD -MF obj/src/ports/fontmgr_FontConfigInterface.SkFontConfigInterface.o.d -DNDEBUG -DSK_CODEC_DECODES_BMP -DSK_CODEC_DECODES_WBMP -DSK_R32_SHIFT=16 -DSK_ENABLE_PRECOMPILE -DSK_GANESH -DSK_DISABLE_TRACING -DSK_USE_PERFETTO -DSK_GAMMA_APPLY_TO_A8 -DSK_ENABLE_AVX512_OPTS -DSKIA_IMPLEMENTATION=1 -DSK_TYPEFACE_FACTORY_FREETYPE -I../../../../../../../../../../../../home/igiona/.cargo/registry/src/index.crates.io-6f17d22bba15001f/skia-bindings-0.78.2/skia -Wno-attributes -fstrict-aliasing -fPIC -fvisibility=hidden -march=armv7-a -mfpu=neon -mthumb -O3 -fdata-sections -ffunction-sections -I=/usr/include/freetype2 -I/usr/include/freetype2 --sysroot=/home/igiona/sdks/lcd_sdk2/sysroots/armv7vet2hf-neon-org-linux-gnueabi -O3 -I/usr/armv7-linux-gnueabihf/include/c++/7/armv7-linux-gnueabihf -I/usr/armv7-linux-gnueabihf/include --target=armv7-unknown-linux-gnueabihf -std=c++17 -fvisibility-inlines-hidden -fno-exceptions -fno-rtti -c ../../../../../../../../../../../../home/igiona/.cargo/registry/src/index.crates.io-6f17d22bba15001f/skia-bindings-0.78.2/skia/src/ports/SkFontConfigInterface.cpp -o obj/src/ports/fontmgr_FontConfigInterface.SkFontConfigInterface.o
  arm-org-linux-gnueabi-g++: error: unrecognized command-line option '--target=armv7-unknown-linux-gnueabihf'

[...]

Any idea what could be wrong here?

[ogoffart]

There is some documentation of some env variables to set here: https://github.com/rust-skia/rust-skia/tree/master/skia-bindings#cross-compiling-for-linux

[tronical]

For the first error, I can see indeed that the sysroot is missing. The link that Olivier pasted is indeed the right starting point probably, it might be sufficient for you to set SDKTARGETSYSROOT.

The unrecognized command-line option '--target=armv7-unknown-linux-gnueabihf' suggests that there's a mismatch between the triplet your Yocto uses and what rust knows (which is consequently turned into a --target= option). In your Yocto SDK environment, do you have the CLANGCXX and CLANGCC environment variables set? If yes, what is their value? They should have a --target=... option in them, and the Skia build should "extract" and re-use them.

[igiona]

@ogoffart thank for the link!

@tronical No, the Yocto SDLK environment doesn't have neither of bot CLANGCXX / CLANGCC .
There are CC and CXX though, with all arch params etc.

The triplet created by Yocto is indeed different than rustc/cargo.
I build with cargo build --release --target armv7-unknown-linux-gnueabihf and our triplet is arm-org-linux-gnueabi .

I set HOST_CC as suggested in the link above, with the same result.

As far as I know, CC doesn't have --target option??

[tronical]

Ah, I think I realize what you might be missing.

The Skia build requires clang, and that clang needs to be entirely aware of your yocto target config and gcc library paths. Sometimes it works to use the host clang, but it's better to use meta-clang. Try this:

1. Add meta-clang to your layers.
2. Add clang to your generated SDK like this: https://github.com/kraj/meta-clang?tab=readme-ov-file#adding-clang-in-generated-sdk-toolchain

From the environment of the resulting SDK, you'll have CLANGCC and CLANGCXX set, the Skia build will pick them up automatically, and it ... should compile.

[igiona]

Fantastic @tronical ! That was it 🥳 !

Now I've got the binary, but I'm still not able to run the application on the device :'(
When I try to execute the application I get:

root@07083577:/usr/bin/ui$ ls -l
-rwxr-xr-x    1 root     root      21472636 Jan  1 01:55 ui-rs
root@07083577:/usr/bin/ui$ ./ui-rs
-sh: ./ui-rs: not found

Do I have to pass some command line parameters?

[tronical]

Could you try running it like this?

LD_DEBUG=all ./ui-rs

Also, what does file ./ui-rs say?

[igiona]

I don't have file on the target, but on the host I get:

ui-rs: ELF 32-bit LSB pie executable, ARM, EABI5 version 1 (GNU/Linux), dynamically linked, interpreter /lib/ld-linux.so.3, BuildID[sha1]=cb9b20138a725b9b473cfd85f6b5c7bfbbf5a6bc, for GNU/Linux 3.2.0, not stripped

Adding the debug variable doesn't help, I get the same result.

LD_DEBUG=all ui-rs
-sh: ui-rs: not found

[tronical]

Sorry, I meant LD_DEBUG=all ./ui-rs or LD_DEBUG=all /usr/bin/ui/ui-rs.