feat: support building for 32-bit ARM Linux (linux-arm)

[ibrahim-mubarak]

What

Adds support for building the SDK for 32-bit ARM Linux (armv7-unknown-linux-gnueabihf, i.e. linux-arm), targeting armv7-a + NEON hard-float as a baseline — which also covers armv8 cores running in AArch32 mode (e.g. Cortex-A32/A35 embedded SoCs).

There are no prebuilt linux-arm webrtc artifacts, so consumers build libwebrtc from source and point LK_CUSTOM_WEBRTC at it:

cd webrtc-sys/libwebrtc
./build_linux.sh --arch arm --profile release
# artifacts land in linux-arm-release/

Changes

• webrtc-sys/libwebrtc/build_linux.sh
  • accept --arch arm; sets arm_float_abi="hard" and arm_use_neon=true (armv7+NEON baseline, same config as the other Linux builds otherwise — X11/PipeWire stay enabled, they are lazy-loaded/dlopen'd at runtime).
  • new optional CLANG_BASE_PATH env: Chromium only publishes x86-64 Linux clang binaries, so on other build hosts (e.g. aarch64) you can point this at a matching LLVM release; it is passed as clang_base_path to gn and its llvm-objcopy is used for the boringssl symbol prefixing step.
• webrtc-sys/build.rs
  • add_gio_headers: map arm → debian_bullseye_armhf-sysroot / arm-linux-gnueabihf.
  • add_lazy_load_so: select a new arm-linux-gnueabihf trampoline directory for arm.
• webrtc-sys/src/lazy_load_deps_for/desktop_capturer/arm-linux-gnueabihf/: Implib.so-generated trampolines for the desktop-capturer X11/drm/gbm libraries (generated with implib-gen.py --target armhf against the Debian bullseye armhf sysroot libs, same procedure as the existing x86_64/aarch64 files).
• webrtc-sys/src/video_decoder_factory.cpp: guard the AV1 format advertisement with RTC_DAV1D_IN_INTERNAL_DECODER_FACTORY. It calls LibaomAv1EncoderSupportedScalabilityModes(), which is undefined in webrtc builds configured without AV1 (enable_libaom=false, dav1d factory off) — useful for footprint-constrained embedded builds. No change for default builds.
• yuv-sys/build.rs: mark YuvConstants as an opaque type for bindgen. Its SIMD vector members give it an alignment bindgen cannot mirror on 32-bit ARM (the generated layout test fails with align 2 vs 8); it is only ever passed by pointer from Rust.

Testing

• Built libwebrtc linux-arm-release from source (webrtc-sdk/webrtc @ m144_release, commit aaeeee80…751ef663 matching the webrtc-51ef663 tag) on an aarch64 Fedora host with LLVM 22.1.8 via CLANG_BASE_PATH.
• cargo build -p livekit-ffi --release --target armv7-unknown-linux-gnueabihf succeeds against it (cross gcc 13.4, glibc 2.39 sysroot); also verified a codec-reduced webrtc build (no AV1/H26x/VP9) links cleanly with the factory guard.
• Resulting liblivekit_ffi.so is a clean 32-bit ARM EABI5 hard-float object whose only hard deps are libc/libm/libstdc++/libgcc.
• Verified on an embedded (Realtek Cortex-A32) sysroot under qemu-arm against livekit-server v1.13.3: SDK unit suite 332/332; integration suite (rooms, VP8 media multistream, data tracks, RPC, session stats) passes except one pre-existing large-frame data-track case that fails identically on aarch64 with the official prebuilts.
• A companion PR to client-sdk-cpp adds the CMake-side cross-compilation support.

🤖 Generated with Claude Code

https://claude.ai/code/session_01L4fDRyTiTphQnidL2Myptq

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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[ibrahim-mubarak]

Closing — will iterate on our fork first.