Unable to cross-compile to Android

[Michael-F-Bryan]

I'm trying to use the tflite crate on Android and iOS, but have been having issues getting it to compile. For some reason it doesn't look like bindgen can find the C++ STL when it tries to generate bindings.

$ RUST_BACKTRACE=1 cargo build --target aarch64-linux-android
   Compiling tflite v0.9.5 (/tmp/tflite-rs)
error: failed to run custom build command for `tflite v0.9.5 (/tmp/tflite-rs)`

Caused by:
  process didn't exit successfully: `/tmp/tflite-rs/target/debug/build/tflite-764e91f18045bab8/build-script-build` (exit status: 101)
  --- stderr
  csrc/stl_wrapper.hpp:1:10: fatal error: 'memory' file not found
  csrc/stl_wrapper.hpp:1:10: fatal error: 'memory' file not found, err: true
  thread 'main' panicked at 'Unable to generate STL bindings: ()', build.rs:299:10
  stack backtrace:
     0: rust_begin_unwind
               at /rustc/1c6868aa21981b37cbd3fc95828ee3b0ac22d494/library/std/src/panicking.rs:515:5
     1: core::panicking::panic_fmt
               at /rustc/1c6868aa21981b37cbd3fc95828ee3b0ac22d494/library/core/src/panicking.rs:92:14
     2: core::result::unwrap_failed
               at /rustc/1c6868aa21981b37cbd3fc95828ee3b0ac22d494/library/core/src/result.rs:1355:5
     3: core::result::Result<T,E>::expect
               at /rustc/1c6868aa21981b37cbd3fc95828ee3b0ac22d494/library/core/src/result.rs:997:23
     4: build_script_build::import_stl_types
               at ./build.rs:282:20
     5: build_script_build::main
               at ./build.rs:530:5
     6: core::ops::function::FnOnce::call_once
               at /rustc/1c6868aa21981b37cbd3fc95828ee3b0ac22d494/library/core/src/ops/function.rs:227:5
  note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

Do you have any suggestions for resolving this?

Full Steps to Reproduce

First, clone the tflite crate:

$ cd /tmp
$ git clone https://github.com/boncheolgu/tflite-rs
$ cd tflite-rs
$ git log -1
commit b206241826e92005ad2155b20f04b6c293892372 (HEAD -> master, origin/master, origin/HEAD)
Author: Boncheol Gu <boncheol.gu@gmail.com>
Date:   Sat Mar 20 17:19:51 2021 +0900

    Bump version to v0.9.5

Next we need to add set up our environment for cross-compiling. This involves adding the aarch64-linux-android target and telling cargo where our C compiler and archiver is.

$ rustup target add aarch64-linux-android
$ rustc --version --verbose
rustc 1.54.0-nightly (1c6868aa2 2021-05-27)
binary: rustc
commit-hash: 1c6868aa21981b37cbd3fc95828ee3b0ac22d494
commit-date: 2021-05-27
host: x86_64-unknown-linux-gnu
release: 1.54.0-nightly
LLVM version: 12.0.1

$ echo $ANDROID_HOME
/home/michael/Android/Sdk
$ echo $NDK_HOME
/home/michael/Android/Sdk/ndk/22.1.7171670

$ cat ~/.cargo/config
[target.aarch64-linux-android]
ar = "/home/michael/Android/Sdk/ndk/22.1.7171670/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android-ar"
linker = "/home/michael/Android/Sdk/ndk/22.1.7171670/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android21-clang"

I had the same issue using the tf_v2.4.1 branch, although I needed to tell cc where the C compiler and archiver is.

$ git checkout tf_v2.4.1
$ git log -1
commit 59894c2ad99bbccc1944d935b97e2863f61f71a4 (HEAD -> tf_v2.4.1, origin/tf_v2.4.1)
Author: Tyler Hawkes <tyler.hawkes@vivint.com>
Date:   Mon May 24 23:44:05 2021 +0000

    Adding send/sync implementations
$ export CXX_aarch64_linux_android=$NDK_HOME/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android21-clang++
$ export CC_aarch64_linux_android=$NDK_HOME/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android21-clang
$ export AR_aarch64_linux_android=$NDK_HOME/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android-ar

$ cargo build --target aarch64-linux-android
   Compiling tflite v0.10.1 (/tmp/tflite-rs)
error: failed to run custom build command for `tflite v0.10.1 (/tmp/tflite-rs)`

Caused by:
  process didn't exit successfully: `/tmp/tflite-rs/target/debug/build/tflite-e5d8c2c5e7f7c2ae/build-script-build` (exit status: 101)
  --- stderr
  csrc/stl_wrapper.hpp:1:10: fatal error: 'memory' file not found
  csrc/stl_wrapper.hpp:1:10: fatal error: 'memory' file not found, err: true
  thread 'main' panicked at 'Unable to generate STL bindings: ()', build.rs:328:10
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[Michael-F-Bryan]

On Discord, @bkirwi pointed out you can use the BINDGEN_EXTRA_CLANG_ARGS environment variable to point bindgen at the STL for your Android NDK so I've now moved on to a different compilation error.

$ export AR_aarch64_linux_android=$NDK_HOME/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android-ar
$ export CC_aarch64_linux_android=$NDK_HOME/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android21-clang
$ export CXX_aarch64_linux_android=$NDK_HOME/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android21-clang++
$ export BINDGEN_EXTRA_CLANG_ARGS=-I$NDK_HOME/sources/cxx-stl/llvm-libc++/include/

$ cargo build --target aarch64-linux-android
   ...
   Compiling tflite v0.9.6
error: failed to run custom build command for `tflite v0.9.6`

Caused by:
  process didn't exit successfully: `/home/michael/Documents/hotg-ai/rune/target/debug/build/tflite-e86bb924f15fa979/build-script-build` (exit status: 101)
  --- stderr
  /home/michael/Android/Sdk/ndk/22.1.7171670/sources/cxx-stl/llvm-libc++/include/typeinfo:222:16: error: reinterpret_cast from 'std::__type_info_implementations::__non_unique_arm_rtti_bit_impl::__type_name_t' (aka 'unsigned int') to 'size_t' (aka 'unsigned long') is not allowed
  /home/michael/Android/Sdk/ndk/22.1.7171670/sources/cxx-stl/llvm-libc++/include/typeinfo:222:16: error: reinterpret_cast from 'std::__type_info_implementations::__non_unique_arm_rtti_bit_impl::__type_name_t' (aka 'unsigned int') to 'size_t' (aka 'unsigned long') is not allowed, err: true
  thread 'main' panicked at 'Unable to generate STL bindings: ()', /home/michael/.cargo/registry/src/github.com-1ecc6299db9ec823/tflite-0.9.6/build.rs:280:10
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
warning: build failed, waiting for other jobs to finish...
error: build failed

It seems like tflite's build script isn't telling bindgen that it is targeting a 64-bit platform because it thinks __type_name_t is an unsigned int instead of a unsigned long.

[fzyzcjy]

Did you solved it?

[Michael-F-Bryan]

Our solution was to create our own library which builds TensorFlow Lite and exposes just enough functionality to suit our needs while also (cross-)compiling to our target devices (Android, iOS, x86/ARM linux, x86 MacOS, Windows, etc.).

[MichaelMcCulloch]

On Discord, @bkirwi pointed out you can use the BINDGEN_EXTRA_CLANG_ARGS environment variable to point bindgen at the STL for your Android NDK so I've now moved on to a different compilation error.

$ export AR_aarch64_linux_android=$NDK_HOME/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android-ar
$ export CC_aarch64_linux_android=$NDK_HOME/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android21-clang
$ export CXX_aarch64_linux_android=$NDK_HOME/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android21-clang++
$ export BINDGEN_EXTRA_CLANG_ARGS=-I$NDK_HOME/sources/cxx-stl/llvm-libc++/include/

$ cargo build --target aarch64-linux-android
   ...
   Compiling tflite v0.9.6
error: failed to run custom build command for `tflite v0.9.6`

Caused by:
  process didn't exit successfully: `/home/michael/Documents/hotg-ai/rune/target/debug/build/tflite-e86bb924f15fa979/build-script-build` (exit status: 101)
  --- stderr
  /home/michael/Android/Sdk/ndk/22.1.7171670/sources/cxx-stl/llvm-libc++/include/typeinfo:222:16: error: reinterpret_cast from 'std::__type_info_implementations::__non_unique_arm_rtti_bit_impl::__type_name_t' (aka 'unsigned int') to 'size_t' (aka 'unsigned long') is not allowed
  /home/michael/Android/Sdk/ndk/22.1.7171670/sources/cxx-stl/llvm-libc++/include/typeinfo:222:16: error: reinterpret_cast from 'std::__type_info_implementations::__non_unique_arm_rtti_bit_impl::__type_name_t' (aka 'unsigned int') to 'size_t' (aka 'unsigned long') is not allowed, err: true
  thread 'main' panicked at 'Unable to generate STL bindings: ()', /home/michael/.cargo/registry/src/github.com-1ecc6299db9ec823/tflite-0.9.6/build.rs:280:10
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
warning: build failed, waiting for other jobs to finish...
error: build failed

It seems like tflite's build script isn't telling bindgen that it is targeting a 64-bit platform because it thinks __type_name_t is an unsigned int instead of a unsigned long.

I hope I'm not wrong to ask this here on such an old thread. But I have exactly the same blocker. I'm wondering if you happen to know what I would have to do to correct bindgen such that it targets a 64 bit platform?

[Michael-F-Bryan]

Sorry, I can't really help you there. We ended up moving away from the tflite-rs crate.

[MichaelMcCulloch]

I don't want to be that guy who found a solution but left no update, so here goes:

Take a look at my solution

I would suggest to build tflitec-rs with a empty (except for the tflitec dependency) cargo project with all the settings configured for Android NDK 21. you'll need bazelisk , android studio and cargo-ndk installed. Take a look at the this folder in this commit in my solution and you'll find the necessary environment variables. There's even a script. I hope it helps. Once you've succeeded in building your project for all platforms, you'll find the built artifact under the /target/-linux-android(eabi)/release/build/tflitec-bl4hbl4hblah/out/libtensorflowlite_c.so. Copy them to the android project jniLibs dir in the appropriate folder, and set the TFLITEC_PREBUILT_PATH_PLAT_FORM_TRIPLET appropriately so you can build again without the hassle. You can then update your project to ndk api 30 as I did in the following commits.

If you're really suffering, you can just grab the 64-bit libs here

[milewski]

And very importantly, make sure you use rust 1.67.1 or BELLOW! since version 1.6.8 rust does not compile with NDK lower than 25

Compatibility Notes #
Only support Android NDK 25 or newer