Android LTO, Clang NDK r14, API {16,21} {armeabi-v7a, arm64-v8a}: OpenCV failed

[ruslo]

Build OpenCV:

[hunter-packages/opencv]> git branch -vv
* hunter-3.0.0 25e3fe7 [origin/hunter-3.0.0] Disable '-Wc++11-narrowing' for Clang

Using this script:

• https://gist.github.com/ruslo/396bb10d4b37c98870fb44c02db71b81

End with:

CMake Error at /.../cmake/share/cmake-3.7/Modules/TestBigEndian.cmake:41 (message):
  no suitable type found
Call Stack (most recent call first):
  CMakeLists.txt:532 (test_big_endian)

[ruslo]

Quite the same for android-ndk-r14-api-21-arm64-v8a-clang-hid-sections-lto

[ruslo]

This is because of MinSizeRel and -Os flag:

/.../android-ndk-r14/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/arm-linux-androideabi/bin/ld.gold:
  fatal error: Optimization level must be between 0 and 3

[ruslo]

Found this one:

• Windows, NDK r14: link time optimization does not work with Clang android/ndk#313
• https://bugs.llvm.org/show_bug.cgi?id=32155

It's a fresh bugs, I'm not sure if we can do anything about it now except to switch to -O3.

[headupinclouds]

Bummer. It seems it isn't just a Windows issue. My understanding is that -O3 with -flto will aim for cross translation unit speed optimizations only, and will not have much impact on size. Is drishti currently building with this toolchain using -O3 and -flto? I'm curious what the final size of this OpenCV benchmark is w/ these settings: drishti/src/benchmarks/opencv_size.

[ruslo]

Is drishti currently building with this toolchain using -O3 and -flto?

Have problems with Boost. Working on fix.

[ruslo]

Working on fix

Testing now: ruslo/hunter#699

[ruslo]

Looks like Clang/ld.gold is more pedantic about PIC vs non-PIC code. Got error:

/.../android-ndk/android-ndk-r14/toolchains/arm-linux-androideabi-4.9/prebuilt/darwin-x86_64/lib/gcc/arm-linux-androideabi/4.9.x/../../../../arm-linux-androideabi/bin/ld.gold:
fatal error: Failed to link module
/.../.hunter/_Base/57991b4/b3b38b9/0f5ce42/Install/lib/libboost_serialization-mt.a.llvm.132988.basic_archive.cpp:
linking module flags 'PIC Level': IDs have conflicting values

Since the final product of build will be shared library I guess we have to use PIC versions of toolchains, i.e.:

• android-ndk-r14-api-16-armeabi-v7a-neon-clang-hid-sections-lto-pic
• android-ndk-r14-api-21-arm64-v8a-clang-hid-sections-lto-pic

[ruslo]

Since the final product of build will be shared library I guess we have to use PIC versions of toolchains, i.e.

Doens't make any difference, reverting. I've run a few toolchain-id tests and it seems that PIC enabled by default for Android. The real problem here I think is the fact that non-CMake packages doesn't respect CMAKE_POSITION_INDEPENDENT_CODE variable. Working on fix.

[ruslo]

Testing with temporary release:

• https://github.com/ruslo/hunter/releases/tag/v0.18.18

It compiles now!

Toolchain android-ndk-r14-api-16-armeabi-v7a-neon-clang-hid-sections-lto + Release produce libdrishti.so with size 9.7 MB. Also one test failed:

CANNOT LINK EXECUTABLE:
  could not load library "libdrishti.so" needed by "/data/local/tmp/drishtisdk/android-ndk-r14-api-16-armeabi-v7a-neon-clang-hid-sections-lto/bin/test-drishti-drishti-eye";
  caused by cannot locate symbol "__tls_get_addr" referenced by "libdrishti.so"...                                                                                                                            

[ruslo]

Toolchain android-ndk-r14-api-21-arm64-v8a-clang-hid-sections-lto + Release produce 9.7 MB too. All tests passed.