[native_toolchain_c] Support minSdkVersion 19 and 20

[dcharkes]

Setting the Android minSdkVersion to 19 or 20 with

native/pkgs/native_assets_cli/lib/src/model/build_config.dart

Lines 70 to 80 in 279094d

	/// When compiling for Android, the minimum Android SDK API version to that
	/// the compiled code will be compatible with.
	///
	/// Required when [targetOs] equals [OS.android].
	///
	/// Not available in [dryRun].
	///
	/// For more information about the Android API version, refer to
	/// [`minSdkVersion`](https://developer.android.com/ndk/guides/sdk-versions#minsdkversion)
	/// in the Android documentation.
	int? get targetAndroidNdkApi {

causes the following at runtime when doing dlopen:

Invalid argument(s): Couldn't resolve native function 'sum' in
'package:my_package/my_package_bindings_generated.dart' : Failed to load dynamic library
'libmy_package.so': Failed to load dynamic library 'libmy_package.so': dlopen failed: TLS symbol
"_ZZN8gwp_asan15getThreadLocalsEvE6Locals" in dlopened
"/data/app/~~II5Pe1_V-_9YOORXFmjkwA==/com.example.my_package-fBAv9YGX7hLvZudMWuFp7g==/lib/arm64/libmy_package.so"
referenced from
"/data/app/~~II5Pe1_V-_9YOORXFmjkwA==/com.example.my_package-fBAv9YGX7hLvZudMWuFp7g==/lib/arm64/libmy_package.so"
using IE access model.

A quick search reveals this might have to do with libc++ linking.

• Upgrade from NDK 19b to 23b causes problems with Pandas library kivy/python-for-android#2654

background info: https://android.googlesource.com/platform/ndk/+/master/docs/BuildSystemMaintainers.md#stl

It could also be related to

native/pkgs/native_toolchain_c/lib/src/cbuilder/run_cbuilder.dart

Lines 130 to 134 in 279094d

	// TODO(dacoharkes): How to solve linking issues?
	// Non-working fix: --sysroot=$NDKPATH/toolchains/llvm/prebuilt/linux-x86_64/sysroot.
	// The sysroot should be discovered automatically after NDK 22.
	// Workaround:
	if (dynamicLibrary != null) '-nostartfiles',

Discovered while testing API versions on

• Native assets support for Android flutter/flutter#135148

[dcharkes]

We should probably also add some tests that:

• Use C++ on Android
• Use Android APIs
• Refuses to build from build.dart with a too low minSdkVersion

[dcharkes]

After #180 the failure on 19 and 20 is a link failure instead of a runtime failure:

Running `/Users/dacoharkes/Library/Android/sdk/ndk/24.0.8215888/toolchains/llvm/prebuilt/darwin-x86_64/bin/clang --target=aarch64-linux-android20 --sysroot=/Users/dacoharkes/Library/Android/sdk/ndk/24.0.8215888/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/ -fPIC -DDEBUG /Users/dacoharkes/src/dacoharkes/playground/my_package/src/my_package.c --shared -o /Users/dacoharkes/src/dacoharkes/playground/my_package/example/.dart_tool/native_assets_builder/f6d0c7f3b4352a2d592f2755006aec56/out/libmy_package.so`.
ld: error: cannot open crtbegin_so.o: No such file or directory
ld: error: cannot open crtend_so.o: No such file or directory
clang-14: error: linker command failed with exit code 1 (use -v to see invocation)

The same compiler invocation with --target=aarch64-linux-android21 and up is fine.

[dcharkes]

Probably related there is no sysroot for 19 and 20 in the NDK:

$ ls /Users/dacoharkes/Library/Android/sdk/ndk/24.0.8215888/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/lib/aarch64-linux-android/
21			27			32			libcompiler_rt-extras.a
22			28			libc++_shared.so	libdl.a
23			29			libc++_static.a		libm.a
24			30			libc++abi.a		libstdc++.a
26			31			libc.a			libz.a

The missing libs are in there

$ ls /Users/dacoharkes/Library/Android/sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/lib/aarch64-linux-android/21/
crtbegin_dynamic.o	libGLESv2.so		libc.a			libm.a
crtbegin_so.o	        ...

[dcharkes]

Wait, it looks like the Android Gradle plugin is not even targetting 19 and 20. When set to 19, the CMake log shows the following.

$ flutter create my_plugin --template=plugin_ffi --platform=android,ios,macos,linux,windows
$ cd my_plugin/example/
# edit android/app/build.gradle to explicitly say 19 on minSdkVersion and targetSdkVersion
$ flutter run -d emu

my_plugin/android/.cxx/Debug/6r5a3f3v/x86_64/CMakeFiles/CMakeOutput.log

"/Users/dacoharkes/Library/Android/sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/darwin-x86_64/bin/clang" -cc1 -triple x86_64-none-linux-android21 -emit-obj -mrelax-all --mrelax-relocations -mnoexecstack -disable-free -disable-llvm-verifier -discard-value-names -main-file-name CMakeCCompilerABI.c -mrelocation-model pic -pic-level 2 -pic-is-pie -mframe-pointer=all -fno-rounding-math -mconstructor-aliases -munwind-tables -target-cpu x86-64 -target-feature +sse4.2 -target-feature +popcnt -target-feature +cx16 -tune-cpu generic -fno-split-dwarf-inlining -debug-info-kind=limited -dwarf-version=4 -debugger-tuning=gdb -target-linker-version 650.9 -v -ffunction-sections -fdata-sections -resource-dir /Users/dacoharkes/Library/Android/sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/darwin-x86_64/lib64/clang/12.0.8 -dependency-file CMakeFiles/cmTC_613bd.dir/CMakeCCompilerABI.c.o.d -MT CMakeFiles/cmTC_613bd.dir/CMakeCCompilerABI.c.o -sys-header-deps -D ANDROID -D _FORTIFY_SOURCE=2 -isysroot /Users/dacoharkes/Library/Android/sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/darwin-x86_64/sysroot -internal-isystem /Users/dacoharkes/Library/Android/sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/local/include -internal-isystem /Users/dacoharkes/Library/Android/sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/darwin-x86_64/lib64/clang/12.0.8/include -internal-externc-isystem /Users/dacoharkes/Library/Android/sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/x86_64-linux-android -internal-externc-isystem /Users/dacoharkes/Library/Android/sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/include -internal-externc-isystem /Users/dacoharkes/Library/Android/sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include -Wformat -fdebug-compilation-dir /Users/dacoharkes/src/dacoharkes/playground/my_plugin/android/.cxx/Debug/6r5a3f3v/x86_64/CMakeFiles/CMakeTmp -ferror-limit 19 -stack-protector 2 -fgnuc-version=4.2.1 -o CMakeFiles/cmTC_613bd.dir/CMakeCCompilerABI.c.o -x c /Users/dacoharkes/Library/Android/sdk/cmake/3.18.1/share/cmake-3.18/Modules/CMakeCCompilerABI.c

Which contains: -triple x86_64-none-linux-android21.

As far as I understand, that should not work on android 19 or 20 devices, because it might use newer features?

If the Android Gradle plugin is ignoring minSdkVersion 19 and 20, but compiling against version 21, we should consider doing the same here.

FYI @reidbaker.

[dcharkes]

cc @HosseinYousefi any chance you have experience with targeting Android 19 and 20?