[BUG] CMake toolchain file sets CMAKE_ANDROID_EXCEPTION instead of CMAKE_ANDROID_EXCEPTIONS

[craigscott-crascit]

Description

The NDK's CMake toolchain file sets a variable named CMAKE_ANDROID_EXCEPTION, but it should be CMAKE_ANDROID_EXCEPTIONS (note the plural rather than singular). This variable will therefore have no effect when CMake is deciding whether to add -fexceptions or -fno-exceptions to the CMAKE_<LANG>_FLAGS_INIT flags, resulting in the flag being determined purely based on the selected STL type. This only affects build arrangements where ANDROID_CPP_FEATURES is set (I'm not sure what situations do that).

Environment Details

Found while working on macOS on an M1 machine. NDK 23.1.7779620 was installed via Android Studio, but the toolchain file from a standalone NDK package (r24-beta1) still has the same problem.

[DanAlbert]

While the fix is trivial, we're having trouble putting together a regression test. What's the behavior difference you're seeing? Exceptions are on by default, and if I pass -DANDROID_CPP_FEATURES=no-exceptions it does actually disable them (maybe CMake understands both options?)

$ cat ./foo.cpp
int main(int argc, char** argv) {
  try {
    throw 42;
  } catch (const int& ex) {
    return ex;
  }
  return 0;
}
$ cat ./CMakeLists.txt
cmake_minimum_required(VERSION 3.6.0)

add_executable(foo foo.cpp)
$ cat ./build.sh
#!/bin/sh
if [ $# -lt 1 ]; then
  >&2 echo "usage: ./gen.sh NDK_PATH"
  exit 1
fi

set -e

NDK_PATH=$(realpath $1)

cd "$(dirname "$0")"
rm -rf build
mkdir build
cd build
~/src/ndk/prebuilts/cmake/linux-x86/bin/cmake \
  -DANDROID_CPP_FEATURES=no-exceptions \
  -DCMAKE_TOOLCHAIN_FILE=$NDK_PATH/build/cmake/android.toolchain.cmake   ${@:2} -GNinja ..

ninja -v

That does fail to build as expected:

FAILED: CMakeFiles/foo.dir/foo.cpp.o 
/home/danalbert/src/ndk/out/linux/android-ndk-r24-canary/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++ --target=armv7-none-linux-androideabi19 --gcc-toolchain=/home/danalbert/src/ndk/out/linux/android-ndk-r24-canary/toolchains/llvm/prebuilt/linux-x86_64 --sysroot=/home/danalbert/src/ndk/out/linux/android-ndk-r24-canary/toolchains/llvm/prebuilt/linux-x86_64/sysroot   -g -DANDROID -fdata-sections -ffunction-sections -funwind-tables -fstack-protector-strong -no-canonical-prefixes -D_FORTIFY_SOURCE=2 -march=armv7-a -mthumb -Wformat -Werror=format-security -fno-exceptions  -fPIE -MD -MT CMakeFiles/foo.dir/foo.cpp.o -MF CMakeFiles/foo.dir/foo.cpp.o.d -o CMakeFiles/foo.dir/foo.cpp.o -c ../foo.cpp
../foo.cpp:3:5: error: cannot use 'throw' with exceptions disabled
    throw 42;
    ^
../foo.cpp:2:3: error: cannot use 'try' with exceptions disabled
  try {
  ^
2 errors generated.

But if I remove the -DANDROID_CPP_FEATURES=no-exceptions flag it builds fine.

[rprichard]

The typo is in the non-legacy toolchain file, so you need to test with a new cmake (3.21.x and up).

[DanAlbert]

Ah, crap. Good catch. My system's CMake is 3.21.4 but the script I used to generate a CMake test case uses the prebuilt :)

[DanAlbert]

Yeah, there we go. The same test case using the correct version of CMake compiles successfully when -DANDROID_CPP_FEATURES=no-exceptions is used, but shouldn't have because exceptions should be disabled.

[DanAlbert]

Should be fixed in r23 build 8486889.