cmake会自动附加-O2标志

Question

我正在从事一个Android Native项目。我在build.gradle

externalNativeBuild {

            cmake {
                arguments "--warn-uninitialized",
                        "-DANDROID_TOOLCHAIN=clang",
                        "-DANDROID_STL=c++_shared",
                        "-DANDROID_PLATFORM=android-21",
                        "-DAPP_ALLOW_MISSING_DEPS=true",
                        "-DSHARED_LIBRARY=1",
                        "-DOFFLINE_SYNC_SUPPORT_ENABLED=0",
                        "-DT5_TARGET_PLATFORM=Android",
                        "-DVERSION_STANDARD=14",
                        "-DREQUIRED_STANDARD=OFF",
                        "-DCMAKE_BUILD_TYPE=Release"
                cFlags "-Werror=return-type", "-Wno-pragmas", "-DBOOST_THREAD_PROVIDES_FUTURE",
                        "-DBOOST_THREAD_PROVIDES_FUTURE_CONTINUATION",
                        "-DJPEG_DISABLE_OPTIM -D_FILE_OFFSET_BITS=32",
                        "-mno-unaligned-access",
                        "-Wno-extern-c-compat"
                cppFlags "-Os", "-Wno-conversion-null", "-fexceptions", "-frtti", "-std=c++14", "-DES_ENABLE_LOGGING"


            }

构建后，我检查build.ninja文件后，我在build.gradle 中都有此配置-O2：

build CMakeFiles/myapp.dir/native-lib.cpp.o: CXX_COMPILER__myapp_Release /Users/vmangal/AndroidStudioProjects/MyApplication2/app/src/main/cpp/native-lib.cpp || cmake_object_order_depends_target_myapp
  DEFINES = -Dmyapp_EXPORTS
  DEP_FILE = CMakeFiles/myapp.dir/native-lib.cpp.o.d
  FLAGS = -g -DANDROID -fdata-sections -ffunction-sections -funwind-tables -fstack-protector-strong -no-canonical-prefixes -D_FORTIFY_SOURCE=2 -Wformat -Werror=format-security  -Os -Wno-conversion-null -fexceptions -frtti -std=c++14 -DES_ENABLE_LOGGING -O2 -DNDEBUG  -fPIC
  OBJECT_DIR = CMakeFiles/myapp.dir
  OBJECT_FILE_DIR = CMakeFiles/myapp.dir

可以在标志中看到-O2标志的标志：

-Os -Wno-conversion-null -fexceptions -frtti -std=c++14 -DES_ENABLE_LOGGING -O2 -DNDEBUG  -fPIC

实际上，我想降低lib的大小。 -os选项似乎被-O2选项覆盖。有没有办法告诉cmake不要附加此类标志。

Answer 1

https://github.com/android/android/ndk/issues/378 。这就是Cmake的行为方式。较少的特定标志是在更具体的标志之前。您将优化标志添加到通用cmake_cxx_flags变量而不是构建模式特定cmake_cxx_flags_release。

cflags和cppflags通常行为不佳。用参数中的-dcmake_cxx_flags_release（或任何构建模式）设置适当的cmake变量 -dcmake_cxx_flags_release 。选项2是更好的IMO，因为它可以将C ++构建配置保持在一个地方。