[CMake] CPU specific compiler flags

[Ciccio Pasticcio]

Hi all,

I'm refactoring some libraries cmake files to be compliant to the use of
targets instead of tons of variables. Since these libraries are
cross-compiled I'm facing some problem finding how to properly set some
specific flags like: -march -marm -mfloat-abi etc. For now I set the
CMAKE_CXX_FLAGS:

set(CMAKE_CXX_FLAGS -march=armv7-a -marm -mthumb-interwork -mfloat-abi=hard
-mfpu=neon -mtune=cortex-a8 -Wno-psabi)

Is this the only way to do this? With targets I do something like this:

add_library(MyLib)
# add sources
...
# Comiler features
TARGET_COMPILE_FEATURES(MyLib PUBLIC cxx_lambdas)

Thanks,
Gabriele

[Eric Noulard]

Post by Ciccio Pasticcio
Hi all,
I'm refactoring some libraries cmake files to be compliant to the use of
targets instead of tons of variables. Since these libraries are
cross-compiled I'm facing some problem finding how to properly set some
specific flags like: -march -marm -mfloat-abi etc. For now I set the
set(CMAKE_CXX_FLAGS -march=armv7-a -marm -mthumb-interwork
-mfloat-abi=hard -mfpu=neon -mtune=cortex-a8 -Wno-psabi)
Is this the only way to do this?

I'm not sure to understand, you can perfectly setup flags on a target
specific way using 'target_compile_option'
https://cmake.org/cmake/help/latest/command/target_compile_options.html

If all your libraries are in a common directory you can use,
COMPILE_OPTIONS property on the directory
https://cmake.org/cmake/help/latest/prop_tgt/COMPILE_OPTIONS.html#prop_tgt:COMPILE_OPTIONS
to avoid repetition for each lib.

All that said, if you are cross-compiling those I bet you are using a
toolchain file (
https://cmake.org/cmake/help/latest/manual/cmake-toolchains.7.html#cross-compiling
)
so if those "target-specific" compile options are global to your target
then you may set
https://cmake.org/cmake/help/latest/variable/CMAKE_LANG_FLAGS.html#variable:CMAKE_%3CLANG%3E_FLAGS
in the toolchain.