On 12-Nov-16 19:09, Florent Castelli wrote:
> On 12/11/2016 06:53, Ruslan Baratov wrote:
>> On 12-Nov-16 08:21, Florent Castelli wrote:
>>> On 10/11/2016 16:05, Ruslan Baratov via cmake-developers wrote:
>>>> Hi,
>>>>
>>>> I wonder if it's possible to introduce next variables describing
>>>> Android
>>>> tools:
>>>> * C preprocessor. Similar to CMAKE_CXX_COMPILER the variable that will
>>>> contain the path to preprocessor. Example:
>>>> * CMAKE_CXX_COMPILER =
>>>> <ndk-root>/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/bin/arm-linux-androideabi-g++
>>>>
>>>>
>>>> * CMAKE_C_PREPROCESSOR =
>>>> <ndk-root>/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/bin/arm-linux-androideabi-cpp
>>>>
>>>>
>>>> * ANDROID_TOOLCHAIN_MACHINE_NAME. In fact I'm not sure what this
>>>> variable mean but it's an important part of move from taka-no-me
>>>> toolchain to CMake 3.7. I guess it's like
>>>> * CMAKE_CXX_COMPILER =
>>>> <ndk-root>/toolchains/${ANDROID_TOOLCHAIN_MACHINE_NAME}-4.9/prebuilt/linux-x86_64/bin/${ANDROID_TOOLCHAIN_MACHINE_NAME}-g++
>>>>
>>>>
>>>>
>>>> Of course if I'm not missing something and they are not already
>>>> somewhere :)
>>>>
>>>> Ruslo
>>> How about ${CMAKE_C/CXX_COMPILER} -E to call the preprocessor?
>> I have no idea and not planning to test it because the old code was
>> using `cpp` preprocessor and I see no point of changing it.
> Well, you can define your preprocessor to be "${CMAKE_C_COMPILER} -E"
> locally and it will work with GCC-like compilers.
> That's a more robust way to call it as there is no
> CMAKE_C_PREPROCESSOR standard value in any CMake file.
> Nobody should call "cpp" manually anymore, but use the compiler driver
> instead to do it for you.
>
> That's why there's no standard CPP variable in CMake, it's not needed
> at all.
> For the same reasons, you rarely have to call the linker directly,
> it's usually done through the compiler driver.
Just like I said I'm not using it - this variable needed for 3rd party
package. I have no idea how it was used, the only thing I know is that
if I remove this variable the package stop working.
>
>>> Calling it directly is kind of dangerous though since you will
>>> probably be missing the proper language information and other options
>>> that might affect the predefined preprocessor defines.
>> I'm not calling it directly, it was used by `configure` script of 3rd
>> party.
>>
>>> gcc has different binaries for different target archs and has some
>>> defines baked in, but this won't apply to Clang that uses only one
>>> binary and a target triple.
>> For clang based android toolchain the CMAKE_CXX_ANDROID_TOOLCHAIN_PREFIX
>> variable points to the directory with gcc, so it will find `cpp`
>> preprocessor too. I don't know if it's good or bad :)
>
> I think that's an implementation detail you shouldn't rely on. The
> compilers in the NDK are changing, GCC is deprecated and you shouldn't
> expect that.
> Clang is mostly self contained and using very little from the GCC
> distribution (binutils), it will be gone at some point, so you should
> be ready for the future.
My goal now is to move from taka-no-me to CMake 3.7+ Android. I don't
bother about the destiny of GCC distribution. When this stuff will
change the problems will appear in both taka-no-me and CMake 3.7+.
>
> If you're updating CMake and changing the toolchain file, then I would
> expect that some work has to be done, including making changes to the
> invocation of a 3rd party script that is using custom variables from
> the old toolchain.
There is a tricky part about that. I do define variables like
CMAKE_SYSTEM_VERSION or CMAKE_ANDROID_ARCH_ABI and CMake gives me back
CMAKE_CXX_ANDROID_TOOLCHAIN_PREFIX. But
CMAKE_CXX_ANDROID_TOOLCHAIN_PREFIX is only available **after** toolchain
processed hence I can't use such variable in toolchain to create my
custom variables. So if we want to have everything play nice this should
be defined in CMake.
> Overall, I consider that taka-no-me Android toolchain to be tech debt.
> It hasn't been updated for a long time, doesn't work with recent NDK
> (unless you resort to use a standalone toolchain), locks people with
> some custom variables making them believe they are standard and has
> tons of other small bugs and issues.
> I understand its appeal for most people, but to me, it has caused more
> trouble than help.
Just like I said before, those variables needed in 3rd party tools which
is not related neither to CMake nor to taka-no-me toolchain. I see no
point of discussing issues you have with taka-no-me toolchain.
> It could have been done so much better.
It's open source world. From my opinion every question like "why it's
not so good?" should really be "why I'm not improving it?" or "why I'm
not doing something better?".
Ruslo
--
Powered by www.kitware.com
Please keep messages on-topic and check the CMake FAQ at:
http://www.cmake.org/Wiki/CMake_FAQ
Kitware offers various services to support the CMake community. For more
information on each offering, please visit:
CMake Support: http://cmake.org/cmake/help/support.html
CMake Consulting: http://cmake.org/cmake/help/consulting.html
CMake Training Courses: http://cmake.org/cmake/help/training.html
Visit other Kitware open-source projects at
http://www.kitware.com/opensource/opensource.html
Follow this link to subscribe/unsubscribe:
http://public.kitware.com/mailman/listinfo/cmake-developers
