[llvm-dev] bug: cross-compile Clang/LLVM for ARM using Clang/LLVM

[James Molloy via llvm-dev]

Hi Liyang,

> The including x86_64 libraries is added because of  some missing libraries

This will never work. The reason the libatomic check is failing is almost
certainly because a path to the C++ headers/libraries is missing. You've
manually added them all:

-I/usr/arm-linux-gnueabihf/include/c++/4.7.3/arm-linux-gnueabihf/
-I/usr/arm-linux-gnueabihf/include/
-I/home/lab/workspace/llvm/llvm-source-code/lib4arm/
-I/home/lab/workspace/llvm/llvm-source-code/lib2ubuntu/
-I/usr/lib/gcc/x86_64-linux-gnu/4.8/libatomic.so
-I/usr/lib/gcc/x86_64-linux-gnu/4.8/libatomic.so
-L/usr/lib/gcc/x86_64-linux-gnu/4.8/libatomic.so
-L/usr/lib/gcc/x86_64-linux-gnu/4.8/libatomic.a

But a much more robust way to do this is just to use a sysroot:

-DCMAKE_CXX_FLAGS='-target armv7a-linux-gnueabihf -mcpu=cortex-a9
--sysroot=/usr/arm-linux-gnueabihf/'

Cheers,

James


On Mon, 25 Apr 2016 at 12:26 李阳 via llvm-dev <llvm-dev at lists.llvm.org>
wrote:

> Hi renato,
>
> 1. The command above is followed by the guide[ HowToCrossCompileLLVM.rst ]
> and I specify some path(ex. <path-to-host-bin>).
>
> 2. The including x86_64 libraries is added because of  some missing
> libraries(ex. "error:  Host compiler appears to require libatomic, but
> cannot find it"). As I have found that the bugs needed to dealt with is
> some ARM-dependent libraries, I cannot download them on Ubuntu14, could you
> share them or some available links?
>
> Thanks very much!
>
> Best,
> Liyang
>
> 2016-04-25 18:33 GMT+08:00 Renato Golin <renato.golin at linaro.org>:
>
>> On 25 April 2016 at 10:39, 李阳 via llvm-dev <llvm-dev at lists.llvm.org>
>> wrote:
>>
>>> CC='clang' CXX='clang++' cmake -G Ninja ../llvm-source-code
>>> -DCMAKE_CROSSCOMPILING=True
>>> -DCMAKE_INSTALL_PREFIX=./llvm
>>> -DLLVM_TABLEGEN=/home/lab/workspace/llvm/build4x86/bin/llvm-tblgen
>>> -DCLANG_TABLEGEN=/home/lab/workspace/llvm/build4x86/bin/clang-tblgen
>>> -DLLVM_DEFAULT_TARGET_TRIPLE=arm-linux-gnueabihf
>>> -DLLVM_TARGET_ARCH=ARM
>>> -DLLVM_TARGETS_TO_BUILD=ARM
>>> -DCMAKE_CXX_FLAGS='-target armv7a-linux-gnueabihf -mcpu=cortex-a9
>>> -I/usr/arm-linux-gnueabihf/include/c++/4.7.3/arm-linux-gnueabihf/
>>> -I/usr/arm-linux-gnueabihf/include/
>>> -I/home/lab/workspace/llvm/llvm-source-code/lib4arm/
>>> -I/home/lab/workspace/llvm/llvm-source-code/lib2ubuntu/
>>> -I/usr/lib/gcc/x86_64-linux-gnu/4.8/libatomic.so
>>> -I/usr/lib/gcc/x86_64-linux-gnu/4.8/libatomic.so
>>> -L/usr/lib/gcc/x86_64-linux-gnu/4.8/libatomic.so
>>> -L/usr/lib/gcc/x86_64-linux-gnu/4.8/libatomic.a -mfloat-abi=hard
>>> -ccc-gcc-name arm-linux-gnueabihf-gcc'
>>> -DLLVM_ENABLE_LIBCXX=ON
>>> -DLLVM_ENABLE_PIC=False
>>>
>>
>> Hi Liyang,
>>
>> You have "LLVM_DEFAULT_TARGET_TRIPLE=arm-linux-gnueabihf"  and
>> "CMAKE_CXX_FLAGS='-target armv7a-linux-gnueabihf" which are different, and
>> may confuse Clang when finding tools and libraries. Use whatever is the ARM
>> triple in your system (looks like it's "arm-linux-gnueabihf") and make both
>> target triple and "-target" to be that exact same string.
>>
>> Also, you're including x86_64 libraries
>> (ex. -L/usr/lib/gcc/x86_64-linux-gnu/4.8/libatomic.so) to an ARM
>> compilation job, that won't work. You have to find the ARM version (maybe
>> /usr/lib/gcc/arm-linux-gnueabihf/ ?).
>>
>> Finally, the include paths with -I are only necessary if Clang cannot
>> find it. The first three should be ok, but using -I on a DSO object
>> (libatomic.so) makes no sense.
>>
>> cheers,
>> --renato
>>
>
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