[llvm-dev] Cross compiling C++ program

[Jonathan Roelofs via llvm-dev]

On 8/4/17 4:29 PM, Goran Mekić wrote:
> On Fri, Aug 04, 2017 at 04:03:35PM -0600, Jonathan Roelofs wrote:
>>>> 1) Pick a directory as your sysroot
>>> ~/arm-sysroot
>>>
>>>> 2) Install the libc headers there (without having built it)
>>> What I did was mv musl-*/include ~/arm-sysroot/usr/include.
>> I think you need to copy them, not move them.
> On a new directories and fresh untar of musl, I don't think there's a difference

I was assuming you'd want to build it from the same sources later...

>
>
>>>> 3) Build clang w/ baremetal cache, pointing it at the partially built
>>>> sysroot.
>>>    cmake -G 'Unix Makefiles' -DBAREMETAL_ARMV7EM_SYSROOT=~/arm-sysroot -C ../../code/clang/cmake/caches/BaremetalARM.cmake ../../code/clang
>> Sorry, I wasn't explicit enough. You need to define all of the variables
>> that the cache is looking for.
>>
>>> loading initial cache file ../../code/clang/cmake/caches/BaremetalARM.cmake
>>> -- Found LLVM_CONFIG as /usr/local/bin/llvm-config
>>> -- Building with -fPIC
>>> -- Could NOT find Z3 (missing:  Z3_LIBRARIES Z3_INCLUDE_DIR) (Required is at least version "4.5")
>>> -- Clang version: 4.0.1
>>> CMake Error at /usr/local/llvm40/lib/cmake/llvm/LLVM-Config.cmake:203 (message):
>>>     Library `BinaryFormat' not found in list of llvm libraries.
>>> Call Stack (most recent call first):
>>>     /usr/local/llvm40/lib/cmake/llvm/AddLLVM.cmake:508 (llvm_map_components_to_libnames)
>>>     cmake/modules/AddClang.cmake:86 (llvm_add_library)
>>>     lib/AST/CMakeLists.txt:6 (add_clang_library)
>>>
>>> -- Configuring incomplete, errors occurred!
>>> See also "/usr/home/meka/repos/clang/build/clang/CMakeFiles/CMakeOutput.log".
>> I think it found an installed llvm, and is trying to use that to build clang
>> against. First, the clang and llvm's versions have to match. Second, when I
>> mentioned building clang, I really meant building llvm+clang... sorry.
>>
>> $ cmake -G 'Unix Makefiles' -DBAREMETAL_ARMV7EM_SYSROOT=~/arm-sysroot -C
>> path/to/copy/of/edited/BaremetalARM.cmake path/to/llvm
>>
>> Where your path/to/llvm has the symlinks:
>>
>>    *  path/to/llvm/tools/clang -> path/to/clang
> ln -s `which clang40` path/to/llvm/tools/clang

No, not the binary, the source.

The closer to top of trunk you pull the source, the easier it'll be to 
get it working. A lot of the upstreaming of baremetal support has been 
*very* recent.... "bleeding edge" recent.

>>    *  path/to/llvm/runtimes/compiler_rt path/to/compiler_rt
> ln -s path/to/llvm/projects/compiler-rt path/to/llvm/runtimes/compiler_rt
>
> Is that right?

Sorry, it should be spelled `compiler-rt`, not `compiler_rt`.

>> And by "edited BaremetalARM.cmake" I mean you can strip out the other
>> targets in there that you don't need.
> So I have copied BaremetalARM.cmake into llvm/cmake/caches/BaremetalARM.cmake to be able to alter it, I've put all other repos in llvm/projects and the command is:

Leave all the others out for now. An in-tree build of them is just going 
to give you host binaries, which isn't helpful in your case. You'll have 
to build them "out of tree".


Might be a helpful exercise for you to try building vanilla clang with 
runtimes for the host, before worrying about how to build everything for 
your baremetal case: 
http://llvm.org/docs/GettingStarted.html#getting-started-quickly-a-summary

>
> # cmake -G 'Unix Makefiles' -DBAREMETAL_ARMV7EM_SYSROOT=~/arm-sysroot -DBAREMETAL_ARMV6M_SYSROOT=~/arm-sysroot -DBAREMETAL_ARMV7M_SYSROOT=~/arm-sysroot -C ../../code/llvm/cmake/caches/BaremetalARM.cmake ../../code/llvm
>
> Before adding all repos into llvm/projects, it complained about 'Specified distribution component 'clang' doesn't have a target' (just an example). Now I have 'Specified distribution component 'builtins-armv6m-none-eabi' doesn't have a target' as error.

I think that error happened because you symlinked the clang binary in, 
not the source.

Jon

-- 
Jon Roelofs
jonathan at codesourcery.com
CodeSourcery / Mentor Embedded / Siemens