[llvm-dev] Cross compiling C++ program

[Goran Mekić via llvm-dev]

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


> > > 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
>   *  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?


>
> 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:

# 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.
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