[llvm-dev] Cross compilation to ARM bare metal is not working

kiwan maeng via llvm-dev llvm-dev at lists.llvm.org
Thu Oct 10 15:19:09 PDT 2019

I am trying to build an LLVM toolchain so that it can cross-compile code 
to my ARMv7EM-based STM32F7 chip (I want to compile the code on an x86 
machine and run it on ARM).

However, a lot of the documents in the web is outdated, pointing to 
different versions of LLVM (with a different folder structure!) and I am 
not skilled enough to deduce a right way to build with the scattered 

I am mainly looking into this: 
(https://llvm.org/docs/HowToCrossCompileLLVM.html), and fiddled around 
to build something that is partially working.

This is the command I am using:


    git clone https://github.com/llvm/llvm-project.gitllvm-v9


    cd ..


    mkdir llvm-install && mkdir llvm-build && cd llvm-build


    cmake -G "Unix Makefiles" -DCMAKE_CROSSCOMPILING=True
    -DCMAKE_INSTALL_PREFIX=../llvm-install/ ../llvm-v9/llvm/

 5. make && make install

It compiles, and if I try to compile C code using the compiled clang, it 
complains about not having clang_rt on the linking stage (it generates 
up to assembly file).

I think it is weird that clang_rt is not there because I enable 
compiler-rt as you can see; anyways, I tried to separately compile 
clang_rt by looking at

(https://llvm.org/docs/HowToCrossCompileBuiltinsOnArm.html) but it 
wasn't successful.

I spent weeks trying out different flag options (some won't even 
compile), or using a gcc-arm-none-eabi linker at the last stage, etc., 
but with no luck.

Can anyone guide me to a more concrete example of how to compile LLVM 
for ARM cross-compilation, or help me out with what is wrong with the 
cmake options I am using?

Alternatively, I just tried downloading clang from apt-get install, but 
that again complained about not having clang_rt.

I would not mind using a lower version of LLVM if that is easier.

Any help or insight would be highly appreciated!

Also, kindly let me know if this is a wrong thread to post. I am new, as 
you can see.

Thank you,

Best Regards,


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