[llvm-dev] Cross compiling C++ program

[Goran Mekić via llvm-dev]

On Thu, Aug 03, 2017 at 08:22:24AM -0600, Jonathan Roelofs wrote:
> IIUC, you don't want to cross compile llvm itself (which is what those
> instructions are for), but instead you want to *use* llvm to cross compile
> things.
>
> To build your sysroot, you'll need to cross-build:
>
>   1) A libc. Good choices for that for baremetal are: newlib or musl.
>   2) Builtins. In llvm, that's provided in the compiler-rt repo. Otherwise
> you can use libgcc from an arm-none-eabi-gcc toolchain.
>   3) If you want c++, you'll also need:
>      3A) c++ abi library. llvm provides this as libcxxabi. There's also
> libsupc++, and libcxxrt, depending on what licenses you're comfortable with.
>      3B) An unwinder. llvm provides libunwind. There's also one packaged in
> libgcc_s (depending on how it was built), and another from the old HP
> libunwind project (different codebase, but same name as the llvm one).
>      3C) A c++ standard library. llvm provides this as libcxx. There's also
> libstdc++.
>
>
> To start with, I recommend using the cmake cache in:
> $clang_src/cmake/caches/BaremetalARM.cmake. You'll want the stuff in it that
> references the armv7em-none-eabi triple. To use it, do something like:
>
> $  cmake -G <build system>
> -DBAREMETAL_ARMV7EM_SYSROOT=path/to/your/v7em/sysroot -C
> path/to/BaremetalARM.cmake [other CMake Options]
>
> Assuming your sysroot has libc headers in it, that should get you a clang
> that's capable of compiling basic things, which you can use to build all the
> libraries above.
>
>
> Jon

Hello,

Your input was very valuable, but I must be too noob so I have to ask. I tried to read as much as I could about musl, compiler-rt and libunwind to understand what are those libs and I decided to go with a "relexed" licenced alternatives. :o) If I got it right, the order of repos I need to compile is:

- musl
- compiler-rt
- libcxxabi
- libunwind
- libcxx
- clang (with the suggestion about baremetal cache)

If you know any doc on how to get clang++ compile for any bare metal arm, I'll be glad to RTFM. :o)
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