[llvm-dev] How to build host cross-toolchain from another operating system?

[unlvsur unlvsur via llvm-dev]

I want to build llvm + clang + lld + compiler-rt on Linux to build a windows host toolchain for example.

 

 

In GNU toolchain, it is 2 step.

 

1. Build a target cross toolchain

Binutils : --target=x86_64-w64-mingw32 (multilib)

        MinGW-w64-crt header files: --target=x86_64-w64-mingw32, --host=x86_64-w64-mingw32

        GCC, gcc part: --target=x86_64-w64-mingw32 (multilib)

        MinGW-w64-crt: --target=x86_64-w64-mingw32, --host=x86_64-w64-mingw32

        GCC libgcc and libstdc++: --target=x86_64-w64-mingw32

Done

2. Use this target x86_64-w64-mingw32 cross toolchain to build a new host toolchain

Binutils : --target=x86_64-w64-mingw32 (multilib) –host= x86_64-w64-mingw32 –disable-gdb

GCC: --target=x86_64-w64-mingw32 (multilib) –host= x86_64-w64-mingw32

 

                Then copy the CRT build from the first target cross toolchain in this host toolchain.

                Then we can use this new host toolchain and use it to build programs.

 

However, I try the same thing with llvm, I could not do it. cmake will do stupid checks to prevent me to just do the 2^nd part.

                I could not even use clang –target=x86_64-windows-gnu -fuse-ld=lld to build a host GCC since it fails to build gmp, only GCC could build that.

               

               

 

I think this is extremely important as a cross compiler. You want to bootstrap another toolchain from this platform to a new platform to make the new platform self host.

However, I guess it is very hard for LLVM, since it requires python and all kinds of other dependencies which the target cross toolchain does not provide.

 

The largest issue is clearly cmake, which prevents cross compilation.

 

I do not know what is the solution here.

 

 

Sent from Mail for Windows 10

 

[Jonathan Smith via llvm-dev]

This is very do-able. I often cross-compile a Windows version of the
toolchain from a Linux build machine, but I admittedly don't use MinGW
in the process -- I use MSVC and Windows SDK headers and libraries
I've copied to the Linux machine. LLVM includes a WinMsvc.cmake
toolchain script to help facilitate this, and I make extensive use of
it in my own toolchain-automating project
(https://github.com/jvstech/llvm-toolchain) because it's so much
easier [for me] than trying to build with MinGW. The only thing I
don't build is Compiler-RT -- not because it can't be done, but
because the MSVC and Windows SDK provide the equivalent functionality
already. It does require a bit more configuration than what I perform
in my project, but I've done it before.

If you'd like to stick with MinGW, another project I recommend is
https://github.com/mstorsjo/llvm-mingw -- which I have used in the
past, as well. Additionally, there is
https://github.com/martell/mingw-w64-clang which is similar, but
hasn't been updated in a while. Regardless, I've also used this
project as a reference for how to do manually what you're trying to
accomplish.

Bottom line: yes, it can be a pain, but it can be and has been done before.

- Jon

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