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

[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


On Tue, Apr 13, 2021 at 12:54 PM unlvsur unlvsur via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
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> I want to build llvm + clang + lld + compiler-rt on Linux to build a windows host toolchain for example.
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> In GNU toolchain, it is 2 step.
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> Build a target cross toolchain
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> Binutils : --target=x86_64-w64-mingw32 (multilib)
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>         MinGW-w64-crt header files: --target=x86_64-w64-mingw32, --host=x86_64-w64-mingw32
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>         GCC, gcc part: --target=x86_64-w64-mingw32 (multilib)
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>         MinGW-w64-crt: --target=x86_64-w64-mingw32, --host=x86_64-w64-mingw32
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>         GCC libgcc and libstdc++: --target=x86_64-w64-mingw32
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> Done
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> Use this target x86_64-w64-mingw32 cross toolchain to build a new host toolchain
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> Binutils : --target=x86_64-w64-mingw32 (multilib) –host= x86_64-w64-mingw32 –disable-gdb
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> GCC: --target=x86_64-w64-mingw32 (multilib) –host= x86_64-w64-mingw32
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>                 Then copy the CRT build from the first target cross toolchain in this host toolchain.
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>                 Then we can use this new host toolchain and use it to build programs.
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> 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 2nd part.
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>                 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.
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> 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.
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> 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.
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> The largest issue is clearly cmake, which prevents cross compilation.
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> I do not know what is the solution here.
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> Sent from Mail for Windows 10
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