Add compilation instructions for RISC-V

[MBCX]

This adds detailed instructions for how to successfully build 4.x (and possibly 3.x) versions of Godot for this ISA.

While these instructions are more focused on cross-compilation, it should also work on native RISC-V devices.

Solves #91381.

[DSOE1024]

nice!

[MBCX]

Squashed the commits, hopefully all is good now!

[aaronfranke]

I tried following these instructions on an Ubuntu 24.04 x86_64 host and it failed at linking: EDIT: 22.04

[Initial build] Compiling core/error/error_list.cpp ...
[Initial build] Compiling core/error/error_macros.cpp ...
[Initial build] progress_finish(["progress_finish"], [])
[Initial build] Generating servers/rendering/renderer_rd/shaders/environment/voxel_gi_sdf.glsl.gen.h ...
[Initial build] Generating servers/rendering/renderer_rd/shaders/giprobe_write.glsl.gen.h ...
[Initial build] Linking Static Library servers/libservers.linuxbsd.editor.rv64.llvm.a ...
Ranlib Library servers/libservers.linuxbsd.editor.rv64.llvm.a ...
[Initial build] Linking Static Library core/libcore.linuxbsd.editor.rv64.llvm.a ...
Ranlib Library core/libcore.linuxbsd.editor.rv64.llvm.a ...
[Initial build] Linking Program bin/godot.linuxbsd.editor.rv64.llvm ...
mold: unknown -m argument: elf64lriscv
clang: error: linker command failed with exit code 1 (use -v to see invocation)
scons: *** [bin/godot.linuxbsd.editor.rv64.llvm] Error 1
scons: building terminated because of errors.
[Time elapsed: 00:02:42.42]

[MBCX]

I tried following these instructions on an Ubuntu 24.04 x86_64 host and it failed at linking:

[Initial build] Compiling core/error/error_list.cpp ...
[Initial build] Compiling core/error/error_macros.cpp ...
[Initial build] progress_finish(["progress_finish"], [])
[Initial build] Generating servers/rendering/renderer_rd/shaders/environment/voxel_gi_sdf.glsl.gen.h ...
[Initial build] Generating servers/rendering/renderer_rd/shaders/giprobe_write.glsl.gen.h ...
[Initial build] Linking Static Library servers/libservers.linuxbsd.editor.rv64.llvm.a ...
Ranlib Library servers/libservers.linuxbsd.editor.rv64.llvm.a ...
[Initial build] Linking Static Library core/libcore.linuxbsd.editor.rv64.llvm.a ...
Ranlib Library core/libcore.linuxbsd.editor.rv64.llvm.a ...
[Initial build] Linking Program bin/godot.linuxbsd.editor.rv64.llvm ...
mold: unknown -m argument: elf64lriscv
clang: error: linker command failed with exit code 1 (use -v to see invocation)
scons: *** [bin/godot.linuxbsd.editor.rv64.llvm] Error 1
scons: building terminated because of errors.
[Time elapsed: 00:02:42.42]

I see elf64lriscv in the mold command, which I will assume you downloaded the wrong toolchain. You have to download the glibc one as I have specifically mention in the documentation.

Direct download to glibc one.

[aaronfranke]

@MBCX That is the exact file I downloaded. Filename riscv64-glibc-ubuntu-18.04-nightly-2021.12.22-nightly.tar.gz with MD5 hash c529cbebf72e358e9a9ce18afee6f9a4.

[MBCX]

Interesting then. Let me try to compile with the prebuilt and see if I can reproduce it (I compile with a custom-built toolchain).

[MBCX]

@aaronfranke Sadly, I wasn't able to reproduce your issue on my Zorin OS 16.3 laptop (Ubuntu 20.04.3 LTS based) with the same toolchain (18.04 and 20.04). I will set-up a Ubuntu 24.04 VM and try to reproduce it there.

In the meantime, could you try enabling verbose=yes and/or trying the 20.04 version of the toolchain and see if that does it for you?

[MBCX]

Still unable to reproduce on my freshly set-up Ubuntu 24.04 VM (and using the 18.04 toolchain).

[DSOE1024]

仍然无法在我新设置的 Ubuntu 24.04 VM 上重现（并使用工具链）。18.04

According to my test, the openKylin 2.0 system can be compiled successfully, which is my compilation step.

https://bbs.openkylin.top/t/topic/171569

Don't forget that you need GCC13

[aaronfranke]

Apologies, I figured out what was wrong. I thought my desktop was Ubuntu 24.04 but it was actually 22.04, which has too old of a Mold version in its repositories.

A simple change to the documentation will fix this: Add a note for how to check the supported architectures of Mold.

[aaronfranke]

Looks good to me!

[skyace65]

Thanks! And congrats on your first merged PR!

[mhilbrunner]

Cherry-picked to 4.3 in #10038.