What is csky?

it's an arch which e_machine code is 252. It will be introduced to rust by rust-lang/rust#113658 soon

But what is it? I've never heard of this architecture. What is the name of some of the processors that use it?

its organization of github is at C-SKY. It's an ISA created by T-head, Alibaba, China. here shows the cpu list including xuantie c801, c806, c860, and it also has the old models like ck860, ck810 and so on.
You can get the method for rust to compile at here ,
the linux system at here or here ,
the gcc compiler at here ,
the llvm and clang support at here

would you like to merge it? @asomers

This is even more obscure than loongarch64. There's virtually no information about this ISA online, at least in English. I don't want to devote significant resources to supporting ISAs like this. However, I'm going to push a separate change that should fix this particular build problem for csky and hopefully other obscure ISA, too.