porting urbit to IBM Z

[Joe Latone]

I'd like to see if I can easily port urbit to an IBM Z (mainframe) running Linux:

Linux silusa03 5.4.0-74-generic #83-Ubuntu SMP Sat May 8 02:30:54 UTC 2021 s390x s390x s390x GNU/Linux

Naturally, the first thing that went wrong was:

nix-build -A urbit -A herb --no-out-link

warning: the group 'nixbld' specified in 'build-users-group' does not exist

error: Unknown CPU type: s390x

(use '--show-trace' to show detailed location information)

make: *** [Makefile:4: build] Error 1

I see a few string references of interest, e.g., x86_64 as well as U3_OS_ENDIAN_little (the Z is big endian).

Before I turn on --show-trace to source the error, is there something simple I can do just to get past the initial unknown CPU type error and see how far it'll compile? I.e., add s390x to the known CPU types somewhere? Open source software running on Z/Linux is well-supported, so I have all the latest build tools/libs. 

And, if I get that far, are there endian issues I need to look at beyond setting U3_OS_ENDIAN_little to 0?

--joe