In twox-hash, I do some bit-banging work. I'm all but certain that I've screwed something up with respect to big- and little-endian, but I only have access to my x86 little-endian laptop, so I can't test to be sure.
Is there some big-endian emulator setup that I can run Rust code in?
if you are using Linux, you can use qemu to run binaries for pretty much any architecture
if you are not using Linux I guess you could run it in a VM^^
qemu-binfmt is pretty cool: https://wiki.debian.org/QemuUserEmulation
with that, you can literally
./binary for binaries that have the "wrong" architecture, and it will transparently use qemu to run it (you need the dynamic linker and libs for that architecture obviously, but at least on debian, thanks to multiarch that all is fairly easyto set up)
alternatively, you could use Miri :D but unfortunately cross-building libstd is not as easy as it could be (https://github.com/rust-lang/rust/issues/56443)
Also see https://github.com/rust-lang/miri/issues/864, I think it should be possible to make it easier to cross-run things with Miri.
https://cfarm.tetaneutral.net/news/ has some big endian targets.
MIPS and SPARC most notably.
I've used https://github.com/rust-embedded/cross in CI for things similar to this